AQA Chemistry, Unit 1, Bonding

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Unit 1 ­ Structure & Bonding
First Ionisation energy is the energy required to remove one electron from each atom in one mole of
gaseous atoms.
Factors affecting ionisation energy
Atomic radius
The further the outer electron from the nucleus, the less energy required to remove it
Nuclear charge
The more protons, the more energy it takes to remove the outer electron
Shielding
More inner shells, more shielding, easier to remove outer electron
Evidence for electron arrangement (from ionisation energies)
Down a Group ­ Decreases
Atomic radius ­ increases ­ easier to remove outer electron
Shielding ­ increases ­ more inner shells- easier to remove outer electron
Nuclear charge ­ increases ­ harder to remove outer electron
Overall decrease ­ easier to remove outer electrons.
Across a period ­ General Increase
Nuclear charge ­ increases - harder to remove outer electron
Shielding ­ no change ­ same number of shells ­ no effect
Atomic radius ­ decreases ­ harder to remove outer electron
Overall increase ­ harder to remove outer electron
Sub-Shells
There are four sub-shells which each hold a different number of electrons
sub-shell max. number of electrons
s 2
p 6
d 10
f 14
Each principal energy level contains a different number of sub-shells.
principal energy level sub-levels max. number of electrons
1 1s 2
2 2s2p 8

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Unit 1 ­ Structure & Bonding
3 3s3p3d 18
4 4s4p4d4f 32
Electrons fill orbitals from the lowest energy upwards.
1s22s22p63s33p64s23d104p6
Examples of Bonding
Sodium Chloride (NaCl)
Giant Ionic Lattice
Melting Point - 801c
C Strong forces of attraction between oppositely charged ions are incredibly
difficult to overcome. Strong ionic bonds require lots of energy to be broken.
Electrical Conductor ­ yes (sort of)
Sodium Chloride conducts electricity only when molten or in a solution (as a liquid).…read more

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Unit 1 ­ Structure & Bonding
Iodine (I2)
Covalent Bonding (Simple Molecular Lattice)
Melting Point ­ 113.6c
Weak Van der Waals' forces are easy to break
Electrical Conductor ­ No
No electrons are free to move; there is a fixed, rigid structure
Other ­
Iodine sublimes from being a black solid to a purple vapour. AS the purple vapour is formed
only weak Van der Waals' forces are being overcome, covalent bonds between iodine
atoms in I2 molecules are not broken.…read more

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Unit 1 ­ Structure & Bonding
Ice (H2O(s))
Molecular Structure
Covalent (Hydrogen) Bonding
Melting Point - 0c
Hydrogen bonding between oxygen and hydrogen atoms is very strong,
as water molecules are polar because O is very electronegative, making
them difficult to break as they are strongly attracted to each other.…read more

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Unit 1 ­ Structure & Bonding
Summary of different compounds and their properties
Ionic
Strong attraction between oppositely charged ions, which form a 3D lattice structure.…read more

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Unit 1 ­ Structure & Bonding
Shape
2 Bonding Pairs linear
Cl ­ Be ­ Cl
3 Bonding Pairs trigonal planar
4 Bonding Pairs tetrahedral
5 Bonding Pairs trigonal bipyramid
6 Bonding Pairs octahedral
Non-bonding (lone) pairs of electrons repel more than bonded pairs and will distort minimum
repulsion geometries, as the electrons are closer to the central atom.
e.g. ammonia (NH3) e.g water (H20)
Pyramidal non-linear (bent)
Bond angles usually reduce by 2.5 for each lone pair.…read more

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Unit 1 ­ Structure & Bonding
Electronegativity is the attraction of an atom for the bonding pair of electrons in a covalent
bond
Polar molecules
Have an overall dipole
The more electronegative atom (or ion) will have a slight negative charge
+ -
H - F
dipole
The 4 most electronegative atoms
F > O > Cl N
Intermolecular Forces
Van der Walls' Forces
Even in non-polar molecules, temporary dipoles are induced due to uneven electron
distribution, due to the constant movement of electrons.…read more

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