The Periodic Table

1
The Periodic Table

• by
• Mr Victor Lee
• 30 Sep 2000
• ? Click on the slide to proceed

2
Periodic Table

• The Periodic Table is a way of classifying
  elements.
• The elements in the periodic table are arranged
  horizontally, in increasing order of their atomic
  number.

3
Structure of the Periodic Table

• The Vertical Column Group
• The Horizontal Row Periods

4
The GROUP

• A vertical column in the periodic table is called
  a group.
• There are 8 Groups I, II, III, IV, V, VI, VII
  and VIII.
• Transition Metals are grouped between Group II
  and III. They have no group numbers.

5
Group Valence Electrons

• The electrons on the outermost shell is called
  the valence electrons.
• The no. of valence electrons group number.
• Elements from the same group form ions with
  similar formulae, form compounds with similar
  formulae and undergo similar chemical reactions.

6
The PERIOD

• A horizontal row in the Periodic Table is called
  a period.
• Each period with the exception of the first
  begins with metals on the left-hand side and ends
  with non-metals on the right-hand side.
• In the first period there are only two elements
  hydrogen and helium.

7
Period Electron Shells

• The period number the number of electronic
  shells the elements possess.
• For example, Sodium in the third period, would
  have 3 electronic shells.
• Elements in the same period have the same number
  of electronic shells.

8
Group I alkali metals

• Valency 1
• Lithium, Sodium, Potassium
• Physical Properties
• Soft metals Na can be cut with razor blade
• Low density Na, density 0.97 glcm3
• gt Sodium can float on water.
• Low m.p. and b.p. Na, m.p. 98?C

9
Group I alkali metals

• all conduct electricity.
• all very reactive with the air and water.
• react with water to form an alkali hydrogen
• alkali metal water ? alkali hydrogen gas
• 2Na H2O ? 2NaOH H2

10
Group I alkali metals

• burn readily in air to form oxides
• alkali metal oxygen gas ? metallic oxide
• 4K O2 ? 2K2O
• The reactivity of the elements increases down the
  group (Li ltNa lt K lt Rb lt Cs).

11
Why does reactivty increases ? down the Group I ?

• Going down the group, the number of electrons
  increases and thus the number of electron shells
  and the atom size increases.
• The valence electron being further from the
  nucleus will experience weaker attraction force
  from the nucleus, thus easier to escape.
• Since reactivity of metals depends on the ability
  to lose its valence electrons, the reactivity
  increases down the Group I.

12
Group VII - Halogens

• Valency -1.
• are non-metals.
• exist as diatomic molecules.
• are all volatile gt low m.p. b.p.
• are non-conductor of electricity.
• all can dissolve in organic solvents.
• colouration of the elements becomes darker
  further down the group.

13
Group VII - Halogens

• The reactivity of the elements decreases as you
  go down the group.
• A more reactive halogen will displace a less
  reactive one from its salt.
• 2KI (aq) Cl2 (g) ? 2KCl (aq) I2 (g)
• Observation Yellow green gas of chlorine will
  disappear into the colourless solution of
  potassium iodide to produce a brown solution of
  Iodine in water, and colourless potassium
  chloride solution.

14
Why does reactivty decreases ? down the Group VII
?

• Going down the group, the number of electrons
  increases and thus the number of electron shells
  and the atom size increases.
• The increase in atomic size makes it more
  difficult for the nucleus to attract an electron
  to form an ion.
• Since reactivity depends on the ability to gain
  an electron to form ion, the reactivity decreases
  down the group.

15
Why does melting and boiling points increases ?
down the Group VII ?

• Consists of small diatomic covalent molecules
  held together by strong covalent bonds within
  each molecules
• The intermolecular forces of attraction (van der
  Waals forces) between the covalent molecules are
  very weak.
• Since these weak intermolecular forces increases
  with the size of the molecules, the m.p. b.p.
  increases down the group.

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Group O or VIII Noble Gas

• valency 0
• are all non-metals.
• exist as monatomic gases.
• Properties
• very low m.p. b.p. which increase down the
  group
• do not conduct electricity
• very unreactive.

17
Transition Elements

• high densities density of iron 7.9 g/cm3
• high m.p. b.p. m.p. of iron 1535?C
• form coloured compounds
• iron(II) sulphate is pale green
• copper (II) sulphate is blue
• strong hard metals
• are good catalysts iron in Haber Process,
  manufacture ammonia gas
• variable valencies Fe2 Fe3

18
Diatomic

• Diatomic molecules are molecules made up of 2
  atoms

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