The Periodic The Periodic TableTable

History of the Periodic History of the Periodic TableTable

In 1869, Dmitri Mendeleev In 1869, Dmitri Mendeleev arranged the elements according to arranged the elements according to atomic mass in an attempt to atomic mass in an attempt to classify them.classify them.

He left spaces for elements that he He left spaces for elements that he predictedpredicted existed, existed, yet hadn’t been yet hadn’t been discovered yet. discovered yet. This set him apart This set him apart from others, and he was later from others, and he was later proven correct.proven correct.

Henry Moseley

In 1913, Henry Moseley developed the concept of atomic numbers. He determined the frequencies of X-rays emitted as different elements were bombarded with high energy electrons.

Each element produces X-rays of unique frequency, and the frequency increased as atomic mass increased.

Atomic Number

Moseley arranged these frequencies in order by assigning a unique whole number, which he called the atomic number.

He correctly identified the atomic number as the number of protons in the nucleus of the atom.

This clarified some problems that Mendeleev had; Ar and K, Te and I.

Mendeleev and the Mendeleev and the Periodic LawPeriodic Law

When elements are arranged When elements are arranged in order of increasing in order of increasing atomic atomic numbernumber, their physical and , their physical and chemical properties show a chemical properties show a pattern or pattern or trend.trend.

Effective Nuclear Charge

Electrons are (-) charged and nuclei have a (+) charge.

Many properties of the atoms depend on their electron configurations and how strongly the valence electrons are attracted to the nucleus.

Effective Nuclear Charge, continued

A valence electron in an atom is attracted to the nucleus, and is repelled by the other electrons in the atom.

The inner electrons (core) are effective in shielding or blocking the nuclear attraction. (Electron shielding effect.)

Effective Nuclear Charge = +1.

Effective Nuclear Charge, continued

Zeff = Z - S Z is the number of protons in the

nucleus S is the screening constant The value of S is usually close to the

number of core electrons in the atom. The effective nuclear charge increases

as we move across a period.

Periodic Table Periodic Table ArrangementArrangement

Periods:Periods: Horizontal Rows Horizontal Rows Indicates the energy level where Indicates the energy level where

the valence electrons are the valence electrons are located. located.

ExampleExample: An element in Period : An element in Period 4 has its valence electrons in the 4 has its valence electrons in the 44thth energy level. energy level.

Periodic Table Periodic Table ArrangementArrangement

Groups/Families:Groups/Families: Vertical Vertical columnscolumns

Elements in the same column Elements in the same column have similar valence electron have similar valence electron configurations and therefore configurations and therefore similar properties.similar properties.

Example:Example: All elements in Group I All elements in Group I have 1 valence electron.have 1 valence electron.

Hydrogen is NOT a part of Group 1. It is a non-

metal and a gas.

Groups 1 and 2Groups 1 and 2

Group 1 – Alkali MetalsGroup 1 – Alkali Metals 1 valence electron1 valence electron VERY reactiveVERY reactive

Group 2 – Alkali Earth MetalsGroup 2 – Alkali Earth Metals 2 valence electrons2 valence electrons Reactive, but not as much as Group Reactive, but not as much as Group

11

Both Group 1 and Group Both Group 1 and Group 22

Reactivity increases as you go down a Reactivity increases as you go down a groupgroup

Form cationsForm cations Found as Found as compoundscompounds onlyonly , in nature , in nature Low ionization energy and low Low ionization energy and low

electronegativityelectronegativity Large radiiLarge radii Radii of positive ions are smaller than the Radii of positive ions are smaller than the

radii of atoms.radii of atoms.

Na 2e-8e-

1e-

2e-

8e-

Sodium atom with 11 electrons

Sodium ion with 10 electrons

Radius of Sodium atom versus its ion

Na

Groups 3 – 11 Groups 3 – 11 Transition ElementsTransition Elements

Metallic characteristicsMetallic characteristics Have multiple (+) ionsHave multiple (+) ions CCoolloorreedd compounds compounds

Group 17 – HalogensGroup 17 – Halogens

7 valence electrons7 valence electrons These are the most active of the non-These are the most active of the non-

metals!metals! Gains electrons easily and forms (-) ionsGains electrons easily and forms (-) ions FF22 is the most reactive and I is the most reactive and I22 is the least is the least

reactivereactive FF22 is the most electronegative and has the is the most electronegative and has the

most ionization energymost ionization energy

Group 18 – Noble GasesGroup 18 – Noble Gases

8 valence electrons8 valence electrons Inactive gases not found in Inactive gases not found in

compounds in naturecompounds in nature

Inner Transition Inner Transition ElementsElements

(Bottom Row)(Bottom Row) LanthanidesLanthanides – Lanthanoid series – ones – Lanthanoid series – ones

that follow the element Lanthanum (#57)that follow the element Lanthanum (#57) Rare earth elements that are less than Rare earth elements that are less than

0.01% in nature0.01% in nature ActinidesActinides – Actinoid series – ones that – Actinoid series – ones that

follow Actinum (#89)follow Actinum (#89) All are radioactive and unstableAll are radioactive and unstable Those after U are not found in natureThose after U are not found in nature Elements above 92 are synthetic Elements above 92 are synthetic

Broad Categories Broad Categories of the Periodic of the Periodic

TableTable

MetalsMetals The elements on the left side of the The elements on the left side of the

table.table. MalleableMalleable DuctileDuctile LustrousLustrous Conducts heat and electricityConducts heat and electricity Low ionization energies and low Low ionization energies and low

electronegativitieselectronegativities Form cations because they lose electronsForm cations because they lose electrons Mostly solidsMostly solids Reactivity increases as you go down a group.Reactivity increases as you go down a group.

Non-MetalsNon-Metals

The elements on the right side of the The elements on the right side of the tabletable Brittle as solids, with no lusterBrittle as solids, with no luster Poor conductors of heat and electricityPoor conductors of heat and electricity High ionization energies and high High ionization energies and high

electronegativitieselectronegativities Reactivities decrease as you go down a Reactivities decrease as you go down a

groupgroup Form anions because they gain electronsForm anions because they gain electrons They can be gases, liquids or solidsThey can be gases, liquids or solids

Semi-Metals (Metalloids)Semi-Metals (Metalloids)

Some properties are metallic, some Some properties are metallic, some are non-metallic and some are in-are non-metallic and some are in-betweenbetween

They are found adjacent to the They are found adjacent to the darkened line darkened line

Other information, Other information, continuedcontinued

Mono-atomic elements – He and all the Mono-atomic elements – He and all the Noble gases in Group 18Noble gases in Group 18

7 Diatomic Elements - BrINClHOF7 Diatomic Elements - BrINClHOF AllotropesAllotropes – Two different structures of – Two different structures of

the same elementthe same element Example – CarbonExample – Carbon

GraphiteGraphite diamonddiamond buckyballsbuckyballs

Buckyball

ElectronegativityElectronegativity

This is the ability to attract electronsThis is the ability to attract electrons Based on Fluorine, which is 4.0Based on Fluorine, which is 4.0 F has the greatest electronegativityF has the greatest electronegativity

(Foxy Fluorine steals other elements (Foxy Fluorine steals other elements electrons!)electrons!)

Ionization EnergyIonization Energy

The first ionization energy (The first ionization energy (II11) is the ) is the ENERGY needed to remove the first ENERGY needed to remove the first electron in a neutral atom. The second electron in a neutral atom. The second ionization energy (ionization energy (II22) is the energy ) is the energy needed to remove the second electron needed to remove the second electron and so on.and so on.

Measured in kJ/molMeasured in kJ/mol The greater the ionization energy the The greater the ionization energy the

more difficult it is to remove an electron.more difficult it is to remove an electron.

Trends Trends in the in the

Periodic TablePeriodic Table

Trends of Atomic RadiiTrends of Atomic Radii(across a period)(across a period)

The trend increases from LEFT to RIGHTThe trend increases from LEFT to RIGHT The radius decreases because the pulling The radius decreases because the pulling

power of the nucleus increases (due to an power of the nucleus increases (due to an increase in the effective nuclear charge.)increase in the effective nuclear charge.)

Na Al Si P

Radius = 190 Radius = 143

Radius = 132 Radius = 128

Atomic # 11

Atomic # 13

Atomic # 14

Atomic # 15

Trend in Atomic Radii

Trends in Atomic RadiiTrends in Atomic Radii(down a group)(down a group)

As you go down (↓) a group, the As you go down (↓) a group, the atomic radius increases.atomic radius increases.

Li 155

Na 190

K 235

Rb 240

Because . . . There is an increase in principal quantum numbers (n).

Na 2e-8e-

1e-

2e-

8e-

Sodium atom with 11 electrons (Na 0)

Radius = 190 pm

Sodium ion with 10 electrons (Na +1)

Radius = 120 pm

Radii of Neutral Atom versus Its Ion

1 e- removed

F 2e-7e-

2e-

8e-

Fluorine atom with 9 electrons (F 0)

Radius = 57 pm

Fluorine ion with 10 electrons (F -

1)

Radius = 95 pm

Radii of Neutral Atom versus Its Ion

1 e- added

F

The difference between the non-bonding atomic radius and the bonding atomic radius.

The bonding atomic radius is shorter than the non-bonding radius.

Atomic Radii and Bond Atomic Radii and Bond LengthsLengths

Knowing atomic radii allows us to Knowing atomic radii allows us to estimate the bond lengths between estimate the bond lengths between different atoms in molecules.different atoms in molecules.

Ex: The ClEx: The Cl � � Cl bond length in ClCl bond length in Cl22 is is 1.99 1.99 Å, Å, so a radius of 0.99Å is so a radius of 0.99Å is assigned to Cl. In CCl4, the assigned to Cl. In CCl4, the measured length of the measured length of the CC � � Cl is Cl is 1.77Å, close to the sum of the atomic 1.77Å, close to the sum of the atomic radii of C and Cl (0.77Å + 0.99Å).radii of C and Cl (0.77Å + 0.99Å).

Isoelectronic SeriesIsoelectronic Series

This is a group of ions all containing This is a group of ions all containing the same number of electrons.the same number of electrons.

The series: OThe series: O-2-2, F, F--, Na, Na++, Mg, Mg2+2+, and , and AlAl3+ 3+ all have 10 electrons.all have 10 electrons.

Nuclear charges increase as you Nuclear charges increase as you move through a series, and the move through a series, and the atomic radius of the ion decreases.atomic radius of the ion decreases.

Trends of Electronegativity Trends of Electronegativity and Ionization Energyand Ionization Energy

(across a period)

Electronegativity INCREASESIonization Energy INCREASES

WHY

?

The increased effective nuclear charge makes it harder to remove electrons.

Trends of Electronegativity Trends of Electronegativity and Ionization Energyand Ionization Energy

(down a group)

Electronegativity

DECREASES

Ionization Energy

DECREASES

WHY?

Electrons are held less tightly because energy levels increase and there is more electron shielding.

Electron AffinityElectron Affinity Most atoms gain electrons to form Most atoms gain electrons to form

anions. The energy change that anions. The energy change that occurs when an electron is added to an occurs when an electron is added to an atom is called electron affinity because atom is called electron affinity because it measures the attraction (or affinity) it measures the attraction (or affinity) of the atom for the added electron.of the atom for the added electron.

For most atoms, energy is For most atoms, energy is releasedreleased when electrons are added.when electrons are added.

Cl(Cl(gg) + e) + e-- → → ClCl--((gg)) ΔΔE = E = --349 kJ/mol349 kJ/mol

Trends of Metallic Trends of Metallic CharacteristicsCharacteristics

Across a period –

DECREASE

In metallic character

Down a group –

INCREASE

in metallic character

(There is an increased

attraction for electrons.)

(There is a decreased

attraction for electrons.)

Metallic CharacterMetallic Character

Metals have low ionization energies and Metals have low ionization energies and therefore tend to form positive ions easily. therefore tend to form positive ions easily.

As a result, metals are oxidized (lose As a result, metals are oxidized (lose electrons – LEO) when they undergo electrons – LEO) when they undergo chemical reactions.chemical reactions.

Most metal oxides are basic. Those that Most metal oxides are basic. Those that dissolve in water react to form metal dissolve in water react to form metal hydroxides.hydroxides.

CaO (CaO (ss) + HOH ) + HOH →→Ca(OH)Ca(OH)22 ( (aqaq))