TWEED RIVER HIGH SCHOOL
2006
PRELIMINARY CHEMISTRY
Unit 1
The Chemical Earth
Part 3
Elements in Earth materials are present mostly as compounds
because of interactions at atomic level.

Identify matter is made of particles that are continuously
moving and interacting.
This was revised as homework at the beginning of Part 1.

Describe qualitatively the energy levels of electrons in
atoms.
1. The Atom revisited.
An atom is made up of electrons, protons and neutrons.
Protons and neutrons are in the nucleus of an atom.
Protons are positively charged, neutrons have no charge.
Electrons have a negative charge.
The Atomic number, Z, of an atom is the number of protons in the
nucleus of that element.
For example, Calcium has 20 protons in its nucleus and has the
atomic number 40.
1
The Mass Number, A, of an element is the number of protons plus
neutrons of an atom of that element.
For example:
Calcium has 20 protons and 20 neutrons, so the mass number of
calcium is 20.
The mass number and atomic number are represented as follows:
A
Z
Mass Number
Element
Atomic Number
X
Therefore, Calcium would be represented as:
40
Ca
20
2. Electron configuration, orbital and energy levels.
Electrons are found in orbitals (or shells) around the nucleus of an
atom.
Each orbital represents and energy level. An electron in an orbit has
a specific energy level.
2
Principal Energy Levels or Shells
Principal energy
Number of
Name of subshells
levels or Shells
subshells
K=1
1
s
L=2
2
s
p
M=3
3
s
P
d
N=4
4
s
p
d
f
Electron Configuration.
The electron configuration of an element is the number of electrons in
each shell of the atom.
For the first twenty elements, the maximum number of electrons in
each shell is 2,8,8,2.
Therefore, Hydrogen, atomic number 1, has the electron configuration
of 1.
Sodium, atomic number 11, has the electron configuration: 2,8,1
3
Homework: Complete the table below filling in all the electron
configurations.
Element
Electron configuration
Hydrogen
1
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
2,8,1
Magnesium
Aluminium
Silicon
Phosphorus
Sulfur
Chlorine
Argon
Potassium
Calcium
4
Filling Subshells
The order in which each shell is filled is as follows:
5s
4s
4p
4d
3s
3p
3d
2s
2p
4f
1s
Homework: Complete the following table, giving the electron
configurations of the first twenty elements in terms of their s,p,d
subshells.
Element
Electron configuration
Hydrogen
1s1
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
5
Neon
Sodium
1S2,2S2,2P6,3S1
Magnesium
Aluminium
Silicon
Phosphorus
Sulfur
Chlorine
Argon
Potassium
Calcium

Describe the formation of ions in terms of atoms gaining or
losing electrons.
Ions:
An ion is an atom that has lost or gained an electron(s).
There are two types of ions:
1. Cation
A cation is an atom that has lost an electron(s).
Cations have a positive charge.
This positive charge comes from there being more protons (+ve)
than there are electrons (-ve).
For example:
The sodium ion.
The sodium atom has one electron in its’ outer shell.
6
(Note: Atoms are more stable with complete outer shells.)
Draw the structure of the sodium atom.
Draw the structure of the sodium ion.
What is the electron configuration of the sodium:
1. Atom
2. Ion
7
Anions
An anion is an atom that has gained an electron(s).
Anions have a negative charge.
Draw the structure of the fluorine atom:
Draw the structure of the fluoride ion
Electronegativity
The Electronegativity of an element is the ability of an atom of the
element to attract electrons.
8

Apply the Periodic Table to predict the ions formed by metals
and non-metals.

Describe the formation of ionic compounds in terms of the
attraction of ions of opposite charge.
In terms of electrostatics, opposites attract. Therefore, positive ions
(cations) will attract negative ions (anions).
When this attraction occurs, ionic compounds form.
Naming Ionic Compounds
1. Valency
The valency or valence of an element or compound is a measure of
its combining power when it takes part in a chemical reaction.
In general the valency of an element relates to it Group number in
the periodic Table, i.e
-
Sodium is in Group 1 and has a valency of +1.
-
Magnesium is in-group 2 and has a valency of +2.
-
Chlorine is in Group 7 and has a valency of –1.
Exceptions to this rule are the multi-valent elements:
Element
Valencies
Copper
Cu+ ; Cu2+
Iron
Fe2+ ; Fe3+
Lead
Pb2+ ; Pb4+
Tin
Sn2+ ; Sn4+
Mercury
Hg+ ; Hg2+
9
Silver – Ag+
Zinc – Zn2+
Polyatomic Ions
Cations:
Ammonium - NH4+
Anions
Polyatomic Anion
Formula
Sulfate
SO42-
Sulfite
SO32-
Nitrate
NO3-
Nitrite
NO2-
Carbonate
CO32-
Hydroxide
OH-
Phosphate
PO43-
Note: The ending –ide refers the anion being and element only, (the
exception being Hydroxide).
Ionic Compounds:
Ionic compounds are named by putting the cation first, followed by the
anion. For example:
Sodium Chloride, NaCl
Magnesium Carbonate, Mg CO3
Note: When ionic compounds form they must be electrically neutral.
10
Ionic compounds with multiple valencies:
1. Using roman numerals
When a cation has a multiple valency, the valency of the cation
is shown by placing roman numerals in brackets after the cation.
For example:
Iron oxide when iron has the valency of 2+
Iron(ii) oxide – Fe2O3
Tin chloride when tin has a valency of 4+
Tin(iv) Chloride = SnCl4
2. Using the suffixes –ous and –ic
The suffix –ous refers to the lower valence cation, while the
suffix –ic refers to the higher valent state.e.g
Iron(ii) oxide – Ferrous oxide
Iron(iii) oxide – Ferric oxide
Homework: Complete the following table.
Ionic Compound Name
Chemical Formula
Potassium Sulfate
PbCl4
Magnesium Hydroxide
CuO
Cupric Chloride
SnO2
Lithium Hydride
Na2SO4
Sodium Carbonate
Mg3(PO4)2
11

Construct ionic equations showing metal and non-metal
atoms forming ions.
Step 1
Write a chemical equation for the reaction.
When writing chemical formula, write down the names of the
elements, including valencies, and transpose the valencies. For
example, if the product of a reaction is calcium oxide then:
2+
Ca
2O
= Ca2O2
Note: When the valencies are the same, the numbers are omitted, i.e
Ca2O2 = CaO
Example 2
Sodium Oxide
+
Na
2-
O
= Na2O
12
Constructing ionic equations
Chemical Equations – show all elements/compounds present
For example, the reaction of magnesium with oxygen is an ionic
reaction, where magnesium forms the magnesium 2+ ion and oxygen
forms the 2- ion.
Mg + O  MgO
The ionic equation is:
Mg + O  Mg2+ + O2Homework: Write chemical and ionic equations for the following
reactions.
Formation of:
1. Potassium chloride
2. Calcium fluoride
3. Lithium sulfide
4. Copper(ii) bromide
5. Tin(iv) oxide
6. Aluminium oxide
13

Apply Lewis electron dot structures to:
-
the formation of ions
-
the electron sharing in some simple molecules
Lewis electron dot structures show only the outer electron shell.
1. The formation of ions.
Example 1 - Sodium
Atom
Ion
Na
Na+
Atom
Ion
Cl
Cl-
Example 2
Chlorine
14
Example 3
Sodium Chloride
Na
Cl
Electron sharing molecules:
1. Hydrogen Chloride
H Cl
2. Water
O
H
H
15

Describe the formation of covalent molecules in terms of
sharing of electrons.

The elements of Group 4 do not form ions.

These elements have 4 electrons in their outer shell and as such
when they form compounds they ‘share’ these electrons.

When two non-metals bond they also share electrons.

Compounds that form through sharing electrons are called
covalent.
Homework:
1. Give two examples of Group 4 elements forming molecules
by sharing electrons.
2. Give two examples of non-metals forming covalent
molecules.
For each example draw Lewis dot structures.

Analyse information by constructing or using models
showing the structure of metals, ionic compounds and
covalent compounds.
Practical/Assignment
1. Research and present in an appropriate format the
structure of metals.
2. Construct, using molecular model kits and following
teacher instructions:
a) ionic compounds
b) covalent compounds
16
Homework:
To be completed by the end of this unit:
Chemistry Contexts 1, page64, 65 and 66.
Questions 6, 7, 8, 19, 20
17