P3
Chemical Reactions, Names and Formulae
This chapter investigates the interaction between substances and the energy changes
involved in physical and chemical reactions. Systematic names and formulae for ionic
and binary covalent compounds are introduced as well as equations used to describe
chemical reactions.
Physical change
A change in which no new substance is formed
Chemical change
(Chemical reaction)
A change in which at least one new substance is formed
Indications of a
chemical reaction
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Reactants
Starting substances of a chemical reaction
Products
Substances that are formed by a chemical reaction
Law of conservation
of mass
Matter can be neither created nor destroyed, but merely
changed from one form to another
Physical properties of
substances
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Melting and boiling points
Appearance
Density
Conductivity of light and heat
Hardness, malleability and ductility
Chemical properties
of substances
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Decomposition by heat, light or electrical energy
Reactivity with oxygen, chlorine or sulfur
Reactions with acids or bases
Strength of chemical
bonds
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The stronger the chemical bonding in a compound the
more energy that is required to break the compound into
elements.
The stronger the chemical bonding in a compound the
more energy that is released when the compound is
formed from its elements
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Chemical equations
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A gas is evolved
A precipitate is formed
Change in colour
Change in temperature
Disappearance of a solid
Odour is produced
Used to describe what happens in chemical reactions
Must have the same number of atoms of each element on
each side of the arrow
Formulae of ionic
compounds
The ions are present in ratios such that the total number of
positive charges is equal to the total number of negative
charges
Valency of elements
The valency of an element in an ionic compound is equal to
the charge carried by an ion of that element
Ionic binary
compounds
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Consists of the atoms of two elements only
The name of the more metallic element is written first
The name of the less metallic element is written last and
the ending of its name is changed to –ide
The valency is shown using Roman numerals after the
name of a metal if it has variable valency
Polyatomic ions
Ions that consist of the atoms of more than one element but
behave as a single entity
Common polyatomic
ions
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Ammonium (NH4+)
Hydroxide (OH-)
Nitrate (NO3-)
Sulfate (SO42-)
Carbonate (CO32-)
Phosphate (PO43-)
Acetate (CH3COO-)
Covalency
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Number of covalent bonds that an element forms
Number of its electrons that the element shares
Covalent binary
compounds
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Consists of the atoms of two non-metallic elements only
The name of the element further to the left hand side of
the periodic table or, if the elements are in the same
group, farther down the group is written first.
The name of the element further to the right hand side of
the periodic table or, if the elements are in the same
group, nearer to the top of the group is written first and
the ending of its name is changed to –ide.
Prefixes are used to indicate the number of atoms of each
element
o Mono- (often omitted)
o Dio Trio Tetrao Pentao Hexa-
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