Chemistry OCR AS Mod 2

Ionisation enery, bonding etc

  • Created by: Ellie
  • Created on: 07-11-13 09:17

Successive Ionization Energies

When working out an element from ionisation energy, find a large jump. The bigger value of the two is a new shell CLOSER to the nucleus. Thus you can find how many electrons the element has in its outer shell which is its group number.

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Factors Affecting Ionisation Energy - Across a Per


Ionisation energy INCREASES because:

  • nuclear charge INCREASES - more protons in the nucleus
  • atomic radius DECREASES - increased nuclear charge so more attraction
  • shielding REMAINS THE SAME - since the same period mean its in the same shell

Therefore MORE ENERGY is required to loose an electron

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Factors Affecting Ionisation Energy - Down A Group


Ionisation Energy DECREASES because:

  • Atomic radius INCREASES - another shell is added
  • shielding INCREASES - more shells between the outer electrons and the nucleus
  • Which both outweigh th INCREASE in nuclear charge

Therefore LESS ENERGY is required to loose an electron

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Covalent Bonds


A Covalent Bond is a shared pair of electrons

A Dative Covalent Bond (or coordinate bond) is a shared pair of electrons which has been provided by one of the bonding atoms only.

Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond

A Lone Pair is an outershell pair of electrons that are not involved in chemical bonding.


Group 5 atoms can form 3 or 5 covalent bonds

Group 6 elements can form 2,4 or 6 covalent bonds

Group 7 elements can form 1,3,5 or 7 covalent bonds

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Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond.

Fluroine is the most electronegative element

In a covalent bond the electrons are shared equally

The GREATER the SIMILARITY in the electronegativities of the bonding atoms the GREATER the COVALENT character of the bond

A POLAR COVALENT BOND is a covalent bond which has a permanent dipole and whoose electrons are unequally shared.

A polar molecule has an overall DIPOLE when any dipoles across the bonds are taken into account

PERMANENT DIPOLE is small charge difference across a bond that results from a difference in the elctronegativities of the bonded atoms

HCl has a polar bond and is a polar molecule since it is NON SYMMETRICAL and there is a CHARGE DIFFERENCE over the entire molecule

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Ionic Bonding

An IONIC BOND is the electrostatic attraction between oppositely charged ions

In an electrons are tranferred from the metal ion to the non metal ion.

  • Oppositely charged ions are formed which are bonded together by electrostatic forces
  • METAL ION = POSITIVE (cation)

A giant ionic lattice is a 3D structure of oppositely charged ions held together by strong ionic bonds

Atoms of metals in group  1-3 LOOSE electrons to form positive ions with the electronic configuration of the previous noble gas in the periodic table

Atoms of non metals in groups 1-7 GAIN electrons to form negative ions with the electronic configuration of the next noble gas in the periodic table

Atoms of Be, B, C and Si do not normally form ions as TOO MUCH ENERGY IS REQUIRED to tranfer outer shell electrons

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Charges on elements and molecules

Charge on group 1 metal = +1

Charge on group 2 metal = +2

Charge on Aluminium = +3

Charge on hydrogen = +1

Charge on a group 6 non metal = -2

Charge of a group 7 non metal = -1

Charge on a Hydroxide ion = OH-

Charge on a sulfate ion =SO4 ^2-

Charge on a Nitrate ion =NO3-

Charge of a carbonate ion =CO3 ^2-

Charge on Phosphate ion=PO4 ^3-

Charge on a Nitrogen ion=N^3-

Charge on a Hydride ion= H-

Charge on a ammonium cation= NH4+

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Shapes of Molecules

3 electron pairs = Triagonal Planar (120 degree angle)

4 electron pairs = Tetrahedral (109.5)

5 electron pairs = Triagonal Bipyramid 

6 electron pairs = Octahedral

1 Lone pair = Pyramidal (107)

2 Lone Pairs = Non linear (104.5)

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Van Der Waal Forces

Van Der Waal forces.

Oscillating electrons in one atom/molecule causes an instantaneous dipole resulting in an individual dipole in a neighbouring molecule.

Weak intermolecular attraction between small temporary dipoles

Going down group 7 = volatility decreases = more electrons = stronger val der waal forces

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Hydrogen Bonding

The electrostatic attraction between d+ hydrogen atoms and a lone pair on a d- oxygen atom occurs in ice. The structure of ice is an open network of water molecules with each oxygen molecule covalentl bonded to two hydrogen atoms

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