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Chemistry > Unit 1: Section 3: Bonding > Flashcards

Unit 1: Section 3: Bonding Flashcards

1
Q

Give the ionic formula for Ammonium

A

(NH)4+

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2
Q

Give the ionic formula for Carbonate

A

(CO3)2-

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3
Q

Give the ionic formula for Hydroxide

A

OH-

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4
Q

Give the ionic formula for Nitrate

A

(NO3)-

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5
Q

Give the ionic formula for Sulfate

A

(SO4)2-

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6
Q

What holds positive and negative ions together

A

Electrostatic attraction

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7
Q

What are ionic crystals (structurally)

A

Giant lattices of ions

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8
Q

Explain the behaviour of ionic compounds

A

Can conduct electricity when they are molten or dissolved but not when they’re solid (ions are not free to move in a solidified form)
Have high melting points because they are held together by strong electrostatic forces
Tend to dissolve in water - part of water molecules are negatively charged and some parts are positively charged, the water molecules pull the ions from the lattice and causes it to dissolve

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9
Q

What is a molecule

A

When two or more atoms bond together

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10
Q

What is a single covalent bond

A

When two atoms share a pair of electrons

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11
Q

What is a giant covalent structure

A

Type of crystal structure
Huge network of covalently bonded atoms (macromolecular structure)

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12
Q

Which element forms giant covalent structures and why

A

Carbon
It can form four strong covalent bonds

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13
Q

Explain the structure of an example of a giant covalent structure

A

Graphite
C atoms are arranged in sheets of flat hexagons covalently bonded with three bonds each
The four outer electron of each carbon atom is delocalised

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14
Q

What are the forces that hold together the bonds in a giant covalent structure

A

van der Waals forces

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15
Q

Explain the properties of graphite

A

Weak bonds between layers - sheets can slide over each other making it slippery
Delocalised electron means that it can conduct electricity
Layers are far apart compared to length of the covalent bonds so it has low density
Because of the strong covalent bonds
Insoluble - covalent bonds are too strong to break

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16
Q

Explain the structure of diamond

A

Each C atom is bonded to 4 other C atoms
Atoms arrange themselves in a tetrahedral shape (crystal lattice structure)

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17
Q

Explain the properties of diamond

A

High melting point - sublimes over 3800K
Hard
Vibrations can travel through the stiff lattice so it’s a good conductor of heat
Can’t conduct electricity
Won’t dissolve in any solvent

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18
Q

What are the unshared electrons in a covalent bond called

A

Lone pairs

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19
Q

What is a charge cloud

A

An area where you have a big chance of finding an electron

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20
Q

Explain Valence Shell Electron Pair Repulsion Theory

A

Charge clouds repel each other more in lone pairs then bonding pairs
So bond angles are reduced because bonding pairs are pushed together by lone-pair repulsion

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21
Q

What is a co-ordinate bond

A

One of the atom provides both of the electrons

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22
Q

What is a dative covalent bond

A

A co-ordinate bond

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23
Q

Give an example of a dative covalent bond

A

Ammonium

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24
Q

When do dative bonds form

A

When one atom has a lone pair of electrons, and the other doesn’t have any electrons available to share

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25
Q

When drawing the shapes of molecules what does the shape of the bonds tell you about the direction

A

Wedged line - shows a bond is pointing towards you
Broken line - shows a bond is pointing away from you
Line - shows bonds aren’t pointing towards or away from you

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26
Q

How do you find the number of electron pairs

A

Find the central atom
Look at its group number to find out the number of outer electrons
Add one electron to every for every atom the central atom is bonded to
Add up all the electrons and divide it by 2 to find the number of electron pairs

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27
Q

Describe the shape of a compound that has a central atom with two electron pairs

A

Bond angle of 180 degrees
Pairs of bonding electrons want to be as far away from each other as possible

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28
Q

Describe the shape of a compound that has a central atom with three electron pairs

A

Shape depends on combination of lone and bonding pairs
If there are three bonding pairs of electrons the bonding angle will be 120 degrees - called trigonal planar
If there is two bonding pairs of electrons and one lone pair the bonding angle will be a little less than 120 degrees

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29
Q

Describe the shape of a compound that has a central atom with four electron pairs

A

If there are four bonding electrons then the bonding angle will be 109.5 degrees
Shape of molecule is tetrahedral
If there are three bonding pairs the repulsion between the lone pairs and bonding pairs will be greater than the bonding pairs and bonding pairs so there will be smaller bond angles between the bonds and larger bonding angles between the lone and bond pairs
The bonding angle is 107 degrees - this is called trigonal pyramidal
If there are two bonding pairs of electrons the two lone pairs will squash the bond angle even further
The bond angle will be around 104.5 degrees

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30
Q

Describe the shape of a compound that has a central atom with five electron pairs

A

Repulsion between bonding pairs cause three atoms to have a bond angle of 120 degrees (trigonal planar shape) and the other two to have a bond angle of 90 degrees
This shape is called a trigonal bipyramidal
If there are four bonding pairs and one lone pair of electrons
the lone pair would be positioned where the bonding pair would’ve been in a trigonal planar shape - called seezaw
If there are three bonding pairs and two lone pairs the molecule will be T-shaped

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31
Q

What does ‘expand the octet’ mean

A

Central atom can have more than eight bonding electron in their outer shells

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32
Q

Describe the shape of a compound that has a central atom with six electron pairs

A

Six bonding pairs means the shape will be an octahedral - all bond angles will be 90 degrees
If there are five bonding pairs and one lone pair the molecule forms a square pyramidal shape - bonding angles are still 90 degrees
If there are four bonding electron pairs and two lone pairs then the molecule will be a square planar

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33
Q

How do you work out molecules that are bonded in double bonds

A

Treat each double bond like an extra single bond so if there is a double bond that mean two single bonds

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34
Q

What is electronegativity

A

The ability to attract the bonding electrons in a covalent bond

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35
Q

How is electronegativity measured

A

Measured on the Pauling Scale
A higher number means the element is better able to attract the bonding electrons

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36
Q

What does polar and non-polar bonds mean

A

Polar - atoms have different electronegativities
Non-polar - atoms have similar or equal negativities

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37
Q

δ - what does this mean

A

Slightly

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38
Q

What is a dipole

A

A difference in charge between the two atoms caused by a shift in electron density in the bond

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39
Q

What causes a dipole

A

The difference of electronegativity causes between the two atoms causes a dipole

40
Q

How is a permanent dipole induced

A

If charge is distributed unevenly over a whole molecule
Molecules that have this are called polar molecules

41
Q

In a simple molecule how is it decided if that molecule has a permanent dipole

A

If one bond is polar then that molecule has a permanent dipole

42
Q

In a complex molecule how is it decided if that molecule has a permanent dipole

A

It will be dependant on its shape
If the molecule is arranged symmetrically then the charge will dipoles will cancel each other out and there won’t be a permanent dipole
If the bonds point roughly in the same direction the dipoles won’t cancel each other out and there will be a permanent dipole

43
Q

What are intermolecular forces

A

Forces between molecules

44
Q

Are intermolecular bonds stronger or weaker than covalent, ionic or metallic bonds

A

They are much weaker

45
Q

What are the three intermolecular forces

A

Induced dipole-dipole forces
Permanent dipole-dipole forces
Hydrogen bonding

46
Q

Which of the three intermolecular forces is the strongest

A

Hydrogen bonding

47
Q

What is another way of saying induced dipole-dipole forces

A

Van der Waals forces

48
Q

Explain Van der Waals forces

A

Electrons in charge clouds move really quickly
At any particular moment there will be more electrons on one side than the other
At this moment the atom will have a temporary dipole in the opposite direction of the neighbouring atom
This will cause another temporary dipole and this will keep happening
The electrons are constantly moving the dipoles are begin constantly created and destroyed over time

49
Q

What is the effect of Van der Waals forces

A

For the atoms to be attracted to each other

50
Q

Do all Van der Waals forces have the same strength

A

No
Larger molecules will have larger charge clouds

51
Q

Explain how the shape of the molecule affects the strength of the van der Waals forces

A

If the bonds are straight rather than branched there molecules can lie closer together and the forces between them will therefore be stronger

52
Q

Give three physical properties that van der Waals forces can affect

A

Viscosity
Boiling point
Melting point

53
Q

Describe the trend of boiling points as you go down the noble gases group

A

The boiling points increase

54
Q

Explain permanent dipole-dipole forces

A

In a substance that has permanent dipoles there will be weak electrostatic attraction between the δ+ and the δ- charges on neighbouring molecules

55
Q

What will happen if you place a negative electrostatically charged rod next to a jet of water

A

Water is a polar liquid because the molecules contain permanent dipoles
The polar molecules of water will move so the oppositely charged molecule is facing the rod so it doesn’t matter what the charge of the rod is

56
Q

When does hydrogen bonding happen

A

When hydrogen is bonded to nitrogen, fluorine or oxygen

57
Q

Explain hydrogen bonding

A

Fluorine, nitrogen and oxygen are very electronegative so they draw the bonding electrons away from the hydrogen atom
The bond is so polarised and hydrogen has such a high charge density that the hydrogen atoms form weak bonds with lone pairs of electrons on the fluorine, nitrogen or oxygen atoms of other molecules

58
Q

Explain the effect that hydrogen bonding has on the properties of substances

A

High boiling points
High melting points

59
Q

Which one is more dense: ice or liquid water and explain why

A

Liquid water is more dense
In ice the molecules are arranged in regular lattice structure where the distance of the molecules is greater than the distance between the molecules in a liquid water

60
Q

Explain the electrical conductivity, melting point and the solubility of simple covalent compounds

A

Do not conduct electricity because there are no free ions or electrons
Low melting points because the weak forces between the molecules are easily broken
Some dissolve in water depending on how polarised the molecules are

61
Q

What is the main factor determining the melting and boiling points

A

The strength of the induced dipole-dipole forces
unless there is a hydrogen bond

62
Q

What do metal elements exist as

A

Giant metallic lattice structures

63
Q

Describe and explain the melting point, ability to be shaped, conductivity and solubility

A

Melting point - high, the strong electrostatic attraction between metal ions and electrons require lots of energy to break
Ability to be shaped - no specific ions to break so layers can slide over each other making the metal malleable and ductile
Conductivity - delocalised electrons can pass kinetic energy to each other making metals good thermal conductors, they can also conduct electricity because there is a sea of delocalised electrons
Solubility - insolube because of the strength of the metallic bonds

64
Q

Why do simple covalent compounds have low boiling and melting points

A

Because you don’t have to break the bonds you just have to break the weak intermolecular forces between the bonds

65
Q

Do giant covalent structures and metallic bonds dissolve in water

A

No

65
Q

What does the solubility of a substance depend on

A

If the substance is polar or charged then it is soluble in water because water is a polar substance

66
Q

If you have an unknown compound and you want to predict the structure what can you do

A

Test the properties and deduce from that the type of structure

67
Q

What is enthalpy change

A

The heat energy transferred in a reaction at constant pressure

68
Q

What is the notation for enthalpy change

A

ΔH

69
Q

What are the units of enthalpy change

A

kj mol^-1

70
Q

What are the standard conditions

A

100kPa or 1 atm of pressure

71
Q

At what temperature are enthalpy changes measured at

A

298 K (25 degrees celcius)

72
Q

What type of value will the enthalpy change be if the reaction is exothermic

A

Negative because the energy is given out to the surroudings

73
Q

What type of value will the enthalpy change be if the reaction is endothermic

A

Positive because it’s taking in energy from the surroundings

74
Q

What is bond enthalpy

A

The energy needed to break a bond

75
Q

Is breaking bonds endothermic or exothermic

A

Need energy to break bonds so bond breaking is endothermic

76
Q

What is the enthalpy change

A

The overall effect of these two changes

77
Q

What is mean bond ethalpies

A

The average energy needed to break a cetain type of bond over a range of compounds

78
Q

How do you calculate the enthalpy change

A

Enthalpy change = Totale energy absorbed - Total energy released

79
Q

How do you find the total energy released by the reaction

A

Find the total energy needed to form all the new bonds

80
Q

What are the three different types of entahlpy change

A

Standard enthalpy chnage of formation
Standard enthalpy change of combustion
Standard entahlpy change of reaction

81
Q

Explain standard enthalpy change of formation

A

The enthalpy change when 1 mole of a compound is formed from its elements in their standard sates under standard conditions

82
Q

Explain standard enthalpy change of combustion

A

The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in the ir standard states

83
Q

Explain standard entahlpy change of reaction

A

The enthalpy change when a reation occurs in molarquantities shown in the chemical equation, under standard conditions with all reactants and products in their standard states

84
Q

What are the three things you need to know when measuring the enthalpy change in a lab

A

Number of moles of stuff that is reacting
Change in temperature
How much stuff you’re heating

85
Q

What are experiments that measure heat given out by reaction called

A

Calorimety experiments

86
Q

Describe the apparatus needed in when measuring enthalpy changes in a lab

A

Polystyrene beaker
Solution inside beaker
Thermometer inside solution

87
Q

Explain how you measure enthalpy change for reactions that happen in solution

A

Use the thermometer to measure the temperature at regular intervals
Use a polystryene beaker to insulate the reaction

88
Q

Describe the apparatus needed to measure the enthalpy change of combustion

A

Stirrer
Thermometer
Water
Combustion chamber
Fuel (reactan)
Air tube
Calorimeter

89
Q

Explain how you measure the enthalpy change of combustion

A

As the fuel burns it heats the water and you can measure the temperature change and find out how much heat the water has absorbed if you know the mass of the water and the specific capacity of the water

90
Q

Explain why the method for working out the enthalpy change of combustion may give inaccurate results

A

Some heat may be lost to surroundings and there might be some incomplete combustion

91
Q

Why is finding the starting value of the water and subtracting it from the final value not a good method of finding out the temperature change when measuring enthalpy change of combustion

A

Because some heat is lost fromp the calorimeter to the surroundings

92
Q

How do calculate the temperature change when measuring enthalpy change of combustion

A

Record temperature at regular intervals (begin a couple of minutes before you start the reaction)
Plot a graph (temp against time)
Plot two lines of best fit one for the results before the reaction and one for after
The distance between the two lines at the time the reaction started is the accurate temperature change for the reaction

93
Q

How do calculate the standard enthalpy change of combustion

A

Calculate the amount of heat lost
Calculate the number of moles of ffuel that caused thsi enthalpy change (number of moles = mass/Mr)
Use the equation - heat change/number of moles of fuel burned - to calculate

94
Q

What is standard enthalpies of combustion measured in

A

kj mol^-1

95
Q

What is the enthalpy of neutralisation

A

The energy change when 1 mole of water is formed by the reation of an acid and an alkali

96
Q

How do you find the enthalpy of neutralisation

A

Add a known volume of acid to an insulated conatainer
Then add known volume of alkali and record the temperature at regular intervals
Stir solution to make sure it’s evenly heated
Work out the heat energy given out by reaction using the heatc change/number of moles equation

Chemistry (7 decks)

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