Atoms, Elements, Compounds and Mixtures

Question 1

What are all substances made out of?

And, what are they?

Answer 1

They’re all made out of atoms

They’re the smallest part of an element that can exist and they make up all matter

Question 2

What is an element?

Answer 2

It is a substance that contains only one sort of atom
There are about 100 different atoms
They’re displayed on the periodic table

Question 3

How are the atoms of each element represented?

Answer 3

They're represented using different chemical symbols 
e.g.
Sodium = Na
Carbon = C
Iron = Fe

Question 4

What are most substances?

Answer 4

Most substances are compounds

Question 5

What do compounds contain?

Answer 5

Compounds contain atoms of 2 or more elements which are chemically combined in fixed proportions

Question 6

How are compounds represented?

Answer 6

They’re represented by a combination of numbers and chemical symbols called a “chemical formula”

Question 7

What are chemical formulae used to show?

Answer 7

They show

• the different elements in a compound
• how many atoms of each element one molecule of the compound contains

Question 8

How can compounds be separated into their component elements?

Answer 8

By chemical reactions or electrolysis

Question 9

What can you use, to sum up what happened during a chemical reaction?

Answer 9

By writing a word equation or a balanced symbol equation

Question 10

What are the reactants?

What are the products?

Answer 10

Reactants - the substances that react (left-hand side)

Products - the new substances that are formed (right-hand side)

Question 11

What is the total mass of the products of a chemical equation?

Answer 11

It is always equal to the total mass of the reactants.

This is because no atoms are lost or made.

Question 12

What do mixtures consist of?

Answer 12

They consist of two or more elements or compounds that aren’t chemically combined

Question 13

What do components of a mixture retain?

Answer 13

They retain their own properties
e.g. 
in a mixture of iron and sulfur...
- iron will still be magnetic
- sulfur will still be yellow

Question 14

How can mixtures be separated?

Answer 14

Using physical processes - they don’t involve chemical reactions

Question 15

What is filtration used for?

Answer 15

It is used to separate soluble solids from insoluble solids

Question 16

What is crystallisation used for?

Answer 16

It is used to obtain a soluble solid from a solution.
e.g.
Salt crystals can be obtained from a solution of slaty water:
- gently warm mixture
- water evaporates leaving crystals of pure salt

Question 17

What is simple distillation used for?

Answer 17

It is used to obtain a solvent from a solution

Question 18

What is fractional distillation used for?

Answer 18

It is used to separate mixtures in which the components have different boiling points
e.g.
oxygen and nitrogen can be obtained from liquid air because they have different boiling points

Question 19

What is chromatography used for?

Answer 19

It is used to separate the different soluble, coloured components of a mixture
e.g.
the different colours added to a fizzy drink can be separated by chromatography

Question 20

What is a compound?

Answer 20

A substance with two or more elements chemically bonded together

Question 21

What is a mixture?

Answer 21

When two or more substances are not chemically joined
e.g.
air is a mixture of oxygen, carbon dioxide, nitrogen and other gases

Question 22

What is a molecule?

Answer 22

Two or more atoms joined together, but they can be the same element

Question 23

What does “dioxide” mean?

Answer 23

Dioxide means 2 oxygens

Question 24

Name 3 properties of metals

Name 3 properties of non-metals

Answer 24

Metals - shiny, can be hammered into shape, good conductors of electricity
Non-metals - poor conductors of electricity, brittle, dull