2.2 - Elements, compounds and mixtures

Air is a mixture of gases. Some of these gases are _______ (eg oxygen and nitrogen) and some are _______ (eg water vapour and CO₂)

• elements

• compounds

A mixture ….

is made up of two or more substances that are mixed together that can be separated by physical means.

What are three examples of mixtures?

• Sea water

• Milk

• Soil

What are 4 properties of mixtures?

• The composition of different substances in a mixture can vary

• No chemical change takes place when a mixture is formed

• Mixtures can be easily separated by physical means

• The components of a mixture keep their original properties, just as they are in their pure form

What is an element

an element is a pure substance which cannot be further divided into simpler substances by chemical methods

Elements contain one ________ only

type of atom

What are 3 examples of elements and why?

• Copper - made up of copper atoms only

• Carbon - made up of carbon atoms only

• Helium - made up of helium atoms only

What are the everyday uses of the following elements?

• Copper

• Carbon

• Aluminum

• Copper - in wires

• Carbon (in the form of graphite) - in pencils

• Aluminum - in window frames

To date - how many chemical elements are there

118

How many:
a. occur naturally

b. are artificially made by scientists

a. 98

b. 20

What are examples of:
a. reactive elements

b. unreactive elements

a. fluorine and chlorine

b. gold and platinum

What are 3 examples of artificially made elements

• Plutonium

• Curium

• Oganesson

Where are all the elements found

In the Periodic Table of the Elements

What is a physical property?

any characteristic of a substance that can be measured (eg, density, melting and boiling point…)

Elements can be classified as a) _________, b) __________, or c) ___________

a. metals

b. non-metals

c. metalloids

What are metalloids?

Elements that have properties of both metals and non-metals

Elements can be

• _________ (made up of one atom)

• _________ (made up of two atoms)

• monoatomic

• diatomic

Give examples of monoatomic and diatomic elements

• monoatomic - noble gases

• diatomic - hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine

What is a compound?

A compound is a pure substance which is made of two or more elements that are chemically combined together

element + element (+more elements) → compound

The elements in a compound are not just mixed…

they are joined together by chemical bonds

What are examples of compounds found in air?

• water vapour

• carbon dioxide

Example of a compound found:
a. in the ground

b. in aquatic environments

a. calcium carbonate (found in limestone)

b. sodium chloride (common salt)

What happens when hydrogen and oxygen react (usually initiated in the presence of a flame)

water is porduced

hydrogen + oxygen → water (word equation of reaction)

how do we know this is a chemical change

because a new substance is formed from a chemical reaction

T/F - Compounds have different chemical and physical properties from the elements of which they are made of

True

properties of hydrogen

• lightest gas in the universe

• very flammable gas

properties of oxygen

• slightly denser than air

• required during combustion reactions

Water →

• Water vapour is the compound formed as hydrogen reacts with oxygen. Water vapour produced condenses to form liquid water.

• Water is used to put out fire