Elements, Compounds And Mixtures Chapter 4 Chemistry

An element is a pure substance that cannot be split up into two or more simpler substances by chemical processes or by electricity.

Sugar is not an element because it can be broken down into water and carbon.

chemists use chemical symbols to represent elements.

Elements are classified into 2 major groups: metals and non-metals.

Metalloids are elements that have properties of both metals and non-metals.

elements that are metalloids;

BAGS

1) Silicon

2)Germanium

3) Boron

4)Arsenic

differences between metals and non-metals:

1) Metals have shiny appearance (lutrous)

Non-metals have a dull appearance if solid(non-lutrous)

2) Metals are solids at r.t.p(except mercury)

Non-metals are either gases, volatile liquids or solids with low melting point at r.t.p(except for carbon)

3) Metals are malleable(can be hammered into different shapes without breaking) , metals are sonorous( make a ringing sound when struck)

Metals are ductile (can be drawn into wires)

Non-metals are brittle if solid( easily broken when hammered)

4) Metals have high melting points and boiling points( except for sodium, potassium and mercury)

Non-metals have low melting points and boiling points(except for carbon and silicon)

5)Metals are good conductors of heat

Non-metals are poor conductors of heat (except carbon in the form of diamond and graphite)

6) Metals are good conductors of electricity in all states of matter.

Non-metals are poor conductors of electricity (except carbon in the form of graphite)

Atoms are the smallest particles of an element that have the chemical properties of that element.

Monatomic elements are elements that exist as individual atoms.

Examples of monatomic elements:

HNAKXR

1)Helium

2)Neon

3)Argon

4)Krypton

5)Xenon

6)radon

A molecule is a group of two or more atoms that are chemically combined together.

The molecular formula of hydrogen is H2.

Diatomic molecules are molecules formed by the combination of 2 atoms.

Triatomic molecules are molecules formed by the combination of 3 atoms.

Polyatomic molecules are molecules formed by the combination of 4 or more atoms.

A compound is a pure substance that contains 2 or more elements chemically combined.

Elements found in marble ( calcium carbonate) ;

1)Calcium

2)Carbon

3)Hydrogen.

The smallest particle of a compound is the molecule.

Compounds can be represented by chemical formula.

A compound can be decomposed by chemical reactions or electricty.

Thermal decomposition is the method where heat is used to break down compounds into elements or simpler compounds.

Mixtures are formed when two substances(elements or compounds)are added together without chemical bonds being formed.

(SPEC)

1)Seperation: the components of a mixture can be seperated by physical methods.

the components of a compound can only be seperated by chemical reactions or by using electricity.

2) Properties: The chemical properties of a mixture is the same as those of its components.

The Physical and chemical properties of a compound are different from those of the elements in the compound.

3)Energy change: No chemical reactions take place when a mixture is formed.There is no energy change.

A chemical reaction takes place when a compound is formed.There is an energy change(the reactants get hot)

4)Composition: The components of a mixture can be mixed in any proportion.

The elements in a compound are always combined in a fixed proportion(by mass).

An alloy is a mixture of metals with other elements(usually metals but sometimes non-metals such as carbon).

The composition(percentage of composition of element by mass)of steel:

99% iron

1% carbon.

The composition(percentage of composition of element by mass)of stainless steel:

73% iron, 18% chromium, 8% nickel, 1% carbon.

The composition(percentage of composition of element by mass)of brass:

Copper(66-70%), zinc(30-34%).

The composition(percentage of composition of element by mass)of duralumin:

Aluminium(95%), copper(4%), magnesium(1%).

The composition(percentage of composition of element by mass)of solder:

67% lead, 33% tin.