Download The Chemical Earth (8.2.3)

The Chemical Earth
(8.2.3)
Elements in Earth materials are
present mostly as compounds
because of interactions at the
atomic level
Answers to 8.2.2
Element
Outer
shell
electrons
No.
Shells
Symbol
Atomic
Number
Atomic
Mass
Metal, semimetal
non-metal
Sulfur
6
3
S
16
32.1
NM
Rubidium
1
5
Rb
37
85.5
M
Selenium
6
4
Se
34
79
NM
Boron
3
2
B
5
10.8
SM
Arsenic
5
4
As
34
74.9
NM
Barium
2
6
Ba
56
137.3
M
Krypton
8
4
Kr
36
83.8
NM
Germanium
4
4
Ge
32
72.6
SM
Bromine
7
4
Br
35
79.9
NM
Answers to 8.2.2 (contd.)
Element
Uses of element
Chlorine
Sterilization of water.
Sodium
Heat transfer fluid in nuclear power plants.
Tungsten
Filaments in light globes, etc.
Gold
Jewellery, etc.
Mercury
Electrical switches, etc.
Zinc
Protecting iron (galvanizing).
Iron
Major building material.
Copper
Copper electrical wire.
Argon
Inert gas used in light bulbs and welding.
Helium
Carry weather balloons aloft.
Magnesium
Structural metal, flares, fireworks.
The Particle Theory
• All matter is composed of particles. These
particles are called atoms.
– Solids – Particles in a solid are packed tightly
together and locked firmly into position. They
can vibrate in position but cannot move.
– Liquids – Particles in liquids are packed tightly
together, but they can slide over each other and
shift position.
– Gases – Particles of gases have little affinity for
each other and move freely about.
Particles of a solid
packed tightly together,
cannot move.
Particles of a liquid, can
move over each other.
Particles of a gas. Free
to move about. Rapid
movement.
Electron Shells
Electron Shells (contd.)
• The lowest energy level is the “K” shell, it is
the nearest to the nucleus. Electrostatic
attraction at this level is greatest for the
electrons.
• As we move away from the nucleus into
higher energy levels, nuclear attraction
becomes less.
(See “Atomic Size” power point file with this unit)
Nobel Gases
Nobel gases have complete outer electron
shells. Because of this, they are Inert or Unreactive. Nobel gases are the only elements
that can exist as single atoms and are
written Ar, Ne, He, etc.. Gases such as
nitrogen, oxygen, etc. must form molecules
of two to remain stable. Groups of two
atoms are called diatomic molecules. O2,
Cl2, N2, etc. Are all diatomic molecules.
Bonding in Compounds
• Ionic Bonds – Form when atoms lose or gain
electrons. Ionic bonds form due to
electrostatic attraction of the ions.
• Covalent Bonds – Form when atoms share
electrons.
– Equal Sharing – Equal sharing forms covalent
molecular* compounds.
– Unequal Sharing – forms slightly polar
compounds call polar covalent compounds.
*Molecules are electrically neutral arrangements of at least two atoms formed
from strong covalent bonds.
Bonding in Compounds
(contd.)
Lewis electron dot diagrams show only the
outer shell of atoms and illustrate bonding.
The lone electron of the hydrogen
atom is shown as an “x”. Oxygen has
six electrons shown as a “dot”. The
molecule of water is shown, with the
oxygen sharing electrons with
hydrogen and vice versa.
Oxygen is a highly electronegative atom and
holds the electrons donated by hydrogen closely
to itself. This produces a Polar Molecule, as
shown to the left.
• Lewis electron dot diagrams of ionic
substances is slightly different.
Na * +
* Mg
* +
Cl
O

[ Na
]+
[Cl]
 [Mg] 2+ [O] 2-
Questions
1. In terms of the particle theory, what is the
difference between solids, liquids and gases.
2. In terms of size and bonding, what is the
difference between argon, oxygen, and helium.
3. Draw Lewis electron dot diagrams for:
a.
b.
c.
d.
Carbon dioxide
Nitrogen
Magnesium chloride
Methane