Lecture 26 11/04/05

1) Write the spdf notation for Cl.2) Which element is larger: Si or Ar?

Trends in Ionization EnergyTrends in Ionization Energy

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 350

500

1000

1500

2000

2500

1st Ionization energy (kJ/mol)

Atomic NumberH Li Na K

HeNe

ArKr

IE increases across a period because Z* increases.

Metals lose electrons more easily than nonmetals.

Trends in Ionization EnergyTrends in Ionization Energy

IE decreases down a group Size increases easier to lose an electron

Electron Affinity

Electron affinity is the energy involved when an atom gains an electron to form an anion.

A(g) + e- ---> A-(g) E.A. = ∆E

Electron Affinity of OxygenElectron Affinity of Oxygen

∆E is exothermic

[He] O atom

EA = - 141 kJ

+ electron

O [He] - ion

Electron Affinity of Nitrogen

∆E is zero for N- due to electron-electron repulsions.

EA = 0 kJ

[He] N atom

[He] N- ion

+ electron

Trends in Electron Affinity

•Electron affinity becomes more negative across a period •Electron affinity becomes less negative down a group

•(except for some elements going from n=2 to n=3).

Fill in the table

On

Ch E M

Element Atomic radius (pm)

90

120

140

180

Compare the elements Na, Mg, and P.

a) Which has the largest atomic radius?b) Which has the most negative electron

affinity?c) Place the elements in the order of

increasing ionization energy.

A = [Ar]4s2 B = [Ar]3d104s24p5

a) Is element A a metal, metalloid, or nonmetal?b) Is element B a metal, metalloid, or nonmetal?c) Which element is expected to have a larger

ionization energy?d) Which element has a smaller atomic radius?

Valence Electrons Electrons in the outermost shell Determines the chemical properties of atoms Reactions involve loss, gain, or rearrangement of

electrons

Core Electrons Electrons in the inner shells Not involved in chemical reactions

Main group elements: Valence electrons = s and p electrons in outermost

shell Valence electrons are equal to the group number

Transition elements: Valence electrons = ns and (n-1)d electrons Valence electrons are equal to the group number

Valence electrons

Valence ElectronsValence

ElectronsB 1s2 2s2 2p1

Core = [He] , valence = 2s2 2p1

Br [Ar] 3d10 4s2 4p5

Core = [Ar] 3d10 , valence = 4s2 4p5

ExampleWrite the spdf, noble gas, and electron

orbital notation for carbon. Which are the valence electrons? Which are the core electrons?

Lewis Electron Dot Symbols

Represents valence shell electrons

Arrange electrons in pairs around the atom Maximum of eight electrons Octet rule

ExampleWrite the Lewis Dot Symbols for:NitrogenPhosphorous

Bonds

1. Atoms achieve noble gas configuration1. Quest for complete octet

2. Products tend to have a lower chemical potential than the reactants

3. The bond that forms has the lowest potential energy (greatest stability)

Bonding

Quest for complete octet

Covalent bonds:Molecular compoundsSharing of valence electronsCl2

Ionic bond Ionic compoundsValence electrons are transferred

from one atom to anotherMetal + non-metalNaCl

Bonding