Topic 2- Bonding, structure and the properties of matter Flashcards
1
Q
What are bonds?
A
Bonds are the glue that holds atoms together.
2
Q
How do atoms react to form chemical bonds?
A
When atoms react to form CHEMICAL bonds, they either LOSE, GAIN, or SHARE electrons.
3
Q
How can you predict what will happen to an atoms electrons when it forms chemical bonds?
A
What happens to electrons will depend upon wether the atoms reacting are metals or non-metals.
4
Q
What are ions?
A
IONS are CHARGED particles-they can be SINGLE ATOMS e.g. Cl- or GROUPS OF ATOMS e.g. NO3-.
5
Q
How do atoms form ions?
A
Atoms lose or gain ELECTRONS to form ions.
6
Q
Why do atoms form ions?
A
Because atoms want to get a FULL OUTER SHELL like a NOBLE GAS which has a stable electronic structure.
Atoms with full outer shells are very STABLE.
7
Q
What charge do atoms have?
A
Atoms do not have an overall charge because the number of protons EQUALS the number of electrons.
8
Q
How do metals behave/ form ions?
A
When METALS form ions, they LOSE electrons from their OUTER SHELL to form POSITIVE IONS.
9
Q
How do non-metals behave/form ions?
A
When NON-METALS form ions, they GAIN electrons into their OUTER SHELL to form NEGATIVE IONS.
10
Q
How can you find the charge of an ion?
A
The NUMBER of electrons lost or gained is the same as the CHARGE on the ion.
E.g. if 2 electrons are LOST the charge is 2+. If 3 electrons are GAINED the charge is 3-.
11
Q
What groups are most likely to form ions?
A
The elements that most readily form ions are those in groups 1, 2, 6 and 7.
12
Q
How do groups 1 and 2 form ions?
A
Group 1 and 2 elements are METALS and they LOSE electrons to form POSITIVE IONS (CATIONS).
13
Q
How do groups 6 and 7 form ions?
A
Group 6 and 7 elements are NON-METALS. They GAIN electrons to form NEGATIVE IONS (ANIONS).
14
Q
What is the electronic structure of ions formed by group 1,2,6 and 7?
A
The electronic structure of ions formed by elements in groups 1, 2, 6 and 7 is the same as that of a NOBLE GAS.
15
Q
Tip- negatively charged ions have the end of their element name replaced with -IDE, e.g. oxide, sulphide, fluoride, bromide.
A
Example:
An oxygen atom has 6 electrons in it outer shell- its electronic structure is 2, 6. It gains two electrons to fill its outer shell O + 2e- ——> O2-
It now has a full outer shell, so is stable.
O atom ——-> oxide, O2- ion
16
Q
What are the three types of strong chemical bonds?
A
1) Ionic 2) Covalent 3) Metallic.
17
Q
What charge are the particles in ionic bonding?
A
For ionic bonding the particles are OPPOSITELY CHARGED IONS.
18
Q
What charge are the particles in covalent bonding?
A
For covalent bonding the particles are atoms which SHARE PAIRS of ELECTRONS.
19
Q
What charge are the particles in metallic bonding?
A
For metallic bonding the particles are atoms which SHARE DELOCALISED ELECTRONS.
20
Q
How do metals and non-metals form ionic bonds?
A
When a metal atom reacts with a non-metal atom electrons in the outer shell of the metal atom are transferred. METAL atoms LOSE electrons to become POSITIVELY CHARGED IONS. NON-METAL atoms GAIN electrons to become NEGATIVELY CHARGED IONS.
The ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have the electronic structure of a noble gas (Group 0).
21
Q
What forces hold ionic bonds together?
A
These oppositely charged ions are STRONGLY ATTRACTED to one another by ELECTROSTATIC FORCES. This attraction is known an IONIC BOND.
22
Q
What are positive ions and negative ions called?
A
POSITIVE ions are called CATIONS.
NEGATIVE ions are called ANIONS.
23
Q
How can the electron transfer during the formation of an ionic compound can be represented?
A
The electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram.
Tip- sometimes only the outer, incomplete electron shells are shown in dot and cross diagrams. This can make it clearer to see whats going on.
24
Q
What are the advantages and disadvantages of using dot and cross diagrams?
A
Dot and cross diagrams are useful for showing how ionic compounds are formed, but they DON’T show the STRUCTURE of the compound, the SIZE of the ions or how they’re ARRANGED.
25
What is the structure of ionic compounds?
Ionic compounds are formed between a NON-METAL and METAL.
Ionic compounds have regular structures (giant ionic lattices).
There are very strong ELECTROSTATIC FORCES of attraction between oppositely charged ions which act in all directions.
Tip-ionic compounds are made up of ions - positive and negatively charged particles. These positive and negative ions attract each other and group together in giant structures called lattices.
26
How can ionic compounds be represented?
1) Dot and cross diagrams
2) 3D models
3) Ball and stick models
27
What are the advantages and disadvantages of dot and cross diagrams?
They are useful for showing how ionic compounds are formed , but they don't show the structure of the compound, the relative sizes of the ions or how they're arranged.
28
What are the advantages and disadvantages of ball and stick models?
Like 3D models, ball and stick models show the regular pattern in an ionic lattice, as well as how all the ions are arranged. In addition, they suggest that the crystal extends beyond what is shown in the diagram.
They may show the relative sizes of the ions, but sometimes the ions are not shown to scale. Another disadvantage of them is that they suggest that there are gaps between the ions, when in reality there aren't.
29
How can you work out the formula of an ionic compound from a dot and cross diagram?
Count up how MANY atoms there are of EACH ELEMENT.
30
How can you work out the formula of an ionic compound from a 3D model or a ball and stick model?
This is slightly trickier. You need to use the diagram to work out what the ionic compound. You then have to balance the charges of the ions so that the overall charge on the compound is zero.
31
How can you work out the empirical formula of an ionic compound from a 3D model or a ball and stick model?
Tip- an empirical formula - the simplest whole number ratio of atoms in a compound. In reality you'd never get just one magnesium ion and two chloride ions stuck together. They form a giant lattice with twice as many chloride ions as magnesium ions.
This is slightly trickier. You need to use the diagram to work out what the ionic compound. You then have to balance the charges of the ions so that the overall charge on the compound is zero.
e.g. because a sodium ion has a 1+ charge and a chloride ion has a 1- charge only one of each ion is needed to balance out the charges.
(+1) + (-1) = 0
So the empirical formula for sodium chloride is NaCl.
32
Describe the melting and boiling point of ionic compounds?
Ionic compounds all have HIGH MELTING POINTS and HIGH BOILING POINTS due to the MANY STRONG BONDS between the ions.
It takes a large amount of energy to overcome this attraction and break the many strong bonds.
33
Describe the solubility of ionic compounds?
Most ionic compounds dissolve easily in water.
Tip- it might seem odd that ionic compounds require a lot of energy to melt, but dissolve so easily in water. This is because parts of water molecules are slightly charged and so can pull the ions away from the lattice.
34
What is an electric current?
An electric current is a flow of charged particles, which can either be ions or free electrons.
35
Describe the electrical conductivity of ionic compounds?
Ionic compounds don't conduct electricity when solid because the ions are all held in fixed positions. However, when they're melted or dissolved in water, the ions are are free to move and they'll carry electric current.
36
Why can ionic compounds conduct electricity when molten or dissolved?
This is because the electrostatic forces are broken and the charged ions are now free to move and carry current.
37
Exam tip- if you're asked to describe the electrical conductivity of a substance, make sure you consider its conductivity in different states, including what happens when the substance is in a solution.
Tip- before working out the formula of a compound, you need to find the charge on each of the ions in the compound using their group numbers.
38
What is the electron configuration of the ionic compound sodium chloride?
A single NaCl salt crystal does not consist of Na+ and Cl- ions continuing in the x, y and z direction.
Also, the idea that only one Na+ bonds to only one Cl- to form a freely mobile NaCl molecule is not true.
Each Na+ is bonded to 6 Cl- ions.
The GIANT IONIC LATTICE is extremely strong, giving NaCl a VERY HIGH MELTING POINT.
39
What types of atoms form covalent bonds?
A covalent bond is formed between two non-metal atoms.
40
How do non-metal and non-metal atoms form bonds?
A pair of electrons is SHARED between two atoms. They only share electrons in their outer shells and both involved in the bond end up with one extra electron in their outer shell.
41
Why do they form these bonds?
This is because non-metal atoms are short of electrons in their outer shells as they require electrons to obtain a FULL OUTER SHELL.
42
What type of bond is made?
When this happens a very STRONG covalent bond is made.
43
What force holds these covalent bonds and where are the forces in the non-metal atoms found?
The positively charged nuclei of the bonded atoms are attracted to the shared pairs of electrons by electrostatic forces, making covalent bonds very strong.
44
What type of structure can covalent bonds form?
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 DIAMONDl and SILICON DIOXIDE.
45
How can the bonds in covalent molecules and giant covalent structures be displayed?
You can use:
- Dot and cross diagrams
- Displayed formula
- 3D model and ball and stick models
46
What are the advantages and limitations of using dot and cross diagrams?
Dot and cross diagrams are useful for showing WHICH ATOMS the electrons in a covalent bond come from, but they DON'T show the relative sizes of the atoms, or how the atoms are ARRANGED in space.
Tip- when drawing these diagrams remember only the outer shell is drawn.
47
What are the advantages and limitations of using displayed formula?
This is a great way of showing how atoms are connected in LARGE molecules. However, they don't show the 3D STRUCTURE of the molecule, or WHICH ATOMS the electrons in the covalent bond have come from.
48
What are the advantages and limitations of using a 3D model or ball and stick models?
The 3D model shows the ATOMS, the COVALENT BONDS and their ARRANGEMENT in space next to each other.
But 3d models can quickly get CONFUSING for large molecules where there are lots of atoms to include. They don't show WHERE the electrons in the bonds have COME FROM, either.
49
Tip- If an atom shares one pair of electrons with one atom and another pair of electrons with another atom then there are two single bonds. You get DOUBLE BONDS when two atoms share two pairs of electrons with each other.
Tip- A molecular formula shows how many atoms of each element are in a molecule. E.g. H2O.
50
How are covalent bonds shown in displayed formulas?
How are double covalent bonds shown in displayed formulas?
By single lines.
By two lines e.g. O=O
51
What are simple molecular substances?
Simle molecular substances are made up of molecules containing only a FEW ATOMS joined together by COVALENT BONDS.
Hydrogen, chlorine, hydrogen chloride, methane, ammonia, water, nitrogen and oxygen are all examples of simple molecules, and you need to know the bonding in them all.
52
What is the bonding in hydrogen (H2)?
Hydrogen atoms have just one electron. They ONLY NEED ONE MORE to complete the first shell, so they often form SINGLE COVALENT BONDS, either with other hydrogen atoms or with other elements, to achieve this.
53
What is the bonding in chlorine (Cl2)?
Each chlorine atom needs just ONE MORE ELECTRON to complete the outer shell, so 2 chlorine atoms each can share one of their electrons to form a chlorine molecule containing one shared pair of electrons- a SINGLE COVALENT BOND.
54
What is the bonding in oxygen?
Each oxygen atom needs TWO MORE ELECTRONS to complete its outer shell, so in OXYGEN GAS two oxygen atoms share TWO PAIRS of electrons with each other making a DOUBLE COVALENT BOND.
55
What is the bonding in nitrogen (N2)?
A nitrogen atom has five electrons in its outer shell, so it needs three more to fill it. Two nitrogen atoms can each fill their shells by sharing electrons. This creates a TRIPLE BOND.
Tip- the triple bond is really strong that is why nitrogen gas is so un-reactive.
56
What is the bonding in methane (CH4)?
Carbon has FOUR OUTER ELECTRONS, which is HALF a full shell. Hydrogen atoms only need to form one covalent bond to achieve a full outer shell. So a carbon atom will form covalent bonds with FOUR hydrogen atoms to form CH4 molecule (methane).
57
What is the bonding in water (H2O)?
Oxygen atoms have six outer electrons. In WATER MOLECULES, the oxygen shares a pair of electrons with two H atoms to form two SINGLE COVALENT BONDS.
58
What is the bonding in hydrogen chloride (HCl)?
The bonding in HCl is very similar to the bonding in H2 and Cl2. Again, both atoms ONLY NEED ONE MORE OUTER ELECTRON to complete their outer shells.
59
Describe the electrical conductivity of simple molecules?
Covalent substances made up of simple molecules DON'T CONDUCT ELECTRICITY in any state as they AREN'T CHARGED. Also there are no ions or FREE electrons so there's nothing to carry an electrical charge.
60
Simple molecular substances have low boiling points, explain why...
Tip- due to their low boiling points most simple molecular substances are mostly gases or liquids at room temperature.
The reason for low boiling points is that, although the atoms within the small molecules form very strong covalent bonds with each other, the forces of attraction between the molecules (INTERMOLECULAR FORCES) are very weak. It's the intermolecular forces that must be overcome in order to melt or boil a simple molecular substance- not the much stronger covalent bonds. Overcoming these weak intermolecular forces doesn't take much energy, so the melting and boiling points are low.
61
What are the trends in melting and boiling points of intermolecular forces?
Exam Tip- if you're asked to compare or explain boiling or melting points of molecular compounds, make sure you look at the number of electron shells the atoms have. The more electron shells, the larger the atom and the greater the intermolecular forces.
As molecules get bigger, the strength of the intermolecular forces increases, so more energy is needed to break them, and the melting and boiling points increase.
62
What are 3 properties of simple molecular substances?
1) Substances containing COVALENT BONDS usually have SIMPLE MOLECULAR STRUCTURES.
2) The atoms within the molecules are held together by VERY STRONG COVALENT BONDS. By contrast, the forces of attraction BETWEEN these molecules are VERY WEAK.
3) As molecules get BIGGER, the strength of the intermolecular forces INCREASES, so MORE ENERGY is needed to break them, and the melting and boiling points INCREASE.
63
Why are these substances called simple molecular substances?
They are called simple because they are simple (only contain a few atoms) and form molecules, and so form SIMPLE MOLECULAR structures.
64
What type of bonding do all simple molecular substances contain?
They have strong strong covalent forces within the molecules (INTRA molecular forces) but weak forces between molecules (INTER molecular forces).
Tip- it is the weak INTERmolecular forces that are broken when the substance melts or boils.
65
What is a polymer?
A polymer consists of lots of SMALL UNITS which are linked together to form a LONG MOLECULE that has repeating sections.
66
How are the atoms in a polymer joined together?
All the atoms in a polymer are joined by strong COVALENT BONDS.
67
How are polymers formed?
Polymer molecules are formed when lots of small units link together.
68
How are polymers drawn?
A polymer can contain thousands or even millions of atoms, so it would be too difficult to draw in full.
Instead you can draw the shortest repeating section called the REPEATING UNIT, put it in large brackets and put an N after the brackets to show it's repeated many times.
69
How do you find the molecular formula of a repeating unit?
To find the MOLECULAR FORMULA of a polymer from its repeating unit, count the number of atoms of each element it contains, put it in BRACKETS and put an n after the brackets.
70
What state are polymers at room temperature and why is this?
The intermolecular forces between polymer molecules are LARGER than between simple covalent molecules, so MORE ENERGY is needed to break them.
This means most polymers are SOLID at room temperature.
71
Describe the melting and boiling points of polymers and compare them to ionic molecules, giant molecular compounds and simple covalent molecules.
Tip- it's only the intermolecular forces that need to be overcome in order to melt a polymer. The covalent bonds inside the molecules don't need to be broken.
Polymers have higher melting and boiling points than SIMPLE COVALENT MOLECULES. This is because the INTERMOLECULAR FORCES between the larger polymer molecules are stronger, so more energy is needed to break them.
However the intermolecular forces are still WEAKER than ionic or covalent bonds, so they generally have LOWER boiling points than IONIC or GIANT MOLECULAR compounds.
72
What are giant covalent structures?
How are they bonded?
Giant covalent structures are similar to giant ionic structures (lattices) but there are no charged ions.
Instead, all the atoms are bonded to each other by strong covalent bonds. So atoms that share electrons can also form giant covalent structures.
73
Give 3 examples of giant covalent structures...
Diamond and graphite (forms of carbon) and silicon (silica) are examples of giant covalent structures.
74
What are the melting and boiling points of giant covalent structures?
Substances that consist of giant covalent structures are SOLIDS with VERY HIGH melting and boiling points as lots of energy is needed to break the covalent bonds between the atoms.
75
Can giant covalent structures conduct electricity?
They DON'T contain charged particles, so they don't conduct electricity- not even when MOLTEN (except for a few weird exceptions such as graphite).
76
What other name is given to giant covalent structures?
Giant covalent structures are also known as macromolecules.
77
What are allotropes?
Allotropes are just different structural forms of the same element in the same physical state, e.g. they're all solids.
78
How many allotropes does carbon have and what are they called?
Carbon has four allotropes you need to know about- diamond, graphite, graphene and fullerenes.
79
What is the structure and bonding of diamond?
In diamond, EACH CARBON ATOM FORMS FOUR COVALENT BONDS with other carbon atoms. This forms a very rigid structure, which is why diamond is VERY HARD.
80
What are the melting point of diamond?
Those STRONG COVALENT BONDS take a lot of energy to break and give diamond a VERY HIGH MELTING POINT.
81
Can diamond conduct electricity?
Although carbon has negatively charged electrons in its outer shell, these are fixed in the covalent bonds so diamond has NO FREE ELECTRONS or ions so DOES NOT conduct electricity.
82
What is the structure of graphite?
In graphite, each carbon atom only forms THREE COVALENT BONDS, creating SHEETS of CARBON ATOMS arranged in hexagons and form HEXAGONAL RINGS.
There AREN'T any covalent bonds BETWEEN the layers- they're held together WEAKLY, so they're free to move over each other.
83
What are the properties of graphite in terms of its structure?
As there aren't any covalent bonds between the layers- they are only held together by weak INTERMOLECULAR FORCES (or van der waals), they're free to move over each other.
This makes graphite SOFT, and SLIPPERY so it is an ideal lubricating material.
84
What is the melting point of graphite?
Graphite's got a HIGH MELTING POINT- the covalent bonds in the layers need LOADS OF ENERGY to break .
85
Can graphite conduct electricity?
Tip- A substance needs charged particles (ions or electrons) which are free to move in order to conduct electricity.
Yes graphite can conduct electricity.
86
How can graphite conduct electricity?
Interestingly unlike other macromolecules graphite is able to conduct electricity as only three out of carbons four outer electrons are used in bonds, so each carbon atom has one electron that's delocalised (free) and can move This means that graphite conducts electricity and thermal energy.
87
What is graphene?
Graphene is a SHEET of carbon atoms joined together in hexagons. So it's basically a single layer of graphite.
The sheet is just 1 atom thick, making it a two- dimensional compound.
88
What are the properties of graphene in terms of its structure?
1) The network of covalent bonds makes it very STRONG.
2) It's also incredibly LIGHT, so can be added to COMPOSITE MATERIALS to improve their STRENGTH without adding much weight.
3) Like graphite, it contains DELOCALISED ELECTRONS so can CONDUCT ELECTRICITY through the WHOLE STRUCTURE. This means it has the potential to be used in ELECTRONICS.
89
What are fullerenes?
Fullerenes are molecules of CARBON, with HOLLOW SHAPES like closed tubes or hollow spheres.
90
What is the structure of fullerenes?
The structure is mainly made up of carbon atoms arranged in HEXAGONS, but can also contain PENTAGONS (rings of five carbon atoms) or HEPTAGONS (rings of seven carbon atoms).
91
What was the first fullerene to be discovered called?
The first fullerene to be discovered was Buckminsterfullerene (C60) which has a spherical shape.
92
What are the uses of fullerenes?
1) IN MEDICINE: Fullerenes can be used to 'CAGE' other molecules. The fullerene structure forms around another atom or molecule, which is then trapped inside. This could be used to DELIVER A DRUG. to where is is needed in a highly controlled way.
2) AS CATALYSTS: Fullerenes have a huge SURFACE AREA, so they could help make great industrial CATALYSTS- individual catalyst molecules could be attached to the fullerenes.
3) AS LUBRICANTS: Coating moving machine parts in fullerenes dramatically reduces friction. They could one day also be used to reduce friction in artificial joints.
93
What is a carbon nanotube?
Carbon nanotubes are CYLINDRICAL fullerenes with a very high length to diameter ratio.
94
What are the properties of nanotubes?
They have high TENSILE STRENGTH, high ELECTRICAL CONDUCTIVITY and high THERMAL CONDUCTIVITY.
95
What do the properties of nanotubes make them useful for?
Their properties make them useful for:
1) STRENGTHING MATERIALS: Nanotubes have a high tensile strength (they don't break when stretched) so can be used to strengthen materials without adding much weight, such as in tennis racket frames.
2) IN ELECTRONICS: Nanotubes can conduct electricity, and they're very small, so they can be used in very small electrical circuits, for example in the microchips found in computers and phones.
3) And nanotechnology.
96
What is the structure of metals?
Metals consist of a GIANT structure. The atoms in a metal are arranged in a regular pattern.
Metals are said to have giant structures because they have lots of atoms.
97
How are metals bonded?
What is this type of bonding called?
In metals, the electrons in the outer shell are said to be DELOCALISED. This means that they aren't associated with a particular atom or bond - they're FREE to move through the whole structure. There are strong forces of ELECTROSTATIC ATTRACTION between the POSITIVE METAL IONS and the NEGATIVE ELECTRONS and these forces known as METALLIC BONDING hold the metal structure together.
98
What substances are held together by metallic bonding?
Metallic ELEMENTS and ALLOYS.
99
What 1 thing produces all the properties of metals?
It's the DELOCALISED ELECTRONS in the metallic bonds which produce ALL the properties of metals.
100
Explain in terms of metallic structure and bonding why metals have high melting and boiling points?
The electrostatic forces between the metal atoms and the delocalised sea of electrons are very STRONG, so need LOTS OF ENERGY to be broken.
This means that most compounds with metallic bonds have very HIGH melting and boiling points, so they're generally SOILD at room temperature.
101
Metals are good conductors of heat. Explain why.
Metals have delocalised electrons that are free to move through the whole structure. Because of this, they are good conductors of thermal energy and electricity. The electrons carry the current or the thermal energy through the structure.
102
What is the malleability of metals?
Metals consist of atoms held together in a regular structure. The atoms form layers that are able to SLIDE over each other. This means they are MALLEABLE- they can be BENT and shaped, as well as HAMMERED or ROLLED into shapes.
103
What is the disadvantage of pure metals?
Pure metals often aren't quite right for certain jobs- they're often too soft when they're pure so are mixed with other metals to make them harder.
104
What are alloys?
Why are they useful?
Most of the metals we use everyday are alloys- a mixture of two or metals or a metal and another element.
Alloys are harder and so more useful than pure metals.
105
Why are alloys harder than pure metals?
Different elements have DIFFERENT SIZED ATOMS. So when another element is mixed with a pure metal, the new element atoms will DISTORT the layers of metal atoms, making it more difficult for them to slide over each other. This is why alloys are HARDER than pure metals.
106
What are the three states of matter?
The three states of matter are solid, liquid and gas.
Melting and freezing take place at the melting point, boiling and condensing take place at the boiling point.
107
How can the three states of matter be represented?
The three states of matter can be represented by small solid spheres. Particle theory can help to explain melting, boiling, freezing and condensing.
108
What does the state of a substance depend upon?
Materials come in THREE different forms- SOILD, LIQUID and GAS. These are the THREE STATES OF MATTER. Which STATE something is at a certain temperature (SOLID, LIQUID or GAS) depends on how STRONG the forces of attraction are between he particles of the material. How strong the forces are depends on THREE THINGS:
a) The MATERIAL (the structure of the substance and the type of bonds holding the particles together).
b) The TEMPERATURE
c) The PRESSURE
109
How much energy is needed to change the state of a substance?
The amount of energy needed to change state from solid to liquid to gas depends on the strength of the forces between the particles of the substance.
110
What is the structure and bonding of solids?
1) In solids, there are STRONG FORCES of attraction between particles, which holds them CLOSE TOGETHER in FIXED POSITIONS to form a very regular LATTICE ARRANGEMENT.
2) The particles DON'T MOVE from their positions, so all solids keep a DEFINITE SHAPE and VOLUME, and don't flow like liquids.
3) The particles VIBRATE about their positions- the HOTTER the solid becomes, the MORE they vibrate (causing solids to EXPAND slightly when heated).
111
What is the structure and bonding of liquids?
1) In liquids, there's a WEAK FORCE of attraction between the particles. They're randomly arranged and FREE to MOVE past each other, but they tend to STICK CLOSELY TOGETHER.
2) Liquids have a definite volume but DON'T keep a DEFINITE SHAPE, and will flow to fill the bottom of a container.
3) The particles are CONSTANTLY moving with RANDOM MOTION. The HOTTER the liquid gets, the FASTER they move. This causes liquids to EXPAND slightly when heated.
112
What is the structure and bonding of gases?
1) In gases, the force of attraction between the particles is VERY WEAK- they're FREE to MOVE and are FAR APART. The particles in gases travel in STRAIGHT LINES.
2) Gases DON'T keep a definite SHAPE or VOLUME and will always FILL any container.
3) The particles move CONSTANTLY with RANDOM MOTION. The HOTTER the gas gets, the FASTER they move. Gases either EXPAND when heated, or their PRESSURE INCREASES.
113
What do the symbols s, l, g, and aq stand for?
s-solid
l-liquid
g-gas
aq- aqueous (a solution in which water is the solvent)
114
What are the melting and boiling points of solids, liquids and gases?
If the forces between the solid particles are strong, then it will require a large amount of heat energy to melt the solid to a liquid; this solid would therefore have a high melting point.
Similarly, if the forces between the liquid particles are strong, then it will require a large amount of heat energy to boil/evaporate the liquid to a gas; this liquid would therefore have a high boiling point.
115
What does the strength of forces between particles depend upon?
Th strength of the forces between particles depends on the nature of the particle, and the type of bonding those particles are using to hold themselves together.
116
What is the melting point of ionic compounds?
Ionic compounds contain only STRONG IONIC BONDS, SO ALWAYS HAVE A HIGH MELTING POINT, e.g. NaCl.
117
What is the melting point of covalent substances?
(Giant) covalent substances containing only covalent bonds holding it together will also have a HIGH MELTING POINT, e.g. diamond (carbon).
However, some covalent substances also contain VERY WEAK ATTRACTIVE FORCES between the molecules, called VAN DER WAALS forces (intermolecular forces), and it is theses weak forces that break when the covalent substance melts, usually at relatively LOW TEMPERATURES.
118
What happens when a substance changes state?
Changes of state are physical changes- only the arrangement or the energy of the particles changes, not the particles themselves.
119
What happens to the structure of particles from solid to liquid-MELTING?
1) When a solid os HEATED, its particles gain more ENERGY.
2) This makes the particle vibrate MORE, which WEAKENS the FORCES that hold the solid together.
3) At a CERTAIN TEMPERATURE, called the MELTING POINT the particles have enough energy to BREAK FREE from their positions. This is called MELTING and the SOLID turns into a LIQUID.
120
What happens to the structure of particles from liquid to gas-BOILING?
1) When a liquid is heated, again the particles get even MORE energy.
2) This energy makes the particles move FASTER, which WEAKENS and BREAKS the bonds holding the liquid together.
3) At a CERTAIN TEMPERATURE, called the BOILING POINT, the particles have ENOUGH energy to BREAK their bonds. This is BOILING (or EVAPORATING). The LIQUID becomes a GAS.
121
What happens to the structure of particles from gas to liquid-CONDENSING?
1) As a gas COOLS, the particles no longer have ENOUGH ENERGY to overcome the forces of attraction between them.
2) BONDS FORM between the particles.
3) At the BOILING POINT, so many bonds have formed between the gas particles that the GAS becomes a LIQUID. This is called CONDENSING.
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What happens to the structure of particles from liquid to solid- FREEZING?
1) When a LIQUID COOLS, the particles have LESS ENERGY, so move around less.
2) There's not enough energy to overcome the attraction between the particles, so more BONDS form between them.
3) At the MELTING POINT, so many bonds have formed between the particles that they're HELD IN PLACE. The LIQUID becomes a SOLID. This is FREEZING.
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How can you predict the state of a substance?
You might be asked to predict WHAT STATE a substance is in at a CERTAIN TEMPERATURE. If the temperature's BELOW the MELTING POINT of substance, it'll be a SOLID. If it's ABOVE the BOILING POINT, it'll be a GAS. If it's IN BETWEEN the two points, then it's a LIQUID.
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What is nano-science?
What are the sizes of nanoparticles, fine particles, and coarse particles.
Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms. Nanoparticles, are smaller than fine particles (PM2.5), which have diameters between 100 and 2500 nm (1 x 10-7 m and 2.5 x 10-6 m). Coarse particles (PM10) have diameters between 1 x 10-5 m and 2.5 x 10-6 m. Coarse particles are often referred to as dust.
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How are particles of different substances organised?
What are tiny particles measured in?
Particles are put into categories depending on their diameter.
Tiny particles are often measured in nanometers (nm) or micrometers (μm).
1 nanometre (nm)= 0.000 000 001 m (or 1 x 10 -9 m in sf)
1 micrometre (μm)=0.000 001 (or 1 x 10-6 m in sf)
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What is nano-science?
Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms.
The study of nanoparticles is called nano science. The reason why nanoparticlesare worthy of having a branch of science devoted to them is that they may have different properties to the material in bulk. For example, the melting point of gold nanoparticles is much lower than the bulk material. Nanoparticles often make good catalysts as their high surface area to volume ratio means that more atoms of each particle is at the surface and so able to interact with the reactants compared to a catalyst made from bulk materials. This means you'll often need less of a material that's made up of nanoparticles to work as an effective catalyst compared to a material made up of 'normal' sized particles (containing billions of atoms rather than a few hundred).
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What are coarse particles?
Coarse particles (PM10) have diameters between 1 x 10-5 m and 2.5 x 10-6 m. Coarse particles are often referred to as dust.
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What are fine particles?
Fine particles (PM2.5), which have diameters between 100 and 2500 nm (1 x 10-7 m and 2.5 x 10-6 m).
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What are nano particles?
Nanoparticles, are smaller than fine particles (PM2.5), which have diameters between 100 and 2500 nm (1 x 10-7 m and 2.5 x 10-6 m).
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What are the properties of nano particles?
As the side of cube decreases by a factor of 10 the surface area to volume ratio increases by a factor of 10.
Nanoparticles may have properties different from those for the same materials in bulk because of their high surface area to volume ratio. It may also mean that smaller quantities are needed to be effective than for materials with normal particle sizes.
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Tip-Imagine splitting a cube up into mini-cubes, then splitting each mini-cube into mini-mini-cubes and so on. You end up with cubes that have a much larger combined surface area but the same volume as the original cube. So, each mini-mini-mini-cube has a high surface area to volume ratio.
That's why the surface area to volume ratio of nanoparticles is so much greater than the bulk material.
Tip- fine particles are air pollution problems. For example, carbon particulates can be inhaled and cause respiratory problems.
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What are the uses of nanoparticles?
*Tip-Know that the use of nanoparticles is an important area of research.
Nanoparticles have many applications in medicine, in electronics, in cosmetics and sun creams, as deodorants, and as catalysts. New applications for nanoparticulate materials are an important area of research.
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How are nanoparticles used as catalysts for fuel cells?
Platinum is typically used as the catalyst in fuel cells. It's really expensive, but because platinum nanoparticles have a huge surface area to volume ratio, only a tiny quantity of them are needed. Alternatively, other types of nanoparticles can be used instead of the expensive platinum.
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How are nanoparticles used in nanomedicine?
This is a hot topic. The idea is that tiny particles (such as fullerenes) are absorbed more easily by the body than most particles. This means that they could deliver drugs right into the cells where they're needed.
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How are nanoparticles used in electronics?
Some nanoparticles conduct electricity, so they can be used in electronics. For example, they can be used to make a really thin, light display screens for devices or really tiny memory chips that hold a vast amount of data.
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How are nanoparticles used in deodorants?
Silver nanoparticles are added to some deodorants as they have antibacterial properties.
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How are nanoparticles used in sun cream?
Titanium dioxide is a white solid used in house paint. But titanium dioxide nanoparticles are so small they cannot reflect visible light, and you cannot see them.
They are used in sun block creams because they can reflect the harmful UV rays without making your skin look white. Therefore some of the benefits of nanoparticles include better skin coverage and more effective protection from the sun's ultraviolet rays.
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How are nanoparticles used in cosmetics?
Nanoparticles are being used in cosmetics. For example, they're used to improve moisturisers without making them really oily, and to deliver active ingredients to lower layers of skin in anti-aging creams.
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Tip- Even if a substance has been used in its bulk form form many years and is regarded as safe, the nanoparticle form of the same material may have unexpected properties and may be able to get into places deep inside the body where the bulk material could not.
Tip- The hazards associated with new technologies need to be balanced against the benefits. However, people can sometimes misunderstand the actual level of risk, especially if the media publish biased or inaccurate reports.
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What are the disadvantages of using nanoparticles?
1) Although nanoparticles are useful, the way they affect the BODY isn't fully understood, so it's important that any new products are TESTED thoroughly to minimise the risks.
2) Some people are worried that PRODUCTS containing nanoparticles have been made available BEFORE the effects on HUMAN HEALTH have been investigated PROPERLY, and that we don't know the LONG-TERM impacts on heath will be.
3) As the long-term impacts aren't known, many people believe that products containing nanoscale particles should be CLEARLY LABELLED, so that consumers can choose wether or not to use them.
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What are the possible negative impacts of the use of nanoparticles in sun cream etc?
It's not yet clear wether the nanoparticles can get into your BODY, and, if they do, wether they might DAMAGE CELLS. There is a potential that breathing in small particles can damage lungs.
It's also possible that when they are WASHED AWAY they might DAMAGE the environment.
