Chemistry Sec 3/4 Chpt 4 : Elements, Compounds And Mixtures

element is a pure substance that cannot be broken down into two or more simpler substances

1) Whether they have metallic, metalloid or non-metallic properties

2) Physical states (at room temperature and pressure - gases, liquids or solid

Appearance:

shiny (lustrous)

physical state at r.t.p. :

mostly solid (except mercury)

melting and boiling points:

high (except sodium, potassium and mercury)

Ductility and malleability:

Ductile (can be drawn into wires)

malleable (can be hammered into different shapes without breaking)

sonorous (make a ringing sound when struck)

Heat conductivity:

good

electrical conductivity:

good

Appearance:

shiny (lustrous)

Physical state in r.t.p.:

solids

Melting and boiling points:

high

ductility and malleability :

brittle (easily broken when hammered)

heat conductivity:

moderate

electrical conductivity

Moderate

Appearance:

dull (non-lustrous)

physical state at r.t.p.

Gases, volatile liquids (easily evaporated) or solid

Melting and boiling points:

low (except for carbon and silicon)

Ductility and malleability:

brittle if solid

Heat conductivity:

poor(except carbon in the form of graphite and diamond)

Atoms meaning: smallest particles of an element that have the chemical properties of that element

Monatomic elements: element contains only one type of atom

e.g. helium, neon, argon, krypton, xenon and radon

Molecules: a group of 2 or more atoms that are chemically combined

Diatomic molecules: made up of two atoms

Polyatomic molecules: made up of three or more atoms

A pure substance containing two or more elements that are chemically combined in a fixed ratio

Can be made up of molecules or

ions (electrically charged particles. An ion carries either positive or negative charges)

A compound has different properties from the elements that form it.

The chemical formula of a compound is written by putting together the chemical symbols of the elements that make up the compound

Chemical formula tells us:

The types of atoms present in the compound

The ratio of the different atoms present in the compound

Chemical processes such as thermal decomposition and electrolysis can be used to decompose compounds

(break down compounds into elements or simpler compounds).

Thermal decomposition involves heating a compound strongly. E.g. mercury (II) oxide is heated strongly, it decomposes to give the elements mercury and oxygen

Electrolysis uses electricity to break down the compound

made up of two or more substances that are not chemically combined

Mixture is formed when we add sulfur powder to iron filings

Separation:

The components of a mixture can be separated by physical processes such as magnetic separation, filtration or distillation.

Properties:

The chemical properties of a mixture are the same as those to its components

Energy change:

No chemical reaction takes place when a mixture is formed - usually there is little or no energy chance

Composition:

The components of a mixture can be mixed in any ratio

Compound:

When the mixture is heated, the mixture glows and a black solid , iron(II) sulfide, is obtained. Iron(II) sulfide is a compound of two elements, iron and sulfur

Separation:

A compound can only be broken down into its elements or into simpler compounds by chemical processes (e.g. thermal decomposition or electrolysis)

Properties:

The physical and chemical properties of a compound are different from those of its constituent elements

energy change:

A chemical reaction takes place when a compound is formed - usually there is an energy change

e.g. the reactants get hot or cold

Composition:

The elements in a compound are always combined in a fixed ratio