1. S2 Chemistry
Formula

2. Valency
The valency of an atom is the number of links which it can form.

3. Valency Atoms usually have a valency of 1, 2, 3 or 4
Magnesium has a valency of 2 and can be drawn as - Mg

4. Valency
Group 1 2 3 4 5 6 7 8
Valency

5. Valency
Group 1 2 3 4 5 6 7 8
Valency
Picture

6. Valency
Group 1 2 3 4 5 6 7 8
Valency
Picture

7. Valency Draw the valency pictures for – hydrogen silicon aluminium
nitrogen oxygen
carbon argon
sulphur

8. Valency
The formula of a compound can be obtained by using the valency pictures

9. Valency
The formula of a compound can be obtained by using the valency pictures
Eg hydrogen oxide

10. Valency
The formula of a compound can be obtained by using the valency pictures
Eg hydrogen oxide
First draw the valency pictures for hydrogen and oxygen.

11. Valency H
hydrogen O
oxygen

12. Valency H
hydrogen O
oxygen

13. Valency H
hydrogen O H
oxygen

14. Valency H
hydrogen O
H2O H
oxygen

15. Valency H
hydrogen O
H2O H
oxygen
All the links must be used.

16. Valency
Eg magnesium oxide Mg O

17. Valency
Eg magnesium oxide Mg O
MgO

18. Relative Atomic Mass
Atoms of different elements are different in size and are different in mass.

19. Naming Compounds
The first part of the name comes from the element that is furthest to the left of the periodic table

20. Naming Compounds
The first part of the name comes from the element that is furthest to the left of the periodic table
If the compound contains only 2 elements, the second part of the name changes to end in -ide

21. Relative Atomic Mass
Atoms of different elements are different in size and are different in mass.
The mass is too small to be measured in grams so it is given a relative value

22. Relative Atomic Mass Element Relative Atomic Mass (RAM) carbon
hydrogen
oxygen
nitrogen
gold

23. Relative Atomic Mass Element Relative Atomic Mass (RAM) carbon 12
hydrogen 1
oxygen 16
nitrogen 14
gold
197

24. Relative Formula Mass
Compounds can be given a formula mass by adding up all the individual elements.

25. Relative Formula Mass
Compounds can be given a formula mass by adding up all the individual elements.
H2O
2 hydrogens = 2 x 1 = 2
1 oxygen = 1 x = 16

26. Relative Formula Mass
Compounds can be given a formula mass by adding up all the individual elements.
H2O
2 hydrogens = 2 x 1 = 2
1 oxygen = 1 x = 16 18

27. The Mole A mole of any element is the relative atomic mass in grams.
Eg a mole of carbon has a mass of 12g

28. The Mole A mole of any compound is the relative formula mass in grams.
Eg a mole of water has a mass of 18g

29. The Mole
A mole of a substance is known as the gram formula mass (gfm)

30. The Mole The following triangle can be used for mole calculations
Mass of substance
mass
Number of
moles n
gfm
Mass of 1 mole

31. The Mole - example
Calculate the mass of 3 moles of water

32. The Mole Calculate the mass of 3 moles of water From the triangle
mass = n x gfm

33. The Mole
H2O
2 hydrogens = 2 x 1 = 2
1 oxygen = 1 x = 16 18

34. The Mole Calculate the mass of 3 moles of water From the triangle
mass = n x gfm
mass = 3 x 18g

35. The Mole Calculate the mass of 3 moles of water From the triangle
mass = n x gfm
mass = 3 x 18g
mass = 54g

36. The Mole
How many moles are present in 9g of water.

37. The Mole How many moles are present in 9g of water. From the triangle
n = mass/gfm

38. The Mole How many moles are present in 9g of water. From the triangle
n = mass/gfm
n = 9/18

39. The Mole How many moles are present in 9g of water. From the triangle
n = mass/gfm
n = 9/18
n = 0.5 moles

40. Word Equations
Learning Intention We are learning to write word equations

41. Word Equations
All chemical reactions can be described using a word equation eg reactants products (what you start with) (what you end up with)

42. Word Equations
eg hydrogen + oxygen hydrogen oxide

43. Word Equations
Write a word equation for the following reaction

44. Word Equations Write a word equation for the following reaction
Carbon dioxide is formed when carbon burns in oxygen.

45. Word Equations Write a word equation for the following reaction
Carbon dioxide is formed when carbon burns in oxygen.
carbon + oxygen carbon dioxide

46. Formula Equations
Instead of using words, the formula for the reactants and products can be used instead. This is called a formula equation.
carbon + oxygen carbon dioxide

47. Formula Equations
Instead of using words, the formula for the reactants and products can be used instead. This is called a formula equation.
carbon + oxygen carbon dioxide
C O2 CO2

48. Formula Equations Eg
hydrogen + oxygen hydrogen oxide

49. Formula Equations Eg
hydrogen + oxygen hydrogen oxide
H2 + O2 H2O

50. Diatomic Elements
Certain elements always go around in pairs. These are the diatomic elements.

51. Diatomic Elements
Certain elements always go around in pairs. These are the diatomic elements.
H2, O2, N2, F2, Cl2, Br2, I2

52. Diatomic Elements
Certain elements always go around in pairs. These are the diatomic elements.
H2, O2, N2, F2, Cl2, Br2, I2
In formula equations they must always be written as pairs.

53. Balancing Equations
A balanced equation is when the number of each element on the product side equals the number of each element on the reactant side.

54. Balancing Equations Eg
C O2 CO2
This is balanced.

55. Balancing Equations Eg
H2 + O2 H2O
This is not balanced.

56. Formulae with Groups
Group ions like sulphate (SO4) and nitrate (NO3) have two or more atoms joined together.

57. Formulae with Groups
Group ions like sulphate (SO4) and nitrate (NO3) have two or more atoms joined together.
The groups have valencies and formula can be worked out in just the same way as elements.

58. Formulae with Groups
Potassium nitrate
K NO3

59. Formulae with Groups
Potassium nitrate
K NO3
KNO3 1 1

60. Formulae with Groups
Calcium Sulphate
Ca SO4

61. Formulae with Groups
Calcium Sulphate
Ca SO4 2 2

62. Formulae with Groups Calcium Sulphate Ca SO4 Ca2(SO4)2 divide by 2

63. Formulae with Groups
Sodium phosphate
Ammonium chloride

64. Formulae with Groups
Sodium phosphate Na3PO4
Ammonium chloride NH4Cl

65. Using Brackets
Roman numerals are often used to indicate the valency of transition metals.
I = 1 II = 2 III = 3 IV = 4

66. Using Brackets State symbols are normally used with formulae
s = solid l = liquid g = gas
aq = aqueous (dissolved in water)

67. Using Brackets
Solid tin(IV) oxide
Sn O

68. Using Brackets
Solid tin(IV) oxide
Sn O
Sn2O4 divide by 2
SnO2(s) 4 2

69. Using Brackets
Melted mercury(II) nitrate
Hg NO3

70. Using Brackets Melted mercury(II) nitrate Hg NO3 HgNO32 Hg(NO3)2(l) 21

71. Using Brackets Phosphorous(III) fluoride gas
Magnesium hydroxide solution

72. Using Brackets Phosphorous(III) fluoride gas PF3(g)
Magnesium hydroxide solution
Mg(OH)2(aq)

73. Solutions and Formulae
This activity is about testing compounds to see if they dissolve in water
Name of Compound
Solubility
a, b, c
x, y, z

74. Solutions and Formulae
This activity is about testing compounds to see if they dissolve in water
Name of Compound
Solubility
a, b, c
x, y, z

75. Solutions and Formulae
Soluble - dissolves
Insoluble - does not dissolve
Solvent - liquid that dissolves a substance
Solute - substance dissolved by the liquid
Solution - mixture made by dissolving something
Saturated - solution will not dissolve any more
(it is full up with dissolved solute)