CHAPTER FIVE: ELEMENTS, COMPOUNDS AND MIXTURES

ELEMENTS AND SYMBOLS

Element is a pure chemical substance that cannot be split into simpler substance by

chemical means.

Elements are the building blocks from which many substances (compounds) are

made. There are over 118 known elements of which most of them are natural and

some are man-made.

Examples of elements include Hydrogen, Helium, lithium, Beryllium, potassium,

sulphur, calcium, Boron, Iron, Carbon, Nitrogen, Oxygen, Fluorine, Copper, Silver,

Gold, Tin, Zinc, Manganese, Magnesium and Lead.

NAMES AND CHEMICAL SYMBOLS OF ELEMENTS

CHEMICAL SYMBOLS

Chemical symbols are abbreviations or short representations of element names.

OR

Chemical symbols are representations of the names of elements using letters.

The chemical symbols are normally derived from one or two letters of a Latin

(Greek) or English names.

If an element is represented by two letters the first one should be capital letter and

the second should be small letter. When an element is represented by one letter it

should be in capital letter.

NB: Chemical symbols are written according to the rules of the

International Union of Pure and Applied Chemistry (IUPAC).

CRITERIA (RULES) FOR ASSIGNING CHEMICAL SYMBOLS

The following are the criteria used for assigning chemical symbols:

1. An element may be represented by a chemical symbol that is derived from the

first letter of its English name.

Examples of some elements with chemical symbols derived from the first letter of

its English name are shown in the table below.

NAME

SYMBOL

H

NAME

SYMBOL

P

Hydrogen

Phosphorus

Carbon

C

Iodine

I

Nitrogen

N

Fluorine

F

Oxygen

Sulphur

Boron

O

S

B

Vanadium

Yttrium

V

Y

2. If different elements have the same first letter, for example calcium, cobalt and

copper it is necessary to differentiate the elements. In this case, another letter,

usually the second or third from the name is used together with the first letter.

Chemical symbols of some elements with two letters from their English names are

shown in the table below:

NAME

SYMBOL

Ca

NAME

SYMBOL

Calcium

Cobalt

Neon

Ne

Al

Co

Aluminium

Argon

Chlorine

Magnesium

Manganese

Helium

Cl

Ar

Be

Li

Mg

Beryllium

Lithium

Mn

He

Silicon

Si

Zinc

Zn

Scandium

Sc

3. In some cases, the chemical symbols are derived from Latin names instead of the

common English names as shown in the table below:

ELEMENT

Sodium

Potassium

Silver

LATIN NAME

Natrium

SYMBOL

Na

K

Kalium

Argentum

Aurum

Ag

Au

Pb

Gold

Lead

Plumbum

Copper

Iron

Cuprum

Cu

Fe

Hg

Sn

Sb

W

Ferrum

Mercury

Tin

Hydrargyrum

Stannum

Stibium

Antimony

Tungsten

Wolfram

SIGNIFICANT (IMPORTANCE) OF CHEMICAL SYMBOLS

The following are the significance of chemical symbols

(a) Quickly understand the elements being referred to, instead of memorizing the full

names.

(b) It is easy to write the chemical equation using symbol instead of writing each

element in its full name.

(c) Help to distinguish one element from the other

Exercise

1. Why is it important to know chemical symbols at early stage of chemistry

learning?

2. Why are the chemical symbols used alongside the common names of

elements?

3. What are challenges might occur if different countries could use different

names for same element?

METALS AND NON-METALS

Elements are classified into Metals and Non-metals.

The systematic method to represent and organise chemical elements in a table format

is called Periodic Table.

Table: Position of metals and non-metals in the periodic table.

METALS

A metal is an element except hydrogen that will lose electron (s) to form positive

charge. Examples; sodium, potassium, lithium, Beryllium, boron, iron, copper, silver,

gold, tin, calcium, zinc, manganese, magnesium and lead.

Location of metals in the periodic table: Metals are mostly found at the left-hand

side and at the middle of the periodic table

NON-METALS

A non-metal is an element that will gain electron (s) to form negative charge.

Examples; oxygen, sulphur, hydrogen, carbon, silicon, chlorine, fluorine, phosphorous

and nitrogen. Most of non-metals exist in gaseous state or liquid state with exception

of few such as carbon sulphur and iodine which exist in solid state.

Note: Although hydrogen is located at the left-hand side of the periodic table, it is a

non-metal because it possesses the characteristics of non-metal.

Metals and non-metals differ in physical and chemical properties

DIFFERENCES IN PHYSICAL PROPERTIES BETWEEN METALS AND NON-METALS

METALS

NON-METALS

Are poor conductors of electricity. They

are insulators except graphite which

conducts electricity.

1. Are good conductor of electricity

Are poor conductors of heat.

2. Are good conductor of heat (this

is why cooking utensils are made

up of metals such as aluminium and

iron)

3. Have high melting points and boiling

Points

They have low melting points and

boiling points.

4. Are ductile. They can be drawn into

thin wires

Are not ductile. They cannot be drawn

into thin wires

5. Are good conductor of sound. They

are sonorous. (which means they

make sounds when hit.)

Are poor conductor of sound. They are

not sonorous.

6. Have high tensile strength

Have low tensile strength

Are not malleable.

7. Are malleable. They can be

hammered into thin sheets.

8. Are lustrous. They produce shining

surface when cut.

Are non-lustrous except a few such as

diamond

Note:

(a) Graphite is a non-metal (carbon) but it is a good conduct of heat and electricity.

(b) Diamond is non-metal (carbon) but has high melting and boiling point.

(c) Some metals have different characteristics from those described above. Example

sodium and potassium. These elements have low densities

(d) All metals are solids at room temperature but mercury is in liquid state at room

temperature.

Exercise

1. Give three examples of metals and non- metals, and explain their uses in daily life.

2. Why are cooking pots made of metals?

3. Describe properties of metals and explain how they make metals useful in various

applications.

COMPOUNDS AND MIXTURES

COMPOUND

A compound is a pure substance made up of two or more elements in a chemical

combination.

A compound is a pure substance which consists of two or more elements which are

chemically combined together.

Examples of compounds are Common salts, water, sugar, carbon dioxide, petrol,

diesel, alcohol and baking powder.

When a compound is made up of two components is referred to as a binary

compound. Examples of binary compounds includes common salt, carbon dioxide and

water.

A binary compound is formed when two or more pure substance of the same or

different types are chemically combined together.

Table below shows examples of substances that combine to make binary compounds.

S/N First part

Second part

Oxygen

Compound

1.

2.

3.

4.

5.

Sulphur

Sodium

Hydrogen

Nitrogen

Zinc

Sulphur dioxide

Sodium chloride (common salt)

Water

Chlorine

Oxygen

Hydrogen

Sulphur

Ammonia

Zinc sulphide

Properties (characteristics) of binary compounds

(a) Its properties are quite different from those of its components.

(b) Whenever a compound is formed the substances in it combine in a definite

proportions. Its components are in fixed ratio.

(c) A compound is formed only by a chemical reaction. Energy is taken or given out in

the form of heat and light when a compound is formed.

(d) Its components can be separated by chemical means only.

DIFFERENCES BETWEEN ELEMENTS AND COMPOUNDS

S/N ELEMENTS

COMPOUNDS

1.

Cannot be separated into simpler

The components can be separated

by chemical means

substances

2.

They are made up of similar

atoms of the same type

Can be made up of two or more

substances that are naturally

different.

3.

Have different characteristics from

their components when they are

made

They maintain their characteristics

when are in mixtures

4.

5.

Contain unique atomic number

Symbols represent the elements.

Have varying total atomic numbers

depending on their components.

Chemical formula represents a

compound.

SIMILARITIES OF ELEMENTS AND COMPOUNDS

(a) Element and compound are both pure substances made from their constituents as

homogenous substances and cannot be separated by physical means.

(b) Elements and compounds are both made from atoms as their building blocks and

their components are mostly combined in fixed ratios.

MIXTURES

Mixture is a physical combination of two or more substances in any ratio. A mixture

is a substance that consists of two or more substances (elements) which are not

chemically combined together.

Since mixtures are not chemically combined, they can be separated by physical

means. Mixtures can be liquid-liquid (for example, oil and water), solid-liquid (for

example, muddy water) or solid-solid (for example, sand and salt).

Other examples of mixtures are: milk, sea water, sugar solution, tea, blood, soda, Air

Types of mixtures: Homogenous and heterogeneous mixtures.

Homogenous mixture is a mixture which has uniform compositions, appearance

and properties. Example, when salt is dissolved in water every section of the solution

is identical in composition, appearance and physical properties. Other examples of

homogenous mixture are tea, air, sugar solution.

Heterogeneous mixture is a mixture which has different compositions, appearance

and properties at various points in the mixture. For example, when sulphur powder

and iron fillings are mixed together, they form heterogeneous mixture. A mixture is

physically combined and can be separated by a bar magnet. Other examples of

heterogeneous mixtures are sand and water, oil and water, chalk powder and water.

Characteristics of mixtures

(a) Its components can be separated by physical means.

(b) Its components are not in fixed ratio.

(c) Its formation involves physical change.

(d) Its properties are those of its components in it.

(e) The components can be seen separately.

(f) No energy change when it is formed.

Differences between homogeneous and heterogeneous mixtures

S/N Homogeneous mixture

Heterogeneous mixtures

Has different composition.

1.

2.

3.

4.

Have uniform composition

Have uniform appearance

Components are completely mixed

Have only one phase

Has different appearance

Components are not completely mixed.

Have two or more phases.

Difference in properties between mixtures and compounds

MIXTURES

COMPOUNDS

The elements in compound cannot be

separated by physical means but can be

separated by chemical methods.

1. The components in mixture can be

separated by physical means

2. Mixtures may vary widely in

The composition of compound is fixed.

compositions. The composition of

mixture is variable

Compounds have always fixed

compositions by mass.

3. No chemical change occurs when

mixtures are formed.

Chemical change occurs when

compounds are formed.

The properties of the compound are very

different from those of the individual

elements.

4. The properties of the mixture are

those of individual components

5. No energy change occurs when

mixtures are formed.

Energy change occurs when compounds

are formed.

Exercise

1. A chemist categorized the following items as elements, mixtures and compounds.

What could be the reasons behind the assigning?

(a) Rock salt as a mixture and table salt as a compound.

(b) Muddy water as a mixture and pure water as a compound.

(c) Charcoal as an element and sugar as a compound.

2. Provide examples of how elements, compounds and mixtures are used in everyday

life.

3. You are provided with the following substances: Common salt, mud, juices, milk,

water, soft drink, kerosene, diesel and air. Classify the substances as either

compounds or mixtures and give reasons for your responses.

SOLUTIONS, SUSPENSIONS AND EMULSIONS

Liquid mixtures can be classified into solutions, suspensions or emulsions depending

on their compositions.

SOLUTIONS

Solution is a homogeneous (uniform) mixture of two or more substances which are

solvent and solute. Such mixtures (solution) may be a solid in a liquid, a liquid in a

liquid, a liquid in a gas and, and a gas in a gas.

Examples of solutions are, solution of sugar in water and salt in water (LIQUID

SOLUTIONS), a solution of zinc in copper (SOLID SOLUTION), Air is a solution of

oxygen in nitrogen (GAS SOLUTION).

A solution is made up of solvent and solute

Solvent is a component of the solution that dissolves the solute.

Solvent is a component that is usually present in large amount in a solution. Examples

of solvent are: water, alcohol, diesel, petrol, kerosene

Solute is component of the solution that is dissolved in the solvent.

Solute is a component of the solution that is usually present in small amount in a

solution. Examples of solute are: sugar, salt, grease.

TYPES OF SOLUTIONS

(i) Unsaturated solution

(ii) Saturated solution

(iii) Super saturated solution

Unsaturated solution

An unsaturated solution is a solution in which solvent can dissolve more solute at a

given temperature and pressure.

(Here the solutes completely dissolve, leaving no remaining solutes)

Saturated solution is a solution in which the solvent can dissolve no more solute at

a given temperature and pressure. It leaves the un-dissolved solutes at the bottom.

Super saturated solution is a solution that holds more solute than the maximum

amount it can dissolve at a given temperature and pressure.

Note: Saturation depends on temperature. As the temperature increases, the kinetic

energy of solvent molecules increases and hence more solute particles dissolve.

APPLICATION OF SATURATION

The concept of saturation can be applied when:

(1) Separating certain mixtures in laboratory

(2) Extracting some minerals such as extracting common salt from sea water.

(3) Cooking and salting food

(4) Using detergents during laundry

(5) Dissolving sugar in tea.

INTERCONVERSION OF THE THREE TYPES OF SOLUTIONS

The three types of solutions can be interconverted without adding any solute in the

solution through the following ways;

(a) Shaking; this involves mixing the components vigorously in a vessel.

(b) Stirring; this involves the mixing of the components in a vessel using a stirrer

(c) Crystallization; this involves separating pure solids (solutes) from solution.

This is achieved by heating the solution to evaporate some of the water. The

solution becomes more concentrated (saturated). If you cool it again, crystals

will start to form.

CLASSIFICATION OF SOLUTIONS INTO THE THREE STATES OF MATTER

Solutions can exist in the three states of matter which are solids, liquids and gases.

The solutes and solvents can be in any state, that is solid, liquid or gas.

Table below shows examples of types of solutions in the three states of matter.

SOLUTE SOLVENT EXAMPLES

SOLID

LIQUID

GAS

Naphthalene slowly sublimes in air to form a solution

Sugar in water and salt in water

Steel and other metal alloys

LIQUID

SOLID

GAS

Water in air

Ethanol (alcohol) in water and various hydrocarbons in

each other (petroleum)

Mercury in gold and hexane in paraffin wax

Oxygen and other gases in the air

Carbon dioxide in water (carbonated water)

Hydrogen in metals

LIQUID

GAS

SOLID

GAS

LIQUID

SOLID

GAS

From the table above, Examples of

SOLID SOLUTION:

LIQUID SOLUTION:

GASEOUS SOLUTION:

Uses of solvents

(i) Steel (solution of carbon, sulphur in iron),

(ii) Brass (solution of zinc in copper)

(i) Alcohol in water

(ii) Vinegar (a solution of acetic acid in water)

(i) Air (solution of oxygen in other gases in air)

(ii) Water vapour in air

Solvents are used in homes, institutions such as schools and colleges, hotels and in

industries. The following are some of the uses of solvents

(a) Are used in cleaning (because they form a solution with the dirt (solute).

(b) Are used in varnish removal

(c) Are used in stain removal

(d) Are used in bleaching

(e) Are used in thinning paints

(f) Are used in degreasing

Note: Water is the most common solvent as it has the capacity (ability) to dissolve

many solutes

SUSPENSIONS

A suspension is heterogeneous mixture of liquid (solvent) and fine particles of solid.

It is the heterogeneous mixture in which the solid particles settle to the bottom on

standing but spread throughout when shaken.

Note:

In suspension the solute particles do not dissolve but get suspended in the liquid.

Examples of suspensions are:

(a) Flour in water. During cooking you have to keep on stirring, otherwise the flour

will settle.

(b) Paints

(c) Porridge

(d) Muddy water

(e) Blood

(f) Chalk powder suspended in water

(g) Sand particles suspended in water

Suspensions composed of either liquid droplets or fine solid particles suspended in a

gas are called Aerosols.

Suspensions are used in many aspects in our daily life and stored in containers

labelled “shake well before use”. Examples of these are medicines (syrups), Body

sprays, some paints, insecticides etc.

Sometimes a liquid may contain very small particles of another substance that neither

dissolve nor settle instead are evenly distributed throughout the liquid; this

type of mixture is called a colloid.

DIFFERENCE BETWEEN SOLUTION AND SUSPENSION

S/N SOLUTIONS

SUSPENSIONS

1.

2.

3.

Homogeneous mixture

Heterogeneous mixture

Opaque (not clear)

Transparent (clear)

Solute particles completely

dissolved in solvent

Solute particles settle if the suspension is

undisturbed

4.

Components are separated by

evaporation

Components can be separated by

filtration.

EMULSIONS

Emulsion is a mixture of liquids that do not completely mix with each other.

An emulsion is usually formed from two liquids, one water-based liquid and the other

oil-base liquid. When shaken the oily forms droplets suspended in the water-based

liquid. The harder the emulsion is shaken, the smaller the droplets, so the emulsion

may appear to be a homogeneous solution. Example of emulsions are:

(a) Milk which contains drops of butter fat in water

(b) Emulsion paint which contains is drops of coloured oils in water

Question

Distinguish between suspension and emulsion

Answer

MISCIBLE AND IMMISCIBLE LIQUIDS

Miscible liquids are liquids which mix up completely without forming layers.

Example; methylated spirit and water, ethanol and water, benzene and paraffin,

water and soda.

Immiscible liquids are liquids which do not mix up completely i.e they form layer.

Example; Kerosene and water, Oil and water, chloroform and water.