Chemistry Unit 1

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Ionisation Energy

is the energy needed to remove 1 electron from an atom in 1 mole of gaseous atoms.

Nuclear charge - More protons = stronger attraction

Distance from nucleus - Fall off rapidly with distance, electron close will be stronger attached


High ionisation energy means theres a high attraction between electron and the nucleus

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Ionisation energy decreases down group 2

- Extra electron shell 

- Extra shielding

- Outer electrons are further away, nucleus attraction will be greatly reduces

Ionisation energy increases across a period

- Number of protons increase, stronger nuclear attraction

- Rougly same energy levels

- Little extra shielding

- The drop shows sub shells filling up, (moving from 's' to 'p')

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Drops Explained

Drop between 2 & 3 shows sub-shell structure.

Aluminiums outer electron is in a 3p orbital rather than 3s, slightly higher energy than 3s. Further from the nucleus.

Additional shielding from the 3s.

Drop between 5 & 6 is due to electron repulsion.

The shielding is identical but in phosphorus the electron is being removed from a singly-occupied orbital. In sulfur the electron is being removed from an orbital containing two electrons. The repulsion between 2 orbitals means that electrons are easier to remove.

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The mole


Moles = Concentration * Volume (in cm3)



Ideal gas equation

pV = nRT            

p = pressure (Pa)
V = volume (m2)
n = number of moles
R = 8.31 J K-1mol-1
T = Temperature (K) 

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Formulas, Yield And Atom Economy

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