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A level- Chemistry > Bonding and Structure > Flashcards

Bonding and Structure Flashcards

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1
Q

Define ionic bonding

A

The electrostatic attraction between a positive and negative ions. Holds together cations and anions in ionic compounds

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2
Q

Draw dot and cross diagrams of Na2O and Magnesium bromide

A

Draw it an look at p11 of study pack

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3
Q

Define covalent bonding

A

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

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4
Q

Draw dot and cross diagrams of CO2 and PCl5

A

Look at p15 of stud pack

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5
Q

What is the octet rule

A

That elements tend to combine in a covalent compound with 8 electrons in their outer shell

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6
Q

What is a lone pair of electrons

A

A pair of electrons in the outer shell not used in bonding

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7
Q

Define dative covalent bond

A

A special type of bond formed from 2 electrons form the same atom e.g. NH4+ (NH3 + H+ –> NH4+)
Both electrons have been donated by one atom

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8
Q

Draw dot and cross diagram for NH4+ and H3O+

A

look at study pack p17

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9
Q

Define average bond enthalpy

A

It is the average enthalpy change which takes place when breaking by homolytic fission one mole of a given type of bond in the molecules of a gaseous species.
Measurement of bond strength

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10
Q

Define metallic bonding

A

The electrostatic attraction between positive metal ions and delocalised electrons.

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11
Q

Why do metals have high melting and boiling points

A

A lot of energy is needed to overcome the strong electrostatic attraction between the cations and electrons.

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12
Q

Why are metals good conductors of electricity

A

Solid- delocalised electrons are mobile so can carry charge

molten- delocalised electrons and the cations can move and carry charge

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13
Q

Why are metals insoluble in water or non-polar solvents

A

Because the strong electrostatic attraction between the positive metal ions and electrons is too strong so a lot of energy is needed to overcome it.

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14
Q

Which out of sodium, magnesium and aluminium is the best conductor of electricity

A

Aluminium- Has a charge of +3 so more delocalised electrons per metal ion, so has the best capacity to carry charge.

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15
Q

Define malleable and ductile

A

Malleable- can easily be bent in to different shapes

Ductile- can be drawn in to a wire

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16
Q

Which metals are present in stainless steel and brass

A

Stainless steel- Fe and Cr

Brass- Cu and Zn

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17
Q

How does an alloy make a metal harder

A

Because each metal is slightly different sizes so they can’t easily slide over each other which means they are harder.

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18
Q

Why do ionic compounds have high melting and boiling points

A

There is a strong electrostatic attraction between the +ve and -ve ions and a lot of energy is needed to overcome this.

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19
Q

Do ionic compounds conduct electricity when solid and molten

A

solid- no- ions aren’t mobile as are in fixed lattice arrangement so can’t carry charge
Molten/ dissolved in water- Ions aren’t in fixed positions in the lattice structure so can move around and carry charge.

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20
Q

Are ionic compounds soluble in water

A

Yes - often they have good solubility in water- water is polar so is attracted to the opposite charges in the compound- water molecules levers it out of it’s compound surrounding it by H2O molecules.

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21
Q

Why are ionic compounds brittle

A

If there is even the smallest movement of a layer the positive ions will be next to other positive ions. this causes repulsion causing the structure to break apart.

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22
Q

Giant covalent lattices- boiling points

A

High- There are strong covalent bonds which need to be broken which requires a lot of energy

23
Q

Simple covalent molecules- boiling points

A

Low- There have very weak intermolecular forces which are easy to overcome, so not much energy is required.

24
Q

Giant covalent lattice- Electrical conductor

A

No- there are no mobile electrons or any other charged particles which can carry charge.

25
Q

Simple covalent molecules- Electrical conductor

A

No- there are no mobile electrons or any other charged particles which can carry charge.

26
Q

Giant covalent lattice- Solubility in non-polar solvents

A

No- The strong covalent bonds that hold it together require too much energy to overcome

27
Q

Simple covalent molecules- Solubility in non-polar solvents

A

Yes- Weak intermolecular forces are easy to break, so the solvent molecules form similar intermolecular bonds with molecules.

28
Q

Draw structure of diamond

A

Draw it and check that each carbon atom is covalently bonded to 4 other carbon atoms. it is a tetrahedral shape

29
Q

Draw structure of graphite

A

Check it p30 of study pack- two layers and weak forces between the layers

30
Q

Diamond- Electrical conductor

A

No- Has no mobile electrons to carry charge

31
Q

Graphite- Electrical conductor

A

Yes- Carbon only forms 3 bonds so each has a spare electron which become delocalised so can move abd carry charge

32
Q

Diamond- hardness

A

Very hard- each carbon atom forms 4 bonds and forms a tetrahedral structure for each atom. Strong covalent bonds need much energy to break

33
Q

Graphite- hardness

A

Soft- there are weak intermolecular forces between layers which can be easily broken and the layers slide over each other.

34
Q

Define giant covalent lattices of atoms

A

It is a 3D structure of atoms which is bonded together by very strong covalent bonds.

35
Q

VSEPR (Valence Shell Electron Pair Repulsion) Theory states

A
  1. Electron pairs around an atom will repel each other
  2. They will tend to get as far apart as possible
  3. Number and type of electron pairs determines the shape
  4. Lone pairs repel more strongly than bonded pairs (this affects bond angle) reduction of about 2.5 degrees per lone pair.
36
Q

If a central atom has 2 bonding pairs and no lone pairs around it what shape and angle will it be?

A

Linear- 180 degrees

37
Q

If a central atom has 3 bonding pairs and no lone pairs around it what shape and angle will it be?

A

Trigonal planar- 120 degrees

38
Q

If a central atom has 4 bonding pairs and no lone pairs around it what shape and angle will it be?

A

Tetrahedral- 109.5 degrees

39
Q

If a central atom has 3 bonding pairs and 1 lone pairs around it what shape and angle will it be?

A

Trigonal pyramidal- 107 degrees

40
Q

If a central atom has 2 bonding pairs and 2 lone pairs around it what shape and angle will it be?

A

Non- linear - 104.5 degrees

41
Q

If a central atom has 6 bonding pairs and no lone pairs around it what shape and angle will it be?

A

Octahedral- 90 degrees

42
Q 
Draw shape and state angle of:
PH3
GeCl2
BF4- ion
AsH3
A

PH3- trigonal pyramidal 107 degrees
GeCl2- non-linear- 117.5 degrees
BF4- ion- tetrahedral- 109.5 degrees
AsH3- Trigonal pyrimidal- 107 degrees

43
Q

What are the types of Van der Waals forces that exist

A

induced dipole-dipole and permanent dipole-dipole

44
Q

London forces description

A

Electrons are permanently moving
At any single instant their distribution in a molecule is not even.
This results in an instantaneous, temporary dipole.
This dipole induces dipoles in neighbouring molecules.
This leads to a small electrostatic attraction between the neighbouring charges in the dipoles.
This attraction between the molecules are London forces.

45
Q

2 factors that affect the strength of London forces

A
  1. Number of electrons in a molecule- more electrons the stronger the force because there are greater fluctuations.
  2. Contact between molecules- only an issue with molecules with approx. same number of electrons.
    Less branched molecules have a higher contact area so stronger London forces
46
Q

Define electronegativity

A

The ability of an atom to attract the bonding electrons in a covalent bond

47
Q

Define permanent dipole

A

A small charge difference between different atoms in a molecule. It does not change across a bond.
If there is a difference in electronegativity between atoms in a compound then they have partial charges and permanent dipoles.

48
Q

Define polar covalent bond

A

It’s a bond with a permanent dipole- contains partial negative and partial positive charges on the bonded atoms

49
Q

Define polar molecule

A

A molecule that has an overall dipole taking into account all dipoles across bonds and the shape of molecules.

50
Q

When are molecules with polar bonds not polar overall

A

When they are symmetrical

51
Q

Decide whether BeCl2, SnCl4 and CH2Cl2 are polar

A

BeCl2- Linear so won’t be polar
SnCl4- Tetrahedral- symmetrical so dipoles cancel each other out so not polar
CH2Cl2- Tetrahedral- C-H bond isn’t polar so dipoles don’t cancel each other out - is polar

52
Q

Define hydrogen bonding

A

A strong dipole-dipole attraction between an electron deficient hydrogen atom of -NH, -OH or -HF on one molecule and a lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule.

53
Q

Which of these molecules have hydrogen bonding:

H2S, CH3OH, PH3, NO2, CH3NH2, CH2=O

A

CH3OH and CH3NH2

the others can’t because they don’t have and N-H, F-H or O-H bonds

54
Q

Describe the density of ice compared to water

A

Ice is less dense than water. For a given volume there are fewer molecules of H2O in ice than in water. The molecules of H2O in solid ice are less closely packed than in liquid water.

A level- Chemistry (31 decks)

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