Term 4 – Year 9 Science

I will understand:
• that chemical reactions occur as a result of the rearranging of particles.
I will be able to:
• interpret chemical formulae
• write word equations.

• Atoms are individual particles that are made up of a nucleus and electrons
• Molecules are groups of atoms that form distinct arrangements of atoms
• Lattices are networks of atoms that make up compounds or elements

• Noble gases exist as single atoms e.g. Helium
• Some elements join to form many compounds or molecules e.g. water sugar
• Metals, carbon and many compounds form lattices. E.g.salt
iron

• All pure substances (elements & compounds) can be represented using chemical formulae
• In a molecule, the formula describes the number of, and types of atoms (eg H
2
O, O
2
)
• In a lattice, the formula describes a ratio of elements (eg Fe,
NaCl, MgCl
2
)
Magnesium
Chloride

Determine the number of atoms and the names of elements in each of the following
• Elements: • Compounds:
- H
2
Hydrogen – 2 - NaOH
Sulfur – 8 - S
8
- C
60
- N
3
- Ar
Carbon – 60
Nitrogen – 3
Argon – 1
- MgCl
2
- H
2
O
2
- H
2
SO
4
- Ca(OH)
2
- Mg
3
(PO
4
)
2

• A chemical reaction occurs when new substances are formed
(ie a chemical change)
• Chemicals that react to cause a chemical change are known as reactants
• Chemicals that are produced during chemical reactions are known as products

• A word equation is a straightforward way to represent a chemical reaction
Reactants→ Products
An example is the reaction between hydrogen and oxygen to produce water.
hydrogen + oxygen → water

Chlorine + methane tetrachloride + hydrogen chloride
• When chlorine gas reacts with methane, carbon tetrachloride and hydrogen chloride are produced.
• When sodium oxide is added to water, sodium hydroxide is produced.
Sodium oxide + water sodium hydroxide
• In a blast furnace, iron oxide and carbon monoxide gas produce carbon
• Sugar reacts with oxygen in cells to produce carbon dioxide and water
Sugar + oxygen carbon dioxide + water

• In this activity you will model a chemical reaction using a molecular model kit.
• The reaction will between hydrochloric acid and sodium hydroxide

• Build a hydrochloric acid molecule with one hydrogen atom and one chlorine atom
• Build a sodium hydroxide molecule with one sodium atom, one oxygen atom and one hydrogen atom
H Cl Na
O
H

• When the two reactants collide, a reaction occurs.
• The hydrochloric acid breaks apart while the
sodium breaks off the hydroxide particle
H Cl Na
O
H

• Join the hydrogen atom from the hydrochloric acid with the
hydroxide particle (OH)
• Join the sodium atom with the chlorine atom
Na Cl
H
O
H

• What held the atoms of the reactants to each other?
• What did you need to do to the reactants in order to begin the chemical reaction?
• What did you need to do to the free atoms in order to create the products?

“A chemical reaction occurs when chemical
bonds are broken and new bonds are formed, creating new substances”

• Molecules are always moving
• Reactions are started when molecules collide and the bonds are broken
• Molecules need to collide with enough energy or force to cause bonds to be broken – this is called the activation energy