8th Class Science Materials : Metals and Non-metals Non-Metals

       Non-Metals

Only eighteen elements in the periodic table are generally considered nonmetals, compared to over eighty metals, but nonmetals make up most of the crust, atmosphere and oceans of the earth. Bulk tissues of living organisms are composed almost entirely of nonmetals. Most nonmetals are monatomic noble gases or form diatomic molecules in their elemental state, unlike metals which (in their elemental state) do not form molecules at all.

Non-metals are basically defined as elements that are not metals.

Their physical properties generally include:

1. They are poor conductors.
2. They are brittle, not ductile in their solid state.
3. They show no metallic lustre.
4. They may be transparent or translucent.
5. They have low density.
6. They are gases, liquids, or solids.
7. Theyform molecules which consists of atoms covalently bonded; the nobel gases are monoatomic.

Theirchemical properties are generally:

1. They usually have four to eight valence electrons.
2. They have high electron affinities, (except noble gases)
3. They are good oxidizing agents, (except noble gases)
4. They have hydroxides which are acidic, (except noble gases)
5. They are electronegative.

         Difference between Metals and Non-Metals

Chemical Properties

Metals:

• Usually have 1-3 electrons in their outer shell.
• Lose their valence electrons easily.
• Form oxides that are basic.
• Are good reducing agents.
• Have lower electronegativities.

Nonmetals:

• Usually have 4-8 electrons in their outer shell.
• Gain or share valence electrons easily.
• Form oxides that are acidic.
• Are good oxidizing agents.
• Have higher electronegativities.

Physical Properties

Metals:

• Good electrical conductors and heat conductors.
• They are malleable i.e.can be beaten into thin sheets.
• They are ductile i.e.can be stretched into wires.
• Possess metallic lustre.
• Opaque as thin sheet.
• Solid at room temperature (except Hg).

Nonmetals:

• Poor conductors of heat and electricity.
• They are brittle if a solid.
• They are non-ductile.
• Do not possess metallic lustre.
• Transparent as a thin sheet.
• Solids, liquids or gases at room temperature.

       A substance composed of two or more metals is called:

(a) Alloys

(b) Metalloids  

(c) Non-metals

(d) All of these

(e) None of these

Answer: (a)

       Which one of the following is a metal?

(a) Aluminium

(b) Gold       

(c) Silver

(d) All of these

(e) None of these

Answer: (d)

• Metals are good conductor of heat and electricity.
• Non-metals are bad conductor of heat and electricity.
• Metals and non-metals are separated in the periodic table by a diagonal line of elements.
• Metals are malleable and ductile.
• Non-metals are brittle..