Topic 5: ELEMENTS, COMPOUNDS AND MIXTURES – Chemistry Notes Form One

Topic 5: ELEMENTS, COMPOUNDS AND MIXTURES – Chemistry Notes Form One

ELEMENT

Definition; 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, Lead etc

NAMES AND CHEMICAL SYMBOLS OF ELEMENTS

CHEMICAL SYMBOLS

Defn: A chemical symbol is representation of the name of element using letters.

OR

A chemical symbol is abbreviation or short representations of an element

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

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	NAME	SYMBOL
Hydrogen	H	Phosphorus	P
Carbon	C	Iodine	I
Nitrogen	N	Fluorine	F
Oxygen	O	Vanadium	V
Sulphur	S	Yttrium	Y
Boron	B

2.If different elements have the same first letter, for example carbon (C), calcium (Ca), cobalt (Co) and copper (Cu) then only one element uses the first letter as its symbol, other elements use first letter plus another letter in the name usually the second or third.

Chemical symbols of some elements with two letters from their English names are shown in the table below

NAME	SYMBOL	NAME	SYMBOL
Calcium	Ca	Neon	Ne
Cobalt	Co	Aluminium	Al
Chlorine	Cl	Argon	Ar
Magnesium	Mg	Beryllium	Be
Manganese	Mn	Lithium	Li
Helium	He	Silicon	Si
Zinc	Zn

4. In some cases, the chemical symbols are derived from  Latin names instead of the common English names as shown in the table below

ELEMENT	LATIN NAME	SYMBOL
Sodium	Natrium	Na
Potassium	Kalium	K
Silver	Argentum	Ag
Gold	Aurum	Au
Lead	Plumbum	Pb
Copper	Cuprum	Cu
Iron	Ferrum	Fe
Mercury	Hydrargyrum	Hg
Tin	Stannum	Sn
Antimony	Stibium	Sb
Tungsten	Wolfram	W

SIGNIFICANT (IMPORTANCE) OF CHEMICAL SYMBOLS

The following are the significance of chemical symbols

(i) Enable chemists to understand elements quickly instead of memorizing full name of element

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

element in full name

(iii) Enable chemists to distinguish one element from the other

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. See diagram below

DRAW

The table above shows position of metals and non-metals in the periodic table.

METALS

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

Eg Sodium, potassium, lithium, Beryllium, boron, iron, copper, silver, gold, tin, calcium, zinc

, manganese, magnesium, lead etc

Metals are mostly found at the left-hand side and at the middle of the periodic table

NON-METALS

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

Eg Oxygen, sulphur, hydrogen, carbon, silicon, chlorine, fluorine, phosphorous, nitrogen etc

Most of non-metals exists in gaseous state or liquid state with exception of few such as carbon

and sulphur which exist in solid state.

NB: 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
1. Are good conductor of heat and electricity	Poor conductors of electricity. (they are insulators) except carbon, in the form of graphite, which conducts electricity
2. Are good conductor of heat (this is why cooking utensils are made up of metals such as aluminium and iron)	Are poor conductor of heat.
2. Have high densities	Have low densities
3. Have high melting points and boiling points	They have low melting points and boiling points
4. Are strong and tough	Are not strong and tough
5. Are ductile ie.they can be drawn into thin wires	Are not ductile. They can not be drawn into thin wires
6. Are good conductor of sound. They are Sonorous. (which means they make sounds when hit.)	Are poor conductor of sound. They are not Sonorous. (which means they do not make sounds when hit.))
7. Have high tensile strength	Have low tensile strength
8. Are malleable (i.e can be made (hammered) into thin sheets)	Are not malleable
9. Are lustrous. They produce shining surface when cut.	Are non – lustrous except a few such as diamond

NB: There are exceptions to the above properties as follow

(i) Graphite is a non metal (Carbon) but it is a good conduct of heat and electricity

(ii) Diamond is non metal (Carbon) but has high melting and boiling point.

(iii) Some metals have different characteristics from those described above, eg sodium and

Potassium. These elements have low densities

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

EXERCISE 1

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 do they make metals useful in various

applications.

COMPOUNDS AND MIXTURES

COMPOUND

Defn. (i) A compound is a pure substance made up of two or more elements in a chemical combination.

OR (ii) 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, baking powder etc.

When a compound is made up of two components is referred to as a binary compound. Examples of binary compounds include 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	COMPOUND
1	Sulphur	Oxygen	Sulphur dioxide
2	Sodium	Chlorine	Sodium chloride
3	Hydrogen	Oxygen	Water
4	Nitrogen	Hydrogen	Ammonia
5	Zinc	Sulphur	Zinc sulphide

Characteristics (properties) of binary compounds

(i) Its components can be separated by chemical means only

(ii) Its components are in fixed ratio. (i.e whenever a compound is formed the substance in it

combine in a definite proportion.

(iii) Its formation involves only chemical change (reaction).

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

(v) The components cannot be seen separately.

(vi) Its formation involves energy change.

DIFFERENCES BETWEEN ELEMENTS AND COMPOUNDS

S/N	ELEMENTS	COMPOUNDS
1	Can not be separated into simpler substances	The components can be separated by chemical means
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	They maintain their characteristics when are in mixtures	Have different characteristics from their components when they are made
4	Contain unique atomic number	Have varying total atomic numbers depending on their components.
5	Symbols represent the elements	Chemical formula represents a compound.

Elements and compounds are similar in

(i) Element and Compound are both pure substances made from their constituents as

homogenous substances and cannot be separated by physical means.

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

components are mostly combined in fixed ratio.

MIXTURES

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

OR

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 (eg Oil and water), Solid – Liquid (eg muddy water) or Solid – Solid (eg Sand and salt).

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

Mixtures can be Homogenous or Heterogeneous.

Homogenous mixture is a mixture which has uniform compositions, appearance and properties.

Eg 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 point 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

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

(ii) Its components are not in fixed ratio.

(iii) Its formation involves physical change.

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

(v) The components can be seen separately.

(vi) No energy change when it is formed.

As seen above, mixtures and compounds have different properties.

The table below shows the difference in properties between mixtures and compounds.

MIXTURE	COMPOUND
1. The components in mixture can be separated by physical means	The elements in compound cannot be separated by physical means, (but can be separated by chemical means)
2. The composition of mixture is variable	The composition of compound is fixed
3. No chemical change occurs when mixtures are formed.	Chemical change occurs when compounds are formed
4. The properties of the mixture are those of individual components	The properties of the compound are very different from those of the individual elements.
5. Components in mixture can be seen separately	Components in compound cannot be seen separately
6. No energy change occurs when it is formed.	Energy change occurs when it is formed.

EXERCISE 2

1. 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.

2. Provide examples of how elements, compounds and mixtures are used in every day life.

SOLUTIONS, SUSPENSIONS AND EMULSIONS

Liquid mixtures can be classified into Solutions, suspensions or emulsions depending on their compositions.

(1) SOLUTION

Defition : 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). etc

A solution is made up of solvent and solute

Definition: (i) Solvent is a component of the solution that dissolves the solute.

OR (ii) Solvent is a substance that dissolves a solute.

Solvent is a component that is usually present in large amount in a solution. Examples of solvent are: water, alcohol, diesel, petrol, kerosene

Definition (i) Solute is component of the solution that is dissolved in the solvent.

OR (ii) Solute is a substance that dissolves in a solvent

Solute is a component that is usually present in small amount in a solution. Examples of solute are: sugar, salt, grease

TYPES OF SOLUTIONS

A solution can either be (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

A saturated solution is a solution in which a solvent cannot dissolve more solute at a given temperature and pressure.

(Saturated solution leaves the undissolved solutes at the bottom)

SUPER SATURATED SOLUTION

A super saturated solution is a solution that holds more solute than the maximum amount it can dissolve at a given temperature and pressure.

NB: Saturation depends on temperature. As the temperature increases, the kinetic energy of solvent molecules increases and hence more solute particles dissolve.

APPLICATION OF SATURATION

Saturation is used when

(i) Separating certain mixtures in laboratory

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

(iii) Cooking and salting food

(iv) Using detergents during laundry

(v) Dissolving sugar in tea.

CLASSIFICATION OF SOLUTIONS INTO 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	GAS	Naphthalene slowly sublimes in air to form a solution
SOLID	LIQUID	Sugar in water and salt in water
SOLID	SOLID	Steel and other metal alloys
LIQUID	GAS	Water in air
LIQUID	LIQUID	Ethanol (alcohol) in water and various hydrocarbons in each other (petroleum)
LIQUID	SOLID	Mercury in gold and hexane in paraffin wax
GAS	GAS	Oxygen and other gases in the air
GAS	LIQUID	Carbon dioxide in water (carbonated water)
GAS	SOLID	Hydrogen in metals

From the table above, Examples of

SOLID SOLUTION: (i) Steel (solution of carbon, sulphur in iron),

(ii) Brass (solution of zinc in copper)

LIQUID SOLUTION: (i) Alcohol in water

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

GASEOUS SOLUTION: (i) Air (solution of oxygen in other gases in air)

(ii) Water vapour in air

USES OF SOLVENTS

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

The following are some of the uses of solvents

(i) Are used in cleaning (because they form a solution with the dirty (solute)

(ii) Are used in varnish removal

(iii) Are used in stain removal

(iv) Are used in bleaching

(v) Are used in thinning paints

(vi) Are used in degreasing

(2) SUSPENSION

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

OR

A suspension is heterogeneous mixture in which the solid particles settle to the bottom on standing but spread throughout when shaken.

In suspension the solute particles do not dissolve but get suspended in the liquid. For example, when you add flour into water during cooking you have to keep on stirring, otherwise the flour will settle. This is an example of suspension.

Other examples of suspension include, Paints, porridge, muddy water, chalk powder in water, blood, sand particles suspended in water, some medicine written shake well before use are suspensions.

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.

DIFFERENCE BETWEEN SOLUTION AND SUSPENSION

SOLUTION	SUSPENSION
1. It is homogeneous mixture	It is heterogeneous mixture
2. It is transparent (clear)	It is opaque (not clear)
3. 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.

(3) EMULSIONS

Definition: 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: Milk, which contains drops of butter fat in water

Emulsion paint, which contains is drops of coloured oils in water

MISCIBLE AND IMMISCIBLE LIQUIDS

Miscible liquids are liquids which mix up completely without forming layers. Eg methylated spirit and water, Ethanol and water, benzene and paraffin, water and soda etc

Immiscible liquids are liquids which do not mix up completely i.e they form layer. Eg Kerosene and water, Oil and water, chloroform and water etc.

SEPARATION OF MIXTURES