Chemistry - A Molecular Science

magnetic classifications for atoms:

1.

Paramagnetic atoms

have unpaired electrons and are attracted by an applied magnetic

field. The attraction is due to the interaction of

the magnetic fields of the unpaired electrons

with the applied magnetic field.

The greater the number of

unpaired electrons, the more

paramagnetic is the atom.

* Diamagnetic atoms are actually repelled slightly by an applied field,

but the reasons for the repulsion are beyond the scope of this discussion.

2.

Diamagnetic atoms

have no unpaired electrons and are not attracted by an applied

magnetic field.*

Although

magnetism is the result of unpaired electrons, it is a bulk property of the

material

; that is, magnetism is a property of larg

e groups of atoms rather than individual

atoms. It is important to realize that individual atoms typically occur only as gases because they interact with one another in the solid

state so strongly that they lose their atomic

identity and become part of a material. Thus, carbon is a paramagnetic atom with two unpaired electrons (valence electron configuration: 2s

2 2p

2 ), but graphite and diamond, the

common forms of elemental carbon, are diama

gnetic because of the manner in which the

carbon atoms interact in the solid. Iron atoms

are also paramagnetic with four unpaired

electrons (4s

2 3d

6 ), and they interact with one anothe

r in the solid. However, some of the

unpaired electrons in iron align over many iron atoms to make iron a

magnetic material

.

We discuss magnetic materials in more detail in Chapter 14.

3.8

CHAPTER SUMMARY AND OBJECTIVES Valence electrons and orbitals, which are t

hose in the outermost s sublevel and any

unfilled sublevels, are involved in bonding and

determine the chemical properties of the

element. Indeed, the periodicity of chemical properties is a result of the periodicity of valence electron configurations. The size and energy of a valence orbital both depend upon the n quantum number and the nuclear charge that it experiences, which is called the effective nuclear charge. The effective nuclear charge increases in going from left to right in the periodic table, while the n quantum number increases in going down a group. Thus, atoms that lie on the right side of the periodic table (nonmetals) at the top of their groups have low energy valence orbitals that are clo

ser to the nucleus, while atoms on the left side

(metals) and at the bottom of their group have high energy electrons that are far from the nucleus. Ionization energy is the energy that is

required to remove an electron, so atoms

on the left side of the periodic table (metal

s) have low ionization energies and lose their

valence electrons easily. Electronegativity is a measure of an atom's ability to attract bonding electrons. Atoms with unfilled orbitals

at low energy are highly electronegative,

Chapter 3 Atomic Structure and Properties

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