Periodic Properties

electron configurations properties

hydrogen atom 1 electron

to remove e- nf = ∞

E = x 6.022 x 1023 atomsatom mol

= 1311 kJmol

Z = 1

from ground state ni = 1

2.178 x 10-18 J

E =1

nf2

-1

ni2

- RH Z2

nuclear charge

1s1

Ionization Energy, I

He+ Z = +2

E =1

nf2

-1

ni2

- RH Z2 = 5250 kJ/mol

1s1 E = 5250 kJ/mol

systems with more than 1 electron

studied experimentally ionization reactions

higher nuclear charge lowers orbital energy

-

+

-

2+

stabilizes system

H 1s1 Z = +1 E = 1311 kJ/mol

1. Effect of 2 electrons in same orbital

He 1s2

Z = +2

E = 2372 kJ/mol

same nuclear charge

-

2+

-

2+ -

orbital energy higher

e- e- repulsion

less stable

easier to remove e-

He+ 1s1 E = 5250 kJ/mol

2. Effect of electrons in different orbital

Li

Li2+

1s2

2s1

Z = +3

E = 2954 kJ/mol

E = 520 kJ/mol

same nuclear charge

3+3+

ground state 2s1

excited state

1s 1s

2s 2s

-

-

-

-

inner electrons shielding chargeZeff < Z

3. Effect of orbital shape

Li

Li

1s2

1s2

Z = +3

E = 341 kJ/mol

E = 520 kJ/mol

same nuclear charge

ground state 2s1

excited state 2p1

3+

1s

2s

3+

1s

2p

-

-

--

-

-

s orbitals penetrating lower energy

determine orbital energiesElectrostatic interactions

1. Greater nuclear charge (Z) lowers energy

2. Electron-electron repulsion raise energy

electrons more difficult to remove

electrons easier to removeelectrons shield Z

inner electrons shield better

3. Orbitals with more penetration lower energy

electrons more difficult to remove

s < p < d < f

Ionization Energy

energy required to remove an e- from gas phase atoms

X+ (g) X2+(g) + e-

first ionization energy I1X (g) X+(g) + e-

second ionization energy I2

lowest I1 Csn = 6

highest I1 Hen = 1

I1 decrease Zeff decreases more shielding e-

I1 increase Z increases shielding stays same

core e-

adding valence e-

core e- unchanged

5+

1s

2s

2p

10+

-

1s

2s

2p

-

-

-

-

-

-

-

-

-

B Ne

-

-

-

-

-

4+

1s

2s

Be B

5+

1s

2s

2p

-

-

N O

-

-

-

-

-

-

-

e- e- repulsion

Second Ionization Energy I2

Na

I1 I2 I3 I4 I5 I6 I7

Mg

AlSi

P

S

Cl

Ar

495

735

580

780

1060

1005

1255

1527

4560

1445

1815

1575

1890

2260

2295

2665

7730

11,600

16,100

21,200

27,000very difficult to removecore electrons

Atomic Radius

metallic radius Al 143 pm

covalent radiusCl 100 pm

C-Cl 177 pm

Cl 100 pm

C 77 pm

Atomic Radiusincrease in size n dominates

decrease in size

Zeff dominates

Ionic sizes

e-

+ -

isoelectronic series

46 e-

+49 +50 +51 ions get smaller

same # electrons