Summary Pearson Edexcel A Level Chemistry (Year 1 and Year 2) - Unit 2 - Bonding and Structure (9CH0)

2 - Bonding and structure

Ionic bonding and structures
●​ ***Ionic bonding: strong electrostatic attraction between oppositely charged ions
●​ ***Lattice: a regular 3-D arrangement of particles in space
𝑄1 (𝑐ℎ𝑎𝑟𝑔𝑒 1 [𝑐𝑎𝑡𝑖𝑜𝑛]) × 𝑄2 (𝑐ℎ𝑎𝑟𝑔𝑒 2 [𝑎𝑛𝑖𝑜𝑛])
●​ ***𝐹 (𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑠𝑡𝑎𝑡𝑖𝑐 𝑓𝑜𝑟𝑐𝑒) ∝ 2
𝑑 (𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑐ℎ𝑎𝑟𝑔𝑒𝑠)
○​ Bigger charges, stronger electrostatic force
○​ Greater distance between charges, weaker electrostatic force (this has a big
effect because it is the square of the distance that affects the force)


Ionic radii (≠ atomic radii)
●​ +ve ions: ionic radii < atomic, -ve: ionic > atomic




●​ Imbalance in no. protons & electrons cause ions to form, ***∴ if no. protons >
electrons (ie +vely charged ions) ionic radii decrease ∵ (outer shell) electrons more
strongly attracted to nucleus due to increased (relative) nuclear charge {vice versa}
○​ Ie given same no. electrons (for “ions of N to Al”),

Ions of Group 1 Li+ Na+ K+ Rb+ Cs+ Fr+

Ionic radii (pm) 76 102 138 152 167 180

Ions of N to Al N3- O2- F- Na+ Mg2+ Al3+

Ionic radii (nm) 146 140 133 102 72 53.5




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, ***(Same as atomic radii) ionic radii decrease across period, increase down
group

●​ ***Covalent bonding: electrostatic attraction between positive nuclei and a shared
pair of electrons
○​ Proof - contours surrounding both atoms on electron density map, ie




​
***Ie in ionic bonding no contours surround >1 atom (electrons NOT shared)


Dative covalent bonding
●​ ***Definition: when one atom supplies both electrons to form the covalent bond
●​ Eg
○​ NH4+




○​ Al2Cl6




○​ H3O+




2

, (← when HCl is aq)
○​ NH3BF3 (ammonia borane)




○​ NO3-




○​ N2O (nitrous oxide)




○​ CO (carbon monoxide)​




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