OCR AS Chemistry (F321.2) - Electrons, Bonding and Structure Revision Notes

These revision notes are for Electrons, Bonding and Structure - the second module of F321 (Atoms, bonds and groups) from OCR AS Chemistry A.

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OCR AS Chemistry Notes


IONISATION ENERGIES
FIRST IONISATION ENERGY

Energy required to remove one electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous
1+ ions
o E.g. N a (g) Na+(g) + 1e-
o H i 1) = + 494 KJ /mol (endothermic)…

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o Energy level n=2 has higher energy electrons (further from nucleus less energy to remove)



Electrons represented as arrows
When energy levels are being filled, electrons pair up
o Electrons in each pair spin in opposite directions
o The spin generates magnetic field
o As they spin in opposite directions,…

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For n=2 (max 8 electrons) 2s2 + 2p6 (2px + 2py + 2pz)
o (1 orbital + 3 orbitals = 4 orbitals)
For n=3 (max 18 electrons) 3s2 + 3p6 + 3d10
o (1 orbital + 3 orbitals + 5 orbitals = 9 orbitals)
For n=4 (max 32 electrons) 4s2…

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1s2 2s2 2p2 2p
2s
1s


NEON:
1s2 2s2 2p6 2p
2s
1s
=Noble gas core [Ne]
ALUMINIUM:
1s2 2s2 2p6 3s2 3p1 3p
=[Ne] 3s2 3p1 3s
2p
2s
1s


ARGON:
1s2 2s2 2p6 3s2 3p6
[Ne] 3s2 3p6
=Noble gas core [Ar]
IRON:
1s2 2s2 2p6 3s2 3p6…

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etc




PERIODIC TABLE + STRUCTURE OF ATOMS
BLOCKS
Periodic table is divided into blocks
o s-block (groups 1+2)
Outermost electron is placed on
s-orbital
o p-block (groups 3-8)
Outermost electron is placed on
p-orbital
o d-block (transition metals)
Outermost electron is placed on
d-orbital
o f-block (inner transition metals: lanthanides…

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Going across the period from group 5 to group 6

NITROGEN: 2p
2s
1s
OXYGEN: 2p
2s


o Group 6 lose the first electron from a paired orbital
The repulsion between those paired electrons gives the electron more energy so it is easier to
remove




EXPLAINING IONISATION ENERGY GROUPS
Example:…

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The first 4 electrons are the easiest to remove (similar ionisation energy)
o But the first one is much easier to remove than the remaining 3



OCR AS Chemistry


IONIC BONDING
PROPERTIES OF IONIC COMPOUNDS
Conduct when molten or dissolved
Crystalline structures
Very high melting point
o Require a lot…

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They achieve noble gas configuration

GIANT IONIC STRUCTURE (LATTICE)
They do not form molecules as electrostatic force acts in all directions
Exist as giant ionic structures
Different types of lattice
Cubic lattice
Each Na+ surrounded by 6 Cl- ions
Each Cl- surrounded by 6 Na+
NaCl lattice has 6:6 coordination…

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o When 2 p orbitals overlap, a pi () orbital bond forms
A and orbital make up a double covalent bond

Triple Covalent Bond

3 pairs of electrons shared

Coordinative (Dative Covalent) Bonding

Some atoms in molecules have pairs of electrons on the outer shell not involved in bonding
o…

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Hydrogen ­ its outer shell can hold max 2 electrons

GIANT COVALENT STRUCTURES
Elements which can form 4 covalent bonds (e.g. C or Si) often form giant covalent structure
o E.g. carbon's allotropes = graphite, diamond, Buckminster Fullerene
Allotrope = different forms of same element which exist at same temperature…

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