1. Hydrogen
Hydrogen H2
• gas
• the most abundant
83.9 % element in the Universe
Universe • colourless
• odourless
• flammable
• the lightest element
63 %
Living things
Earth's crust
0.22 % Sun

2. Helium
Helium He
• a noble gas
15.9 % • formed by single atoms
• lighter than air
Universe • not flammable
1868 – It was first discovered on the Sun during a solar eclipse.
helium
eclipse helium balloons

3. Nitrogen
Nitrogen N2
• the most abundant
gas in the atmosphere
• colourless
78 % • odourless
• inert
Atmosphere
proteins
nitrates
1.4 %
Living things

4. Oxygen
Oxygen O2
• gas
• colourless
21 % • odourless
Atmosphere • the most abundant
element on Earth
25.5 % O3
Living things
ozone
H2O
47 %
Earth's crust water

5. Carbon
Carbon C
• the basis of all
organic compounds
0.03 % • has a unique ability to
Atmosphere form compounds
9.5 %
coal
Living things
graphite
0.19 % carbon
Earth's crust oil dioxide

6. Elements in the Earth's crust
Silicon
28 %
47 % Oxygen (O)
28 % Silicon (Si) Aluminium
7.9 % Aluminium (Al)
4.5 % Iron (Fe)
7.9 %
3.5 % Calcium (Ca) Iron
2.5 % Sodium (Na)
2.5 % Potassium (K) 4.5 %
2.2 % Magnesium (Mg) Calcium
3.5 %
Magnesium
2.2 %

7. Elements in the Earth's crust
Silicon
28 %
• solid substance
• brown colour
• generally found as a
compound
quartz
silica (SiO2)
microchip

8. Elements in the Earth's crust
Aluminium
7.9 %
• soft, light metal
• light grey colour
• only found as a compound
• obtained from bauxite
feldspars
micas

9. Elements in the Earth's crust
Iron
4.5 %
• metal
• grey colour
• generally found as a
compound
hematite
iron and oxygen
steel
pyrite
iron and sulphur iron and carbon

10. Elements in the Earth's crust
Magnesium
2.2 %
• metal
• silver-white colour
• found as a compound
olivine fireworks
talc

11. Elements in the Earth's crust
Calcium
3.5 %
• metal
• greyish white colour
• found only as a compound
calcium
carbonate
calcite
limestone stalactites

12. Elements in sea water
Chlorine
Sodium
Potassium
composition of sea
water
characteristics of
water

13. Elements in sea water
Chlorine
Sodium
• yellowish green gas
• denser than air
• irritating and toxic
• used to disinfect swimming pools
Potassium
composition of sea
water
characteristics of
water

14. Elements in sea water
Chlorine
Sodium
• metal
• soft
halite
• shiny
• only found in compounds
• reacts easily with oxygen
Potassium
composition of sea
water
characteristics of
water

15. Elements in sea water
Chlorine
Sodium
potassium
Potassium chloride
• metal
composition of sea • soft
water • shiny
characteristics of • only found in compounds
water

16. Elements in sea water
Chlorine
Average chemical composition of sea water Sodium
Salts Grams per litre
sodium chloride 24
magnesium chloride 5
sodium sulphate 4
calcium chloride 1.1
potassium chloride 0.7 Potassium
sodium bicarbonate 0.2
others 0.5
composition of sea
TOTAL water 35.5
characteristics of
water
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17. Water
hydrogen bridges
water
molecules
(H2O)
68 % water
characteristics of
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water