four atomic orbitals |
s, p, d, f |
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s orbitals are spherical |
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p orbitals are dumbell shaped |
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spin |
electrons in same orbital have opposite spin |
first ionisation energy |
energy required to remove 1mol of electrons from 1mol of gaseous atoms |
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always refer to "1 mole" |
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lower ionisation energy = easier to form ion |
general equation (ionisation energy) |
X₍₉₎ --> X+₍₉₎ + e¯ |
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state symbols are important!! |
factors affecting ionisation energy: |
> nuclear charge |
more protons = more positively charged = stronger e¯ attraction = higher ionisation energy |
> distance from nucleus |
e¯ closer to nucleus = stronger attraction = higher ionisation energy |
> shielding |
higher num orbitals between nucleus and outer e¯ = weaker attraction = lower ionisation energy |
trends in ionisation energy |
down a group: |
decreases |
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> each element down a group has an extra e¯ shell |
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- extra inner shells shield outer e¯ from attraction to nucleus |
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- extra shells also mean outer e¯ are further from nucleus |
across a period |
generally increases |
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> proton num increasing |
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- which means there's a stronger nuclear attraction |
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> little extra shielding or nuclear distance |
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- as all elements across period have same number of shells |
(across a period cont) |
focusing on period three elements |
dip between group 2 and 3 |
ie between Mg and Al |
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Mg is 1s² 2s² 2p⁶ 3s² |
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Al is 1s² 2s² 2p⁶ 3s² 3p¹ |
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Al outer e¯ is in 3p orbital |
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- 3p has a slightly higher energy level so is slightly further from nucleus |
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- shielded by 3s orbital |
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so ionisation energy drops slightly |
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provides evidence for electron subshell theory |
dip between group 5 and 6 |
ie P and S |
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P is 1s² 2s² 2p⁶ 3s² 3p³ |
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S is 1s² 2s² 2p⁶ 3s² 3p⁴ |
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e¯ from S is being removed from orbital with two e¯ |
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repulsion between e¯ in same orbital means e¯ are easier to remove |
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(P has single occupied orbital so no added repulsion) |
