THE VARIETY OF

RESOURCES ON

EARTH

NATURAL RESOURCES ON EARTH

SOIL

MINERALS

AIRWATER

LIVING THINGSPLANTS AND ANIMALS

FOSSIL FUEL

gas

ELEMENTS COMPAUNS

AND MIXTURE

ELEMENTS

An ELEMENT is a subtance made up of ONLY ONE TYPE OF PARTICLE.

CANNOT be broken down into any simpler subtances by any physical or chemical method.

Helium atoms Mercury

COPPER WIRES

IRON NAIL

SULPHUR

ALUMINIUM

GOLD

DIAMOND

Example of ELEMENTS

CARBON

Example of elements

COMPOUNDS

Note that a compound: • is subtance made up of two or more types of particles bound together (chemically combined).

• can be broken down into a simpler subtance (elements) by chemical method (but not by physical method), • has properties that are different from its component elements, and •always contains the same ratio of its component

atoms.

SUGAR (CHO)SALT (NaCl)

Example of COMPOUNDS

RUST (FeO)

SAND (SO)

WATER (H2O)

MIXTURES Is a substance made up of two or more types of particles are not bound together (not chemically combined)

can separate the components of a mixture by using physical methods such as evaporation and filtration.

Example of mixture

GOLD

A GAIN

ALUMINIUM

Elements can be monatomic or polyatomic.Example

A compound is a pure substance made of different elements. Substances can only be decomposed chemically. Binary compounds contain two elements. Example

ExampleElectricity is used to chemically decompose water into oxygen and hydrogen gas.2 H2O(l) ---electricity---> 2 H2(g) + O2(g)

Mixtures are composed of two or more different substances that can be separated by physical means. When different substances are mixed together, a homogeneous or heterogeneous mixture is formed. The proportions of components in a mixture can be varied. Each component in a mixture retains its original properties. Example 

A homogeneous mixture or solution has the same properties throughout.Example Air is a gaseous solution composed of N2(g) + O2 (g) + Ar(g) + CO2 (g) + other rare gases.

ExampleSalted water, NaCl(aq), is a liquid solution. Note: (aq) = aqueous or H2O(l)

Therefore, NaCl(aq) means that NaCl(s) is dissolved in water.ExampleBrass is a solid solution composed of Cu(s) and Zn(s)  A heterogeneous mixture does not have the same properties throughout. ExampleConcrete, sand in water, pizza, etc.

1. Which diagram represents a mixture?

TEST YOUR UNDERSTANDING

Q21 One similarity between all mixtures and compounds is that both (1) are heterogeneous  (2) are homogeneous (3) combine in a definite ratio  (4) consist of two or more substances

2 Draw two different compounds using the representations for atoms of element X and element Z given below.

3  Draw a mixture of these two compounds.

Q3

1. Which of these contains only one substance? (1) distilled water (2) sugar water (3) saltwater (4) rainwater

2. Given the diagrams X, Y, and Z below:  

Which diagram or diagrams represent a mixture of elements A and B? (1) X, only (3) X and Y (2) Z, only (4) X and Z

Q4Which particle diagram represents one pure substance, only?

Q5 Two substances, A and Z, are to be identified. Substance A can not be broken down by a chemical change. Substance Z can be broken down by a chemical change. What can be concluded about these substances? (1) Both substances are elements. (2) Both substances are compounds. (3) Substance A is an element and substance Z is a compound. (4) Substance A is a compound and substance Z is an element.

Gases produced, color changes, heat & light emitted,new substances produced, old substances destroyed.

The diagram shows five particles of elements and compounds. Each circle represents an atom of an element. Match the pictures A to E to the following questions.

Diagram(a) Which particle picture represents a mixture of two compounds? ____

(b) Which particle picture represents a pure compound? ____(c) Which particle picture represents a mixture of an element and

a compound? ____(d) Which particle picture represents a pure element? ____(e) Which particle picture represents a mixture of two elements? ____(f) Which particle picture could represent pure water? ____(g) Which particle picture could represent something dissolved

in water? ____

SummaryIn particle pictures, a pure substance will be represented by a single type of particle, either a single circle for one atom (element) or several atoms joined together to form a molecule (element or compound).

In a particle picture of a mixture, there will be at least two different types of particles, which can be elements (single atoms or larger molecules of two or more atoms) or compounds (molecules of two or more atoms of different elements combined together).

Task 2: Differences between pure substances and mixtures

The following statements apply either to pure substances or mixtures but not both. Decide which statement applies to which:

(a) It is made up of elements in fixed proportions.(b) The components can be readily separated, e.g. by filtration or distillation.(c) The boiling point changes (rises) as the substance boils away in distillation.(d) It is very difficult to separate the components of the substance.(e) The elements or compounds are not in fixed proportions.(f) The substance melts or boils at a specific temperature.(g) The substance melts gradually over a few degrees temperature range.(h) There is no significant energy change on its formation.

SummaryPure substances melt and boil at a fixed temperature; their composition is fixed, i.e. the same atomic ratio or molecular formula; it is not easy to separate the atoms whether it is an element molecule or a compound.

In a mixture, the melting and boiling points vary depending on the proportions of the components (elements or compounds); the proportions of the components are not fixed and vary; the components are readily separated from each other; the mixture properties are often similar to those of the components themselves.

MetalsMost of the elements are metals.

They have these things in common with each other. They are:

solid at room temperature (except for mercury) shiny when cut strong and can be hammered into shape good conductors of electricity good conductors of heat.

Some common metals are gold and copper.

Non-metalsA quarter of the elements are non-metals.

They have these things in common with each other. They are: solid, liquid or gas at room temperature mostly dull in appearance mostly brittle, and break easily when hammered poor conductors of electricity (except for carbon) poor conductors of heat

Can you recognise elements, compounds and mixtures?

An element contains just one type of atom.

A compound contains two or more types of atom joined together.

A mixture contains two or more different substances that are not joined together.

The different substances in a mixture can be elements or compounds.

Description Example Diagram

Pure element oxygen

Pure compound carbon dioxide

Mixture of elements oxygen and helium

Mixture of compounds alcohol and water

Mixture of elements and compounds air

The table shows some examples.

                                                                                                                                                                                                                   

Notice that the different substances in a mixture can be single atoms, molecules of elements or molecules of compounds.

Figure 1.4 The three physical states of water are water vapor, liquid water, and ice. In this photo we see both the liquid and solid states of water. We cannot see water vapor. What we see when we look at steam or clouds is tiny droplets of liquid water dispersed in the atmosphere. The molecular views show that the molecules in the solid are arranged in a more orderly way than in the liquid. The molecules in the gas are much farther apart than those in the liquid or the solid.