Ch 8 Periodic Relationships

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Periodic Relationships Amongthe Elements

Chapter 8

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When the Elements Were Discovered

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n s 1

n s 2

n s 2 n p 1

n s 2 n p 2

n s 2 n p 3

n s 2 n p 4

n s 2 n p 5

n s 2 n p 6

d 1

d 5

d 1 0

4f

5f

Ground State Electron Configurations of the Elements

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Classification of the Elements

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Electron Configurations of Cations and Anions

Na [Ne]3s1 Na+ [Ne]

Ca [Ar]4s2 Ca2+ [Ar]

Al [Ne]3s23p1 Al3+ [Ne]

Atoms lose electrons so thatcation has a noble-gas outerelectron configuration.

H 1s1 H- 1s2 or [He]

F 1s22s22p5 F- 1s22s22p6 or [Ne]

O 1s22s22p4 O2- 1s22s22p6 or [Ne]

N 1s22s22p3 N3- 1s22s22p6 or [Ne]

Atoms gain electronsso that anion has anoble-gas outerelectron configuration.

Of Representative Elements

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+ 1

+ 2

+ 3

- 1

- 2

- 3

Cations and Anions Of Representative Elements



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Na+: [Ne] Al3+: [Ne] F-: 1s22s22p6 or [Ne]

O2-: 1s22s22p6 or [Ne] N3-: 1s22s22p6 or [Ne]

Na+, Al3+, F-, O2-, and N3- are all isoelectronic with Ne

What neutral atom is isoelectronic with H- ?

H-: 1s2 same electron configuration as He

Isoelectronic: have the same number of electrons, andhence the same ground-state electron configuration

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Electron Configurations of Cations of Transition Metals

When a cation is formed from an atom of a transition metal,electrons are always removed first from the ns orbital and

then from the (n – 1)d orbitals.

Fe: [Ar]4s23d6

Fe2+: [Ar]4s03d6 or [Ar]3d6

Fe3+: [Ar]4s03d5 or [Ar]3d5

Mn: [Ar]4s23d5

Mn2+: [Ar]4s03d5 or [Ar]3d5

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Effective nuclear charge (Z eff) is the “positive charge” feltby an electron.

Na

Mg

Al

Si

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12

13

14

10

10

10

10

1

2

3

4

186

160

143

132

Z effCoreZ Radius (pm)

Z eff = Z - σ 0 < σ < Z (σ = shielding constant)

Z eff ≈ Z – number of inner or core electrons

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Effective Nuclear Charge (Z eff)

increasing Z eff

i n c r e a s i n g

Z e f f

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Atomic Radii

metallic radius covalent radius

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Trends in Atomic Radii

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Comparison of Atomic Radii with Ionic Radii

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Cation is always smaller than atom fromwhich it is formed.Anion is always larger than atom fromwhich it is formed.

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The Radii (in pm) of Ions of Familiar Elements

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Chemistry in Action: The 3rd Liquid Element?

L i q ui d ?

117 elements, 2 are liquids at 250C –Br2 and Hg

223Fr, t1/2 = 21 minutes

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Ionization energy is the minimum energy (kJ/mol) requiredto remove an electron from a gaseous atom in its groundstate.

I 1 + X (g) X+(g) + e-

I 2 + X+(g) X2+

(g) + e-

I 3 + X2+(g) X3+

(g) + e-

I 1 first ionization energy

I 2 second ionization energy

I 3 third ionization energy

I 1 < I 2 < I 3



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Filled n=1 shell

Filled n=2 shell

Filled n=3 shell

Filled n=4 shellFilled n=5 shell

Variation of the First Ionization Energy with Atomic Number

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General Trends in First Ionization Energies

Increasing First Ionization Energy

I n c r e a s i n g

F i r s t I o n i z a t i o n

E n e r g y

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Electron affinity is the negative of the energy change thatoccurs when an electron is accepted by an atom in thegaseous state to form an anion.

X (g) + e - X-(g)

F (g) + e - X-(g)

O (g) + e - O-(g)

∆H = -328 kJ/mol EA = +328 kJ/mol

∆H = -141 kJ/mol EA = +141 kJ/mol

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Variation of Electron Affinity With Atomic Number (H – Ba)

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Ch 8 Periodic Relationships