SS3 First Term Chemistry Lesson Note – Metals and Their Compounds

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WEEK 5

TOPIC: METALS AND THEIR COMPOUNDS

CONTENTS:

1. Relative abundance and chemical characteristics of metals,
2. Compounds of metals and principles of extraction of metals
3. Sodium-extraction, properties
4. Compounds of sodium and uses of sodium

PERIOD 1: RELATIVE ABUNDANCE OF METALS AND CHEMICAL CHARACTERISTICS

RELATIVE ABUNDANCE

Metals are widely distributed in the earth’s crust either as compounds or in the free metallic form. More than 80 of the known elements are metals except for metals like silver, gold, and platinum, most metals are not found free in nature. They are rather too reactive to exist as free elements. They are more often found as compounds in the form of ores. These ores can exist either as the oxides, hydroxides, trioxocarbonates, sulphates, sulphides, chlorides or nitrate of the metals. Some of the metals are also found in the form of solutions because their stable compounds are stable.

The very reactive metals for example sodium and potassium usually found combined with other elements. For example, they are found as chlorides or carbonates which are very stable compounds. Moderately reactive metals, such as zinc and lead, are usually found as oxides or sulphide while the least reactive metals are usually found in un combined state, for example, gold which is found almost entirely as the free metals.

CHEMICAL CHARACTERISTICS OF METALS

1. When metals react, they ionize by loss of electrons to form cations such as Na+, Ca²+ and Al³⁺, hence they are reducing agents.
2. A metal reacts with oxygen to form one or more oxides e.g Na₂O, MgO, FeO, Fe₂O₃, Fe₃O₄, CuO, Cu₂O etc. Oxides of metals are generally basic.
3. Metals react with dilute mineral acids, such as Hcl and H₂SO₄, to liberate hydrogen (except metals that are below hydrogen in the reactivity series. Zn(s) + H₂SO₄            Zn SO_4(aq) + H₂
4. They form electrovalent (ionic) compounds with non-metals such as chlorine. Ca(s) + Cl₂(g)            CaCl_2(s)

Activity Series of Metals

The reactivity of a metal depends on the ease with which its atoms lose electrons; the ease varies from one metal to another. When common metals are arranged in the order of their ability to lose electrons and act as reducing agents, the activity series is obtained.

K

Na

Ca                    Very Reactive

Mg

Al

Zn

Fe

Sn                    Moderately Reactive

Pb

(H)

Cu

Hg

Ag                   Least Reactive

Pt

Au                   Least reactive (weakest reducing agent)

Of all the metals listed above, potassium K is the most electropositive and hence the strongest reducing agent, white fold, an is the weakest.

The activity series arranges the metals in the order of their ability to react and displace the ions of one another from the solutions of their salts. Generally, a metal higher up in the series will displace the ions of metals lower down the series from the solutions of their salts. For instance, Zn metal will displace or replace ions of copper in a solution of a copper II salt.

Zn(s) + CuSO_{4 (aq)}           →       Cu(s) + ZnSO_4(aq)

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