Bonding Flashcards
1
Q
What are the three types of strong chemical bonds?
A
Ionic, covalent and metallic
2
Q
Definition of an ionic bond
A
An ionic bond is the electrostatic attraction between oppositely charged ions
3
Q
Definition of a covalent bond
A
A covalent bond is the electrostatic force of attraction between the negatively charged pair of electrons and the positively charged nuclei of the adjacent atoms
4
Q
Explain why nitrogen is a gas at room temperature
Answer in terms of nitrogen’s structure
A
- Nitrogen is bonded with covalent bonds- very strong
- However, nitrogen is a simple covalent substance
- So intermolecular forces between nitrogen are v. weak
- So v. little energy is required to break them
- Meaning the boiling/melting point of nitrogen is very low
- So at room temperature, the temperature is high enough for nitrogen to be a gas
5
Q
Graphite and fullerenes are forms of carbon.
Graphite is soft and is a good conductor of electricity. Explain why graphite has these properties.
Answer in terms of structure and bonding.
A
- In graphite, each carbon atom has 3 electrons in its outer shell, used in covalent bonds with other carbon atoms
- Leaves 1 electron that is free
- Because it is a charged particle that can move
- Electricity could be conducted in this way, making graphite a good conductor
- Graphite is also arranged in layers, that can slide over each other
- Making graphite soft as bonding between these layers isn’t very strong
- This means graphite layers can move and slide, making it soft
6
Q
A lubricant is a substance that allows materials to move over one another easily. Suggest why graphite is a good lubricant
A
- Graphite is soft
- because the layers in graphite aren’t bonded strongly together
- So they can slide
- makes graphite a good lubricant
- as it can ease movement between materials
- the layers aren’t bonded strongly because only 1 electron per carbon atom is used for this bonding
7
Q
Silicon dioxide, SiO2 has a similar structure to diamond. Explain why its melting point in 1710°C
A
- Silicon dioxide is a giant covalent substance
- so throughout the substance, there are strong covalent bonds that require lots of energy to break, requiring a high melting point.
- all 4 of the electrons in the outer shell of silicon are bonded with strong covalent bonds, increasing energy needed to break the bonds rather than just having 1 strong covalent bond
- This means the melting points is very high, 1710°C
8
Q
Magnesium reacts with fluorine to produce the ionic compound magnesium fluoride. Describe what happens in terms of electrons when magnesium reacts with fluorine.
A
- Magnesium is a metal and so has few electrons in its outer shell (for magnesium, 2)
- Means that it is easier for magnesium to lose electrons rather than gain them
- Fluorine is a non-metal so it is easier for it to gain 1 electron than lose all 7 of the electrons in its outer shell
- When they react, each magnesium reacts with 2 fluorine to lose both of its 2 electrons, giving one electron to each
- This means magnesium and fluorine are now stable with a full outer shells, so they form the ionic compound magnesium fluoride
9
Q
Magnesium oxide is a compound formed from the metal magnesium and the non-metal oxygen. Describe what happens when a magnesium atom reacts with an oxygen atom.
You should refer to electrons in your answer
A
- Magnesium atom loses electrons
- oxygen atom gains electrons
- two electrons are transferred
- Magnesium ions and oxide ions are formed
10
Q
Give one limitation of using a dot and cross diagram to represent an ammonia molecule
A
- Does not show the shape
11
Q
Ionic formula of ammonium
A
NH4+ (+1)
12
Q
Ionic formula of carbonate
A
CO₃²⁻
(2-)
13
Q
Ionic formula hydroxide
A
OH− (1-)
14
Q
Ionic formula of nitrate
A
NO3- (1-)
15
Q
Ionic formula sulfate
A
SO42- (2-)
16
Q
What is a compound?
A
A pure substance made from more than one type of element chemically bonded together
17
Q
How do elements form compounds?
A
Through chemical reactions
18
Q
How are covalent bonds formed?
A
A covalent bond is formed when a pair of electrons is shared between two atoms
19
Q
What is ionic bonding?
A
- Bonding between particles that are oppositely charged ions. Ionic bonding occurs in compounds formed from metals combined with non-metals
20
Q
What is covalent bonding?
A
- Bonding in which the particles are atoms which share pairs of electrons. Covalent bonding occurs in most non-metallic elements and in compounds of non-metals
21
Q
What is metallic bonding?
A
- Bonding where the particles are atoms which share delocalised electrons. Metallic bonding occurs in metallic elements and alloys
22
Q
What is an ionic structure?
A
Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions in the lattice and this is called ionic bonding.
23
Q
What is the empirical formula of an ionic compound?
A
The empirical formula of an ionic compound is the ratio of each type of ion present. In sodium chloride there is one sodium ion for every chloride ion, meaning the ration is 1:1. This gives sodium chloride the formula NaCl
24
Q
Properties of Ionic Compounds
A
- Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions
- These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds
- When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow.
25
Structure and bonding: Covalent bonding
- When atoms share pairs of electrons, they form covalent bonds
- These bonds between atoms are strong
- Covalently bonded substances may consist of small molecules
- Some covalently bonded substances have very large molecules, such as polymers
- Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide.
26
How can the molecular of a covalent substance be worked out?
The molecular formula of a substance can be worked out from a given model or diagram by counting the number of atoms of each type. For example, ammonia is NH3
27
How can covalent bonds be represented?
Covalent bonds can be represented in a number of different ways:
- The simplest format is a straight line. One line (-) represents a single bond, two lines (=) a double bond, and so on. This model shows how many bonds are present very easily. These models do not show 3D shape. This model also ignores electrons that are not involved in bonding.
28
Properties of Simple Molecular Substances
- usually gases or liquids
- have relatively low melting points and boiling points
- have only weak forces between the molecules (intermolecular forces)
- It is these intermolecular forces that are overcomes, not the covalent bonds, when the substance melts or boils
- The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points
- do not conduct electricity because the molecules do not have an overall electric charge
- Intermolecular forces are weak compared with covalent bonds. This explains the bulk properties of molecular substances
29
Giant covalent substances: Diamond
In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a very high melting point and does not conduct electricity
30
Giant Covalent Substances: Graphite
- each carbon atom forms three covalent bonds with three other carbon atoms
- forming layers of hexagonal rings which have no covalent bonds between the layers
- one electron from each carbon atom is delocalised
- Graphite is similar to metals in that it has delocalised electrons
31
Giant Covalent Substances: Graphene
Graphene is a single layer of graphite and has properties that make it useful in electronics and composites
32
Giant Covalent Substances: Nanotubes
- cylindrical fullerenes
- very high length to diameter ratios.
- Their properties make them useful for nanotechnology, electronics and materials
33
Structure and bonding: metallic bonding
Metals consist of giant structures of ions arranged in a regular pattern. The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure. The sharing of delocalised electrons gives rise to strong metallic bonds.
34
Properties of Metallic Substances
- Metals have giant structures of ions with strong metallic bonding. This means that most metals have high melting and boiling points
- In pure metals, ions are arranged in layers, which allows metals to be bent and shaped.
- Pure metals are too soft for many uses and so are mixed with other metals to make alloys which are harder. Alloys are harder than pure metals as the differing sized ions prevent the layers of ions from being able to slide over one another
- Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal. Metals are good conductors of thermal energy because energy is transferred by the delocalised electrons
35
Why do ionic compounds have high melting and boiling points?
Ionic compounds have giant structures in which the ions are held tightly together by the electrostatic attraction between oppositely charged ions. A lot of thermal energy is needed to overcome the strong ionic bonds. Therefore ionic compounds have high melting and boiling points
36
Why are ionic compounds brittle?
Ionic compounds are brittle as any small deformation of the lattice can result in like charges being arranged next to one another. This results in repulsion
37
Why don't ionic compounds conduct electricity when solid?
In solid ionic compounds, the ions are held firmly in place by the strong electrostatic force, so are unable to move and carry charge
38
Why do ionic compounds conduct electricity when dissolved in liquid or molten?
When ionic compounds are dissolved in water the ions are separated from one another by the water molecules/ they are freer to move when molten. The ions are then free to move and able to carry charge.
39
What is a covalent bond?
A covalent bond is the electrostatic force of attraction between the negatively charged pair of electrons and the positively charged nuclei of the adjacent atoms
40
How do giant ionic lattices form?
- electrons are transferred
- ions are formed
- electrostatic attraction between oppositely charged ions
- each ion attracts oppositely charged ions from all directions in a regular pattern
- each of these ions in turn attracts more ions
- a giant ionic structure made up of millions of ions in a lattice is built up
41
Why do simple molecular substances have low melting and boiling points?
The forces of attraction between the molecules (intermolecular forces) are very weak and require little energy to overcome.
42
Why don't simple covalent compounds conduct electricity?
Electrons are held tightly in the atoms or fixed within the covalent bonds and therefore cannot move between molecules, so there are no ions or delocalised electrons to carry charge.
43
General properties of giant covalent substances
- high melting points
- cannot conduct electricity
44
How many covalent bonds formed per carbon atom in graphite?
3
45
How many covalent bonds formed per carbon atom in diamond?
4
46
Properties of graphite
- very high melting point
- soft and slippery
- conducts heat and electricity
47
Properties of diamond
- very high melting point
- very hard
- does not conduct heat and electricity
48
Why do graphite and diamond have very high melting and boiling points?
There are lots of strong covalent bonds that have to be broken
49
Why is graphite soft and slippery?
Layers of atoms can slide over each other
50
Why is diamond very hard?
The atoms are bonded together in a rigid network and so cannot move
51
Why does graphite conduct heat and electricity?
There are some delocalised electrons which can carry charge
52
Why doesn't diamond conduct heat and electricity?
There are no delocalised electrons to carry charge
53
What are delocalised electrons?
Delocalised electrons are free moving or mobile electrons that are not bound to one particular atom. This means delocalised electrons can carry charge
54
What is a lattice?
A regularly arranged structure with repeating units
55
What is an allotrope?
Different physical forms of the same element
56
Definition of metallic bonding
The strong electrostatic force of attraction between the positive metal ions and the sea of delocalised electrons
57
Structure of fullerenes
Fullerenes are molecules of carbon atoms with hollow shapes. The structure of fullerenes is based on hexagonal rings of carbon atoms but they can also contain rings with five or seven carbon atoms
58
Structure of graphene
Graphene is a single layer of graphite and has properties that make it useful in electronics and composites
59
Properties of fullerenes
- can be used for the delivery of medicine
- low melting and boiling point
- good lubricant (soft and slippery)
- good catalyst
60
Why can fullerenes be used for the delivery of medicine?
Cage-like structures can hold pharmaceutical drugs
61
Why do fullerenes have a low melting and boiling point?
Requires breaking weak intermolecular forces between molecules
62
Why are fullerenes a good lubricant?
Spherical molecules can roll over each other and have weak intermolecular forces between molecules
63
Why are fullerenes a good catalyst?
Large surface area to volume ratio
64
Properties of graphene
- very thin and most reactive form of carbon
- very high melting and boiling point
- high tensile strength
- high electrical/thermal conductivity
65
Why is graphene the most reactive form of carbon?
Very thin (only one atom thick) and every carbon atom is available to react
66
Why does graphene have a very high melting and boiling point?
Requires breaking strong covalent bonds
67
Why does graphene have high tensile strength?
Very strong covalent bonds between the carbon atoms
68
Why does graphene have high electrical/thermal conductivity?
Very similar bonding to graphite, so contains delocalised electrons
69
How are ions arranged in metals?
There is a giant lattice of positively charged ions in a sea of delocalised electrons
70
Why are metals good conductors of electricity and heat?
The delocalised electrons can move through the giant metallic lattice and can transfer electrical charge (and thermal energy through the metal)
71
Why do metals have high melting and boiling points?
- There is strong electrostatic attraction between the delocalised electrons and positive metal ions
- a lot of energy is required to break the strong electrostatic forces of attraction in metallic bonding
72
Why are metals malleable/ductile?
- Metals are malleable and ductile because the layers of positive ions are able to slide over one another without breaking/cracking
- The delocalised electrons continue to flow throughout the structure and maintain attraction between the metal ions
73
Why are alloys harder than pure metals?
- The metal atoms in alloys are different sizes
- This distorts the layers of metal atoms, making it harder for them to move over one another
- more force is required to get the layers to move hence alloys are harder than pure metals
74
how many m is a centimetre?
1 x 10 to the -2
75
How many m in a millimetre (mm)?
1 x 10 to the -3
76
How many metres (m) in a micrometre (μm)
1 x 10 to the -6
77
How many metres (m) in a nanometre (nm)?
1 x 10 to the -9
78
How many metres in a picometre (pm)?
1 x 10 to the -12
79
What are cylindrical fullerenes/nanotubes?
Cylindrical fullerenes (also called nanotubes) are incredibly thin cylinders, whose length is much greater than their diameter
80
Properties of nanotubes
- high tensile strength (can withstand a lot of force while being pulled or stretched)
- excellent electrical and thermal conductors
81
What is meant by nanoscience?
The study of small particles between 1-100nm in size
82
How are nanoparticles used in clothing?
used as coating to:
- increase durability
- strengthen
- water proofing
- repel stains
83
How are nanoparticles used in medicines?
- drug delivery
- cancer radiation treatment
- nanotube sensors (helps monitor medical conditions)
- silver nanoparticles are anti-microbial
84
How are nanoparticles used in electronics?
- nanotubes and nanowires
- incredibly small electronic circuits
- much improved memory and speed for computers
- lightweight electronics
- touchscreens
85
How are nanoparticles used in cosmetics and sun creams?
- moisturising creams can be more readily absorbed by the skin
- sun cream containing zinc oxide/titanium oxide can block or absorb UV radiation preventing sun burn and damage
86
How are nanoparticles used in catalysts?
-nanoparticles have a very high surface area to volume ratio
- making them very reactive
- so can be used as catalyst
- much less needs to be used
- more sustainable
87
Why are nanoparticles so much more reactive than bulk materials?
- They have a very high surface area to volume ratio
- they can react more easily
88
How can nanoparticles be considered more environmentally friendly than bulk materials?
- less is used
- can be recycled
- less precious metals have to be mined
89
Risks associated with the use of nanoparticles
- could cause damage to the lungs/other diseases if they enter the blood stream
- pollution
- increased reactivity can make them very dangerous
90
Giant covalent substances: Glass
Most of the glass we use is soda-lime glass, made by heating a mixture of sand, sodium carbonate and limestone. Borosilicate glass, made from sand and boron trioxide, melts at higher temperatures than soda-lime glass.
91
Giant covalent substances: Polymers
The properties of polymers depend on what monomers they are made from and the conditions under which they are made. For example, low density and high density poly(ethene) are produced from ethene. Thermosoftening polymers melt when they are heated.
92
Giant covalent substances: Composites
Most composites are made of two materials, a matrix or binder surrounding and binding together fibres or fragments of the other material, which is called the reinforcement
93
How are clay ceramics made?
Clay ceramics, including pottery and bricks, are made by shaping wet clay and then heating in a furnace
94
What are some properties of glass?
- transparent
- hard
- brittle
95
What are the two types of glass?
- Soda-lime glass
- Borosilicate glass
96
Uses of soda-lime glass
drinking glasses, bottles, windows
97
Uses of borosilicate glass
laboratory equipment
98
What are the two components of most composite materials?
- the reinforcement
- the matrix, which binds the reinforcement together
99
What are fullerenes?
Molecules of carbon atoms with hollow shapes
100
What is the structure of fullerenes?
The structure of fullerenes is based on hexagonal rings of carbon atoms but they may also contain rings with five or seven carbon atoms
101
What was the first fullerene to be discovered?
Buckminsterfullerene (C60)
102
Shape of Buckminsterfullerene
spherical
103
Uses of fullerenes
- as a transport mechanism for drugs to specific sites in the body
- catalysts
- reinforcements for composite materials
