structure and bonding Flashcards
1
Q
What are the three types of strong chemical bonds?
A
- ionic
- covalent
- metallic
2
Q
Describe ionic bonding
A
- the particles are oppositely charged ions
- occurs in compounds formed from metals combined with non-metals
3
Q
Describe covalent bonding
A
- particles are atoms which share pairs of electrons
- occurs in most non-metallic elements and in compounds of non-metals
4
Q
Describe metallic bonding
A
- the particles are atoms which share delocalised electrons
- occurs in metallic elements and alloys
5
Q
Define an ion
A
- an atom that has lost or gained electrons
6
Q
How are ionic bonds formed?
A
- when a metal atom reacts with a non-metal atom, electrons in the outer shell of the metal atom are transferred.
- the metal atoms lose electrons to become positively charged ions,
- while the non-metal atoms gain electrons to become negatively charged ions.
- the positive and negative metal and non-metal ion now experience an electrostatic force of attraction which forms the strong ionic bond
7
Q
What happens after ionic bonding?
A
- the ions produced by metals in group 1 and 2 and by non-metals in group 6 and 7 have the electronic structure of a noble gas (full outer shell)
8
Q
How can you represent electron transfer through ionic bonding?
A
- dot and cross diagram (either drawing the full electronic configuration or by just writing the element
- e.g. Na and displaying the dots and crosses of only the outer shell)
9
Q
What does the charge on the ions produced by metals and non-metals relate to?
A
- the group number of the element in the periodic table
- e.g. Na forms Na¹⁺, meaning it is in group 1
10
Q
What are ionic compounds?
A
- giant ionic lattices
- which have a regular closely-packed ion arrangement
11
Q
How are ionic compounds held together?
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 (since its 3D) and this is called ionic bonding
12
Q
What models can be used to represent ionic compounds?
A
- dot and cross diagrams,
- 3d models
- ball and stick models
13
Q
What are the pros of dot and cross diagrams for ionic compounds?
A
- they are useful for showing how ionic compounds are formed
14
Q
What are the cons of dot and cross diagrams for ionic compounds?
A
- they don’t show the structure of the compound
- they don’t show the relative sizes of the ions or how they are arranged
15
Q
What are the pros of 3D diagrams for ionic compounds?
A
- they show the relative sizes of ions and the regular pattern
16
Q
What are the cons of 3D diagrams for ionic compounds?
A
- they only let you see the outer layer of the compound
17
Q
What are the pros of ball and stick diagrams for ionic compounds?
A
- they show the regular pattern in an ionic lattice
- they show how the ions are arranged
- they show how the crystal extends beyond what is shown
- they show the relative sizes of the ions
18
Q
What are the cons of ball and stick diagrams for ionic compounds?
A
- they suggest that there are gaps between ions when, in reality, there aren’t
- they show the ions as solid spheres which they are not
19
Q
Why do ionic compounds have high melting and boiling points?
A
- due to the strong electrostatic forces of attraction between the oppositely-charged ions which act in all directions.
- these take a large amount of energy to overcome and break the many strong bonds
20
Q
When do ionic compounds conduct electricity?
A
- they don’t conduct electricity when solid,
- but do conduct electricity when molten or dissolved in aqueous solution
21
Q
Why do ionic compounds only conduct in certain conditions?
A
- when solid, the electrostatic forces of attraction hold the ions in fixed positions so they cannot move.
- when molten or dissolved in aqueous solution, ions are free to move and carry charge throughout the structure
22
Q
Name the 3 main properties of ionic compounds
A
- high melting and boiling points
- soluble in water
- conduct electricity when molten or dissolved in aqueous solution
23
Q
How are covalent bonds formed?
A
- when a pair of electrons is shared between two non-metal atoms.
- both atoms end up with one extra electron in their outer shell. * the positively charged nuclei of the atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong
24
Q
What can covalently bonded substances be?
A
- very large molecules e.g. polymers
- giant covalent structures e.g. diamond
- small molecules e.g. hydrogen
25
What is the difference between electrostatic forces and intermolecular forces of attraction?
* electrostatic forces of attraction are in ionic bonds and are between positive and negatively charged atoms
* intermolecular forces of attraction are in covalent bonds
26
What are small molecules?
* they’re made up of only a few atoms joined together by covalent bonds,
* are usually gases or liquids that have relatively low melting and boiling points
27
Why do small molecules have low melting and boiling points?
* they have very weak intermolecular forces of attraction between the molecules which require very little energy to overcome,
* hence they have low melting and boiling points; hence they are mostly gases or liquids at room temperature
28
Why do small molecules not conduct electricity in any state?
* because the molecules do not have an overall electric charge as * there are no ions and no delocalised electrons, so they cannot carry charge
29
What happens as the size of the small covalent molecule increases?
* the melting and boiling points also increase because as molecules get bigger,
* the intermolecular forces strengthen, so more energy is required to overcome them
30
You need to overcome the strong covalent bonds between atoms within small molecules to melt or boil it (T/F)
* FALSE, you have to overcome the intermolecular forces
31
Describe the properties of small molecules
* low melting and boiling points
* very weak intermolecular forces of attraction
* don’t conduct electricity
32
What is a giant covalent structure?
* consists of many atoms covalently bonded in a lattice structure
33
Name the difference in ions between giant covalent structures and giant ionic lattices
* giant covalent structures (otherwise known as macromolecules) are similar to giant ionic lattices but have no charged ions
34
Why do giant covalent structures have very high melting and boiling points?
* to melt or boil giant covalent structures, you need lots of energy to overcome all of the many strong covalent bonds between atoms.
* for this reason they are solid at room temperature
35
Name examples of giant covalent structures
* diamond, graphite, silicon dioxide
36
Name examples of small molecules
* hydrogen, chlorine, methane
37
What are the properties of giant covalent structures?
* no charged ions
* strong covalent bonds
* high boiling and melting points
38
How can you represent covalent bonds in different substances?
* dot and crosses
* shown as repeat units for poolers using single lie to represent a single bond
* ball and stick
* two and three-dimensional diagrams
39
What do metals consist of?
* giant structures of atoms arranged in a regular pattern
40
How are metallic bonds formed?
* the electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure and carry charge.
* the sharing of delocalised electrons gives rise to strong metallic bonds
41
Why do metals have high melting and boiling points?
* there are strong electrostatic forces of attraction between the negatively charged sea of delocalised electrons and the positive metal ions,
* which require lots of energy to overcome.
* this means that most metals are solid at room temperature
42
Why can metals conduct electricity?
* the sea of delocalised electrons are free to move and carry charge throughout the structure
43
What can particle theory help explain?
* melting, boiling, freezing and condensing
44
What does the state that a material is in depend on?
* the strength of the forces of attraction between particles of a material.
45
Describe the relationship between the forces between particles and the melting and boiling point
* the stronger the forces the higher the melting point and boiling point
46
What does the strength of the forces between particles depend on?
* the material
* the structure of the substance,
* the types of bonds holding the particle together
* the temperature
* the pressure
47
What are the limitations of the simple model for the states of matter?
* forces of attraction between particles are not shown
* all particles are represented as inelastic spheres
* it models particles as solids
48
Describe the particle theory of a solid
* very strong forces of attraction between particles
* which hold particles close together in fixed positions
* to form a very regular lattice arrangement
* the particles do not move from positions, so solids have a definite shape and volume
* they don’t flow - the particles vibrate on the spot and as temperature increases, particles vibrate faster
49
Describe the particle theory of a liquid
* there are relatively weak forces of attraction between particles,
* so particles are randomly arranged and are free to move around each other, but remain in contact with one another
* have a fixed volume but not a fixed shape and will take the shape of the container they are in * the hotter a liquid gets, the faster the particles move around each other
50
Describe the particle theory of a gas
* forces of attraction between particles are very weak,
* hence particles are free to move in a random, rapid motion
* particles travel at different speeds but in straight lines
* particles collide with each other and with the sides of the container
* gases do not have a fixed shape or a fixed volume and will always fill any container
* as temperature increases, the faster particles move and the more frequently (and with more energy) they hit the walls of the container, causing the gas pressure to increase or the volume to increase if the container is not sealed
51
What are polymers?
* they have very large molecules * in which the atoms are linked to other atoms by strong covalent bonds
52
What state are polymers at room temperature and why?
* they’re solids at room temperature
* because of the relatively strong intermolecular forces between polymer molecules which require a lot of energy to overcome
53
Describe the structure of pure metals and explain what properties this gives
* in pure metals, the atoms are arranged in layers which can easily slide over each other,
* allowing metals to be bent and shaped.
* this also makes metals soft and malleable
54
What is an alloy?
* a mixture of metals and other elements that are harder and more useful than pure metals
55
Why are alloys formed?
* because pure metals are too soft for many uses
56
How are alloys harder than pure metals?
* different elements have different sized atoms so, when another element is mixed with a pure metal, the regular layers are distorted,
* meaning that they cannot easily slide over each other
* hence alloys are harder than pure metals
57
What are metals good conductors of and why?
* they’re good conductors of electricity
* because the delocalised electrons in the metal are free to move and carry electrical charge through the structure
* they’re good conductors of thermal energy
* because energy is transferred by the delocalised electrons
58
Define an allotrope
* a different structural form of the same element in the same physical state of matter
59
What are the the main allotropes of carbon?
* diamond, graphite, graphene and fullerenes
60
Describe the structure of diamond
* giant covalent structure in which each carbon atom forms four covalent bonds with adjacent carbon atoms
* this forms a very rigid structure as the strong covalent bonds fix atoms in place,
* making diamond very hard
61
Describe the properties of metals
* good conductors of electricity and thermal energy
* soft and malleable
* arranged in layers which can easily slide over eachother
high melting and boiling points
62
Why does diamond have a very high melting point?
* giant covalent structure so it has many strong covalent bonds acting in all directions between the carbon atoms
* which requires a lot of energy to overcome
63
Why does diamond not conduct electricity?
* because each carbon atom bonds to 4 other carbon atoms,
* so all electrons are being used for bonding, meaning none are delocalised
64
Describe the properties of diamond
* each carbon atoms forms four covalent bonds
* very high melting point
* cannot conduct electricity
* giant covalent structure
* very hard due to rigid structure
65
Describe the structure of graphite
* each carbon atom forms three covalent bonds with three adjacent carbon atom,
* forming layers of hexagonal rings which have no covalent bonds between the layers.
* instead, the layers are held together by weak intermolecular forces
66
What can graphite conduct and why?
* it can conduct electricity because only 3 out of 4 outer electrons are used in bonding,
* so each carbon atom has one delocalised electron which is free to move and carry charge throughout the structure
* it can conduct thermal energy because the delocalised electron transfers energy
67
Why does graphite have a high melting point?
* because the covalent bonds within the layers require a lot of energy to overcome,
* despite graphite having weak intermolecular forces between the layers
68
Why is graphite soft and slippery?
* as there are only weak intermolecular forces between the layers,
* they can easily slide over each other, making graphite soft and slippery;
* it is ideal as a lubricating material
69
Describe the properties of graphite
* each carbon atom is covalently bonded to three other carbon atoms
* forms layers of hexagonal rings
no covalent bonds between the layers
* weak intermolecular forces between layers
* high melting point
* soft and slippery
* conductor of electricity and thermal energy
70
How is graphite similar to metals?
* they both have delocalised electrons
71
What is graphene?
* a single layer of graphite
* making it a 2D substance
72
Why is graphene strong?
* atoms within its layers are very tightly bonded due to the network of strong covalent bonds
73
Why can graphene conduct electricity?
* it contains delocalised electrons so can conduct electricity throughout the whole structure,
* making it useful in electronics
74
Why is graphene elastic?
* because the planes of atoms can flex relatively easily without the atoms breaking apart
75
Name a special feature of graphene
* it is incredibly light,
* so can be added to composite materials to improve strength without adding much weight
76
Describe the properties of graphene
* single layer of graphite
very strong network of covalent bonds
* incredibly light
* contains delocalised electrons
can conduct electricity
77
What are fullerenes?
* molecules of carbon atoms with hollow shapes that can either be tubes or spherical
78
Describe the structure of fullerenes
* based on hexagonal rings of carbon atoms,
* in which each carbon atom is bonded to 3 other carbon atoms
* so they can conduct electricity due to delocalised electron.
* they may also contain rings with five or seven carbon atoms.
79
What are buckminsterfullerenes?
* the first fullerene to be discovered
* spherical in shape, forming a hollow sphere containing 20 hexagons and 12 pentagons
* it has the molecular formula C₆₀
80
What are carbon nanotubes?
* small cylindrical fullerenes with very high length to diameter ratios.
* their properties make them useful for nanotechnology, electronics and materials;
* they’re good conductors of heat and electricity
81
What are some uses of fullerenes (nanoparticles)?
* in medicines for drug delivery
* as catalysts due to their large surface area
* as lubricants; there are no bonds between molecules so they are soft and reduce friction
* strengthening materials
in electronics
82
What is nanoscience?
* the reference to structures that are 1 to 100nm in size
83
What are nanoparticles smaller than?
* fine particles (diameter 100-2500nm)
* coarse particles (diameter 1x10^-5m and 2.5x10^-6m) aka dust
84
As the side of cube decreases by a factor of 10, what happens?
* the surface area to volume ratio increases by a factor of 10
85
Why may nanoparticles have properties different from those for the same materials?
* because of their high SA:V ratio, with a high percentage of their atoms exposed at their surface
86
What can nanoparticles result in?
* smaller quantities being needed to be effective than for materials with normal particle sizes
* e.g. catalysts for industrial processes
87
Why are new applications for nanoparticles important?
* they could improve many aspects of modern life
88
What are the pros of nanoparticles?
* they may catalyse reactions more efficiently (high SA:V ratio)
* they may catalyse different reactions
* nanocages of gold can be used to deliver drugs to where they need to go in the body
* e.g. carrying cancer-fighting drugs to the tumour
* they are used to reinforce materials
* e.g. sport -> making very strong but light tennis racquets
* can be used in sun-screens to block ultra-violet light
* can be used in face creams to deliver active ingredients deeper beneath surface of skin
* can conduct electricitty
* reduce friction
89
What are the uses of nanoparticles?
* in medicine to deliver drugs in the body
* in electronics
* in cosmetics
* as sun creams
* as deodorants
* as catalysts
* lubricants
* produce highly selective sensors
90
What are the cons of nanoparticles?
* nanoparticle sunscreens tend to clump together, making them difficult to apply
* it may be more difficult to tell where you have applied the sunscreen if you can’t see it on your skin
* toxic substances could bind to them because of their large SA:V ratios, harming health if the nanoparticles do get into the body
* breathing in the nanoparticles could damage the lungs
* nanoparticles could enter the bloodstream from their use in cosmetics, with unpredictable effects on our cells
* if a spark is made near a large quantity of the catalyst (nanoparticles), due to their large SA:V ratio, there could be a violent explosion
91
What are uses of silver nanoparticles?
* antibactericides in fridges
* sprays in operating theatres
* wound dressings
* on clothes
92
What are the pros of silver nanoparticles?
* they inhibit the growth of microorganisms
* they can clean operating theatres in hospitals
* they can be used as antimicrobial coatings
93
What are the cons of silver nanoparticles?
* these nanoparticles could enter the environment and affect aquatic life by accumulating in organisms over time
94
As the number of outer electrons increase, what else increases?
The greater the number of outer electrons that the metal has, the higher its melting/boiling point. This is due to the increased positive charge on the metal ion and the increased number of electrons that are delocalised, resulting in stronger bonding.
