Chapter 9 Electrons in Atoms and the Periodic Table

Chapter 9Chapter 9Electrons in AtomsElectrons in Atoms

and theand thePeriodic TablePeriodic Table

HomeworkHomework Assigned Problems (odd numbers only)Assigned Problems (odd numbers only)

““Questions” (page 310-11)Questions” (page 310-11)

““Problems” 31 to 89 (page 311-14)Problems” 31 to 89 (page 311-14)

““Cumulative Problems” 91-113 Cumulative Problems” 91-113 (page 315-17)(page 315-17)

Highlight Problems 115 (optional)Highlight Problems 115 (optional)

Light: Electromagnetic RadiationLight: Electromagnetic Radiation Energy is the capacity to do workEnergy is the capacity to do work The process of moving matter against an opposing force.The process of moving matter against an opposing force. Forms of energy include heat, electrical, and lightForms of energy include heat, electrical, and light One way energy is transmitted through space is by One way energy is transmitted through space is by

electromagnetic radiationelectromagnetic radiation A form of energy that travels through space at the speed A form of energy that travels through space at the speed

of lightof light Transmits from one place to another in the form of a Transmits from one place to another in the form of a

wavewave Given off by atoms when they have been excited by any Given off by atoms when they have been excited by any

form of energyform of energy

Electromagnetic radiationElectromagnetic radiation carries (radiant) energy through carries (radiant) energy through space and travels in waves at the speed of lightspace and travels in waves at the speed of light

Waves are periodic: The pattern of peaks and troughs Waves are periodic: The pattern of peaks and troughs repeats itself at regular intervalsrepeats itself at regular intervals

Light: Electromagnetic RadiationLight: Electromagnetic Radiation The waves have three basic characteristics: The waves have three basic characteristics: wavelengthwavelength, ,

frequencyfrequency, and , and speedspeed WavelengthWavelength ( ( is the distance (in nm) between neighboring is the distance (in nm) between neighboring

peaks in a wavepeaks in a wave The highest point on the wave is a peakThe highest point on the wave is a peak Shorter wavelengths are Shorter wavelengths are higherhigher in energy in energy Longer wavelengths, are Longer wavelengths, are lowerlower in energy in energy

Light: Electromagnetic RadiationLight: Electromagnetic Radiation FrequencyFrequency ( () is the number of waves that pass a fixed point ) is the number of waves that pass a fixed point

in one unit of timein one unit of time measured in Hertz (Hz), measured in Hertz (Hz), 1 Hz = 1 wave/sec = 1 sec1 Hz = 1 wave/sec = 1 sec-1-1

VelocityVelocity (v = how fast the wave is moving) (v = how fast the wave is moving) c c = speed of light = speed of light 3.00 x 103.00 x 1088 m/s m/s

AmplitudeAmplitude the height of the wave. It is the distance from the the height of the wave. It is the distance from the rest position to crest position or from rest position to trough rest position to crest position or from rest position to trough positionposition

amplitude

Wavelength and FrequencyWavelength and Frequency

Because all EM radiation travels at the Because all EM radiation travels at the speed of light (c), a relationship exists speed of light (c), a relationship exists between wavelength and frequencybetween wavelength and frequency

This is an inverse relationship so that if This is an inverse relationship so that if the wavelength doubles, the frequency is the wavelength doubles, the frequency is halved. If the wavelength is halved, the halved. If the wavelength is halved, the frequency doubles (and vice-versa)frequency doubles (and vice-versa)

C = C = λλѵѵ

C = 2 C = 2 λλ · ½ · ½ ѵѵ C = ½C = ½ λλ · 2 · 2 ѵѵ

WavesWaves

C = speed of lightC = speed of light

frequencyfrequency

frequencyfrequency

wavelengthwavelength

wavelengthwavelength

C = C = λλѵѵ

The Electromagnetic SpectrumThe Electromagnetic Spectrum

Light (radiant) energy is the energy of Light (radiant) energy is the energy of

electromagnetic waves and it is classified into electromagnetic waves and it is classified into

types according to the frequency of the wavetypes according to the frequency of the wave Sunlight, visible light, radio waves, microwaves Sunlight, visible light, radio waves, microwaves

(ovens), X-rays, and heat from a fire (infrared), are (ovens), X-rays, and heat from a fire (infrared), are all forms of this radiant energyall forms of this radiant energy

These forms of radiant energy exhibit the same These forms of radiant energy exhibit the same wavelike characteristicswavelike characteristics

The electromagnetic spectrum ranges from high-The electromagnetic spectrum ranges from high-energy gamma and X-rays to very low-energy energy gamma and X-rays to very low-energy radio and TV waves radio and TV waves

The Electromagnetic SpectrumThe Electromagnetic Spectrum EM radiation is classified by wavelength: EM radiation is classified by wavelength:

Lower energy (Lower energy (longer longer wavelength, lower frequencywavelength, lower frequency) ) Higher energy (Higher energy (shorter shorter wavelength, higher frequencywavelength, higher frequency))

Radiowaves:Radiowaves: AM/FM/TV signals, cell phones, low frequency AM/FM/TV signals, cell phones, low frequency and energyand energy

Microwaves:Microwaves: Microwave ovens and radarMicrowave ovens and radar Infrared (IR):Infrared (IR): Heat from sunlight, infrared lamps for heatingHeat from sunlight, infrared lamps for heating Visible: Visible: The only EM radiation detected by the human eyeThe only EM radiation detected by the human eye

RROOYYGGBBIIVV Ultraviolet: Ultraviolet: Shorter in wavelength than visible violet light, Shorter in wavelength than visible violet light,

sunlightsunlight X-rays: X-rays: Higher in energy than UVHigher in energy than UV Gamma rays:Gamma rays: Highest in energy, harmful to cells Highest in energy, harmful to cells

Wavelengths of EM RadiationWavelengths of EM Radiation The electromagnetic spectrum ranges from high-energy The electromagnetic spectrum ranges from high-energy

gamma gamma and and X-raysX-rays to very low-energy to very low-energy radioradio and and TV wavesTV waves The visible region of light is a narrow range of wavelengths The visible region of light is a narrow range of wavelengths

between these two extremes between these two extremes

Light Emission by Different ElementsLight Emission by Different Elements

When white light passes through a prism it When white light passes through a prism it separates and produces a continuous rainbow separates and produces a continuous rainbow of colors from (of colors from (redred,, orangeorange,, yellowyellow,, greengreen,, blueblue,, indigoindigo,, and, and, violetviolet))

From red light to violet light the wavelength From red light to violet light the wavelength becomes shorter (700 nm to 400 nm)becomes shorter (700 nm to 400 nm)

Light Emission by Different ElementsLight Emission by Different Elements

When an element is When an element is heated its atoms heated its atoms absorb energy and absorb energy and re-emits that energyre-emits that energy

Light is produced Light is produced If this light is passed If this light is passed

through a prism, it through a prism, it does not produce a does not produce a continuous rainbow, continuous rainbow, only certain colorsonly certain colors

Emission SpectraEmission Spectra

Only specific colors are Only specific colors are produced in the visible region. produced in the visible region. This is called a “This is called a “bright-line bright-line spectrumspectrum””

Each line produced is a Each line produced is a specific color, and thus has a specific color, and thus has a specific energyspecific energy

Each element produces a Each element produces a unique set of lines (colors) unique set of lines (colors) which represents energy which represents energy associated with a specific associated with a specific process in the atomprocess in the atom

Lines are also produced in the Lines are also produced in the infrared and ultraviolet regionsinfrared and ultraviolet regions

White light produces a continuous spectra

Each element produces a different discontinuous spectra

Emission SpectraEmission Spectra Scientists first detected the line Scientists first detected the line

spectrum of hydrogen (mid-1800’s) spectrum of hydrogen (mid-1800’s) which produced only four lineswhich produced only four lines

Emission SpectraEmission Spectra Scientist could not explain why atoms excited with energy produced Scientist could not explain why atoms excited with energy produced

discontinuous spectradiscontinuous spectra After the discovery of the nuclear structure of the atom (Rutherford, 1911), After the discovery of the nuclear structure of the atom (Rutherford, 1911),

scientist thought of the atom as a scientist thought of the atom as a microscopic solar systemmicroscopic solar system with electrons with electrons orbiting the nucleusorbiting the nucleus

To explain the bright line spectrum of hydrogen, Bohr’s theory of the To explain the bright line spectrum of hydrogen, Bohr’s theory of the hydrogen atom began with this idea and assumed the electrons move in hydrogen atom began with this idea and assumed the electrons move in circular orbits around the nucleuscircular orbits around the nucleus

Light emitted from hydrogen produces only specific wavelengths of light

Emission Spectra for Hydrogen: Emission Spectra for Hydrogen: The Bohr ModelThe Bohr Model

In 1913 Bohr In 1913 Bohr developed a developed a quantum model quantum model based on the based on the emission spectrum emission spectrum for hydrogenfor hydrogen

The proposal was The proposal was based on the based on the electron in hydrogen electron in hydrogen moving around the moving around the nucleus in a circular nucleus in a circular orbitorbit

The Bohr Model: Atoms with OrbitsThe Bohr Model: Atoms with Orbits

The Bohr atom has several orbits with The Bohr atom has several orbits with a specific radius and specific energya specific radius and specific energy

Each orbit or energy level is identified Each orbit or energy level is identified by “by “nn” ” the principal quantum numberthe principal quantum number

The values of The values of nn are positive, whole are positive, whole numbers 1, 2, 3, etc.numbers 1, 2, 3, etc.

The principal energy level (The principal energy level (nn =1) has =1) has the lowest energy and the smallest the lowest energy and the smallest radiusradius

Electrons can be “excited” to a higher Electrons can be “excited” to a higher energy level with absorption of energy energy level with absorption of energy

The energy absorbed and released is The energy absorbed and released is equal to the energy difference equal to the energy difference between the two statesbetween the two states

nucleusnucleus

The Bohr Model: Atoms with OrbitsThe Bohr Model: Atoms with Orbits

The different lines in an The different lines in an emission spectrum are emission spectrum are associated with changes in associated with changes in an electron’s energyan electron’s energy

Each electron resides in a Each electron resides in a specific E level called it’s specific E level called it’s principal quantum numberprincipal quantum number ((nn, where , where nn=1, =1, nn=2…)=2…)

Electrons closer to nucleus Electrons closer to nucleus have have lowerlower energy ( energy (lower lower nn valuesvalues))

Electrons farther from the Electrons farther from the nucleus have nucleus have higherhigher energy energy ((higher higher nn values values))

The Bohr Model: Excitation and EmissionThe Bohr Model: Excitation and Emission Scientists associated the lines of an atomic spectrum with Scientists associated the lines of an atomic spectrum with

changes in an electrons energy (changes in an electrons energy (““Bohr ModelBohr Model””)) An electron excited to a higher energy state will return to a An electron excited to a higher energy state will return to a

lower energy statelower energy state The energy that is given off (emitted) is a photon of light that The energy that is given off (emitted) is a photon of light that

corresponds to the energy difference between the higher and corresponds to the energy difference between the higher and lower energy stateslower energy states

This precise amount of energy is called aThis precise amount of energy is called a quantum quantum

A photon (of light)

The Bohr Model: Excitation and The Bohr Model: Excitation and EmissionEmission

The energy of a photon is related by the The energy of a photon is related by the equation:equation:

““The energy of a photon is directly The energy of a photon is directly proportional to its frequency”proportional to its frequency”

““The energy of a photon is inversely The energy of a photon is inversely proportional to its wavelength”proportional to its wavelength”

Energy transitions between orbits closer Energy transitions between orbits closer together produce photons of light with longer together produce photons of light with longer wavelengths (lower energy)wavelengths (lower energy)

E = hѵ c = c = λλѵѵѵ ѵ = c/= c/λλEE = hc/= hc/λλ

The Bohr Model: Electron Energy LevelsThe Bohr Model: Electron Energy Levels Electrons possess energy; they are in constant Electrons possess energy; they are in constant

motion in the large empty space of the atommotion in the large empty space of the atom The arrangement of electrons in an atom The arrangement of electrons in an atom

corresponds to an electron’s energycorresponds to an electron’s energy The electron resides outside the nucleus in one of The electron resides outside the nucleus in one of

seven fixed energy levelsseven fixed energy levels Energy levels are Energy levels are quantized: quantized: Only certain energy Only certain energy

values are allowedvalues are allowed

The Bohr Model: Electron Energy LevelsThe Bohr Model: Electron Energy Levels

Electrons can be “excited” Electrons can be “excited”

to a higher E level with the to a higher E level with the

absorption of E absorption of E

The energy absorbed is The energy absorbed is

equal to the difference equal to the difference

between the two E statesbetween the two E states

When an electron loses E When an electron loses E

and falls to a lower E level, and falls to a lower E level,

it emits it emits EM radiationEM radiation

(photon)(photon)


If the EM radiation wavelength is in the If the EM radiation wavelength is in the visible spectrum a color is seenvisible spectrum a color is seen


The energy levels calculated by the Bohr model The energy levels calculated by the Bohr model closely agreed with the values obtained from the closely agreed with the values obtained from the hydrogen emission spectrumhydrogen emission spectrum

The Bohr model did not work for other atomsThe Bohr model did not work for other atoms Energy levels were OK but model could not predict Energy levels were OK but model could not predict

emission spectra for an element with more than one emission spectra for an element with more than one electronelectron

Shrodinger in 1926 (DeBroglie, Heisenberg) Shrodinger in 1926 (DeBroglie, Heisenberg) developed the more precise quantum-mechanical developed the more precise quantum-mechanical modelmodel

The quantum (wave) mechanical model is the The quantum (wave) mechanical model is the current theory of atomic structurecurrent theory of atomic structure

The Quantum-Mechanical Model:The Quantum-Mechanical Model:From Orbits to OrbitalsFrom Orbits to Orbitals

The quantum-mechanical model gives a new way to The quantum-mechanical model gives a new way to view electronic structureview electronic structure

This model combines the wavelike and particle-like This model combines the wavelike and particle-like behavior of the electronbehavior of the electron

For the hydrogen atom, the allowed energy states are For the hydrogen atom, the allowed energy states are the same as that predicted by the Bohr modelthe same as that predicted by the Bohr model

The Bohr model assumes the electron is in a circular The Bohr model assumes the electron is in a circular orbit of some distance from the nucleusorbit of some distance from the nucleus

In the quantum-mechanical model, the electron’s In the quantum-mechanical model, the electron’s location cannot be described exactlylocation cannot be described exactly

The electron’s location is described as region of space The electron’s location is described as region of space (probability) where the electron will be at any given (probability) where the electron will be at any given instantinstant

The Quantum-Mechanical Model:The Quantum-Mechanical Model:From Orbits to OrbitalsFrom Orbits to Orbitals

The electron is treated not as a particle but as a The electron is treated not as a particle but as a wave bound to the nucleuswave bound to the nucleus

The electron does not move around the nucleus in a The electron does not move around the nucleus in a circular path (orbit)circular path (orbit)

Instead, the electron is found in orbitals. It is not a Instead, the electron is found in orbitals. It is not a circular path for the electroncircular path for the electron

An An orbitalorbital indicates the probability of finding an indicates the probability of finding an electron near a particular point in spaceelectron near a particular point in space

An orbital is a map of electron density in 3-D spaceAn orbital is a map of electron density in 3-D space Each orbital is characterized by a series of numbers Each orbital is characterized by a series of numbers

called quantum numberscalled quantum numbers

The Quantum-Mechanical Model: The Quantum-Mechanical Model: Electron Energy LevelsElectron Energy Levels

Electrons with higher E will tend to be farther Electrons with higher E will tend to be farther from the nucleus than those of lower Efrom the nucleus than those of lower E

The energy of an electron and its various The energy of an electron and its various distances from the nucleus can be grouped into distances from the nucleus can be grouped into levelslevels or or shellsshells

Principal quantum number Principal quantum number ““nn” is the major energy ” is the major energy level in the atom: It has values of level in the atom: It has values of nn =1, 2, 3, etc. =1, 2, 3, etc.

As “As “nn” increases the size of the principal ” increases the size of the principal energyenergy level (shell) increaseslevel (shell) increases

Principal shell electron capacity = 2n2

The Quantum-Mechanical Model: The Quantum-Mechanical Model: Electron SublevelsElectron Sublevels

All electrons in a principal shell (E level) All electrons in a principal shell (E level) do not have the same energydo not have the same energy

The energy of electrons in the same shell The energy of electrons in the same shell have energies close in magnitude, but have energies close in magnitude, but not identicalnot identical

The range of energies for electrons in a The range of energies for electrons in a shell is due to the existence of electron shell is due to the existence of electron subshells (or energy sublevels)subshells (or energy sublevels)

An An electronelectron subshellsubshell is an energy level is an energy level within an electron shell in which within an electron shell in which electrons all have the same energyelectrons all have the same energy


The number of subshells (sublevels) within a principle shell (E The number of subshells (sublevels) within a principle shell (E level), level), nn, varies, varies

Each principal shell is divided into 1, 2, 3, or 4 subshellsEach principal shell is divided into 1, 2, 3, or 4 subshells Subshells are identified by a number and a letter: Subshells are identified by a number and a letter: s, p, d, and fs, p, d, and f Each principal shell contains the same number of subshells Each principal shell contains the same number of subshells

as its own principal shell number:as its own principal shell number:

No. of subshells in a principal shell = n

Two electrons per subshell


The order of the increasing energy for subshells The order of the increasing energy for subshells ((withinwithin an shellan shell))

The subshells with the lowest to highest energy:The subshells with the lowest to highest energy: s subshell (holds up to 2 electrons)s subshell (holds up to 2 electrons) p subshell (holds up to 6 electrons)p subshell (holds up to 6 electrons) d subshell (holds up to 10 electrons) d subshell (holds up to 10 electrons) f subshell (holds up to 14 electrons)f subshell (holds up to 14 electrons)

s < p < d < fLowestLowestenergyenergy

HighestHighestenergyenergy

Quantum-Mechanical OrbitalsQuantum-Mechanical Orbitals

The third term used to describe electron The third term used to describe electron arrangement about the atomic nucleus (shells, arrangement about the atomic nucleus (shells, subshells)subshells) is theis the orbitalorbital

Since the electron location cannot be known Since the electron location cannot be known exactly, the location of the electron is described exactly, the location of the electron is described in term of probability, not exact pathsin term of probability, not exact paths

The orbital is a region of space where an electron The orbital is a region of space where an electron assigned to that orbital is likely to be foundassigned to that orbital is likely to be found

Region in space around the nucleus where there Region in space around the nucleus where there is a high (90%) probability of finding an electron is a high (90%) probability of finding an electron of a specific energyof a specific energy


Each orbital can hold up to 2 electronsEach orbital can hold up to 2 electrons Each subshell is composed of one or more Each subshell is composed of one or more

orbitalsorbitals One orbital in an s-subshell One orbital in an s-subshell Three orbitals in a p-subshellThree orbitals in a p-subshell Five orbitals in a d-subshell Five orbitals in a d-subshell Seven orbitals in an f-subshellSeven orbitals in an f-subshell

Orbitals within the same subshell differ mainly Orbitals within the same subshell differ mainly in orientationin orientation


The orbitals in each of the four subshells The orbitals in each of the four subshells (sublevels) have characteristic shapes(sublevels) have characteristic shapes

Orbitals in an s-subshell do not have the same Orbitals in an s-subshell do not have the same shape as orbitals in a p-subshell, etc.shape as orbitals in a p-subshell, etc.

Orbitals of the same type, but in different principal Orbitals of the same type, but in different principal shells/E levels (e.g. 1s, 2s, 3s) have the same shells/E levels (e.g. 1s, 2s, 3s) have the same general shape, but differ in sizegeneral shape, but differ in size

The nucleus is located at the center of each The nucleus is located at the center of each orbitalorbital

Quantum-Mechanical Orbitals:Quantum-Mechanical Orbitals: s-Orbitals s-Orbitals

There is one s-orbital in each s-subshellThere is one s-orbital in each s-subshell Every principal shell contains only one Every principal shell contains only one

s-orbital within an s-subshells-orbital within an s-subshell S-orbitals are spherical in shapeS-orbitals are spherical in shape The larger the principal shell (energy The larger the principal shell (energy

level), the larger the spherelevel), the larger the sphere An s-sublevel can hold a total of two An s-sublevel can hold a total of two

electronselectrons within the s-orbital within the s-orbital

Quantum Mechanical Orbitals:Quantum Mechanical Orbitals:s-Orbitalss-Orbitals

The spherical s-orbital gets larger as n increasesThe spherical s-orbital gets larger as n increases

Fig10_23

3s2s1s

nucleusnucleus

Quantum Mechanical Orbitals:Quantum Mechanical Orbitals:p-Orbitalsp-Orbitals

The p-orbitals come in sets of three within each The p-orbitals come in sets of three within each p-subshell p-subshell

All of equal energyAll of equal energy The three p-orbitals first occur in the n=2 (or The three p-orbitals first occur in the n=2 (or

higher) levelshigher) levels P-orbitals are dumb-bell in shapeP-orbitals are dumb-bell in shape The three orbitals within a p-sublevel are The three orbitals within a p-sublevel are

oriented at right angles to one another and oriented at right angles to one another and labeled as (plabeled as (pxx, p, pyy and p and pzz) )

p-subshell can hold a total of six electronsp-subshell can hold a total of six electrons, two , two electrons in each of the p-orbitals (pelectrons in each of the p-orbitals (pxx, p, pyy and p and pzz))

Fig10_21

(b) (c)

(a)

x

zy

x

zy

x

zy

Quantum Mechanical Orbitals:Quantum Mechanical Orbitals:p-Orbitalsp-Orbitals

p-orbitals have a two-lobe, dumbbellp-orbitals have a two-lobe, dumbbellshape. The nucleus is at the point where the two shape. The nucleus is at the point where the two lobes meetlobes meet

nucleusnucleus

Quantum Mechanical Orbitals:Quantum Mechanical Orbitals:d-Orbitalsd-Orbitals

d-orbitals come in sets of five within d-orbitals come in sets of five within each d-subshelleach d-subshell

All of equal energyAll of equal energy The five orbitals first occur in the n=3 The five orbitals first occur in the n=3

shellshell Odd shapes (don’t need to know them)Odd shapes (don’t need to know them) d-subshell can hold a total of 10 d-subshell can hold a total of 10

electronselectrons, 2 electrons in each of five d-, 2 electrons in each of five d-orbitalsorbitals

Fig10_24

dyz

yz

x

dxz

yz

x

dxy

y

z

x

dx2 - y2

y

z

x

dz2

y

z

x

d-d-OrbitalsOrbitals

f-Orbitalsf-Orbitals f-orbitals come in sets of seven within f-orbitals come in sets of seven within

each f-subshelleach f-subshell All of equal energyAll of equal energy The seven orbitals first occur in the n=4 The seven orbitals first occur in the n=4

shellshell Shapes are very difficult, so you don’t Shapes are very difficult, so you don’t

need to know them eitherneed to know them either f-subshell can hold a total of 14 electronsf-subshell can hold a total of 14 electrons, ,

2 electrons in each of seven f-orbitals2 electrons in each of seven f-orbitals

Electron Configurations: Electron Configurations: How Electrons Occupy OrbitalsHow Electrons Occupy Orbitals

Two ways to show how the electrons Two ways to show how the electrons are distributed in the principal shells are distributed in the principal shells within an atomwithin an atom Orbital diagrams Orbital diagrams Electron configurationsElectron configurations

The most stable arrangement of The most stable arrangement of electrons is one where the electrons electrons is one where the electrons are in the are in the lowest energylowest energy subshells subshells possiblepossible

Electron Configurations: Electron Configurations: How Electrons Occupy OrbitalsHow Electrons Occupy Orbitals

The most stable arrangement of The most stable arrangement of electrons is called “electrons is called “ground-state ground-state electronic configurationelectronic configuration””

The most stable, lowest energy The most stable, lowest energy arrangement of the electronsarrangement of the electrons

The GS configuration for an element The GS configuration for an element with many electrons is determined by with many electrons is determined by a a building-up processbuilding-up process

Writing Orbital Diagrams and Writing Orbital Diagrams and Electron ConfigurationsElectron Configurations

For the building-up process, begin by For the building-up process, begin by adding electrons to specific principal adding electrons to specific principal shells (E levels) beginning with the 1s shells (E levels) beginning with the 1s subshellsubshell

Continue in the order of increasing Continue in the order of increasing subshell energies:subshell energies:

1s→2s →2p →3s →3p →4s →3d →4p →5s →4d →etc.

Writing Orbital Diagrams andWriting Orbital Diagrams andElectron ConfigurationsElectron Configurations

The notation illustrates the electron arrangement in terms of which The notation illustrates the electron arrangement in terms of which energy levels (energy levels (shellsshells) and sublevels () and sublevels (subshellssubshells) are occupied) are occupied

The orbital diagram uses the building-up principal The orbital diagram uses the building-up principal Hund’s Rule: When electrons are placed in a set of orbitals of equal Hund’s Rule: When electrons are placed in a set of orbitals of equal

energy, the orbitals will be occupied by energy, the orbitals will be occupied by oneone electron each before electron each before pairing togetherpairing together

Electron SpinElectron Spin Electrons behave as if they are spinning on an axisElectrons behave as if they are spinning on an axis A spinning electron behaves like a small bar magnet with north A spinning electron behaves like a small bar magnet with north

and south polesand south poles Small arrows (pointed up or downward) are used to indicate the Small arrows (pointed up or downward) are used to indicate the

two orientations of spintwo orientations of spin Two electrons in the same orbital must spin in opposite directionsTwo electrons in the same orbital must spin in opposite directions Pauli Exclusion Principle: No more than two electrons can be Pauli Exclusion Principle: No more than two electrons can be

placed in a single orbital and must be paired (have spins in placed in a single orbital and must be paired (have spins in opposite directions) opposite directions)

orbital

Orbital DiagramsOrbital Diagrams Orbital Diagram Notation:Orbital Diagram Notation: Draw a box to represent each orbitalDraw a box to represent each orbital Use an arrow up or down to represent an Use an arrow up or down to represent an

electronelectron Two electrons in the same orbital (box) must Two electrons in the same orbital (box) must

have spins in opposite directions: Only one up have spins in opposite directions: Only one up and one down arrow is allowed in a box (paired and one down arrow is allowed in a box (paired electrons)electrons)

1s 2s 2p

Orbital DiagramsOrbital Diagrams

In General:In General: Begin filling from the Begin filling from the lowestlowest to the to the highesthighest

energy levelenergy level If there is more than one orbital possible, If there is more than one orbital possible,

e.g., e.g., ppxx, , ppyy, , ppzz, place electrons alone before , place electrons alone before

pairing up (pairing up (Hund’s RuleHund’s Rule)) Once each orbital is filled with one electron Once each orbital is filled with one electron

they will pair up but they will pair up but mustmust have opposite have opposite spins (spins (Pauli Exclusion PrincipalPauli Exclusion Principal))

s-orbitalss-orbitals Only one per Only one per nn Can hold two electrons for a total of Can hold two electrons for a total of

two electrons in an s-subleveltwo electrons in an s-sublevel

p-orbitalsp-orbitals Three per Three per nn Each can hold two electrons for a total Each can hold two electrons for a total

of 6 electrons in a p-sublevelof 6 electrons in a p-sublevel


Orbital DiagramsOrbital Diagrams d-orbitalsd-orbitals

Five per nFive per n Each can hold two electrons for a total Each can hold two electrons for a total

of 10 electrons in a d-sublevelof 10 electrons in a d-sublevel

f-orbitalsf-orbitals Seven per nSeven per n Each can hold two electrons for a total Each can hold two electrons for a total

of 14 electrons in an f-sublevelof 14 electrons in an f-sublevel

hydrogenhydrogen Only one electronOnly one electron Occupies the 1s orbitalOccupies the 1s orbital

heliumhelium Two electronsTwo electrons Both occupy the 1s orbitalBoth occupy the 1s orbital

lithiumlithium Three electronsThree electrons

Two occupy the 1s orbital, one occupiesTwo occupy the 1s orbital, one occupies the 2s the 2s orbitalorbital


1s

1s

1s 2s

Electron ConfigurationsElectron Configurationsand the Periodic Tableand the Periodic Table

The elements in the periodic table are arranged in order of The elements in the periodic table are arranged in order of increasing atomic number increasing atomic number

The basic shape and structure of the table is consistent with The basic shape and structure of the table is consistent with (and can be explained by) the sequence used to build (and can be explained by) the sequence used to build electron configurations electron configurations

The table is divided into sections based on the type of The table is divided into sections based on the type of subshell (s, p, d, or f) that receives the last electron in the subshell (s, p, d, or f) that receives the last electron in the building-up processbuilding-up process

Electron Configurations and theElectron Configurations and thePeriodic TablePeriodic Table

You can “build-up” atoms by reading across the You can “build-up” atoms by reading across the periods from left to rightperiods from left to right

It is not necessary to memorize the filling order of the It is not necessary to memorize the filling order of the electron, just use the electron, just use the periodic tableperiodic table

Follow a path (left to right) across each period (row) of Follow a path (left to right) across each period (row) of the table and note the various subshells as they are the table and note the various subshells as they are encounteredencountered

The atomic numbers are increasing across each The atomic numbers are increasing across each period and this corresponds to increasing subshell period and this corresponds to increasing subshell energyenergy

Since atomic numbers are increasing, each box in the Since atomic numbers are increasing, each box in the table (across a period) is also an increase in one table (across a period) is also an increase in one electronelectron

Electron Configurations and the Electron Configurations and the Periodic TablePeriodic Table

The elements are arranged by increasing atomic numberThe elements are arranged by increasing atomic number The periodic table is divided into sections based on the The periodic table is divided into sections based on the

type of subshell (s, p, d, or f) which receives the type of subshell (s, p, d, or f) which receives the last last electron electron in the build up processin the build up process

Different blocks on the periodic table correspond to the s, Different blocks on the periodic table correspond to the s, p, d, or f sublevelsp, d, or f sublevels

Electron Configurations and theElectron Configurations and thePeriodic TablePeriodic Table

The specific location of an element in the periodic table can be used to obtain information about its electron configuration

An electron configuration is a statement of how many electrons an atom has in each of its subshells

To write a complete electron configuration: The order in which the various subshells are filled can be obtained

by following a path of increasing atomic number through the table (also taking account of the various subshells along the path)

The periodic table can be used to determine the shell in which the last electron added is located

It is this last electron added that causes an element’s electron configuration to differ from the preceding element


s-s-block elementsblock elements (Groups 1A and 2A) gain (Groups 1A and 2A) gain their last electron in an their last electron in an s-s-sublevel sublevel

pp-block elements-block elements (Groups 3A to 8A) gain their (Groups 3A to 8A) gain their last electron in a last electron in a pp-sublevel-sublevel

dd-block elements-block elements (transition metals) gain their (transition metals) gain their last electron in a last electron in a dd-sublevel. First appear after -sublevel. First appear after calcium (element 20) calcium (element 20) dd-sublevel is (n-1) less than the period number-sublevel is (n-1) less than the period number

ff-block elements -block elements are in the two bottom rows are in the two bottom rows of the periodic tableof the periodic table ff-sublevel is (n-2) less than the period number-sublevel is (n-2) less than the period number

1234567

Subshell Filling OrderSubshell Filling Order

nsnp

(n-1)d

(n-2) f

Writing Electron ConfigurationsWriting Electron Configurationsfrom the from the

Periodic TablePeriodic Table

Locate the element, the number of electrons is Locate the element, the number of electrons is equal to the atomic numberequal to the atomic number

Start at hydrogen and move from box to box, Start at hydrogen and move from box to box, in order of increasing atomic number in order of increasing atomic number

The lowest energy sublevel fills first, then the The lowest energy sublevel fills first, then the next lowest following a path across each next lowest following a path across each periodperiod

The configuration of each element builds on The configuration of each element builds on the previous elementthe previous element

The p, d, or f sublevels must completely fill The p, d, or f sublevels must completely fill with electrons before moving to the next with electrons before moving to the next higher sublevelhigher sublevel

Electron Configuration Example #1Electron Configuration Example #1

Write the complete electron Write the complete electron configuration for chlorine configuration for chlorine

Chlorine is atomic number 17 (on the Chlorine is atomic number 17 (on the periodic table) so the neutral atom periodic table) so the neutral atom has 17 electronshas 17 electrons

Writing sublevel blocks in order up to Writing sublevel blocks in order up to chlorine gives:chlorine gives:

1s22s22p63s23px

1234567


nsnp

(n-1) d

(n-2) f


Cl : 1s2 2s2 2p6 3s2 3p5

or [Ne] 3s2 3p5

1s1s 2s2s 2p2p 3s3s 3p3p

Orbital diagramHund’s Rule


Write the complete electron Write the complete electron configuration for calcium configuration for calcium

Calcium is atomic number 20 (on the Calcium is atomic number 20 (on the periodic table) so the neutral atom periodic table) so the neutral atom has 20 electronshas 20 electrons

Writing sublevel blocks in order up to Writing sublevel blocks in order up to calcium gives:calcium gives:

1s22s22p63s23p64sx

1234567


nsnp

(n-1) d

(n-2) f


4s [Ar]or

4s 3p 3s 2p 2s 1s :Ca2

262622

1s1s 2s2s 2p2p 3s3s 3p3p 4s4s

Orbital diagramHund’s Rule

Electron Configurations Electron Configurations ExamplesExamples

May also use the condensed (inner) electron configuration

This shorthand notation uses the noble gas that precedes a particular element and places it inside square brackets

Ca : 1s2 2s2 2p6 3s2 3p6 4s2

or [Ar] 4s2 abbrev. electronconfiguration

[[ ]]

Noble gas core


The periodic table graphically represents The periodic table graphically represents the behavior of the elements described the behavior of the elements described by periodic lawby periodic law

Elements are arranged by increasing Elements are arranged by increasing atomic numberatomic number

In the periodic table, elements with In the periodic table, elements with similar properties occur at regular similar properties occur at regular intervals (in the same vertical column)intervals (in the same vertical column)

The arrangement of electrons and not The arrangement of electrons and not the mass determines chemical properties the mass determines chemical properties of the elementsof the elements

Valence ElectronsValence Electrons

Valence electronsValence electrons are those electrons in the are those electrons in the outermost (highest) energy level “n” (where n outermost (highest) energy level “n” (where n = 1, 2, 3 …)= 1, 2, 3 …)

Those electrons not in the outermost (highest) Those electrons not in the outermost (highest) energy level are called energy level are called core electronscore electrons

Valence electrons are the most important Valence electrons are the most important (chemically) (chemically)

Always found in the outermost s or p sublevels Always found in the outermost s or p sublevels in the representative elementsin the representative elements

For elements in columns 1A-8A, group For elements in columns 1A-8A, group number equals the number of valence number equals the number of valence electronselectrons

Valence ElectronsValence Electrons

All elements within a column (group) have the same All elements within a column (group) have the same number of valence electrons and similar outer number of valence electrons and similar outer electron configurationselectron configurations

Group IA elements have one valence electron: Group IA elements have one valence electron: nsns1

Group IIA elements have two valence electrons: Group IIA elements have two valence electrons: nsns22

Group IIIA elements have three valence electrons: Group IIIA elements have three valence electrons: nsns22npnp11

Periodic Trends of the Periodic Trends of the Elements/Valence ElectronsElements/Valence Electrons

Write the electron configuration for lithiumWrite the electron configuration for lithium

Write the electron configuration for sodiumWrite the electron configuration for sodium

Each group 1A element has a single Each group 1A element has a single electron in an s-sublevel. This is the (one) electron in an s-sublevel. This is the (one) valence electronvalence electron

Li: 1sLi: 1s222s2s11

Na: 1sNa: 1s222s2s222p2p663s3s11


The periodic table list elements by increasing The periodic table list elements by increasing atomic number and arranges them in groups atomic number and arranges them in groups with similar chemical propertieswith similar chemical properties

Similar chemical properties arise in every Similar chemical properties arise in every eighth element due to the similarity in eighth element due to the similarity in electronic configurations (every eighth electronic configurations (every eighth element for main group elements)element for main group elements)

Across a period, elements become less Across a period, elements become less metallic and more nonmetallicmetallic and more nonmetallic

Metals tend to lose electrons in chemical Metals tend to lose electrons in chemical reactionsreactions


Alkali metals lose their one and only Alkali metals lose their one and only oneone valence valence electronelectron in chemical reactions forming in chemical reactions forming an ion with a an ion with a single positive chargesingle positive charge and a stable noble gas and a stable noble gas electronic configurationelectronic configuration

Group IIA metals lose their Group IIA metals lose their two valence electrons two valence electrons in in chemical reactions forming an chemical reactions forming an ion with a 2ion with a 2++ charge charge and a stable noble gas electronic configurationand a stable noble gas electronic configuration

Group VIIA nonmetals readily Group VIIA nonmetals readily gain one electron gain one electron in in chemical reactions forming an chemical reactions forming an ion with a single ion with a single negative chargenegative charge and obtain the stable electron and obtain the stable electron configuration of the next higher noble gasconfiguration of the next higher noble gas

Atomic SizeAtomic Size Atoms are considered spherical in shape and Atoms are considered spherical in shape and

their size (atomic radius) is very dependent on their size (atomic radius) is very dependent on the electronic configuration of the atomthe electronic configuration of the atom

The electronic configuration gives trends in The electronic configuration gives trends in atomic size atomic size within groups and across periods in within groups and across periods in the periodic table (representative elements)the periodic table (representative elements)

Within groups, the atomic radius increases with Within groups, the atomic radius increases with the period number (increase from top to bottom)the period number (increase from top to bottom)

Across periods, the atomic radius decreases from Across periods, the atomic radius decreases from left to right with increasing atomic number left to right with increasing atomic number (decrease from left to right)(decrease from left to right)

Atomic SizeAtomic Size Within groups:Within groups:

The period number increases The period number increases downward in a groupdownward in a group

Principal E level (n) increasesPrincipal E level (n) increases Valence electron is further Valence electron is further

from the nucleusfrom the nucleus Across periods: Across periods:

The atomic radius decreases The atomic radius decreases from LEFT to RIGHT with from LEFT to RIGHT with increasing atomic numberincreasing atomic number

As atomic number increases, As atomic number increases, so does the number of so does the number of electronselectrons

The increase in positive The increase in positive charge pulls the outermost charge pulls the outermost electrons closer to the electrons closer to the nucleusnucleus

Size of Atoms and Size of Atoms and Their IonsTheir Ions

The formation of a positive ion The formation of a positive ion requires the loss of one or more requires the loss of one or more valence electronsvalence electrons

Loss of the outermost (valence) Loss of the outermost (valence) electron causes a reduction in electron causes a reduction in atomic sizeatomic size

Positive ions are always smaller Positive ions are always smaller than their parent ionsthan their parent ions

Size of Atoms and Size of Atoms and Their IonsTheir Ions

The formation of a negative The formation of a negative ion ion requires the addition of one or requires the addition of one or more electrons to the valence more electrons to the valence shell of an atom shell of an atom

There is no increase in + nuclear There is no increase in + nuclear charge to offset the added charge to offset the added electron’s - chargeelectron’s - charge

Increase in size due to repulsion Increase in size due to repulsion between electronsbetween electrons

Ionization EnergyIonization Energy The minimum energy required to The minimum energy required to

remove one electron from an atom of remove one electron from an atom of an element (physical state is a gas)an element (physical state is a gas)

The more tightly an electron is held, The more tightly an electron is held, the higher the ionization energythe higher the ionization energy

The trend in ionization energy parallels The trend in ionization energy parallels the metallic to nonmetallic trend in the the metallic to nonmetallic trend in the chemical properties of the elements in chemical properties of the elements in a perioda period

Ionization EnergyIonization Energy In the same group (top to bottom) In the same group (top to bottom)

ionization Energy ionization Energy decreasesdecreases Energy required to remove an electron decreasesEnergy required to remove an electron decreases Due to larger principal energy level (larger Due to larger principal energy level (larger nn value) value) This puts outer electron farther from nucleusThis puts outer electron farther from nucleus As As nn increases, ionization energy decreases increases, ionization energy decreases

Across same period (left to right) Across same period (left to right) ionization Energy ionization Energy increasesincreases Metals (left end) have lower ionization EMetals (left end) have lower ionization E Tend to lose electrons to form Tend to lose electrons to form + ions+ ions Nonmetals (right end) have higher ionization ENonmetals (right end) have higher ionization E Tend to gain electrons in chemical reactionsTend to gain electrons in chemical reactions

EndEnd

Documents

Chapter 9 Electrons in Atoms and the Periodic Table