Saturday, September 18, 2021

3. Metals and Non-metals | Class 10 CBSE | Web Notes | Part 3 | How do Metals and Non-metals React?

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
LiCl
CaCl
2
CaO
MgCl
2

1074
887
1045
2850
981

1686
1600
1900
3120
1685

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



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