3. METALS AND NON-METALS
HOW DO
METALS AND NON-METALS REACT?
- Noble gases have a completely filled valence shell. So they show little chemical activity.
-
It means reactivity of elements is
a tendency to attain a completely filled valence shell (noble gas
configuration).
Electronic
configurations of some elements:
|
Type of
element |
Element |
Atomic
number |
Number of
electrons in shells |
|||
|
K |
L |
M |
N |
|||
|
Noble gases |
Helium (He) |
2 |
2 |
|
|
|
|
Neon (Ne) |
10 |
2 |
8 |
|
|
|
|
Argon (Ar) |
18 |
2 |
8 |
8 |
|
|
|
Metals |
Sodium (Na) |
11 |
2 |
8 |
1 |
|
|
Magnesium (Mg) |
12 |
2 |
8 |
2 |
|
|
|
Aluminium (Al) |
13 |
2 |
8 |
3 |
|
|
|
Potassium (K) |
19 |
2 |
8 |
8 |
1 |
|
|
Calcium (Ca) |
20 |
2 |
8 |
8 |
2 |
|
|
Non-metals |
Nitrogen (N) |
7 |
2 |
5 |
|
|
|
Oxygen (O) |
8 |
2 |
6 |
|
|
|
|
Fluorine (F) |
9 |
2 |
7 |
|
|
|
|
Phosphorus (P) |
15 |
2 |
8 |
5 |
|
|
|
Sulphur (S) |
16 |
2 |
8 |
6 |
|
|
|
Chlorine (Cl) |
17 |
2 |
8 |
7 |
|
|
- A
sodium atom has one electron in outermost shell (M).
- If
it loses the electron from M shell then its L shell becomes the outermost shell
giving a stable octet. Now the number of electrons is 10 but the nucleus
has 11 protons. So there is a net positive charge giving a sodium
cation (Na+).
- Chlorine
has 7 electrons in outermost shell (M) and it needs one more electron to
complete its octet.
- When
sodium reacts with chlorine, the electron lost by sodium is taken up by
chlorine. Thus chlorine gets a stable octet and total 18 electrons in K, L and
M shells. But its nucleus has only 17 protons. So, the chlorine atom gets a
unit negative charge forming a chloride anion (Cl–). Thus, Na
and Cl have a give-and-take relation.
Na → Na+ + e–
2,8,1 2,8
Cl + e– → Cl–
2,8,7 2,8,8
Formation of sodium chloride
-
Being oppositely charged, Sodium &
chloride ions are held by strong electrostatic forces of attraction to exist as
sodium chloride (NaCl). NaCl does not exist
as molecules but aggregates of oppositely charged ions.
Formation
of magnesium chloride (MgCl2):
Mg → Mg2+ + 2e–
2, 8, 2 2, 8
(Magnesium cation)
Cl + e–
→ Cl– (Chloride ion)
2, 8, 7 2, 8, 8
- The
compounds formed by the transfer of electrons from a metal to a non-metal are called
ionic compounds or electrovalent compounds.
Properties of Ionic
Compounds
-
Take salt samples such as sodium
chloride, potassium iodide (KI), barium chloride (BaCl2) etc.
-
Their physical state is hard and
brittle. Soluble in water, but insoluble in petrol and kerosene.
-
Heat each sample directly on the
flame using a spatula. They do not melt. Flame colour changes (NaCl = orange
yellow, KI = violet and BaCl2 = green).
-
Make a circuit and insert the electrodes
into a solution of each salt. Salt solution conducts electricity.
Melting
& boiling points of some ionic compounds
|
Ionic compound |
Melting
point (K) |
Boiling
point (K) |
|
NaCl |
1074 |
1686 |
General properties for ionic compounds:
a.
Physical
nature: Ionic compounds are solids and are hard due to
strong force of attraction between positive & negative ions. They are
generally brittle and break into pieces when pressure is applied.
b. High Melting & Boiling points:
This is because a considerable amount of energy is needed to
break the strong inter-ionic attraction.
c.
Solubility:
Generally soluble in water and insoluble in solvents such as kerosene, petrol,
etc.
d. Conduction of Electricity: It occurs through a solution by the movement of charged particles. A solution of an ionic compound in water contains ions. When electricity is passed, ions move to opposite electrodes. Solid ionic compounds do not conduct electricity because ions cannot move due to rigidity. But they conduct electricity in molten state because electrostatic forces of attraction between ions are overcome due to heat. Thus, the ions move freely and conduct electricity.
Select Your Next Topic 👇
👉 Part 1: Physical Properties
👉 Part 2: Chemical Properties
👉 Part 3: How do Metals and Non-metals React?
👉 Part 4: Occurrence of Metals
👉 Part 5: Corrosion
