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Chemistry A2 > Last Minute > Flashcards

Last Minute Flashcards

Forces, bonds, attraction, periodicity, etc

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1
Q

What are the trends as you go down a group?

A

1st ionisation decreases

Number of shells increase
》the distance from nucleus
》weaker attractive force

Shielding increases

Ionic radius increases

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2
Q

What is the trend across a period?

A

Atomic radius decreases

No change in shielding (same number of shells)

Increased nuclear charge
》increased nuclear attraction

Protons increase
》General increase of 1st ionisation energy

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3
Q

Define isotope.

A

Isotopes are atoms of the same element that have different neutrons.

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4
Q

What is the atomic number?

A

Number of protons

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5
Q

Define relative atomic mass.

A

The weighted mean mass if an atom compared to 1/12 of the mass of carbon-12.

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6
Q

In period 3 explain the melting points of Na to Al.

A

Electrons in outer shell increase
》More electrons in delocalised sea

Charge on cations increases (+1 to +3)

Ionic radius decreases
》Delocalised elections are closer to nucleus

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7
Q

Explain the melting point of Silicon in the trend of period 3.

A

It is Giant Covalent

》Large increased melting point

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8
Q

Explain the trend in melting point in period 3 from P to Ar.

A

Simple covalent
》lower melting points

Weak intermolecular london forces

Larger the molecule the great the london forces
》Hense P4, S8, Cl2, Ar

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9
Q

What state is S8 at room temperature?

A

Solid

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10
Q

Compare the strength of intermolecular forces

A

HBond > permanent > London

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11
Q

Key point of London Forces.

A

They induce dipoles in neighbouring molecules (like bumpercars) that attact eachother.

No polar bonds

Very weak and short lived

The bigger the molecule the greater the forces
eg C3H6 -89C , C4H8 -43C

The more points of contact, the greater the attraction

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12
Q

Key points on permanent dipole-dipole forces.

A

Polar bonds with overall dipole

Asymmetrical
》polar

Attractions between these and neighbouring molecules eg. H-Cl molecules

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13
Q

Key points of Hydrogen bonding.

A

H atom bonded to a very electronegative element (F, O, N)

Bond between H and lone pair on F, O, N

Stronger that London or permanent dipole-dipole forces.

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14
Q

Define electronegativity.

A

Measure of attraction of an atom in a covalent molecule for the bondinh pair of electrons.

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15
Q

What makes a molecule polar or non-polar?

A

Polar = Asymmetric

Non-Polar = Symmetric

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16
Q

What are the effects of hydrogen bonds in ice?

A

Ice is less dense than water due to hydrogen bonding because of large areas of empty space.
Ice has ‘diamond-like’ structure.

Permifrost traps methane in empty space.

17
Q

Does ammonia or water have a higher boiling point?

A

Water because it has 2 hydrogen bonds per molecule, whereas ammonia only has 1.

18
Q

Why do boiling points decrease down a group generally?

A

Increased electrons means increased london forces between molecules.

19
Q

What is the bond angle of trigonal planner?

A

120

20
Q

What is the bond angle of linear?

A

180

21
Q

What is the bond angle of non-linear / bent?

A

104.5

22
Q

What is the bond angle of tetrahedral?

A

109.5

23
Q

What is the bond angle of trigonal planer?

A

107

24
Q

What is the bond angle of square planar and octahedral?

A

90

25
Q

What is the temperature used for the habor process and why?

A

450C
Compromise on yield and rate as:

Lower temp gives higher yield of NH3 and forward reaction is exothermic.

High temp gives faster rate.

26
Q

What is the pressure used in the habor process and why?

A

200atm
Compromise on yield and cost as:

High pressure gives higher yield of NH3 as less gass molecules on the right of the equation.

High pressure is very expensive.

27
Q

What is the catalyst for the haber process?

A

Iron

Increases rate but has no effect on yield or position.

28
Q

State Le Châtelier’s principle.

A

If conditions of a system at equilibrium changes then the position of equilibrium moves to oppose the change.

29
Q

What effect does pressure have on Kc?

A

No effect.

30
Q

What is meant by dynamic equilibrium?

A

Both forward and backward reactions occur at the same time and rate.

Concentration for reactants and products is constant.

31
Q

What is the difference between homogeneous and heterogeneous equilibrium?

A

Homogeneous: All reactants and products are in the same state.

Heterogeneous: All the reactants and products aren’t in the same state.

Chemistry A2 (6 decks)

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