0.77 + 1.14

Approximate bonding atomicradii for the elements havebeen tabulated.

The distance between bonded nuclei can beapproximated by adding radii from both atoms.

e.g., Bonding atomic radii are as follows:

So the approximate distance betweenbonded C and Br nuclei = = 1.91 A

C = 0.77 A, Br = 1.14 A

r rd

more p+, but no new (i.e., farther away) energy levels

Atomic Radius

As we go down a group,atomic radius…

-- principal quantum numberincreases (i.e., a newenergy level is added)

increases.

As we go from left to right across theTable, atomic radius… decreases.

-- effective nuclear charge increases, but principal quantum number is constant

Coulombic attraction depends on…

2– 2+

2+ 2– 1–

2–

1+

2+

amount of charge distance between charges

+ + – –

H

He

+ –

+ – + –

As we go , more coulombic

attraction, no new energy level, more pull, smaller size

Sr < Ba < Cs

Arrange the following atoms in order of increasingatomic radius: Sr, Ba, Cs

Ionization Energy: the minimum energy needed to remove an e– from an atom or ion

M(g) + 1st I.E. M+(g) + e–

M+(g) + 2nd I.E. M2+(g) + e–

M2+(g) + 3rd I.E. M3+(g) + e–

Successive ionization energiesare larger than previous ones.

-- (+) attractive force remains the same, but there is less e–/e– repulsion

I.E. e –

The ionization energy increases sharply whenwe try to remove an inner-shell electron.

e.g., For Mg, 1st IE = 738 kJ/mol 2nd IE = 1,450 kJ/mol 3rd IE = 7,730 kJ/mol

As we go down a group, 1st IE… decreases.

-- more e–/e– repulsion and more shielding

(strong evidence that only valence e– are involved in bonding)

Generally, as we go from left to right, 1st IE…

Exceptions: e.g., B < Be

Be: 1s2 2s2

B: 1s2 2s2 2p1 B doesn’t like

2p

(easier to remove B’s single 2p e– than one of Be’s two 2s e–s)

N: 1s2 2s2 2p3

O: 1s2 2s2 2p4

More stable to have

than to have

2p

Subshells prefer to beeither completely filled

OR half-filled.

This e– is easier to remove…

…than any of these.

Firs

t

acro

ss a

per

iod…

across a perio

d…

down a group…

released.

Electron affinity: the energy change that occurs when an e– is added to a gaseous atom

For most atoms, adding an e–

causes energy to be…

Exceptions:

noble gases: the added e– must go into a new, higher energy level

group 2 metals: the added e– must go into a higher-energy p orbital

group 15 elements: the added e– is the first one to double-up a p orbital

eq. for e– affinity: A + e– A–

I.E. e –

e– energy

ener

gy

more (–)e– affinity

The halogens have the most (–) electronaffinities, meaning that they become verystable when theyaccept electrons.

Electron affinities don’t varymuch going down a group.

more willing toaccept an e–=

–328F

Cl

Br

I

O

S

Se

Te

Ne

Ar

Kr

Xe

He

–349

–325

–295

–141

–200

–195

–190

+

+

+

+

+