METALS AND THEIR COMPOUNDS
Week: ONE Date:
Period: Duration: 1 HR 20 MIN. Average age of learners: 17YEARS
Subject: CHEMISTRY Class: SS 3
Topic: METALS AND THEIR COMPOUNDS
Sub topic: PRINCIPLE OF EXTRACTION
Reference
materials:
(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA
(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO
(3) INTERNET
Instructional materials: Iron nail, aluminium foils
Entry behavior: The students have been familiar with materials made of metal
Behavioural objective: At the end of the week the students should be able to:
1. Explain metal
2. State the physical properties of metal
3. Explain the chemical behavior of metal
4. Explain the principle of extraction of metal
5. State the physical properties of alkali metal
CONTENT
METALS AND THEIR COMPOUNDS
Metals are solids at room temperature and exist as crystal lattice in which their atoms are held together by strong metallic bonds, except mercury which is liquid at room temperature.
PHYSICAL PROPERTIES OF METALS
I. High melting and boiling points.
II. Characteristic luster.
III. Malleable, i.e. can be hammered into sheets.
IV. Ductile, i.e. can be drawn into thin wire.
V. Sonorous i.e. it gives off a note when hit.
VI. Hard but not brittle, with great tensile strength.
VII. Relatively high densities.
VIII. Good conductors of heat and electricity.
IX. Solid at room temperature except mercury
Some exceptions to these are the metals such as sodium and calcium (very soft), mercury (liquid, low melting and boiling point), gold and copper (yellowish colour).
CHEMICAL PROPERTIES OF METALS
1. Ionization behavior: Metallic atoms have few valence electrons, and so have a great tendency to ionize and form positive ions by losing electrons i.e. electropositive e.g
Na Na+ (univalent) + e-
Pb Pb2+ (divalent) +2e-
Al Al3+ (trivalent) + 3e-
These positive ions react with a negative ions or radical to form ionic or electrovalence compound.
2. Reducing agents: Metals are reducing agents because they tend to donate their electron readily during chemical reactions.
2Na(s) +1/2O2(g) Na+2 O2-(s)
3. Reaction with acid: Metals which are more electropositive than hydrogen readily displace the hydrogen ion, H+ from an acid.
Zn(s) +2H+ + 2Cl Zn2+ (Cl-)2 + H2
4. Nature of
oxides: Most metals react with oxygen to form basic oxides which
dissolves in water to form alkali e.g Ca(s)
+1/2O2(g) Ca2+
O2-(s)
COMPONENTS OF METALS
Most metals come from minerals. A mineral is a naturally occurring substance with a range of chemical deposition. Often, these minerals are found mixed with earthy materials as ores. Ores are usually concentrated and change to oxides before extraction.
The most abundant metals which as mineral in earth’s crust, are Al, Fe, Ca, Mg, Na, K, Ti, and Mg. Seawater is a rich source of some metal ions including Na+, Mg2+ and Ca2+. Also, vast area of the ocean floor are covered with manganese nodules, which are made up mostly of manganese, along with Fe, Ni, Cu, and Co in a chemical combine state.
Metallurgy is the science and technology of separating metals from theirs ores and of compounding alloy. The three principal steps in the recovery of a metal from its ore are:
I. Preparation of the ores.
II. Production of the metal.
III. Purification of the metal.
EXTRACTION OF METALS
More than 80 of the known elements are metals. They are widely distributed in the earth’s crust either as a free metals or in combination with other elements. The form in which a metal exists in nature is related to its reactivity. The most reactive metals e.g. sodium , potassium are found as chlorides or trioxocarbonate (iv), which are stable compounds; the moderately reactive metals e.g. zinc and lead, are found as oxides or sulphides; while the least reactive metals like gold and silver are found in an uncombined state.
PRINCIPLE OF EXTRACTION OF METALS
Metals that are found in combined forms in their ores exist as positive ions. During extraction, the metallic ions must be reduced to the corresponding metal. This can be done electrolytically or by chemical and thermal methods. The method chosen for the extraction of a particular metal depends on the stability of the ore, which in turn depends on the position of the metal in the activity series.
It is very difficult to reduce the metallic ions in the ores of reactive metal like Na and K with common reducing agent like coke because of their negative electrode potential value and the fact that they exist as positive ions. Electrolytic reduction method is used. Chemical and thermal reduction are used for less reactive metal like zinc, iron etc.
i.CHEMICAL AND THERMAL REDUCTION: Metals like Pb, Zn, Sn, Fe, which are less electropositive are usually obtained by reducing their oxides with coke or carbon (ii) oxide.
In the extraction of Zn from Zn blend (ZnS), the sulphide is first converted to the oxide by roasting. The oxide is later heated with coke.
Oxidation: C + O2- CO +2e-
Reduction: Zn2+ + 2e- Zn
C + ZnO Zn + CO
ii.ELECTROLYTIC METHOD: The most reactive metals like K, Na, Ca and Mg are obtained by electrolysis. Electricity is passed through the molten compound which contain metallic cation. The cation are attracted to the cathode (negative electrode) while the anions moves towards the anode (positive electrode).
The cation receive electrons from the cathode and pure metal is deposited. The electrolyte is always a salt of the metal e.g a chloride or an oxide with high melting point. The electrolytic method is always expensive to maintain.
THE ALKALI METAL
The Alkali metal are the group I elements which include Lithium, Sodium, Potassium, Rubidium, Caesium anf Francium. Francium is a short-lived radioactive elements.
PHYSICAL PROPERTIES OF ALKALI METALS
1. They are strongly electropositive element.
2. The atom of alkali metal has a larger radius than any of the atoms of elements in the same period.
3. Ionization energy decreases progressively down the group
4. Its electronegativity decreases down the group due to the screening effect of inner electron shell on the outermost electron.
5. The atoms of the alkali metals are held in closely-packed structure by weak metallic bond.
6. They are good conductor of heat and electricity.
7. They are good reducing agent being potential donor of electrons.
CHEMICAL PROPERTIES OF ALKALI METALS
1. The relative reactivities of the alkali metal are reflected by their reaction with water. Thus, potassium reacts explosively with water, while sodium react vigorously.
2K + H2O 2KOH + H2
2Na + H2O 2NaOH + H2
2. Lithium is less reactive in dry air because it is stable in dry air at room temperature.
3. Alkali metals tarnish easily when exposed to damp air because they are readily oxidized by atmospheric oxygen to form their oxides.
4. Alkali metal react vigorously with dilute acid liberating hydrogen gas and forming the corresponding salt.
2X(s) + 2HCl(aq) 2XCl(aq) + H2(g)
5. It react with hydrogen on heating to form hydride. 2X + H2 XH
6. It react violently with the halogen to form the halides. X + H XH
PRESENTATION
i. Teacher tests the students by given them questions based on their
knowledge in ss2 (welcome test).
1. define oxidation in term of oxygen
Answer : oxidation is the addition of oxygen to a substance
2. give any two examples of primary cell.
Answer: Daniel cell, leclanche cell, votaic cell.
3. write the structure of 2-methyl pentane
Ans: CH3CH(CH3)CH3
ii.The teacher explains metal and state the properties of metal.
iii. The students chorus the physical properties of metal
iv. The teacher mentions and explains the principle of extraction of metals.
v. The teacher states the physical and chemical properties of alkali earth metals
EVALUATION
The teacher evaluates the lessons by asking the following questions:-
1. Explain metal
2. State the physical properties of metal
3. Explain the chemical behavior of metal
4. Explain the principle of extraction of metal
5. State the physical properties of alkali metal
ASSIGNMENT
Giving different examples, mention one metal in each case which produces hydrogen on reacting with:
(a) Dilute mineral acid
(b) Cold water
(c.) Steam
(d) Hot concentrated alkali
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