Chapter 4Elements, Compounds and Mixtures

• Chemical Composition of Matter

• What are Elements?

• What are Compounds?

• What are Mixtures?

What you will be learning…

• Chemical composition is the chemical components that make up a substance.

What is chemical composition?

Building Blocks of Matter?• All matter in the universe is made up of

elements.

What is an element?

• An element is a substance which cannot be broken down into two or more simpler substances by chemical methods.

aluminium

carbon

sulfur

copper

mercury

gold

Classifying Elements

• Elements can be classified into two general

categories: metals and non-metals.

General properties Metals Non-metals

Appearance • Shiny, can be

polished

• Usually dull

State of matter at

room temperature

• Solids except

for mercury

• Mostly liquid or

gas, some are

solids

Classifying Elements

General properties Metals Non-metals

Ability to withstand

stress

• Malleable – can

be beaten into

sheets

• Ductile – can

be drawn into

wires without

breaking

• Brittle (for

solids) – can

snap or break

easily

• Non-ductile

Density • High • Low

Melting and boiling

points

• High • Low

Classifying Elements

General properties Metals Non-metals

Ability to conduct

electricity (electrical

conductivity)

• Good • Poor

Ability to conduct

heat (thermal

conductivity)

• Good • Poor

• The properties of elements have helped

scientists and researchers to use metals and

non-metals for various purposes.

Periodic Table• In order to study the properties of elements

systematically, scientists have organized the

elements into a table called the Periodic Table.

Some elements have properties of both metals and non-metals (metalloids)E.g. • Silicon• Germanium• Boron• Arsenic

Two major groups:• metals• non-metals

metallic non-metallic

• The names of elements are represented by chemical symbols.

Names and chemical symbols of some common elements.

Representing elements

Sulfur

• Elements that are arranged in the same vertical column

belong to the same group.

• Elements in the same group have the same chemical

properties.

group

• Elements that are arranged in the same horizontal row

belong to the same period.

• As we move from the left to right along one period, the

properties of elements slowly change from those of

metals to those of non-metals.

period

13

Give three reasons why pure copper is a good choice for making electrical wires.

Think-Tank!

• Ductile and malleable

• Good conductor of electricity

• Solid at room temperature & pressure (r.t.p.)

Uses of some non-metals

Diamond (Carbon)

• Diamond drills like this can

help to cut through very hard

metals.

• Nitrogen is used to

make fertilisers for

farms.

Oxygen gas in the tank allows scuba divers to breathe in water.

Oxygen is used in the flame for welding.

Chlorine is

used in

bleaches for

our clothes.

Uses of some metals

Click here for a music video that introduces various elements.List the elements found in the video and state how they can be used in your everyday lives.

Iron is often used to

make cutlery.Magnesium is used to make milk of magnesia, which is used to relieve acid indigestion.

Aluminium is

used to make

aircraft bodies.

Copper is

often used to

make pipes/

copper wires.

What are Compounds?

• A compound is a substance which is made up of two or more different elements chemically combined together.

Glass

Water

Elements in the

compound:

Silicon, oxygen

Elements in the

compound:

Hydrogen, oxygen

Compound Elements present

Sodium chloride (table salt) Sodium, chlorine

Carbon dioxide Carbon, oxygen

Copper (II) sulfate Copper, sulfur, oxygen

Hydrogen chloride Hydrogen, chlorine

Calcium carbonate

(chalk/marble chip)

Calcium, carbon, oxygen

More examples of compounds… Properties of compounds

1. Compounds have very different properties from the elements that form them.

• E.g.: Formation of Sodium chloride, NaCl

+

sodium

chlorinesodium chloride

Sodium is a highly reactive

solid at room temperature. It

burns vigorously when in

contact with water.

Chlorine is a

greenish-yellow

poisonous gas at

room temperature.

Sodium chloride/ table

salt, is used in foods

to improve their taste

and in preservatives.

Properties of Compounds

2. The constituent elements of a compound are

always combined in a fixed proportion by mass.

• For example, sodium and chlorine always combine chemically in the ratio of 1:1 to form table salt.

• Hence, the ratio of sodium to chlorine by mass is fixed.

Properties of Compounds

3. A compound cannot be broken down by

physical methods.

• For example, sodium and chloride cannot be separated by physical methods such as filtration.

Compounds can be broken down by using

- electricity (electrolysis) or

- heat (thermal decomposition).

EXCEPTION:

Extra information:

Naming compounds

KCl Start with the name of the element to the left Add – ide to the second element stem name Name: Potassium chloride

Rule 1

CaORule 1

Start with the name of the element to the left Add – ide to the second element stem name Name: Calcium oxide

Rule 1)

A compound made up of two elements has a name that ends in –ide.

What are Mixtures?

• A mixture consists of two or more different substances that are mixed but not chemically combined together.

• The substances that make up a mixture may be

- elements,

- compounds or

- both elements and compounds.

Milk is a mixture of compounds such as proteins and fats.

Air is a mixture of elements, such as nitrogen and oxygen, and compounds such as carbon dioxide and water vapour.

• Examples of mixtures:

Properties of mixtures

A mixture has the properties of the substance it is

made up of.

The components of mixtures are not mixed in any

fixed proportion.

When a mixture is formed, no chemical reaction

occurs. Hence, a mixture can be easily separated

by physical methods.

Click here for an activity on compounds and mixtures.

Video to show differences between mixtures & compounds (using iron & sulfur)

Different types of mixtures

• Solid-solid mixtures (e.g. bronze)

• Solid-liquid mixtures (e.g. Calamine lotion)

• Liquid-liquid mixtures (e.g. Vinegar )

• Liquid-gas (e.g. Soda drinks )

• Gas-gas (e.g. air)

COMPOSITION OF MIXTURES

A mixture of two or more elements

Mixture of two elements Mixture of three elements

A mixture of one (or more) element and one (or more) compound

Mixture of two elements and one compound

Mixture of one element and one compound

COMPOSITION OF MIXTURES

A mixture of two (or more) compounds

Mixture of two compounds Mixture of three compounds

COMPOSITION OF MIXTURES

Which one of the diagrams, A, B or C, represents

a) Oxygen (O2)?

b) A mixture of two elements?

c) A mixture of compounds, e.g. ammonia (NH3) and carbon dioxide (CO2)?

Think-Tank!

B

C

A

Solutions & Suspensions

Matter

Pure substances Mixtures

Elements Compounds Solutions Suspensions

Definitions• Solute:- The substance (e.g. sugar) that dissolves in a solvent

(e.g. water).

• Solvent:- The substance that dissolves the solute.

• Solution:- A mixture of the solute and the solvent.

• Suspension:- A mixture in which insoluble substances are

suspended in a liquid or gas.

Solution around us…

Carbonated drinks:Carbon dioxide is dissolved in sugar solution to make carbonated drinks.

Syrup:Syrup is dissolved in water to make drinks.

Can you think of more examples of solution around

us?

Suspensions around us….

orange juice

antibiotics

drain water

Can you think of more examples of

suspension?

Solutions vs Suspensions

Solution SuspensionHomogeneous Non-homogeneous

No particles settle when

left to stand

Particles settle when left

to stand

When filtered, no residue

remains on the filter

paper.

When filtered, insoluble

solid (residue) remains

on the filter paper.

Cannot be separated by

filtration

Can be separated by

filtration

E.g. Salt solution, soap

solution

E.g. Sand + water

What is Solubility?

Solubility is the ability of a

solute to dissolve in a

solvent.

Factors affecting solubility

• Nature of solvent- Same solute will have different solubilities when placed

in different solvents.

• Nature of solute- Different solutes will have different solubilities when

placed in same solvent.

• Temperature- Usually, the higher the temperature,, the greater the

solubility of a substance.

ExamplesNature of solventAn example would be how salt

dissolves in water, but not in oil, as

seen in the stir-frying of vegetables.

This shows that water is a solvent for

salt but oil is not.

Temperature When we make sugar

syrup, we dissolve sugar in

hot water instead of water

at room temperature. This

is because more solute can

dissolve at a higher

temperature.

Nature of solute Sugar dissolves

easily in water but oil

does not. This shows

that different solutes

have different

solubilities in the

same solvent.

Rate of dissolving

• The rate of dissolving is the amount

of solute that dissolves in a fixed

amount of solvent, given a fixed

amount of time.

Factors affecting rate of dissolving

• Temperature- Higher temperature, faster rate of dissolving.

• Rate of stirring- Stir the mixture faster, greater amount of

solute to dissolve in the same amount of time.

• Size of solute particles- Smaller solute particles, dissolve faster.

- Small particles have greater surface area that comes in contact with the solvent.

- E.g baking soda powder dissolves faster than sugar cube in 10ml of water at

30oC