CHEMICAL FORMULA

D. Crowley, 2007

Chemical Formula

To understand chemical formula

Definitions

Define an element, compound and mixture

An element is made up of just one type of atom

A compound is two or more elements, chemically bound

A mixture is made of different substances, not chemically bound

Elements & Compounds

Look at the rocket - it uses liquid hydrogen as a fuel The engine mixes this hydrogen with oxygen, adds a

spark and the reaction takes place

The elements are

They react together, forming a compound called

Elements & Compounds

Look at the rocket - it uses liquid hydrogen as a fuel The engine mixes this hydrogen with oxygen, adds a

spark and the reaction takes place

The elements are hydrogen and oxygen

They react together, forming a compound calledhydrogen oxide (water)!

Chemical Equations

Chemical equations show us our reactants and products

reactants products

They can be word or symbol equations, e.g.

Carbon + oxygen carbon monoxide

C + O CO

Formula

Elements and compounds can be represented using chemical formula We use numbers in the formula, which represents the number of

atoms present (as a ratio)

C = 1 atom of carbon (C)

O2 = 2 atoms of oxygen (O)

CO2 = 1 atom of carbon (C); 2 atoms of oxygen (O)

NaCl = 1 atom of sodium (Na); 1 atom of chlorine (Cl)

H2SO4 = 2 atoms of hydrogen (H); 1 atom of sulphur (S); 4 atoms of oxygen (O)

Graphical

Can you draw the following substances The formula should help you graphically represent them…

Carbon dioxideCO2

Sodium chlorideNaCl

Sulphuric acidH2SO4

OxygenO2

CarbonC

Nitric acidHNO3

Graphical

Can you draw the following substances The formula should help you graphically represent them…

Carbon dioxideCO2

Sodium chlorideNaCl

Sulphuric acidH2SO4

OxygenO2

CarbonC

Nitric acidHNO3

Graphical

Can you draw the following substances The formula should help you graphically represent them…

Carbon dioxideCO2

Sodium chlorideNaCl

Sulphuric acidH2SO4

OxygenO2

CarbonC

Nitric acidHNO3

Graphical

Can you draw the following substances The formula should help you graphically represent them…

Carbon dioxideCO2

Sulphuric acidH2SO4

OxygenO2

CarbonC

Sodium chlorideNaCl

Nitric acidHNO3

Graphical

Can you draw the following substances The formula should help you graphically represent them…

Carbon dioxideCO2

Sulphuric acidH2SO4

OxygenO2

CarbonC

Sodium chlorideNaCl

Nitric acidHNO3

Graphical

Can you draw the following substances The formula should help you graphically represent them…

Carbon dioxideCO2

Sulphuric acidH2SO4

OxygenO2

CarbonC

Sodium chlorideNaCl

Nitric acidHNO3

Questions

Write down how many atoms there are (and of what element) for the following: -

1) C - e.g. 1 x carbon (C) 2) CO2

3) H2O

4) CaCO3

5) H2SO4

6) NaCl7) HNO3

8) CuCO3

9) MgCl210) Carbon monoxide11) Hydrogen oxide

Presentation

If there is time left, produce a poster in your book which explains formula (as a revision guide)

You may wish to add examples, and ways to work out the ratio of atoms…