C3 Chemistry
History of the
Periodic Table
1866: John Newlands Table
Newlands ordered the elements according to atomic mass. He
also put them into groups with similar properties. He called
his table the ‘law of octaves’:
Problems with his table:
 More than one element in some boxes (Co, Ni)
 Metals in same groups as non-metals (Ni, Br)
 Groups only work for first 17 elements
 Elements were still being discovered
1869: Dmitri Mendeleev’s Table
Mendeleev also ordered the elements using atomic mass but
reversed the positions of certain elements so that they
fitted the pattern better. He also left gaps for elements yet
to be discovered:
The Modern
Periodic Table
The modern periodic table is based on
Mendeleev’s table but arranges the elements
in order of atomic number.
Columns of the Periodic Table
alkali
metals Elements are put into
groups that have similar
chemical properties and
the same number of
outer shell electrons.
transition metals
nobel gases
halogens
Rows of the Periodic Table
XX
X
The number of outer
shells determines the
period (horizontal row)
of an element.
X
X
XX
XX
X
2
3
5
6
X
X
X
XX
1
4
Ne
X X
X X
Ar
X
XX
XX
X X
X X
Group 1: The
Alkali Metals
Chemical Properties:
 Very reactive (stored in oil)
 Lose their outer electron to
become 1+ ions
X
Li
X
X
Physical Properties:
 Low density
 Soft and weak
 Shiny when cut
 Good conductors
X
Li
X
1+
Reactivity of Group 1
Reactivity increases as you go down the group:
 Outer shell is further from the nucleus
 Leaving electron is more shielded from the
nucleus by other electrons
 Electron is lost more easily
X
Li
X
X
X
X
XX
X
Na X
XX
X
XX
XX
XX
XX
XX
X
K
X
XX
XX
XX
XX X
Reaction with Oxygen
metal
+
oxygen

metal oxide
4Na(s)
+
O2 (g)

2Na2O(s)
Observations:
 Metals are shiny when first cut
 A white oxide layer quickly forms on surface of
metal
Reaction with Water
metal
metal + water  hydroxide + hydrogen
2K(s) + 2H2O(l)

2KOH(aq)
+ H2(g)
Observations:
 Floats and moves on surface of water
 Fizzing/bubbles of gas
 Metal disappears
 Produces an alkaline solution which turns Universal
indicator purple
Group 7: The
Halogens
The halogens have 7 electrons in their outer shell
They exist as covalently bonded diatomic molecules
XX
F2: Pale yellow gas
Cl2: Pale green gas
X
X
X
F
X
I
XX
XX
Br2: Red/brown liquid
I2: Black/purple solid
F
X
X
I
XX
Reaction with metals:
 Halogens form ionic bonds with metals
 They gain an electron to become halide ions
e.g fluoride ions = F-
X
Li
X
-1
+1
X
F
Reactivity of Group 7
Reactivity decreases as you go down the group:
 Outer shell is further from the nucleus
 Incoming electron is more shielded from the
nucleus by other electrons
 Electron is less easily gained
XX
XX
XX
XX
XX
XX
X
X
X
X
XX X XX
X
X
X
XX
F X
X
Cl
X
Br
XX X
X
X
XX
X
X
X
XX
XX
XX
XX
XX
XX
Halogens + Halide ions
A more reactive halogen will displace a less
reactive halide ion from a solution of its salt.
Examples
Cl2 + 2KBr 
Br2 + 2KCl
Cl2 displaces Br- because it is more reactive
I2 + 2KBr 
Iodine is less reactive than bromine
The Transition
Metals
 Found in middle block of the periodic table
 They have 2 electrons in their outer (4th) shell
 The 3rd shell is then filled to have a total of 18
electrons!!
Properties:
Excellent conductors of heat & electricity
Hard & strong with high densities & melting points
Less reactive than group 1
Make excellent catalysts
Can form more than one type of ion shown using
Roman numerals. e.g. Cu(I) = Cu+, Cu(II) = Cu2+
Form coloured compounds
Cr (III)
Cr (II)
Cr (VI)
Mn (VI)
Mn (VII)
What is Hard
Water?
Hard water contains dissolved calcium or magnesium
ions (Ca2+ or Mg2+).
Hard water leads to solid scum forming when it is
mixed with soap instead of a nice lather:
sodium stearate + calcium  calcium stearate + sodium
(soap)
ions
(scum)
ions
This increases the cost of washing because more
soap is needed before it becomes effective.
soft
water
hard
water
LATHER
SCUM
Temporary Hard Water
1. CO2 dissolves in rain water to make it acidic
2. Calcium carbonate (in limestone) dissolves in the
acidic water to form soluble calcium ions and
hydrogen carbonate ions:
CaCO3(s) + H2O(l) + CO2(aq)
limestone
CaCO3(s)
Ca2+(aq) + 2HCO3-(aq)
Ca2+(aq) +
HCO3-(aq)
CaCO3(s) + H2O(l) + CO2(aq)
Heating temporary hard
water causes the HCO3ions to decompose which
reverses the reaction.
This softens the water
but produces scale (solid
calcium carbonate).
Scale reduces the
efficiency of heating
systems and kettles.
Ca2+(aq) + 2HCO3-(aq)
Permanent Hard Water
This is hard water that cannot be softened by boiling.
It forms when calcium sulphate (in gypsum) dissolves in
water.
Gypsum
CaSO4(s)
CaSO4(aq)
Benefits of Hard Water
 Calcium ions in drinking water leads to strong
bones and teeth
 It could also reduce the risk of heart disease
Removing
Hardness
Washing Soda
Soda crystals are used in
washing machines and dish
washers and contain sodium
carbonate.
The carbonate ions react with
the ions in hard water to
produce insoluble metal
carbonates:
Ca2+(aq) + CO32-(aq)

CaCO3(s)
This eliminates the need to
heat water in order to soften
it which saves energy.
Ion-Exchange Columns
Dishwashers contain columns
which are filled with resin
beads which are packed with
sodium ions (Na+).
The Ca2+ and Mg2+ ions in
hard water are exchanged
for the Na+ ions as water
passes through the column.
The resin beads can be
recharged by washing the
column with sodium chloride
(salt) solution.
Before - Hard
After - Soft
Water
Treatment
Filter Jugs
These remove some of the
impurities found in tap water:
 Activated carbon removes
toxic chlorine compounds
 Ion-exchange resin removes
metal ions such as Ca2+ & Mg2+
 Silver nanoparticles kill
bacteria
Filter jugs do not produce completely pure water.
100% pure water can only be achieved by distillation.
This would require
huge amounts of
energy and would be
very expensive!
thermometer
1
water
out
2
condenser
s4olution
water in
5
6
HEAT
pure liquid
7
Water
Fluoridation
For fluoridation
Against fluoridation
 Fluoride protects the teeth of
those with poor dental care
 The benefits of fluoridation
are not significant. Toothpaste
and mouthwashes are for more
important for dental health
 Fluoride decreases teeth
cavities by about 30% by killing
bacteria
 Excess fluoride can lead to
fluorosis in children
 This bacteria also causes some
types of heart disease
 Excess fluoride in adults can
lead to weaker bones
 Fluoride is only added in tiny
amounts (0.0001%)
 Some studies even suggest
excess fluoride can lead to
 There is no solid proof that
learning difficulties and
fluoridation harms our health
Alzheimer's disease
 It is unethical to give
treatments to people that they
have not consented to