10th Class Science Metals and Non-metals Metalloids

Metalloids

Category : 10th Class

Metalloids

There are those elements which behave as metals as well as non-metals. They have four valence electrons.

e.g.

Carbon (C-6) : 2,4

Silicon (Si-14) : 2, 8, 4

Which one of the following is the poorest conductor of electricity?

(a) Copper

(b) Aluminium

(d) Silver

(e) None of these

Sodium is a metal because:

(a) It is an element

(b) It has 11 electrons

(c) It has one valence electron

(d) It has 11 protons

(e) None of these

Explanation

It is one valence electron. So it can donate one electron and form cations.

Physical Properties of Metals

• Most metals are solid at room temperature except mercury and gallium, which are liquid at room temperature.
• Uncorrode or freshly cut metals have shiny surface which is called metallic luster.
• Metals are hard except sodium and potassium, which are soft and can be cut with knife.
• Metals are sonorous i.e. they produce sound when hit against hard surface.
• Metals have high melting and high boiling point. Sodium, potassium, mercury and gallium have low boiling point.
• Metals are malleable i.e. they can be beaten into sheets. However Zinc, antimony, bismuth and arsenic are not malleable.
• Metals are ductile i.e. they can be drawn into wires except zinc, antimony, bismuth and arsenic.
• Metals are good conductor of heat and electricity. Silver is the best conductor while Bismuth, lead and tungsten do not conduct heat through them.
• Metals have high tensile strength.

Physical properties of non-metals

• Non-metals exist in all the three physical states. For example carbon, phosphorous and sulphur are solid, while bromine is liquid, rest all are gaseous at room temperature.
• Most of the non-metals are soft, except diamond, which is an allotrope of carbon.
• They have low density except bromine, iodine which are quite heavy.
• Non-metals are neither malleable nor ductile.
• They have low melting and boiling points.
• Non-metals have low tensile strength except carbon fibres.
• Non-metal are poor conductor of heat and electricity except graphite.

Chemical Properties of Metals

• Metals are electropositive elements i.e. they have tendency to form cation by loosing electrons.
• Reaction with Oxygen

Metals + Oxygen $\to$ Metal oxides

Metal oxides are basic oxides and they react with acids to form salt and water

$4Na+{{O}_{2}}\to 2N{{a}_{2}}O$

$N{{a}_{2}}O+{{H}_{2}}O\to 2NaOH$

$3Fe+2{{O}_{2}}\to F{{e}_{3}}{{O}_{4}}$

Reactivity of metals with oxygen is : $K>Na>Mg>Zn>Fe>Cu$

Metal oxides, which are water soluble, are called alkali, e.g. $N{{a}_{2}}O,\,\,{{K}_{2}}O$

• Reaction with Water

Metals + Water $\to$ Metal oxide + Hydrogen gas

$2Na+2{{H}_{2}}O\to 2NaOH+{{H}_{2}}$

$Mg+{{H}_{2}}O\to MgO+{{H}_{2}}$

$3Fe+4{{H}_{2}}O\to F{{e}_{3}}{{O}_{4}}+4{{H}_{2}}$

• Reaction with Acids

Metals above hydrogen in reactivity series react with dilute acids to liberate hydrogen gas.

Metal + Acid $\to$ Metal salt + Hydrogen gas

$2Na+2HCl\to 2NaCl+{{H}_{2}}$

$Zn+{{H}_{2}}S{{O}_{4}}\to ZnS{{O}_{4}}+{{H}_{2}}$

• On reaction with Nitric acid no hydrogen gas is liberated. It is because nitric acid is an oxidizing agent and it oxidize hydrogen gas to water and itself get reduced to $N{{O}_{2}}$ or $NO$.

$3Fe+8HN{{O}_{3}}\to 3Fe{{(N{{O}_{3}})}_{2}}+4{{H}_{2}}O+2NO$

• Magnesium and manganese react with very dilute nitric acid (about 1%) to liberate hydrogen gas.

$Mg+2HN{{O}_{3}}\to Mg\,{{(N{{O}_{3}})}_{2}}+{{H}_{2}}$

(1 % Conc.)

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