The Atom

Concepts to Master• How big are subatomic particles in

relationship to one another and to the whole atom?

• Where are the subatomic particles located within the atom?

• What are the charges of the subatomic particles?

• Which atomic theory is most current?• Which atomic theory states that electrons are

in clouds?• What is Dalton’s contribution to chemistry?• Who discovered that electrons are negatively

charged?• What was the name of Rutherford’s

experiment why was it so important?• Whose model is like the planetary model?• What are differences between Bohr’s model

and the wave-mechanical model of the atom?• What is the mass number equal to?• What is the atomic number equal to?• How do you write the symbols for isotopes of

the same element?• How do you calculate atomic mass?• When is an atom neutral?

• Where are valence electrons found?• What do the chemical properties of an element

depend on?• How are ions formed and how are they

written?• How do you write an equation that shows

magnesium losing electrons?• How do you write an equation that shows

phosphorous gaining electrons?• Why do ions form?• Counting subatomic particles for neutral atoms

and ions• How do you draw a Lewis dot diagram for a

neutral atom, a cation, and an anion?• What is the relationship between an electron’s

energy and its distance to the nucleus?• What do electrons do when they gain energy?• What do electrons do when they lose energy?• How can you tell the difference between an

atom in the excited state and an atom in the ground state?

• Recognize an emission spectrum and an absorption spectrum.

• Identify an element based on its spectrum.

Vocab• Absorption spectrum• Anion• Atom• Atomic mass• Atomic number• Cation• Chemical property• Compound• Continuous spectrum• Dual nature concept• Electromagnetic spectrum• Electron• Electron configuration• Emission spectrum• Excited state• Ground state• Ionic charge

• Ions• Isotope• Mass number• Matter• Neutron• Nucleus• Octet rule• Orbitals• Orbits• Oxidation number• Proton• Subatomic particle• Valence electrons• Valence shell

Labs

• Atomic Structure

• Atomic Mass of Beadrock

• Atomic Spectrum

The Atom• The smallest component of an element.

– So if there are103 different elements there are 103 different types of atoms.

• Basic unit of all matter.– Matter is anything that has mass and volume.

Subatomic Particles• Protons• Neutrons• Electrons

• Mass– electron mass = 9.10938188 × 10-31 kg– neutron mass = 1.6749286 × 10-27 kg– proton mass = 1.67262158 × 10-27 kg

• amu– Atomic mass unit– 1 amu = mass of 1 proton– 1 amu = mass of 1 neutron– Easier for scientists to write in terms of amu

• Mass of an electron is approximately 1/1836 of the mass of a proton or 1/1836 th of an amu.

Nucleons located inthe Nucleus of an atom

Proton -skyscraper

Electron - Rat at the bottom of the skyscraper

Atomic Structure Theories

• Dalton– atoms are the basic units of matter

• JJ Thompson– Plum pudding where the raisin are electrons

• Rutherford– Atoms are mostly empty space

• Bohr– Electrons are located in specific orbits around the

nucleus• Wave Mechanical Model

– Electrons exist in “clouds” around the nucleus

Pg 66-69

Dalton

• Elements are composed of extremely small particles called atoms.

• All atoms of a given element have identical properties.

• Compounds are formed when atoms of different elements combine with one another in small whole numbers.

• The relative numbers and kinds of atoms are constant in a given compound.

Dalton’s Elements in 1805

JJ Thompson1903

• Atom can be divided into parts. One of which is an electron.

• These are negatively charged particles embedded in a positively charged atom.

• Raisins embedded in plum pudding

Rutherford

• An atom contains a dense positively charged nucleus.

• The rest of the atom is mostly empty space where the electrons are.

• Determined this theory after performing the gold-foil experiment.

1909

Rutherford’s Gold-foil Experiment

•Rutherford directed alpha particles (radioactive source) which are positively charged and smaller than atoms at a thin piece of gold foil.

•He expected all the alpha particles to pass through (detected by the fluorescent screen) with just a few being slightly defected.

Rutherford’s Gold-foil Experiment

Results:1. Most of the particles did go straight through (atoms are mostly empty space).2. A few were slightly deflected. BUT, some were GREATLY deflected. They

were strongly repelled by a dense, positive, central core and bounced back

Bohr• Electrons are located in specific orbits around the

nucleus.• Each electron must contain a certain amount of energy

to stay in its orbit. The further the electron is from the nucleus, the more energy it contains.

PlanetaryModel

1913

Pg 80-82

Wave – Mechanical Model• Previously matter was

considered a particle and energy was considered a wave.

• This current model predicts that matter and energy can act like waves or particles – Dual Nature Concept

• In this model (aka - the electron cloud model), the electrons are in orbitals, which are defined as regions of the most probable electron location.

Pg 82-85 (2.9-2.10)

Bohr’s Model versus the Wave – Mechanical Model

• The difference is in the description of electron location around the nucleus.

• Bohr suggested well defined, fixed orbits.• The wave-mechanical model shows

electrons located around the nucleus in orbitals.

• An orbital is a region in which an electron with a certain amount of energy is most likely to be located (like a cloud).

• Rutherford’s Ghost – 2:30 min

• http://www.youtube.com/watch?v=ic5Q3_W7q7w&feature=related

• Electron in motion – wave mechanical model – 1 min – notice electrons don’t stay in a single path, more of a vibration cloud

• http://www.youtube.com/watch?v=32uEvwxNJvE&feature=related

The Nucleus

• Contains both protons and neutrons– Similar in size– Protons are positively charged– Neutrons are not charged, they’re neutral– So overall charge of the nucleus is POSITIVE

Pg 70-75 (2.5-2.6)

Atomic Number

• Equals the number of protons in an atoms nucleus.

• It identifies the element.• It NEVER changes unless

the element has changed.• All atoms of Lithium will

have 3 Protons.

Nucleus of atom like Nucleus inside of cell

• Both contain information that is critical for identification– Cell nucleus contains

DNA that identifies the functions of that cell.

– Atomic nucleus contains a certain number of protons that identifies the element and its properties.

Mass Number

• Equals the number of Protons + Neutrons in the nucleus.

• Does NOT identify the element.

• Li : mass # = 7

• The # of neutrons an the nucleus can change thus mass # can change.

Isotopes

• Atoms of the same protons but with a different number of neutrons.

• The number of protons does NOT change.

Isotopes

31H = H3

1 =H3= H-3

126C 13

6C 146C

• The Element is __________• The number 6 refers to the # of ________• The numbers 12,13,14 refer to the # of _______• How many protons and neutrons are in the first

isotope?• How many protons and neutrons are in the

second isotope?• How many protons and neutrons are in the third

isotope?

Atomic mass• Decimal• Average of all the isotopes that occur in

nature.

C-12C-13C-14

Calculating Atomic Mass

• Of all the naturally occurring Copper, 30.8% are atoms of Copper-65 and 69.2% of copper-63. What is the atomic mass of Cu?

• Step 1 - convert percentages into decimals

30.8/100 = .308 69.2/100 = .692

• Step 2 – Calculate the contribution of each isotope to the atomic mass by multiplying the decimal percentage by the mass # for each isotope.

0.308 x 65 AMU = 20.2 AMU0.692 x 63 AMU = 43.596 AMU

• Step 3 – Add them together to get the weighted average for the atomic mass.

20.2 AMU+ 43.596 AMU 63.796 AMU

UraniumIsotope Atomic

#

Mass

#

# of Protons

# of Neutrons

# of Electrons

% found in

NATURE

U-235

23592U

0.7

U-238

23892U

99.3

Calculate ATOMIC MASS

BoronIsotope Atomic

#

Mass

#

# of Protons

# of Neutrons

# of Electrons

% found in

NATURE

B-10

105B

19.9

B-11

115B

80.1

Calculate ATOMIC MASS

• Discovering the elements• Handout is Introduction to the elements• 36 min from intro to size of atoms segment• http://player.discoveryeducation.com/index.cfm?

guidAssetId=2113C4B6-CECB-42E5-B8E4-1244EB5EC32F&blnFromSearch=1

• Physical Science Series: Atomic Structure and the Periodic Table

• 11 min from intro thru electron segment • Handout is atomic structure• http://player.discoveryeducation.com/index.cfm?

guidAssetId=298799C9-686A-461A-A060-851A721FB678&blnFromSearch=1

Electrons 101

• Found in energy levels around the nucleus (orbitals according to the wave-mechanical model)

• Negatively charged• Very, Very, Very small• When atoms are neutral (no charge), protons =

electrons, Na0.• Can be gained or lost from the outer most

energy level– Valence electrons are found in the valence shell.– These are responsible for most chemical reactions

and in the formation of compounds.– Every atom wants 8 valence electrons (unless it has

only 1 energy level, then it wants only 2).

Valence Electrons

In general, the number of valence electrons affects the chemical properties of an element.Valence electron # = Group # of the periodic table.

unless it has only 1 energy level, then it wants only 2

In an effort to achieve an octet atoms becomes charged and

IONS are formed.

Ion Types - Cations• Sodium has 3 orbits (Bohr Model)• The third orbit has 1 electron. • To be more stable

– give away the only electron it has in the third orbit

– receive 7 more electrons from another atom in order for it to have 8 electrons on the outer orbit.

– Both processes would have sodium ending up with 8 electrons on its outer orbit.

– Giving away 1 electron is easier than receiving 7 electrons.

• Sodium will lose 1 electron which means that it now has 10 electrons and 11 protons.

• It has 1 less electron than proton so it’s charge is +1.

• Na --> Na+1 + 1e

Cats are +

• Oxygen has 2 orbits (Bohr Model).• The second orbit has 6 electrons. • To be more stable

– give away all the 6 electrons on the second orbit

– receive 2 more electrons from another atom.

– Both processes will lead to oxygen having 8 electrons on its outer orbit.

– receiving 2 more electrons from another atoms is easier than giving away all its 6 electrons.

• Oxygen will receive 2 more electrons which means it now has 10 electrons and 8 protons.

• It has 2 more electrons than protons so it’s charge is -2.

• O + 2e --> O-2

Ion Types - Anions

+ 2 e

IONS

Oxidation Number

Ionic Charge = Oxidation Number

ION Oxidation Number

Na+

Mg+2

Cl-

O-2

H+

S-2

Fe+3

Cu+1

Na and Cl

Na

(Metal)

Cl

(non-Metal)

# of valence electrons?

How many will be lost or gained to achieve an octet?

Ion type

Oxidation #

Ca and Cl

Ca

(Metal)

Cl

(non-Metal)

# of valence electrons?

How many will be lost or gained to achieve an octet?

Ion Type

Oxidation #

Al and O

Al

(Metal)

O

(non-Metal)

# of valence electrons?

How many will be lost or gained to achieve an octet?

Ion Type

Oxidation #

Counting Subatomic Particles

• Bi– Number of protons = a– Number of electrons = b– Number of neutrons = c– Atomic number = 83 – Mass # = 209

• As-3

– Number of protons = 33– Number of electrons = a– Number of neutrons = 42– Atomic number = b – Mass # = c

Atomic Mass = Mass #

Counting Subatomic Particles

• Te+6

– Number of protons = 52– Number of electrons = a– Number of neutrons = b– Atomic number = c – Mass # = 128

Atomic Mass = Mass #

• Os+4

– Number of protons = a– Number of electrons = b– Number of neutrons = 114– Atomic number = 76 – Mass # = c

• http://player.discoveryeducation.com/index.cfm?guidAssetId=AE2C7A14-611A-4857-86F2-66933E4C286A&blnFromSearch=1&productcode=US

• How boron ions form – 2 min

Lewis Dot Diagrams

• Show only Valence Electrons for the element.• Steps for drawing them

– Write the elemental symbols for the atoms

– Fill in the electrons• If more than 2, place 1 electrons at each side of the element

symbol and then double up as needed.

• If there are 2 valence electrons, place both of them on the same side of the element symbol.

S

Ca

Atoms versus Ions

O vs O-2

Mg vs Mg+2

P vs P-3

Lewis Dot Diagrams

• Cations have NO electrons in the outermost orbital.

• Anions have 8 in the outermost orbital.

Cs

I-1

+1

Which diagrams show a full valence shell?

Zn+2

Ag+1

Electrons 102• Each electron in an atom has its own distinct

amount of energy.– depending on their orbital

• Electrons in orbitals closer to the nucleus have less energy and are more stable

• Electrons in orbitals further from the nucleus have more energy and are less stable

• When all electrons in an atom are in their lowest possible energy level, the atom is at its ground state.– The number of electrons found in each orbital when

an atom is at the ground state can be found on the periodic table.

– This is the atoms electron configuration.Pg 76-79 (2.7-2.8)

Phosphorus (P): 2-8-5Ground State

• P has 3 orbitals• The first orbital closest to

the nucleus contains 2 electrons.

• The second contains 8.• The third contains 5.• P has 5 valence electrons

(the # of electrons in the outermost shell)

2-8-5 is the P atom’s electron configuration

Iron (Fe): 2-8-14-2Ground State

• Fe has 4 orbitals• The first orbital closest to

the nucleus contains 2 electrons.

• The second contains 8.• The third contains 14.• The fourth contains 2• Fe has 2 valence electrons

(the # of electrons in the outermost shell)

2-8-14-2 is the Fe atom’s electron configuration

Electrons ABSORB energy to become EXCITED

• When an electron in an atom gains a specific amount of energy, the electron becomes excited and jumps to a higher energy level (orbital).

– The energy can come from outside sources like heat, light, electricity.

– Copper is absorbing energy from a Bunsen burner flame.

• The ground state configuration changes.

• But the total number of electrons stays the same.

• Ground state = 2-8-5 – Total electrons = 15

• Excited State = 2-7-6 – Total electrons = 15

Phosphorus (P): 2-7-6Excited State

Iron (Fe): 2-8-13-3Excited State

• Ground state = 2-8-14-2– Total electrons = 26

• Excited State = 2-8-13-3– Total electrons = 26

Electrons EMIT energy to go back to the Ground State

• After jumping to a higher level, the electron will very quickly return to its original level.– The energy they previously

absorbed is now released as infrared, ultraviolet, or visible light.

– This emitted energy can be used to identify an element.

– Copper emits blue light as its electrons return to the ground state.

Electricity

Ground State Absorption of energy

Excited State

The amount of energy absorbed

the amount of energy emitted=

Electromagnetic Spectrum

• The energy released as the electron returns to the ground state has a certain wavelength.

• Every electron within an atom has a specific energy which when released will correspond with a specific wavelength.

Conservation of EnergyEnergy can not be created or destroyed

(but it can change form)

The amount of energy absorbedby the electron

The amount of energy emittedby the electron

=

SO

Electric Pickle Demo

Atomic Spectrum

• Elements can be identified by the wavelengths of energy that each of their electrons absorbs or emits.– Emission spectrum– Absorption spectrum

http://jersey.uoregon.edu/vlab/elements/Elements.html

Types of Spectrum

Continuous

Emission

Absorption

Which element is it?

Fe

C

Ne

Na

Unknown

Are these emission or absorption spectrum?

IONS and Electron Configuration

Mg Mg+2

Lewis Dot Diagram

Electron Configuration 2-8-2 2-8

+2

IONS and Electron ConfigurationElement Atom electron

configurationIon electron configuration

(top ox # on periodic table)

Br

Al

Sc

Sr [Kr]

N

Cs

IONS and Electron ConfigurationElement Atom electron

configurationIon electron configuration

(top ox # on periodic table)

Br 2-8-18-7 [2-8-18-8]-1

Al 2-8-3 [2-8]+3

Sr [Kr]-8-2 [{Kr}-8]+2

N 2-5 [2-5-3]-3

Cs [Xe] - 1 [2-8-18-18-8]+1

IONS and Electron Configuration

Mg Mg+2

Lewis Dot Diagram

Electron Configuration 2-8-2 2-8

+2

Check

• P-3 • Number of protons = a• Number of electrons = 18• Number of neutrons = b

• Atomic number = c • Mass number = 31

• a = __________• b = _________• c = _________

•Give the electron configuration for sulfur in ground state and the excited state:

2-8-62-7-7