This document discusses several key atomic and molecular properties including electron configurations, ionization energies, atomic and ionic radii, and electron affinity. It explains how atoms gain or lose electrons to form ions that have noble gas configurations. Cations are typically smaller than the parent atom, while anions are larger. Trends in various properties across the periodic table are also examined, such as how ionization energy generally increases moving left to right and up a group, and how atomic radius decreases with increasing nuclear charge. Diagonal relationships between elements are explained in terms of similar cation charge densities.

1. Properties of Atoms and the ionic bond
Chapter 7

2. 8.1
When the Elements Were Discovered

3. 8.2
ns1
ns2
ns2
np1
ns2
np2
ns2
np3
ns2
np4
ns2
np5
ns2
np6
d1
d5
d10
4f
5f
Ground State Electron Configurations of the Elements

4. Classification of the Elements

5. Electron Configurations of Cations and Anions
Na [Ne]3s1
Na+
[Ne]
Ca [Ar]4s2
Ca2+
[Ar]
Al [Ne]3s2
3p1
Al3+
[Ne]
Atoms lose electrons so that
cation has a noble-gas outer
electron configuration.
H 1s1
H-
1s2
or [He]
F 1s2
2s2
2p5
F-
1s2
2s2
2p6
or [Ne]
O 1s2
2s2
2p4
O2-
1s2
2s2
2p6
or [Ne]
N 1s2
2s2
2p3
N3-
1s2
2s2
2p6
or [Ne]
Atoms gain electrons
so that anion has a
noble-gas outer
electron configuration.
Of Representative Elements
8.2

6. +1
+2
+3
-1
-2
-3
Cations and Anions Of Representative Elements
8.2

7. Na+
: [Ne] Al3+
: [Ne] F-
: 1s2
2s2
2p6
or [Ne]
O2-
: 1s2
2s2
2p6
or [Ne] N3-
: 1s2
2s2
2p6
or [Ne]
Na+
, Al3+
, F-
, O2-
, and N3-
are all isoelectronic with Ne
What neutral atom is isoelectronic with H-
?
__________________________________
8.2

8. Electron Configurations of Cations of Transition Metals
8.2
When a cation is formed from an atom of a transition metals, electrons are always
removed first from the ns orbital and then from the (n – 1)d orbitals.
Fe: [Ar]4s2
3d6
Fe2+
: [Ar]4s0
3d6
or [Ar]3d6
Fe3+
: [Ar]4s0
3d5
or [Ar]3d5
Mn: [Ar]4s2
3d5
Mn2+
: [Ar]4s0
3d5
or [Ar]3d5

9. Nuclear effective charge (Zeff) is the nuclear charge felt by an
electron when both the actual nuclear charge (Z) and the repulsive
effects (shielding) of the other electrons are taken into account.
Na
Mg
Al
Si
11
12
13
14
10
10
10
10
1
2
3
4
186
160
143
132
ZeffCoreZ Radius (pm)
Zeff = Z - σ 0 < σ < Z (σ = shielding constant or screening constant)
Zeff ≈ Z – number of inner or core electrons
Within a Period
as Zeff increases,
Radius
decreases
8.3
Atomic radius

10. Zeff for He
Zeff second period

11. Atomic radius, which is one-half the distance between the two nuclei
in two adjacent metal atoms or in a diatomic molecule .
In metals such as beryllium, the atomic
radius is defined as one-half the
distance between the centers of two
adjacent atoms.
For elements that exist as diatomic molecules, such
as iodine, the radius of the atom is defined as one-
half the distance between the centers of the atoms in
the molecule.

12. Atomic radii (in
picometers) of
representative elements
according to their
positions in the periodic
table. Note that there is
no general agreement on
the size of atomic
radii. We focus only on
the trends in atomic
radii, not on their
precise values.

13. Class practice problems:
1.Referring to a periodic table, arrange the following atoms in order of increasing
atomic radius: P, Si, N.
2. Compare the size of each pair of atoms listed here:
A. Be, Ba;
B. Al, S;
C. 12
C, 13
C.

14. Atomic Radii
Plot of atomic radii (in picometers) of elements against their atomic numbers.

15. Ionic Radius
It is the radius of a cation or an anion.
Ionic radius affects the physical and chemical properties of an
ionic compound.
For example, the three-dimensional structure of an ionic
compound dependson therelativesizesof itscationsand anions.
For isoelectronic ions, the size of the ion is based on the size
of the electron cloud, not on the number of protons in the
nucleus.

16. 8.3
Comparison of atomic radii with ionic radii.
Alkali metals and
alkali
metal cations.
Halogens and halide ions.

17. Cation is always smaller than atom from which it is formed.
Anion is always larger than atom from which it is formed.
8.3
Changesin thesizesof Li and F when they react to form LiF.

18. The radii (in picometers) of ions of familiar elements arranged
according to the elements’ positions in the periodic table.

19. Class practice problem: For each of the following pairs,
indicatewhich oneof thetwo speciesislarger:
A.N3-
or F2-
;
B.Mg2+
or Ca2+
;
C.Fe2+
or Fe3+
.

20. Ionization energy is the minimum energy (kJ/mol) required to
remove an electron from a gaseous atom in its ground state.
In other words, ionization energy is the amount of energy in
kilojoules needed to strip 1 mole of electrons from 1 mole of
gaseous atoms.
I1 + X (g) X+
(g) + e-
I2 + X (g) X2+
(g) + e-
I3 + X (g) X3+
(g) + e-
I1 first ionization energy
I2 second ionization energy
I3 third ionization energy
8.4
I1 < I2 < I3
Ionization energy

21. Filled n=1 shell
Filled n=2 shell
Filled n=3 shell
Filled n=4 shell
Filled n=5 shell
8.4

22. General Trend in First Ionization Energies
8.4
Increasing First Ionization Energy
IncreasingFirstIonizationEnergy

23. Electron affinity is the negative of the energy change
that occurs when an electron is accepted by an atom in
the gaseous state to form an anion.
X (g) + e-
X-
(g)
8.5
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
Electron affinity

24. 8.5

25. Diagonal relationships are similarities between pairs of elements
in different groups and periods of the periodic table .
The reason for this phenomenon is the closeness of the charge
densities of their cations. (Charge density is the charge of an
ion divided by itsvolume.)