1
Q
Define covalent bonding.
A
Sharing of electrons
2
Q
What would be needed to separate a covalent bond?
A
Energy
3
Q
Name the key points for naming a covalent molecular substance.
A
- name leftmost element first
- same group-> name bottommost first
- hydrogen has to be placed between N and O
4
Q
A double bond is _______ than a single bond.
A
Stronger
5
Q
What are the 3 probable identities of hydrogen?
A
Naming: between N and O
Ionic bonding: -1 spot (love to take
covalent bonding: +1 spot (love to give
6
Q
Unequal sharing
A
When the electrons spend more time closer to an element than the other.
7
Q
What does the bar in a structural diagram represent?
A
A shared electron pair
8
Q
What is the definition of covalent network substances?
A
Covalent bonds in a continuous network
9
Q
What are the 3 features of a covalent network substance?
A
- keeps growing in 3D
- molecules contains unknown billions of atoms
- no individual molecule- may be considered a macromolecule
10
Q
Define allotropes.
A
- Different forms of the same element
- formed by different bonding arrangements that result in different structures
- with different chemical and physical properties
11
Q
How are natural allotropes of carbon formed? Give an example.
A
High temperature and pressure in the underground. Carbon atoms arrange themselves into 2D or 3D networks under conditions (mentioned above).
12
Q
How to describe a structure of a covalent network substance?
A
Covalent network
13
Q
What are some key covalent network substances?
A
graphite, silicon dioxide
14
Q
How is a substance lustrous?
A
- When a significant portion of incident light reflects off a smooth surface
15
Q
What is graphene?
A
A single sheet of graphite.
16
Q
Describe the electrical conduction of graphene in both exam terms and explanation terms.
A
Explain:
- electron pushes original electrons within graphene along as it enters
- resulting in an electron getting pushed out on the other end.
Exam:
- electrons are moving within the bond causing current to flow.
17
Q
What is a nanotube?
A
Roll of graphene.
18
Q
Properties question:
Solid aluminium oxide is hard, while solid sulfur monoxide is not, explain?
A
- Aluminium oxide forms an ionic lattice structure
- Ionic bonds require lots of energy to break
- therefore difficult to scratch ions off
- (hard)
- Sulfur monoxide is a covalent molecular substance
- Weak intermolecular forces require a small amount of energy to break
- therefore easier to scratch ions off
- (soft)
19
Q
Properties questions:
Calcium fluoride is solid at normal temperature and pressure, but fluorine is not, why?
A
- Calcium fluoride is ionically bonded.
- Strong bonds within ionic lattice require a lot of energy to break and separate ions
- Therefore high MP
- Fluorine is a covalent molecular substance
- Weak intermolecular forces require very little energy to break
- therefore low MP
- (strong intramolecular covalent bonds between molecules does not need to be broken to form a liquid)
20
Q
Properties question:
Potassium phosphide does not conduct electricity as a solid but does as a liquid. Selenium iodide does not conduct electricity in either state, why?
A
- Potassium phosphide forms an ionic lattice structure
- Ions held in the lattice by strong ionic bonds when solid, electrons localised in ions
- will not conduct when solid as no mobile charge carrier
- as a liquid however, ionic lattice has been broken down and ions are free to move
- Selenium iodide is a covalent molecular substance
- no ions= localized electron in each molecule= no mobile charge carrier
- therefore not conductible in either state
21
Q
non-metals+ non-metals=
Non-metals + metal=
metals+metals=
(state the type of bonding for each of these pairings)
A
Covalent
Ionic
Metallic
22
Q
Why are electrons delocalized in a metal? How does this change the charges of atoms?
A
Metals consist of a large number of atoms closely packed together in a three-dimensional lattice. This close packing means that each valence electron is shared among a large number of positively charged atomic nuclei. (
- this causes atoms to all become positively charged ions as they have all lost electrons
23
Q
what holds everything in a metal together?
A
Electrostatic force of attraction occurs between electrons and ions in a metal, which holds particles within it together in a regular structure.
24
Q
Why do metals have a high MP and BP?
A
Lots of energy are required to break the strong electrostatic forces between its particles
25
Why are metals good conductors?
Because the delocalized electrons are able to carry electrical currents throughout the structure.
26
How are metals malleable?
- Because of its regular structure, layers slide over one another when hit and changes shape
27
What are alloys?
Metallic substance containing two or more elements.
28
Why are alloys much harder than pure metal?
Because it is usually made of different-sized elements.
- therefore not regular structure and can't easily slide over other layers
- therefore not malleable
29
Describe the structure inside a metal
Cations inside a sea of electrons.
30
Name the type of bonding present in hydrogen iodide.
Covalent and intermolecular
31
3. Which of the following is the best description of metallic bonding? Explain.
(a) Electrons are shared between two atoms
(b) Electrons are transferred from one atom to another
(c) Electrons are free to move
(d) Molecules attract each other.
(c) Electrons are free to move
32
Describe the experimental tests you would do to decide whether a solid is an ionic substance.
If the sample does not conduct electricity in solid form but it does in molten form then it is an ionic substance.
33
Ionic compounds are hard, but brittle. Explain what this means. Explain the causes of these properties.
The strong bonds within the lattice make it difficult to remove surface atons (ie hard).
Significant deformation causes like ions to align and repel, and thus the crystal shatters.
34
Using the relevant bonding models to assist, explain why potassium chloride conduct electricity when molten but not when solid?
In molten potassium chloride, the K+ and Cl ions are free to move. In solid potassium chloride they are not (except for vibrations) as they are bound tightly within the ionic
lattice.
35
Using the relevant bonding models to assist, explain why silver is malleable, but silver nitrate is brittle.
Silver is a metal. The metallic bonding allows the cations to be moved without breaking the bonds and thus it is malleable. Silver nitrate, however, forms an ionic lattice.
Significant deformation causes like ions within the lattice to align and repel, and thus the crystal shatters
36
Using the relevant bonding models to assist, explain why the melting point of chlorine, Cl2 is much lower than that of magnesium chloride.
Chlorine is a covalent molecular substance, magnesium chloride is ionic. The intermolecular forces holding chlorine molecules together are weaker than the ionic bonds holding magnesium and chloride ions together in the lattice. (The strong covalent bonds within each chlorine molecule do not need to be broken to melt it)
37
Using the relevant bonding model(s) to assist, explain why:
(a) solid sodium, Na, conducts electricity
(a) Solid sodium is held together by metallic bonds (Cations in a sea of electrons). The delocalised electrons are free.
38
Using the relevant bonding model(s) to assist, explain why:
(b) solid iodine, I2, does not conduct electricity
(b) There are no charged particles free to move. There are no ions and the electrons are localised in each atom
39
Using the relevant bonding model(s) to assist, explain why:
(c) solid sodium iodide, NaI, does not conduct electricity
(c) The ions are held in fixed positions in the ionic lattice and all electrons are localised in each ion
40
Name the particles that carry the charge when electricity flows in the following
substances.
(a) Solid copper
(a) Electrons
41
Name the particles that carry the charge when electricity flows in the following
substances.
Molten sodium chloride
(b) Na+ and Cl ions
42
Name the particles that carry the charge when electricity flows in the following
substances.
An aqueous solution of copper (II) sulfate
(c) Cu2+(aq) and S04 2-(aq) ions
43
Name the particles that carry the charge when electricity flows in the following
substances.
Molten copper
(d) Electrons and Cu2+ ions.
44
Explain why the chemical reactivity of nitrogen depends on the strength of covalent bonds, but its boiling point does not
For nitrogen to react chemically (form a new chemical substance) the strong triple bond within the molecule need to be broken.
To melt solid N2, only the relatively weak
intermolecular forces need to be overcome by the heating process.
45
Use the relevant bonding models to account for differences in the melting points of:
(a) silicon dioxide, SiO2, and carbon dioxide, CO2
(a) In SiO2, the atoms are held together by strong covalent bonds within the network, and lots of energy is needed to break these. However, only the weak intermolecular forces between CO2 molecules need to be overcome in the melting
process and little energy is required to do this.
46
Use the relevant bonding models to account for differences in the melting points of:
(b) lead sulfide, PbS, and hydrogen sulfide, H2S.
(b) PbS is an ionic substance and significant energy is needed to break the strong
ionic bonds within the lattice. However, only the weak intermolecular forces
between H2S molecules need to be overcome in the melting process and little
energy is required to do this.
47
Describe the kinds of attractive forces that must be overcome for each of the following to occur.
(a) Ice melts.
(b) Sugar dissolves in water.
(c) Diamond is crushed with a hammer,
(a) Intermolecular forces (between H2O molecules).
(b) Intermolecular forces (between sugar molecules and between water molecules).
(c) Covalent bonds
48
Describe the kinds of attractive forces that must be overcome for each of the following
to occur.
(d) Copper wire is broken.
(e) Petrol boils.
(f) A pencil leaves a black mark on paper.
(g) Sodium chloride dissolves in water
(d) Metallic bonding.
(e) Intermolecular forces (between ‘petrol molecules).
(f) Dispersion forces (between layers of covalently bound carbon atoms).
(g) Ionic bonds (between sodium ions and chloride ions) and intermolecular forces
(between water molecules).
49
Explain the following,
(a) Diamond can cut paper, but graphite leaves a black mark on paper.
In diamond, all of the carbon atoms are held together by strong covalent bonds in a 3D network.
This makes it hard. In graphite, layers of carbon atoms are only
weakly attracted to each other and slide past each other relatively easily.
This makes graphite soft.
50
Explain the following,
(b) A polystyrene cup of hot coffee is easier to hold than the stainless steel spoon used to stir the coffee. (Polystyrene is a hydrocarbon)
- Steel (a metal) is a good conductor of heat because the delocalized electrons move easily within the structure. - - --------- Polystyrene is a solid form of a covalent molecular
substance and there are no mobile particles to transfer the heat easily.
(The air bubbles trapped within the polystyrene also inhibit heat transfer)
51
Sketch the electron dot diagram for H2
52
Sketch the electron dot diagram for O2
53
Sketch the electron dot diagram for H2O
54
The intramolecular bond strengths between atoms in each of H2, O2, and H2O are similar in strength. Yet water is a liquid at room temperature and H2 and Ox are both gases under the same conditions. With the aid of a diagram, explain this difference.
- MP is dictated by the strength of the intermolecular forces between molecules, e.g. strong IM forces means high MP
- diagram showing polarity
- H2 and O2 have very weak IM forces as they are non-polar
- H2O is a highly polar covalent molecule and has strong IM forces
55
What are alloys?
Alloys are mixtures or solid solutions of two or more elements, with at least one of them being a metal.
- Alloys are created by combining different metallic elements or adding non-metallic elements to a metal.
- The atoms of the different elements mix together on a microscopic scale
- resulting in a material with unique properties that are different from those of the individual elements.
56
How to draw a 3D ionic lattice diagram? E.g. NaCl
Na-Cl-Na-Cl-Na-Cl-
Cl-Na-Cl-Na-Cl-Na-
Na-Cl-Na-Cl-Na-Cl-
Cl-Na-Cl-Na-Cl-Na-
57
Define dispersion forces.
- a temporary attractive force due to the formation of temporary dipoles in a nonpolar molecule
- Electrons are often distributed unevenly within an atom
- Forming dipoles (less electron side attract more electron side of another atom, forming dipoles in that one too)
- This attraction force is called dispersion force.
58
How to write a chemical equation, full ionic equation, and net ionic equation, being given two compounds?
Chemical:
- swap things into correct order and amount
- balance
- include state
Full ionic:
- pull chemical equation apart into each separate element
- include charges
- keep state
Net ionic:
- take away spectators (ones that remain the same before and after reaction)
- keep state
59
In fact, carbon dioxide is a gas at room temperature while silicon dioxide is a hard, crystalline solid with a melting point of around 1600°C. Explain this difference in terms of the bonding present in both substances.
- Co2 is a covalent molecular substance
- strong covalent bonds inside molecules but weak intermolecular forces between them -> low boiling point
- SiO2 is covalent network
- sti=rong covalent bonds throughout entire structure -> high MP
60
Explain why methane does not conduct electricity.
It is a covalent molecular substance and therefore has no free charge carriers.
61
Pyrite is a mineral which has a similar appearance to gold, which is why it is often called “fool’s gold”. It has a golden, lustrous appearance and a high density. The chemical formula for pyrite is iron (II) sulfide, FeS.
(a) Describe the type of bonding likely to be present in pyrite. (2 marks)
- FeS contains ionic bonds
- Fe loses 2 electrons to achieve lower energy state
- S gains 2 electrons
- electrostatic forces between the ions cause them to attract
62
Pyrite is a mineral which has a similar appearance to gold, which is why it is often called “fool’s gold”. It has a golden, lustrous appearance and a high density. The chemical formula for pyrite is iron (II) sulfide, FeS.
(b) Explain how you could use the differences in the properties of the two substances to tell the difference between a sample of pyrite and a sample of real gold.
(2 marks)
- Gold contains metallic bonds and so conducts electricity
- Ionic bonds in FeS means it won't conduct electricity in solid state
- Use electrical conductivity test to distinguish between them
63
C7 MYE 2022
Write equations for the reactions between each copper(II) nitrate and sodium sulphide.
Chemical equation:
Full ionic equation:
Net ionic equation:
What are the spectator ions?
64
Explain why reactivity increases down group I but up group VII on the periodic table.
Group I:
- wants to gain 1 electron
- atomic radius increases as moving down column
- the bigger the atomic radius is, the least attraction force the nucleus has to valence electrons, the quicker they can be removed, thus increasing reactivity down group 1
Group II:
- wants to lose one electron
- smaller force of attraction as move down group
- therefore difficult to attract new electron to form full valence shell
- the higher the element is in the group, the stronger its attraction force to attract new electron therefore reactivity increases up group
65
Compare polar and non-polar molecules.
Polar Molecules:
Uneven distribution of electrical charge.
Have a dipole moment.
Have atoms with different electronegativities.
Examples: Water (H2O), ammonia (NH3).
Non-Polar Molecules:
Even distribution of electrical charge.
Have no dipole moment (dipole moment is zero).
Have atoms with similar electronegativities.
Examples: Carbon dioxide (CO2), methane (CH4).
The polarity of a molecule affects its physical and chemical properties, such as boiling points and solubilities.
66
Lithium can be made into thin sheets. Refer to the structure of lithium to explain this property.
- Li consists of Li+ cations surrounded by a sea of
delocalised valence electrons.
- When pressure/force is applied to make a sheet, the
cations are forced to move relative to each other.
- The repulsion from distortion of the lattice is overcome
as the sea of delocalized electrons maintains
electrostatic attraction between cations and electrons.
67
Explain why nanotubes have high electrical conductivity.
- Each carbon in the fused hexagonal rings have 3 valence electrons localised in covalent bonds with three- other C atoms.
- The 4th valence electron of each carbon atom is free to
move when an electric field is applied.
68
Explain how an ionic bond is formed between the two reactant atoms- lithium and hydrogen.
- Li donates one electron to H, so forming the Li+ and H ions.
- There is an electrostatic attraction between these ions,
forming the ionic bonds within a 3-D lattice
69
Explain how an ionic bond is formed between the two reactant atoms- lithium and hydrogen.
- Li donates one electron to H, so forming the Li+ and H ions.
- There is an electrostatic attraction between these ions,
forming the ionic bonds within a 3-D lattice
70
Methane and water are molecules of similar size, however, at room temperature methane is a gas and water is a liquid. Explain this difference with reference to their structure and bonding, using a diagram of the water molecule to support your answer.
- Water is a polar molecule whereas methane is non-polar:
Stronger Intermolecular bonds (Hydrogen bonds) form
between the H+ atoms and O atoms of adjacent molecules.
- diagram: 2 water molecules bonded tgt by weak intermolecular bonds, show strong covalent bonds between molecules, show polarity
Statement of polarity for H2O and CH4
½ mark for water is polar
Some labeling of diagram expected:
With correct polarity 1 mark. No polarity no marks
71
What are the four common acids and their formula?
HCl (aq)- hydrochloric acid
HNO3 (aq)- nitric acid
H2SO4 (aq)- sulfuric acid
CH3COOH (aq)- acetic acid/ ethanoic acid
72
What are the three common bases and their formula?
Sodium hydroxide- NaOH
Potassium hydroxide- KOH
Calcium hydroxide- Ca(OH)2
73
What's a highly polar covalent molecule?
A highly polar covalent molecule is a molecule in which the shared electrons between atoms are unevenly distributed, resulting in a significant separation of electrical charge. This occurs when there is a large difference in electronegativity between the atoms participating in the covalent bond.
74
How can a molecule be non-polar?
nonpolar molecules can arise from equal sharing of electrons between atoms or from a symmetrical arrangement of atoms that balances out any uneven charge distribution.
75
What does saturated mean?
"saturated" refers to compounds that contain only single bonds between carbon atoms
76
groups practice (in photos)
photos
77
List 3 common tests for gases and what they are used for.
Tests are to be ran when we know that there is gas coming out of a chemical reaction but wish to know what gas it is (hydrogen, oxygen, or carbon dioxide)
Pop test-> hydrogen
Limewater test-> Co2
Glowing splint test-> O2
78
How do u do the pop test?
Place a burning splint near mouth of test tube, a pop will be heard if hydrogen is present.
79
How do u do the limewater test?
Put limewater in one test tube
Guide the gas from the other test tube where the chemical reaction occured into the limewater
*If the limewater turns white, there is carbon dioxide in the gas
80
How do u do the glowing splint test?
Light a splint and let it go out while light remains. Shove the splint into test tube and the flame should become brighter if there is oxygen being emitted.
81
Explain why a sucrose solution does not conduct electricity whereas a solution of silver nitrate does.
- sucrose is a covalent molecular substance
- therefore has no mobile ions to act as charge carriers
- silver nitrate is ionically bonded in a 3D lattice structure
- ions are mobile when in malleable solution state, therefore can act as charge carriers and conduct electricity.
82
draw an electron dot diagram for ethene.
photos
83
Explain why the melting point of water is higher than that of ethene.
- water molecules are polar and have intermolecular dipole dipole attractions
- ethene is non-polar so the intermolecular attractions are only weak dispersion forces thus C2H4 is a gas at room temperature and H2O is a liquid.
i.e. weaker forces -> lower MP
84
Which of the substances (water- MP 0°c, magnesium- MP 650°c, ethene- MP -169°c) does not exist as molecules at -10°c. Explain.
Mg is a metallic solid at -10°c, as it does not form molecules. Unlike the other two who form covalent molecular substances.
85
In terms of bonding, explain why chlorine is able to form a greater variety of compounds than sodium. Support your answer by using suitable examples.
- Chlorine is a non-metal and is able to form both ionic compounds with metals and covalent molecular compounds with other non-metals. E.g. NaCl, Cl2O, ClBr.
- While sodium is a metal and is only able to form ionic compounds by combining with non-metals. E.g. Na2O
86
Tasc exam paper 2019 Question 18b (early periodic table)
Reason for not including silver in group I:
Ag has v. low reactivity
87
Tasc exam paper 2019 Question 18c (early periodic table)
State one difference in Group VIII (now also called group 18) in the modern periodic table and Group VIII in the above table.
Group VIII in the modern table consists of noble gases (at room temp). The early table had no noble gases known.
88
Explain why potassium is more reactive than lithium.
- both react by loss of 1 electron to form ions. The outer electron in K is in the 4th shell and is much further from the nucleus than with Li (electron in 2nd shell).
- Greater distance in K means weaker attractive force on the valence electron therefore more easily lost them in the case for Li.
89
Name or give the formula of a compound with similar chemical properties to Sr(OH)2
Magnesium hydroxide
90
Explain why group 17 elements are diamotic.
By sharing an electron pair, each chlorine atom achieves a stable octet of electron, thus halogens exist as diatomic molecules (e.g. f2, cl2...)
91
Sodium is a group 1 element. A group of cordial includes the nutritional information of "Sodium 20mg" on its label.
Suggest a more chemically correct term to use on the label instead of "sodium". Explain your choice.
More suitable term: Na+ or sodium ions.
- the cordial contains compounds of sodium (e.g. NaCl, NaHCO3) with the mass of Na+ being 20 mg
92
The chemical reactivity of group 1 elements increases down the group yet fluorine is the most reactive of the group 17 elements. Explain.
Group I elements react by loss of 1 electron (forming M+ ions) and so the larger the radius from Li, the further the electron is from the nucleus and thus more easily lost therefore more reactive.
Group 17 react by gaining 1 electron per atom (forming X- ions) and so the strongest electron attraction occurs with the smallest radius atom, namely fluorine with its valence electron shell nearest the nucleus.
93
Which of (sodium oxide, magnesium oxide, silicon oxide, and sulfur oxide) are more likely to conduct electricity in the molten state? Explain.
Na2O and MgO being ionic solids will have mobile ions once the solid is melted and these ions act as charge carriers is the resulting electrical conductivity (SiO2 and SO2 have no ions)
94
Why does the structural formula of an organic compound convey more information than the molelar formula?
The same molecular formula can give rise to often many different structures= isomers. Therefore molecular formula is insufficient information.
95
Tasc pp 2021 q 20d
Group A cannot differentiate between Na2SO4 and Na2CO3 as both produce precipitates when reacted with AgNO3 and BaSO4.
Group B can identify the salts- NaCl won't react in either case; Na2CO3 is the only one that gives off a gas. discriminates
between Na2SO4 and Na2CO3
96
2021 pp q19a
identify the most reactive metal.
Na
97
tasc 2021 pp q18 all
photos
98
Graphite is an allotrope of carbon. It is soft and does conduct ekectricity. With the aid of a diagram outline the structure of graphite and explain why it is soft and conductive.
Graphite is a layer lattice where each carbon bonds to three other carbon atoms in a 2D layer. Between the layers is a sea
of delocalised electrons.
The delocalised electrons conduct electricity and the layers can slide over each other, hence graphite is soft.
99
(b) Use diagrams to help you describe and compare the bonding in a sample of
fluoromethane liquid and a piece of magnesium fluoride.
diagram in photos
CH3F, single covalent bonds within the molecule
- sharing electrons/ strong electrostatic forces/ hard to decompose
- weak intermolecular forces between molecules
- low energy need for state change/ low MP AND BP
- MgF2- ionic bonds between ions, forming 3D lattice
- electrons transferred/ strong electrostatic forces throughout
High MP and MP
100
List one property that is different for fluoromethane liquid and magnesium fluoride and explain this difference in terms of the bonding involved.
MP/BP: Weak intermolecular forces in CH3F therefore low MP/BP. Strong ionic bonds in MGF2-> high MP/BP
Conductivity: liquid CH3F has no charge carriers -> doesn't conduct
Liquid MgF2 has mobile charge carriers in the ions-> does conduct
101
2023 MYE Q2
When hit with a hammer, pure copper will simply flatten whereas a crystal of copper
sulphate will shatter. Use diagrams to help explain this difference in properties.
pdf
102
2023 MYE Q5B
(b) Describe the two types of bonds that elements in group 1 can form.
PDF
103
Bromine water is added to butane. Describe what you would expect to happen.
Very slowly becomes colorless (UV light speeds it up)
104
Bromine water is added to butene. Describe what you would expect to happen.
Quickly becomes colourless.
105
If there is not a plentiful supply of air as the propene burns... what is this process called?
Incomplete combustion.
106
The two compounds carbon dioxide, CO2 and silicon dioxide, SiO2, do not conduct electricity in the liquid state.
a) Based on the periodic table, is it reasonable to expect these two compounds to have similar properties? Explain your answer.
107
The two compounds carbon dioxide, CO2 and silicon dioxide, SiO2, do not conduct electricity in the liquid state.
a) Based on the periodic table, is it reasonable to expect these two compounds to have similar properties? Explain your answer.
108
The two compounds carbon dioxide, CO2 and silicon dioxide, SiO2, do not conduct electricity in the liquid state.
a) Based on the periodic table, is it reasonable to expect these two compounds to have similar properties? Explain your answer.
Yes. Both C and Si tend to share 4 electrons when bonding, both compounds contain 2x O so, from this information, fair to assume same structure and properties.
109
Why are the surfaces of some substances smooth? (salts, metals, and some covalent networks)
- The smooth surfaces of salts, metals, and some covalent networks are caused by the regular arrangement of the atoms within the structure.
110
What are some examples of alloys?
Steel, Bronze, Pewter, Rose gold
111
Sodium is a malleable and electrically conductive metal.
Describe the bonding in metallic sodium using a diagram to assist, that explains its properties of electrical conductivity and malleablility. (3 marks)
Diagram indicates cations
surrounded by a sea of
delocalised electrons
(SDE).
This creates non-directional bonds between the
cations and the SDE allowing atoms/layers to move
past each other without disrupting the force
between atoms/layers.
The delocalised electrons can move and so conduct.
If the metal is deformed non-directional forces
between delocalised electrons and the cation lattice
hold the lattice together
112
The intramolecular bond strengths between atoms in each of h2, o2 and h2o are similar in strength, Yet water is a liquid at room temperature and h2 and o2 are both gases under the same conditions. With the aid of a diagram, explain this difference. (3 marks)
Melting point is dictated by the strength of the
intermolecular forces between molecules; i.e., strong
IM forces means high MP.
Diagram showing polarity
H2 and O2 have have very weak IM foces as they are
non-polar
H2O is a highly polar covalent molecule and has
strong IM forces
113
Lithium reacts with hydrogen to form an ionic compound called lithium hydride, LiH. Explain how an ionic bond is formed between the two reactant atoms. (2 marks)
Li (2,1) donates one electron to H(1), so forming the
Li+ and H ions.
There is an electrostatic attraction between these ions,
forming the ionic bonds within a 3-D lattice
114
Using examples, explain how the bromine test shows if a hydrocarbon is saturated or not. (4 marks)
Br2 water is yellow because of Br2 molecules present when mixed with C2H4(diagram) the double bond breaks, forming (diagram after reaction) and removing Br2 (+yellow colour) from the water.
When mixed with C2H6 a substitution reaction will only occur with UV catalyst so no reaction occurs, so Br2 remains, so yellow colouring remains.
115
Why is graphene flexible?
Only one atom thick so bond angles can change
116
Why are metals conductive?
The delocalized electrons are free to move, hence conduct electricity.
117
why doesn't liquid methane conduct electricity?
Covalent molecular structure
- no ions
- no free electrons
118
In terms of its bonding, explain why methane has a low boiling point. (2 marks)
The weak intermolecular forces require little energy to break.
Do not need to break the strong covalent bonds within the molecule to change state.
119
With the aid of a diagram, explain the structure of graphene. (2 marks)
Each carbon atom bonded covalently to 3 others
2D hexagonal structure
120
Why is graphene strong?
The covalent bonds are difficult to break
121
What are fullerenes? List examples and give properties of each.
1. Buckyball
- made up of pentagons and hexagons
- made up of 60 carbon atoms, formula c60)
2. Nanotube
- hexagonal structure
- rolled up sheet of graphene
3. graphene, graphite
122
will cyclopentane go through similar reactions to 2-methylbut-2-ene?
No
Being a saturated hydrocarbon, it cannot go through an addition reaction but rather it goes through with substitution reaction.
123
One type of an electric drill bit is tipped with diamond. It is used to drill through ceramic tiles. Use bonding concepts to explain the advantage of using diamond. (2 marks)
- diamond forms a 3d covalent network structure
- the strong three dimensional bonding makes it very hard and thus suitable for drilling through tiles.
- has a very high mp
