Elements, Atoms, Compounds and Mixtures
- There are about 100 elements in total, although only about 20 are in everyday use.
- An element is the simplest of all chemical substances.
- It is made up of only one kind of atom and cannot be decomposed.
Structure of an atom:
An atom is far too small to see, even with a microscope.
Each atom has a central nucleus (made up of protons and neutrons) with electrons moving around it.
Every element has a symbol. Each symbol represents one atom.
eg O= oxygen atom, C= Carbon atom, Fe = iron atom.
The symbols always start with a capital letter.
If the symbol contains two letters the second letter is always small.
Blue = metal
Pink = non-metal
Properties of an element
- Each element has its own property.
- The elements are often placed into groups with similar properties and form a chart called the periodic table
(You do not need to know anything about the periodic table but to find out more click here)
Metals and non-metals
One important group of elements are the metals and non-metals.
An element is either a metal or a non-metal according to its properties.
|Usually strong||Usually weak|
|High melting point
(metals are usually solid)
|Low melting point
(non-metals are usually gas or liquid)
|Good conductors of electricity||Poor conductors of electricity
(except carbon, which does conduct)
|Good conductors of heat
(good thermal conductors)
|Poor conductors of heat
poor thermal conductivity
|Metals are sometimes magnetic||Non-metals are never magnetic|
|The oxides of a metal, when soluble,
form an alkaline solution.
|The oxides of a non-metal usually form an acidic solution|
Other things you need to know about metals:
Metals can react with other substance:
Metals react with oxygen to produce oxides (see action of heat)
Metals react with acids to produce hydrogen (see acids and alkalis)
Some metals are more reactive than others (see activity series)
A molecule is formed when two or more atoms chemically join together.
An interactive game to teach you more about atoms
Two (or more) elements can combine together to form a COMPOUND
Equation showing oxygen and water combining to form water:
Hydrogen+ oxygen → water
A compound must be made of at least two elements chemically joined together.
|magnesium + oxygen → magnesium oxide
(element) (element) (compound)
Naming a compound
Compounds often seem to have confusing names but there are some simple rules to help work out the name of a compound
- When two elements combine the compound will end in ‘ide‘
eg sodium + chloride → sodium chloride
Copper + oxygen → copper oxide
- When a compound contains three or more elements, one of which is oxygen, it’s name will end in ‘ate‘
eg copper sulfate contains copper, sulfur and oxygen
Each compound has it’s own formula which shows the atoms it contains
The formulae of some common compounds
Carbon dioxide CO2
Copper oxide CuO
Copper Sulphate CuSO4
Copper carbonate CuCO3
Magnesium oxide MgO
Salt (sodium chloride) NaCl
Sulphur dioxide SO2
Zinc oxide ZnO
A substance is a mixture if it contains more than one substance which are not chemically joined.
Which of the boxes below contains a mixture? ANSWER
The main differences between a compound and mixture are summarized in the table below:
|A mixture contains two or more substances NOT chemically joined.||Contains at least two elements chemically joined together|
|The different substances may be visible and the appearance may not be uniform||Will look uniform in appearance (ie the same all the way through).|
|The substances can often be easily separated eg by filtration, evaporation, distillation, chromatography, using a magnet or a separating funnel.||The elements in a compound cannot be separated without a chemical change. ie a new substance will always be formed.|
|The substances can be mixed in any proportion.||The elements in a compound are always present in a fixed proportion.|
A substance is an element if it contains only a single kind of atom and can NEVER be decomposed.
eg copper, oxygen, carbon, iron, sulfur, zinc, gold
A substance is a compound if it contains more then one element chemically joined together.
eg water, magnesium oxide, copper sulfate, calcium carbonate, cobalt chloride, petrol
A mixture exists when there are at least two substances present (either elements, compounds or a combination of the two).
These two substances are not chemically joined and can often be easily separated.
eg air, ink, orange juice, wood, salty water