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Chapter 4: Chemical bonding, structure and properties of materials -…
Chapter 4: Chemical bonding, structure and properties of materials
Ionic bonding
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the metal loses electrons while the non-metal gains electrons to obtain a fully filled valence electron shell
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high melting and boiling point due to strong electrostatic forces of attraction between oppositely-charged ions which require a large amount of energy to overcome them
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in solid state ions are held in fixed position in an ionic lattice so they cannot move to conduct electricity
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Covalent bonding
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low melting and boiling point due to weak intermolecular forces of attraction between molecules which require little amount of energy to overcome
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Common questions
Why does carbon dioxide exists as a gas but sodium chloride is a solid at room temperature and pressure?
Carbon dioxide is made up of simple covalent molecules with weak intermolecular forces of attraction between the molecules. Only a small amount of energy is required to overcome these attractions.
Sodium chloride is an ionic compound with strong electrostatic forces of attraction between oppositely-charged ions. Hence a large amount of energy is required to overcome these attractions.
Why does simple covalent molecult like carbon dioxide have low melting and boiling point (or exists as a gas)?
Carbon dioxide is made up of simple covalent molecules with weak intermolecular forces of attraction between the molecules. Only a small amount of energy is required to overcome these attractions. Thus, it has a low melting point and boiling point which is why simple covalent molecules like carbon dioxide exist as a gas at room temperature.
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Properties of metals
high density and high m.p./b.p. - atoms of a metal are packed tightly in layers held together by strong attractive forces known as metallic bonds, large amount of energy is needed to break these bonds
soft, ductile, malleable - atoms of a metal are the same size and packed regularly in layers, layers slide over one another when a force is applied
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Alloys
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the different size of one element disrupts the regular arrangement, preventing the atoms from sliding over one another easily
Pure metals
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atoms are of the same size and packed regularly in layers, the layers slide past over one another easily when a force is applied
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