r dr
Approximate bonding atomic
radii for the elements have
been tabulated.
The distance between bonded nuclei can be
approximated by adding radii from both atoms.
e.g., Bonding atomic radii are as follows:
C = 0.77 A, Br = 1.14 A
So the approximate distance between
bonded C and Br nuclei = 0.77 + 1.14 =
1.91 A
Atomic Radius
As we go down a group,
atomic radius… increases.
-- principal quantum number
increases (i.e., a new
energy level is added)
As we go from left to right across the
Table, atomic radius… decreases.
-- effective nuclear charge increases, but
principal quantum number is constant
more p+, but no new (i.e., farther away) energy levels
Coulombic attraction depends on…
amount of charge
2+
2–
1+
1–
distance between charges
2+
2+
–
+
H
He
++
+ +
– –
– –
2–
2–
As we go
,
more coulombic
attraction, no new
energy level, more
pull, smaller size
Arrange the following atoms in order of increasing
atomic radius: Sr, Ba, Cs
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 energies
are larger than previous ones.
-- (+) attractive force remains the same,
but there is less e–/e– repulsion
The ionization energy increases sharply when
we 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
(strong evidence that
only valence e– are
involved in bonding)
As we go down a group, 1st IE… decreases.
-- more e–/e– repulsion and more shielding
Generally, as we go from left to right, 1st IE…
Exceptions:
Be:
1s2
2s2
B:
1s2
2s2 2p1
e.g., B < Be
2p
B doesn’t like
Subshells prefer to be
either completely filled
OR half-filled.
(easier to remove B’s
single 2p e– than one
of Be’s two 2s e–s)
…than any
of these.
N:
1s2 2s2 2p3
More stable to have
O:
1s2 2s2 2p4
than to have
2p
This e–
is easier to remove…
First
down a group…
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… released.
eq. for e– affinity:
A + e–
A–
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
The halogens have the most (–) electron
affinities, meaning that they become very
stable when they
accept electrons.
O
F
more (–)
more willing to –141 –328
=
–
e affinity
accept an e–
S
Cl
–200 –349
Electron affinities don’t vary
Se
Br
much going down a group.
–195 –325
Te
I
–190 –295
He
+
Ne
+
Ar
+
Kr
+
Xe
+