Bonding and structure

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  • Created by: Paula_
  • Created on: 18-05-17 15:34
What is ionic bonding?
Strong net force of electrostatic attraction between two oppositely charged ions, holding them together.
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What are the 2 factors affecting the strength of ionic bond?
Size of an ion. ionic charge
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What is the trend in separation energy in group 7?
It decreases due to: increased atomic radius and increased shielding
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What is the trend in separation energy in group 1?
It decreases: larger radius, and bigger shielding
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What are isoelectronic elements?
Elements with the same number and arrangement of electrons.
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What is considered the evidence for the existence of ions?
Properties of compound, Electron density maps, Electrolysis
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Define covalent bonding
Sharing of pairs of electrons due to the strong electrostatic forces of attraction between two nuclei and shared electrons.
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What are 2 types of covalent bonds?
Sigma and Pi bonds.
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How is bond strength affected by bond length?
As the bond length increases, bond strength decreases.
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Which element is the exception for the trend in bond strength and why?
Fluorine. It has shorter bond length but lower bond strength than chlorine. This is due to high repulsion between 2 Fluorine atoms with small ionic radius but large effective nuclear charge.
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What is the molecule which is electron deficient?
BF3
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What are the molecules with expanded octet?
PCl5 or SF6
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What is dative covalent bond?
When both electrons in a shared pair are donated by the same atom. It's also called co-ordinate bond. e.g. NH4^+
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What are 3 examples of dative pairs?
Al2Cl3, NH4^+ and H3O^+
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What is electronegativity?
The ability of an atom to attract a bonding pair of electrons.
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What is the trend in electonegativity down a group?
It decreases
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What is the electronegativity across the period?
It increases from left to right.
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What causes polarity in a bond?
Difference in electronegativity. The bigger the difference the more polar the bond.
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Can Ions be polarised?
Yes. small cations with large charge are very polarising and large anions can be polarised easily. This may cause the formation of polar molecule.
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What is metallic bonding?
Strong electrostatic attraction between the nuclei of metal cations and de-localised electrons
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What are factors affecting strength of metallic bond?
Size of ions and charge
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What are physical properties of metals?
High melting point, Thermal conductivity and malleability and ductility.
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What determines the shape of molecules and ions?
The repulsion between the electron pairs that surround the central atom.
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What are 3 VSEPR rules for determining shape of molecule?
1. The electron pairs arrange themselves to minimise repulsion. 2. Lone Pairs have higher repulsion than bonding pairs. 3. Double or triple bond behaves like single bond.
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What is the angle and number of electron pairs in linear molecule?
180, and it has 2 BP, eg CO2, BeCl2
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What is the angle and number of electron pairs in trigonal planar molecule?
120, 3 BP, e.g. BCl3.
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What is the angle and number of electron pairs in tetrahedral molecule?
109.5, 4 BP, e.g. CH4
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What is the angle and number of electron pairs in trigonal pyramidal molecule?
107, 1 LP and 3 BP, e.g. NH3
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What is the angle and number of electron pairs in V-shaped/bent molecule?
104.5 2 LP, 2 BP, e.g. H2O
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What is the angle and number of electron pairs in trigonal bi-pyramidal molecule?
90 and 120. 5 BP, e.g. PCl5
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What is the angle and number of electron pairs in hexagonal/ octohedral molecule?
90, 6 BP. e.g. SF6
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What are 3 types of intramolecular interactions?
London forces, Hydrogen bonding, permanent dipoles.
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What are atoms or ions which can form hydrogen bonds?
N, O, S, F, Cl-, F-
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What is enthalpy change of vaporisation ?
Measure of amount of energy that is required to completely separate the molecules of a liquid and convert it into a gas at the same temp.
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What are 2 strange properties of water and why?
High melting point due to strong hydrogen bonds. Density of ice is lower than that of water as the molecules arrange themselves into rings of 6 due to hydrogen bonds.
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What is the trend for boiling temperatures in un-branched alkanes?
Boiling point increases as the chain length increases.
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How does this trend differ for branched alkanes?
As the number of branches increases, the boiling point decreases due to fewer points of contact between chains.
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What is the general trend in boiling temp of hydrogen halides?
The temperature increases as we go down the group from HCl to Hi.
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What is the exception to this trend and why?
HF. This is because it has strong hydrogen bonds which require more energy to be separated.
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What are the conditions for dissolving a substance?
solute particles have to be surrounded by solvent particles and the forces of attraction between solute-solvent have to be greater than other forces of attraction present.
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What is the trend of solubility of alcohols?
It decreases as carbon chain increases- london forces start to dominate.
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Name 4 solid covalent lattices.
Diamond, Graphite, Graphene, Silicon (IV) Oxide.
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Card 3

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What is the trend in separation energy in group 7?

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Card 4

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What is the trend in separation energy in group 1?

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Card 5

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