THE PERIODIC TABLE
The periodic table is a tabular arrangement of the chemical elements. It is organized in order of:
- increasing atomic number.
- In relation to the electron structure of their atoms
- In relation to their chemical properties.
There are 18 groups in the periodic table but there are 8 main groups.
PERIODS
These are horizontal rows of elements. There are seven periods numbered 1 to 7.
- Elements of one period all have the same number of electron shells
- Going across a period, each element has one more proton and one more electron than the
previous element
- Going across a period, the chemical properties of elements become less metallic and more nonmetallic.
GROUPS
These are vertical columns of elements. There are 8 groups numbered vii with a final group 0.
- Elements in the same group have similar chemical properties.
- Each element in a group has the same number of electrons in its outer shell. – for groups I to
vii, this number is the same as the group number.
- Between groups ii and iii are the transition metals. All have two electrons in their outer shell.
- Group 0, have full outer shells which makes them very unreactive, hence the name inert or
noble gases.
- Group 7 is referred to as halogens.
The particles that make up matter are:
- Atoms: smallest particle of an element.
- Molecules: groups of atoms bonded together and can exist as separate units
- Ions: electrically charged particles formed from atoms or groups of atoms bonded together.
Atoms are the smallest particle of an element. It is consisted of and made up of three sub - atomic
particles: protons, neutrons, and electrons.
The number of protons and electrons is the same in any atom. Therefore, atoms have no charge.
Atoms can be assigned two numbers:
- Atomic number: the number of protons in the nucleus of one atom of an element.
- Mass number, the total number of protons plus neutrons in the nucleus of one atom of an
element.
EXAMPLE:
Hence, Mass number = 16
Atomic number = 8
Number of protons = 8, Number of electrons = 8
Number of neutrons = Mass number – atomic number
= 16 – 8 = 8
ARRANGEMENT OF SUB-ATOMIC PARTICLES
Atoms are composed of two parts:
1. A central nucleus containing the protons and neutrons tightly packed together.
2. One or more shells or energy levels surrounding the nucleus containing electrons revolving at
high speeds:
• Shells closest to the nucleus fills us first
• Each shell contains up to a fixed number of electrons:
βͺ The first shell contains 2 electrons
βͺ The second shell contains up to 8 electrons
βͺ The third shell may be considered to contain up to 8 electrons.
EXAMPLE:
The hydrogen atom
1
1π» contains 1 proton
1 electron – arrangement 1
0 neutrons
P
N
The calcium atom
40
20πΆπ contains 20 protons
20 electrons - arrangement 2, 8, 8, 2
Neutrons = 40 – 20 = 20.
Arrangements of the electrons is known as electronic configuration.
P
N
TABLE SHOWING THE FIRST 20 ELEMENTS OF THE PERIODIC TABLE
#
ELEMENT
SYMBOL
ATOMIC
#
MASS
#
PROTONS
ELECTRONS
NEUTRONS
(MASS – ATOMIC)
ELECTRONIC
CONFIGURATION
1
1
HYDROGEN
π
ππ
1
1
1
1
0
2
2
HELIUM
π
πππ
2
4
2
2
2
2, 1
3
LITHIUM
π
πππ’
3
7
3
3
4
2, 2
4
BERYLIUM
π
πππ
4
9
4
4
5
2, 3
5
BORON
ππ
ππ
5
11
6
6
5
2, 4
6
CARBON
ππ
ππ
6
12
6
6
6
2, 5
7
NITROGEN
ππ
ππ
7
14
7
7
7
2, 6
8
OXYGEN
ππ
ππ
8
16
8
8
8
2, 7
9
FLUORINE
ππ
ππ
9
19
9
9
10
2, 8
10
NEON
ππ
ππππ
10
20
10
10
10
2, 8, 1
11
SODIUM
ππ
ππππ
11
23
11
11
12
2, 8, 2
12
MAGNESIUM
ππ
ππππ
12
24
12
12
12
2, 8, 3
13
ALUMINIUM
ππ
ππππ₯
13
27
13
13
14
2, 8, 4
14
SILICON
ππ
ππππ’
14
28
14
14
14
2, 8, 5
15
PHOSPHOROUS
ππ
πππ
15
31
15
15
16
2, 8, 6
16
SULPHUR
ππ
πππ
16
32
16
16
16
2, 8, 7
17
CHLORINE
ππ.π
ππππ₯
17
35.5
17
17
18.5
2, 8, 8
18
ARGON
ππ
ππππ«
18
40
18
18
22
2, 8, 8, 1
19
POSTASSIUM
ππ
πππ
19
39
19
19
20
2, 8, 8, 2
20
CALCIUM
ππ
ππππ
20
40
20
20
20
CHEMICAL BONDING
Atoms of elements Group 0 of the periodic table have full outer shells of electrons. They are stable
and unreactive and exist in nature as individual atoms. Atoms of all other elements do not have full
outer shells; therefore, they are not stable. They attempt to gain full outer shells and become stable by:
- Losing electrons from their outer shell, or
- Gaining electrons from their outer shell, or
- Sharing electrons in their outer shell with other atoms
In doing this, atoms bond with each other. There are three types of bonding:
- Ionic or electrovalent bonding
- Covalent bonding
- Metallic bonding
Valency of elements: valency is the number of electrons an atom must lose, gain, or share to attain a
stable electronic structure.
GROUP IN
PERIODIC TABLE
Valency
I
II
Transition Metals
III
IV
V
VI
VII
0
1
2
Variable – often 2
3
Usually, 4
Usually, 3
2
1
0
IONIC/ ELECTROVALENT BONDING
This occurs when a metal bonds with a non-metal.
It involves the complete transfer of outer (valency) electrons from the metal atom, or atoms, to the
non-metal atom, or atoms.
The metal ions form positive ions called cations and the non-metal form negative ions called anions.
Ions have full outer shells of electrons.
EXAMPLE:
SODIUM CHLORIDE → CHEMICAL FORMULA = NaCl
1 sodium atom
(2,8,1)
1 chlorine atom
(2,8,7)
1 sodium ion
(2,8)
Sodium atom transfers its valency electron (e-) to the chlorine atom.
1 chlorine ion
(2,8,8)
COVALENT BONDING
This occurs when two or more non-metal atoms bond. It involves the sharing of valency electrons.
The shared electrons orbit the nuclei of both atoms sharing them, forming strong covalent bonds. One
shared pair form one covalent bond. Covalent bonding results in the formation of molecules.
Formation of covalent compounds represent one molecule of the compound and are called molecular
formulae.
EXAMPLE:
CHLORINE MOLECULE → CHEMICAL FORMULA: Cl2
1 chlorine atom
(2,8,7)
1 chlorine atom
(2,8,7)
1 shared pair of electrons
form one covalent bond.
1 chlorine molecule or Cl
Cl (a single covalent bond)
METALLIC BONDING
This occurs in metals. The metal atoms are packed tightly in rows and the valency electrons from each
atom are lost to a “sea of electrons”. These electrons are mobile and bind together the cations formed
because of the atom losing electrons.
EXAMPLE: THE SODIUM LATTICE
EXERCISE: SAMPLE QUESTIONS
Draw diagrams to illustrate the formation of the following compounds from their elements and
determine whether it is ionic or covalent bonding:
a. Aluminum oxide
Ionic bonding since metal is present.
b. Carbon dioxide molecule
Covalent bonding since non-metals are bonding
c. Magnesium nitride
Ionic bonding since metal is present
0
