Chemical PeriodicityChemical Periodicity

Mendeleev’s Periodic TableMendeleev’s Periodic Table In 1871, Dmitri In 1871, Dmitri

Mendeleev arranged Mendeleev arranged all of the then-all of the then-known elements by known elements by order of order of increasing increasing atomic mass.atomic mass.

The Modern Periodic TableThe Modern Periodic Table

In 1913, Henry Moseley In 1913, Henry Moseley created a more accurate created a more accurate positioning of the positioning of the elements in the modern elements in the modern periodic table. He periodic table. He arranged the elements in arranged the elements in order of order of increasing increasing atomic number.atomic number.

He was killed in action at He was killed in action at Gallipoli in 1915 at the age of Gallipoli in 1915 at the age of 28.28.

The Modern Periodic TableThe Modern Periodic Table

The Periodic TableThe Periodic Table

RememberRemember…… Vertical columns are Vertical columns are groupsgroups.. Horizontal rows are Horizontal rows are periodsperiods..

andand…… Valence electronsValence electrons – electrons in the – electrons in the

outermost (highest) principal energy level outermost (highest) principal energy level of an atom of an atom

Core electronsCore electrons – inner electrons – inner electrons

Patterns in the electron Patterns in the electron configurations of the elementsconfigurations of the elements

The noble gasesThe noble gases:: these are elements in which the these are elements in which the

outermost outermost ss and and pp sublevels are sublevels are completely filled.completely filled.• He: 1sHe: 1s22

• Ne: 1sNe: 1s22 2s 2s22 2p 2p66

• Ar: 1sAr: 1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66

Patterns in the electron Patterns in the electron configurations of the elementsconfigurations of the elements

The representative elementsThe representative elements:: these elements have the outermost these elements have the outermost ss

and and pp sublevel only partially filled. sublevel only partially filled.

• Li: 1sLi: 1s22 2s 2s11 • Na: 1sNa: 1s22 2s 2s22 2p 2p66 3s 3s11 • K: 1sK: 1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p6 6 4s4s11

Patterns in the electron Patterns in the electron configurations of the elementsconfigurations of the elements

The transition metalsThe transition metals:: In these metallic elements, the In these metallic elements, the

outermost outermost ss and nearby and nearby dd sublevel sublevel contain electrons.contain electrons.

The inner transition metalsThe inner transition metals:: In these metallic elements, the In these metallic elements, the

outermost outermost ss and nearby and nearby ff sublevel sublevel generally contain electrons.generally contain electrons.

Patterns in the electron Patterns in the electron configurations of the elementsconfigurations of the elements

Elements with the same valence electron Elements with the same valence electron arrangement show very similar chemical arrangement show very similar chemical behavior. behavior.

Electron configurations for K through KrElectron configurations for K through Kr

Electron Configurations and the Electron Configurations and the Periodic TablePeriodic Table

Practice writing electron Practice writing electron configurations from the periodic table.configurations from the periodic table.

Covalent atomic radiusCovalent atomic radius

It is not possible to directly measure the size of It is not possible to directly measure the size of an atom.an atom.

Chemists determine the distance between the Chemists determine the distance between the nuclei in atoms of diatomic elements, then divide nuclei in atoms of diatomic elements, then divide this by 2 to find the radius of one atom.this by 2 to find the radius of one atom.

I. Periodic Trend in I. Periodic Trend in Atomic SizeAtomic Size

Atomic radius tends to increase down the group.

Atomic radius tends to decrease across the period.

Atomic radiusAtomic radius

Atomic radiusAtomic radius

Reason for the trendsReason for the trends

Atomic size decreases across the period Atomic size decreases across the period because the because the effective nuclear chargeeffective nuclear charge increases increases across the period.across the period.

Atomic size increases down the group because Atomic size increases down the group because the shielding effect increases down the group.the shielding effect increases down the group.

((Shielding effectShielding effect occurs as the core electronsoccurs as the core electrons shield the attraction of the nucleus on the shield the attraction of the nucleus on the outermost electrons.)outermost electrons.)

II. Periodic Trend in II. Periodic Trend in Ionization Energy (IE)Ionization Energy (IE)

Ionization EnergyIonization Energy (IE) is the (IE) is the energy required to remove an energy required to remove an electron from a gaseous atom.electron from a gaseous atom.

NaNa(g)(g) Na Na++(g) (g) + e+ e--

Ionization energyIonization energy

Ionization Ionization Energy (IE) in Energy (IE) in kilojoules/molekilojoules/mole

First IEFirst IE is the energy is the energy required to remove required to remove the first electron.the first electron.

Second IESecond IE is the is the energy required to energy required to remove the second remove the second electron (NOT both electron (NOT both first + second), etc.first + second), etc.

Explain why there is Explain why there is a large increase a large increase between the first between the first and second IE for and second IE for Na. Na.

Explain why there is Explain why there is a large increase a large increase between the between the second and third IE second and third IE for Mg.for Mg.

Predict where there Predict where there will be a large will be a large increase in IE for increase in IE for Al.Al.

Ionization Energy (IE)Ionization Energy (IE) Ionization energy

tends to decrease down a group.

Ionization energy tends to increase across a period.

Explain why the trend is as described (same reason as for the size trend).

Explain why these elements do Explain why these elements do notnot follow follow the trend...the trend...

Consider the electron Consider the electron configurations as you configurations as you explain why the trend explain why the trend is not always is not always consistent as you consistent as you move across the move across the period (such as period (such as across period 2, from across period 2, from Li to Ne). Li to Ne).

Why is the IE lower Why is the IE lower than predicted by the than predicted by the trend for B? …for O?trend for B? …for O?

Ionization energyIonization energy

IE in MetalsIE in Metals Metals tend to lose electrons to Metals tend to lose electrons to

form positive ions because their form positive ions because their ionization energies are low. ionization energies are low.

III. Periodic Trend in III. Periodic Trend in Electron Affinity (EA)Electron Affinity (EA)

Electron affinityElectron affinity (EA) is the energy (EA) is the energy change that accompanies the addition change that accompanies the addition of an electron to a gaseous atom.of an electron to a gaseous atom.

BrBr(g)(g) + e + e-- Br Br--(g)(g)

Electron affinityElectron affinity

Electron AffinityElectron Affinity

Electron Affinities for the Representative Elements (in kilojoules/mole)Electron Affinities for the Representative Elements (in kilojoules/mole)

Electron AffinityElectron Affinity

Electron AffinityElectron Affinity tends to decrease down a group.

Electron AffinityElectron Affinity tends to increase across a period.

Explain why the trend is as described (same reason as for the size trend).

Electron affinityElectron affinity

IV. Periodic Trend in Ionic SizeIV. Periodic Trend in Ionic Size

Cations are smaller than their original Cations are smaller than their original atoms. (Remember; atoms lose electrons atoms. (Remember; atoms lose electrons to form “+” cations.)to form “+” cations.)

Anions are larger than their original atoms. Anions are larger than their original atoms. (Atoms gain electrons to form “-” anions)(Atoms gain electrons to form “-” anions)

Ionic radius increases down the group (as Ionic radius increases down the group (as does atomic radius).does atomic radius).

Ionic SizeIonic Size

V. Periodic Trend in EV. Periodic Trend in Electronegativitylectronegativity

ElectronegativityElectronegativity – the tendency for the – the tendency for the atom to attract electrons to itself in a atom to attract electrons to itself in a chemical bond chemical bond

Increases from left to right across a Increases from left to right across a period period

Decreases down a groupDecreases down a group

Pauli Electronegativity ValuesPauli Electronegativity Values

ElectronegativityElectronegativity

ElectronegativityElectronegativity

Linus Pauling Linus Pauling established the established the concept of concept of electronegativity and and developed a developed a scale that helped to predict that helped to predict the nature of chemical the nature of chemical bonding. bonding.

In 1954, Pauling was In 1954, Pauling was awarded the awarded the Nobel Prize in Chemistry. .

Summary of Periodic TrendsSummary of Periodic Trends

Review Group NamesReview Group Names

Remember:Remember:

Group 1A = Alkali metalsGroup 1A = Alkali metals Group 2A = Alkaline earth metalsGroup 2A = Alkaline earth metals Group 7 A = HalogensGroup 7 A = Halogens Group 0 = Noble GasesGroup 0 = Noble Gases