Page 115 - ICSE Chemistry 8

Chemical equa on: A chemical reac on represented using symbols and formulae
Word equa on: A chemical reac on wri en using only the names of the reactants involved
and products formed
Skeletal or unbalanced equa on: A chemical equa on in which the number of atoms of one or more reactants
and products is unequal
Balance equa on: A chemical equa on which has an equal number of atoms of one or more
elements in the reactants

Quick Review
• An element is the simplest form of a pure substance which is made up of only one kind of atom and is
represented by a chemical symbol.
• Each element is represented using a symbol. The symbols used to represent elements are usually the
short forms or abbreviated names of the elements.
• A compound is represented using a chemical formula which represents the number of the elements
that a molecule of a compound consists of.
• Valency is the combining capacity of an element. The valency of an element is always a whole number
that varies from 1 to 8.
• An ion is formed when an atom or a group of atoms gains or loses electrons. A ca on is a posi vely
charged ion and an anion is a nega vely charged ion.
• A radical refers to a group of diff erent atoms present as a single unit having a posi ve or nega ve
charge on it.
• A molecule of a compound is represented using a chemical formula.
• A chemical equa on represents a chemical reac on using symbols and formulae.
• A word equa on represents the chemical reac on wri en using only the names of the reactants
involved and products formed.
• The atomic theory states that atoms of the reac ng molecules involved in a chemical reac on do not
change.
• The law of conserva on of mass states that ma er is neither created nor destroyed in a chemical
reac on. This law can be applied to the atomic masses of reactants and products to balance chemical
equa on.

EXERCISES

BE PROMPT
A. Fill in the blanks.

1. An _____________ is the simplest form of a pure substance which is made up of only one kind of
atom.
2. _____________ refers to the combining capacity of an element.
3. A _____________ is formed when an atom or a group of atoms loses electron(s) by developing a
posi ve charge.
4. A chemical equa on consists of _____________ present on the le -hand side and _____________
present on the right-hand side.

101