Chemical Formulae, symbols and Equation

WEEK 3

DATE………………

TOPIC: CHEMICAL SYMBOLS, FORMULAE AND EQUATIONS

CONTENT

<![if !supportLists]>1.      <![endif]>Meaning
of chemical symbols;Groups of chemical symbols

<![if !supportLists]>2.      <![endif]>Chemical
Formulae and Equations

Sub-Topic 1: MEANING OF CHEMICAL SYMBOLS

A chemical symbol is an
abbreviated form of the name of an element. It represents one atom of the
element.

GROUPS OF CHEMICAL SYMBOLS

There are four groups of symbols
namely;

<![if !supportLists]>(i)
<![endif]>Symbols which are the first letter of the name of the
element. These symbols are written in capital letters.

<![if !supportLists]>(ii)
<![endif]>Symbols which are the first two letters in the name of
the element. The first letter of the symbol is a capital letter while the
second letter is a small letter.

<![if !supportLists]>(iii)
<![endif]>Symbols which are the first letter and another letter
in the name of the element.

<![if !supportLists]>(iv)
<![endif]>Symbols of elements derived from the Latin name of the
element.

CONCEPT OF THE PERIODIC TABLE

The most important classification
of chemical substances is the arrangement of the elements in the Periodic
Table/Chart. A Russian scientist called Mendeleev (1869) was the first to
construct a periodic table. He arranged elements in order of increasing
relative atomic mass. However, scientists have discovered that elements vary
regularly with their atomic number. Each element in the periodic table is
represented by a chemical symbol which makes it easy to identify them. Elements
that share a column in the table have similar properties. The first twenty
elements in the periodic table are;

1. Hydrogen

2.
Helium

3.
Lithium

4.
Beryllium

5.
Boron

6.
Carbon

7.
Nitrogen

8.
Oxygen

9.
Fluorine

10.
Neon

11.
Sodium

12.
Magnesium

13.
Aluminum

14.
Silicon

15.
Phosphorus

16.
Sulphur

17.
Chlorine

18.
Argon

19.
Potassium

20.
Calcium

EVALUATION

<![if !supportLists]>1.
<![endif]>What is a chemical symbol?

<![if !supportLists]>2.
<![endif]>Enumerate the four groups of chemical symbols and
give three examples of each.

      3.
The periodic table shows the classification of elements in what order?

      4.
Mention the first twenty elements in the periodic table.

Sub-Topic 2: CHEMICAL FORMULAE AND
EQUATIONS

CHEMICAL FORMULAE: A chemical formula
is the representation of a substance using symbols and numbers. A chemical
formula represents a molecule of a substance(an element or compound) and gives
information about the types of atoms present in the substance and their
number/proportion.

Every
element and every compound has itsown formula e.g. the chemical formula for one
molecule of water is H₂O. This means that one molecule of water
consists of two atoms of hydrogen
and one atom of oxygen.

<![if !vml]><![endif]>

 Other examples are;

Chemical formulae are written in
a particular way to obey certain rules. Each element in the substance is
written in capital letter and its proportion/number in the substance is written
as a subscript. A subscript applies to the symbol before it e.g. in the formula
NH_3, the subscript(3) refers to H(hydrogen) only.

Combining Powers (Valency) of Elements

When atoms of different elements
combine during a chemical reaction, the atom that loses electrons becomes
positively charged (cation). The atoms that gain electrons become negatively
charged (anion). The number of electrons lost or gained by an atom is it’s
combining power/ valency. This is in order to attain the
nearest noble gas electronic configuration that is, a neutral state.

Metals show positively charged
combining power. Non-metals such as chlorine have negative combining power.
However, some elements exhibit more than one type of combining power.

Examples;

To write the chemical formula of
an ionic compound superscripts are used for the ions, this makes the total
positive charges equal the total negative charges. For example Sodium chloride
is formed from a combination of a positively charged Sodium ion, Na⁺
and a negatively charged Chlorine ion, Cl^– , thus the chemical
formula of Sodium chloride is Na⁺Cl^– simply written as
NaCl. Other examples are;

<![if !supportLists]>1.      <![endif]>Magnesium
SulphideMg²⁺S^– (MgS)

<![if !supportLists]>2.      <![endif]>Magnesium
Chloride         Mg²⁺Cl^–
(MgCl)

<![if !supportLists]>3.      <![endif]>Sodium
Sulphide               Na⁺S^2-(Na₂S)

<![if !supportLists]>4.      <![endif]>AluminiumSulphideAl³⁺S^2-
(Al₂S₃)

A group of atoms carrying either positive or negative charge is
called a radical(polyatomic ions)e.g.
SO₄^2-, OH^–, NO₃^–. The
combining powers of such radicals are the net number of positive or negative
charges they carry. The chemical formula for such polyatomic ions is written in
brackets and the superscript/subscript is placed outside the bracket. Examples;

<![if !supportLists]>1.      <![endif]>Trioxonitrate
(v) ion           (NO₃)^–

<![if !supportLists]>2.      <![endif]>Tetraoxosulphate
(vi) ion    (SO₄)^2-

<![if !supportLists]>3.      <![endif]>Trioxocarbonate
(iv) ion     (CO₃)^2-

<![if !supportLists]>4.      <![endif]>Sodium
trioxonitrate (v)     Na⁺NO₃^–=
NaNO3

<![if !supportLists]>5.      <![endif]>Aluminiumtetraoxosulphate(vi)    Al³⁺⁽SO₄)^2-
=Al₂(SO₄)₃

CHEMICAL EQUATIONS: A chemical equation is a condensed statement of
facts about a chemical reaction. A chemical reaction takes place whenever a
substance undergoes chemical change. A chemical equation is thus used to
represent the changes in bonding and changes in energy that take place in the
reaction.

 Chemical reactions involve reactants
and products.
The reactants are the substances that existed before the chemical reaction took
place. The products are the substances formed as a result of the reaction. For
example, hydrogen gas reacts with oxygen gas to produce water (liquid). This
statement can be written as;

Hydrogen gas + Oxygen gas → Water

The reactants which are hydrogen
gas and oxygen gas are written on the left of the arrow while the product which
is water is written on the right of the arrow. This statement can be written
with chemical formulae thus;

                                                                        H_2
(g) + O_{2 (g)} → H₂O _(l)

During a chemical reaction atoms
may be re-arranged to form new substances but they are never created or
destroyed. The equation above is referred to as an unbalanced equation this is
because the number of Oxygen atoms on the right is not the same as the number
on the left. To balance chemical equations coefficients are used. A coefficient is a number written in front of a formula
to balance the equation. Coefficients indicate the smallest number of molecules
of a substance that may take part in a reaction. So to balance the equation
above a coefficient of 2 is introduced;

2 H₂ + O₂ → 2H₂O

The balanced equation reads, two
molecules of hydrogen react with one molecule of oxygen to produce two
molecules of water. The coefficient multiplies all the atoms in the reaction
so; four atoms of Hydrogen react with two atoms of Oxygen to produce four atoms
of Hydrogen and two atoms of Oxygen, a balanced reaction. Since the number of
atoms in the reactants equal the number of atoms in the products, the arrow may
be replaced with equality sign and written as;

                    2 H₂
+ O₂= 2H₂O

The major steps in writing a
balanced equation are;

<![if !supportLists]>1.      <![endif]>Know
all the reactants and products

<![if !supportLists]>2.      <![endif]>Write
a word equation.

<![if !supportLists]>3.      <![endif]>Write
an unbalanced formula equation.

<![if !supportLists]>4.      <![endif]>Check
the number of each type of atom on the left and right sides of the arrow.

<![if !supportLists]>5.      <![endif]>Write
coefficients to balance the formula equation.

Other examples are;

<![if !supportLists]>1.      <![endif]>When
Calcium trioxocarbonate(iv) is heated it decomposes and forms Calcium Oxide and
Carbondioxide

                    CaCO₃ →
CaO + CO₂

<![if !supportLists]>2.      <![endif]>Tin
reacts with Oxygen to form Tin oxide

Sn + O₂
→ SnO₂

EVALUATION

<![if !supportLists]>1.
<![endif]>Write the formula for each of the following:

<![if !supportLists]>(a)
<![endif]>Water

<![if !supportLists]>(b)
<![endif]>Zinc chloride

<![if !supportLists]>(c)
<![endif]>Calcium hydroxide

<![if !supportLists]>(d)
<![endif]>Aluminiumtrioxocarbonate(iv)

<![if !supportLists]>2.      <![endif]>Write
and balance each of the following equations

<![if !supportLists]>(a)
<![endif]>Sodium reacts with chlorine gas to produce Sodium
chloride

<![if !supportLists]>(b)
<![endif]>Cl₂ + NaBr → Br₂ + NaCl

WEEKEND ASSIGNMENT

<![if !supportLists]>1.      <![endif]>Make
a model of the periodic table

<![if !supportLists]>2.      <![endif]>Write
out the chemical equations for and the names of the following;

<![if !supportLists]>(a)
<![endif]>a compound that contains one carbon atom and four
hydrogen atoms.

<![if !supportLists]>(b)
<![endif]>a compound that contains one atom of Calcium, one atom
of Carbon and three atoms of Oxygen.

<![if !supportLists]>3.      <![endif]>Calculate
the total number of atoms in four molecules of water.

<![if !supportLists]>4.      <![endif]>Balance
the following equations

<![if !supportLists]>(a)
<![endif]>Cl₂ + Na → NaCl

<![if !supportLists]>(b)
<![endif]>Cu + H₂SO₄ → CuSO₄
+ H₂O + SO₂

READING ASSIGNMENT

Functional Basic Science for JJS
Book 3; by Onyirioha, C. U et al. (pgs 70-80)