1. Elements, Mixtures & Compounds
Syllabus objectives:
Describe the differences between elements, compounds and mixtures
State the symbols of the elements and formulae of the compounds mentioned in the syllabus.
Deduce the formulae of simple compounds from the relative numbers of atoms present and vice versa.

2. Types of particles
Particles
Ions
Atoms
Molecules

3. Atoms and Molecules
Matter is made up of tiny particles. These particles are called atoms.
Atoms are the smallest particle of an element that can still have the chemical properties of that element.
A molecule is made up of two or more atoms chemically joined together by covalent bond.
(Can a molecule be joined together by ionic bonds?)
Some substances exist as atoms while others exist as molecules.

4. Atoms and Molecules Examples of substances that exist as atoms
All metals e.g. Gold (Au), Copper (Cu)
Noble gases e.g. helium (He), neon (Ne)
E.g. helium

5. Atoms and Molecules Examples of substances that exist as molecules
Diatomic molecules eg.
oxygen (O2)
hydrogen(H2)
hydrogen chloride (HCl)
Tri-atomic molecules eg.
water (H2O),
Carbon dioxide (CO2)

6. Atoms and Molecules
Atoms of the same element that are chemically joined together form molecules of elements.
Atoms of different elements that are chemically joined together form molecules of compounds.
element
compound
compound
element

7. Examples of substances that exist as molecules :-
Nitrogen gas (N2)
Bromine liquid (Br2)
These are
ELEMENTS !
Hydrogen gas (H2) Oxygen gas (O2) Chlorine gas (Cl2)

8. Examples of substances that exist as molecules :-
Carbon dioxide gas(CO2) Water(H2O) Ammonia gas (NH3)
Methane gas(CH4)
These are COMPOUNDS !

9. Elements
An element is a substance which which cannot be broken down into simpler substances by chemical means.
Elements contain only one type of atom.
Egs. Aluminium, carbon, sulfur

10. Al C Cu Hg S Elements Elements are represented by symbols Examples..
Aluminium Carbon Copper Mercury Sulfur

11. Metals & Non-metals Elements can be classified as metals or non-metals
Shiny
Solids at r.t.p. (except Hg)
Malleable and ductile
High melting pt. & boiling pt.
Good conductors of heat
Good conductors of electricity
dull
Either gases, liquids or solids at r.t.p.
brittle
low melting pt. & boiling pt. (except C)
Poor conductors of heat
Poor conductors of electricity (except graphite)

12. Compounds
A compound is a substance which is made up of 2 or more elements chemically combined together.
Compounds contain only one type of molecule
E.g.s. Water (H2O), common salt (NaCl), carbon dioxide (CO2)

13. Compounds
A chemical reaction takes place when a compound is formed.

14. Compounds A chemical reaction takes place when a compound is formed.
oxygen (
(silvery solid)
a bright white light;
ELEMENTS
COMPOUND
magnesium oxide
colourless
gas)
magnesium
magnesium burns with

15. Compounds A chemical reaction takes place when a compound is formed.
ELEMENTS
COMPOUND
lighted
splint
hydrogen
oxygen
(colourless
gas)
colourless
gas)
heat, light
water

17. Mixtures
A mixture contains 2 or more substances which can be easily separated by physical means.
Mixtures contain two or more types of atoms or molecules
(physical means include : filtration, evaporation, distillation, chromatography etc.)

18. Representing atoms, molecules, elements, mixtures and compounds:

19. Representing atoms, molecules, elements, mixtures and compounds:

20. Representing atoms, molecules, elements, mixtures and compounds:

22. How do we deduce the formulae?
Molecular Formulae
How do we deduce the formulae?
With the presence of both metallic and non-metallic elements, write the metallic element first.
E.g. CaO, NaCl, FeS.
Number of atoms is written as a subscript except for “1”.
E.g. FeCl2 (not Fe1Cl2); K2Cr2O7 (not K2Cr2O7)
Write oxygen atom at the end of the formula.
E.g. H2O, CuO, MgCO3

23. Naming of compounds -ide: The compound has only 2 elements.
Sodium chloride (NaCl)
Iron (II) Sulfide (FeS)
-Hydroxide: The compound has OH- ion.
Sodium hydroxide (NaOH)
Ammonium hydroxide (NH4OH)
-ate or -ite: The compound has element oxygen. The former one has more oxygen atoms than the latter one.
Sodium nitrate (NaNO3) & sodium nitrite (NaNO2)

24. Chemical Formula provides information about
the type of element present in the compound
the relative number of atoms (ratio) present
Eg. (NH4)2SO4 contains..
CuSO4.5H2O contains…