2Y: Elements, Compounds & Mixtures

Question 1

What is an element?

Answer 1

An element is a substance that cannot be split up into simpler substances by chemical means. Elements contain only one type of atom.

Copper is an example of an element. Copper just contains copper atoms and nothing else.

Question 2

Where would you find a list of the known elements?

Answer 2

All of the known elements are listed in a table called the Periodic Table of the Elements.

Question 3

What is a compound?

Answer 3

A compound is a substance that is made up of two or more different elements combined together chemically. Compounds contain two or more different types of atoms.

Water is called a compound because it contains two different elements combined together chemically. The two elements are hydrogen and oxygen H₂O.

Question 4

How many compounds are there?

Answer 4

• Although there are only about 100 elements, there are millions of compounds.
• Compounds are formed when elements combine together in a chemical reaction
• The properties of compounds usually differ completely from those of the elements from which they are made. For example, magnesium is a shiny metal. Oxygen is a colourless gas. However, when these elements combine chemically, they form a white solid.

Question 5

What is a mixture?

Answer 5

A mixture consists of two or more different substances mingled with each other but not chemically combined.

Some important points about mixtures:

• The substances in the mixture are just mingled together. They are not chemically combined.
• In a mixture, the substances that make up the mixture can be present in any amounts.

Question 6

What are the differences between mixtures and compounds? (5)

Answer 6

(1)

• The amounts of the substances in the mixture can vary.
• The elements in a compound are always present in the same amount.

(2)

• A mixture contains two or more substances.
• A compound is a single substance.

(3)

• The properties of a mixture are similar to those of the substances in the mixture.
• The properties of a compound are different to those of the elements that reacted to form the compound.

(4)

• It is usually easy to separate the parts of a mixture.
• It is usually difficult to separate the elements in a compound (only possible using suitable experiments).

(5)

• There are almost no energy changes when a mixture is made.
• Heat is usually given out or taken in when a compound is formed.