Unit 2a - Bonding And Calculations Flashcards
1
Q
What does the mass number tell you?
A
Total number of protons and neutrons (bigger number)
2
Q
How to get the number of neutrons in an atom?
A
Subtract the atomic number from the mass number
3
Q
What are the masses of protons, neutrons and electrons?
A
1,1, very small
4
Q
How do compounds form?
A
When atoms of two or more elements are chemically combined together so it is difficult to separate the two original elements again
5
Q
What is carbon dioxide?
A
A compound formed from a chemical reaction between carbon and oxygen
6
Q
What is an isotope?
A
Different atomic forms of the same element, they have the same number of protons but a different number of neutrons. They have the same atomic number but different mass numbers
7
Q
What are a popular pair of isotopes and their particles?
A
Carbon 12 - 6 protons, 6 electrons, 6 neutrons
Carbon 14 - 6 protons, 6 electrons, 8 neutrons
8
Q
What happens in ionic bonding?
A
Atoms lose or gain electrons to form charged particles which are then strongly attracted to one and and other because of the attraction of opposite charges
9
Q
What is an ion?
A
Charged particles from ionic bonding
10
Q
Why are atoms with one or two electrons in their outer shell so keep to get rid of them?
A
Because they’ll only have full shells left, same as a noble gas
11
Q
Why do atoms from group 6 and group 7 gain electrons?
A
Because they have other shells which are nearly full so they want to gain an extra few electrons to fill it up and become an ion
12
Q
What is a classic case of ionic bonding?
A
Sodium chlorine.
The sodium atom fives up its outer electron to become s positively charged ion and the chlorine has picked up the ion to become negatively charged. The ions then bond together.
13
Q
What are the properties of ionic compounds structure?
A
- Giant ionic lattices
- ions form closely packed regular lattice arrangement
- very strong electrostatic forces of attraction between oppositely charged ions in all direction
14
Q
Explain sodium chloride (salt)?
A
One giant ionic lattice which is why salt crystals tend to be cuboid shape. The Na+ and Cl- ions are held together in a regular lattice
15
Q
What are the similar properties ionic compounds have?
A
- high melting and boiling points due to strong attraction between the ions as it takes a lot of energy to over come it
- when they melt the ions are free to move and carry electric current
- dissolve easily in water. Ions separate and are free to move so they carry electric current
16
Q
What does the atomic number tell you?
A
How many protons there are (the smaller number)
17
Q
Which groups are the ones which readily form ions?
A
1,2,6 and 7
18
Q
When do group 1 elements form ionic compounds with non metals?
A
When the metal ion has a 1+ charge e.g K+Cl-
19
Q
What are group 6 and 7 and what do they do?
A
Non metals that gain electrons to form negative ions
20
Q
What do the halogens (group 7) do?
A
Form ionic compounds with the alkali metals (group 1) where the halide ion has a 1+ charge e.g Na+Cl-
21
Q
What is the charge on the positive ions the same as?
A
The group number of the element e.g Be2+ is in group 2
22
Q
What does the + and - charges tell you?
A
What type of ion the atom will form in a chemical reaction. The atoms are neutral until they react with substances.
23
Q
How to work out the formula of an ionic compound?
A
- all the negative charges in a compound must balance all the positive ones
- use the charges on the individual ions to work out the formula
E.g magnesium chloride contains Mg2+ (+2) and Cl- (-1) ions.
Because Choride only has a 1- charge we will need two of them to balance out the magnesium 2+. So MgCl2
24
Q
What is the basics to how to draw an ionic compound?
A
Square brackets around each of the ions, the electron that is being transferred is different to the ones on the atom already, the + or - along with the number in the right hand corner.
25
How do you know if it's - or + charged?
- when electrons are gained because the ion is negatively charged and + when electrons are lost because the ion becomes positively charged
26
How you would draw the electronic structure of calcium chloride with diagrams
Both the Clorines with square brackets and - charged as they have both gained an electron from the calcium. The calcium in square brackets with 2+ charge in the corner because it has lost electrons.
27
What is covalent bonding?
Where atoms share electrons with each other so they've got a full outer shell
28
What does each covalent bond provide?
One extra shared electrons for each atom so each atom have to make enough covalent bonds to fill up its outer shell
29
How does hydrogen complete its shell? H2
Covalent bond of two of them because they only need one more to fill up their shell
30
How does chlorine fill up its shell? Cl2
It only needs one more electron to fill up its shell so only two are needed to form a single covalent bond
31
How does methane atoms reach a full outer shell? CH4
Carbon has four outer electrons so it needed to form four covalent bonds with four atoms of hydrogen
32
How does hydrogen chloride atoms form a completed outer shell? HCl
Both hydrogen and chlorine only need one more atom to complete their outer shells so one covalent bond
33
How does ammonia atoms complete their outer shells? NH3
Nitrogen has five outer electrons so it needs to form three covalent bonds with hydrogen to make up the extra three electrons needed
34
How do water atoms reach a full outer shell? H2O
Oxygen atoms have six outer electrons so it shares two electrons with two hydrogen atoms in two covalent bonds
35
How does oxygen reach a full outer shell?
In oxygen gas oxygen shares two electrons with another oxygen atom to get a full outer shell. This is known as a double covalent bond.
36
What are two other ways besides drawing the outer shells to show covalent bonds?
Cl-Cl
Or
Dot and cross diagrams showing electrons but no shell
37
What are the two possibilities of substances with covalent bonds being?
Simple molecules or giant structures
38
What are the five properties of a simple molecular substance?
1. Very strong covalent bonds to form small molecules of several atoms
2. Very weak forces of attraction between molecules
3. Melting point and boiling point are low be of this
4. Most are gases or liquids at room temp but can be solid
5. Don't conduct electricity
39
Why can't simple molecular substances conduct electricity?
There are no ions so there's no electrical charge
40
Why are the melting points and boiling points so low in simple molecular substances?
The molecules are easily parted from each other, it's the intermolecular forces that get broken when the substances melt or boil not the much stronger covalent bonds.
41
What are examples of simple molecular substances?
Chlorine, oxygen, water
| All the atoms travel around as molecules with pairs of atoms e.g Cl-Cl and 0=O and H-O-H
42
What are giant covalent structures called?
Macromolecules
43
What are the properties of giant covalent structures?
1. All atoms are bonded to each other by strong covalent bonds
2. Very high melting and boiling point
3. Don't conduct electricity even when molten (besides graphite)
4. No charged ions
44
What are the three main examples of giant covalent structures?
```
Diamond , graphite (both made only from carbon atoms).
Silicon dioxide (silica)
```
45
Structure and properties of diamond
Each carbon atom forms four covalent bonds in a very rigid giant covalent structure.
This makes diamond the hardest natural substance so it's good for drill tips and its sparkly too.
46
Structure of silicon dioxide
This is what sand is made of.
| Each grain of sand is one giant structure of silicon and oxygen.
47
Structure of graphite
Each carbon atom only forms three covalent bonds so this creates layers which are free to slide over each other.
48
What are the properties and uses of graphite?
1. It is soft and slippery.
2. The layers are help together loosely so they can be rubbed off onto paper - like a pencil.
3. Weak intermolecular forces allow that to happen.
4. Only non metal which is a good conductor of heat and electricity because each carbon has one delocalised electron which conducts them.
49
What are metals properties all due to?
The sea of free electrons
50
What is the structure to metallic bonding?
1. Free electrons which produce the properties of metals
2. Good conductors of heat and electricity
3. Electrons hold the atoms together in a regular structure as there are strong forces of electrostatic attraction between the positive metal ions and negative electrons.
4. Can be bent and shaped because the electrons allow the layers of atoms to slide over each other.
51
Why can metals conduct electricity?
Because the delocalised electrons are free to move through the whole structure so metals are good conductors of heat and electricity
52
What is an alloy?
When scientists mix two or more metals together to create a substance with properties they like because pure metals are often not right for s job
53
Why are alloys harder than pure metals?
Because different elements have different sized atoms. This means when two metals are mixed the layers with distort making it more difficult for them to slide over each other.
54
What are the two new materials that have been developed?
Smart materials and nanoparticles
55
What do smart materials do?
Behave differently depending on the conditions e.g temperature.
56
What is a good example of a smart material?
Nitinol - a "shape memory alloy"
57
How does nitinol work?
It's a metal alloy (nickel, titanium) that when its cool you can bend it and twist it like rubber but bend it too far and it stays bent.
It you heat it above a certain temperature it goes back to a remembered shape.
58
What is nitinol used for?
Glasses frames - if you bend them you can pop them in a bowl of hot water and they'll jump back into place
Dental braces - in the mouth it warms and tries to return to its remembered shape and gently pulls the teeth with it
59
What are nanoparticles?
Really tiny particles about 1-100 nanometres across.
60
What do nanoparticles contain?
Roughly a few hundred atoms.
| They have fullerenes.
61
What are fullerenes?
Molecules of carbon shaped like hollow balls or closed tubes. The carbon atoms are arranged in hexagonal rings and different fullerenes contain different numbers of carbon atoms.
62
What kind of properties do nanoparticles have compared to the bulk chemical that it's made from?
Very different e.g fullerenes have different properties from big lumps of carbon
63
Why are carbon nanotubes strong?
Fullerenes can be joined together to form nanotubes and all the covalent bonds make them very strong. Can be used to reinforce graphite in tennis rackets.
64
What are nanotubes?
Very tiny hollow carbon tubes, a few manometers across
65
What is using nanoparticles known as?
Nanoscience
66
What can nanoparticles be used for? (7)
- industrial catalysts
- sensors
- stronger, lighter building material
- new cosmetics
- nanomedicine
- new lubricant coatings
- electric circuits for computer chips
67
Why can nanoparticles be used in new industrial catalysts?
They have a huge surface area to volume ratio
68
Why can nanoparticles be used in sensors?
You can make the sensors detect one type of molecule and nothing else. The highly specific sensors are already used to test water purity.
69
Why can nanoparticles be used to make new cosmetics?
E.g suntan cream and deodorant because the small particles do the job but don't leave white marks on the skin
70
Why can nanoparticles be used in nanomedicine?
The tiny fullerenes are absorbed more easily by the body than most particles. This means they could deliver drugs right into the cells where they are needed.
71
Why can nanoparticles be used in lubricant coatings?
The coatings reduce friction a bit like ball bearings and could be used in all sorts of places like artificial joints to gears.
72
Why can nanoparticles be used in electric circuits for computer chips?
Nanotubes conduct electricity
73
What can silver nanoparticles do?
Kill bacteria
74
What determines the properties of plastics?
Forces between the molecules
75
What holds the atoms in polymers together in long chains?
Strong covalent bonds
76
What are the properties of weak forces in polymers?
Individual tangled chains of polymers are held together by weak intermolecular forces and are free to slide over each other
77
Explain thermosoftening polymers?
They don't have cross linking between chains.
The forces between the chains are easy to overcome so it's easy to melt the plastic.
When it cools the polymer hardens into a new shape.
You can melt and remould them as much as you like.
78
What are the properties of strong forces in polymers?
Strong intermolecular forces between the polymer chains called cross links that hold the chains firmly together.
79
Explain thermosetting polymers
They have cross links.
These hold the chains together in a solid structure.
The polymer doesn't soften when heated.
They are strong, hard and rigid.
80
What two things affects the properties of a polymer?
The starting material and reaction conditions
81
What conditions is low density polythene made in?
Heating ethene to about 200*c under high pressure. It's flexible and used for bags and bottles.
82
What condition is high density polythene made in?
Lower temperature and pressure with a catalyst. It's more rigid and is used for water tanks and drainpipes.
83
What is relative atomic mass usually the same as? (Ar)
The mass number of the element (the biggest number)
84
What is the relative atomic mass when an element has more than one stable isotope?
The average value of all the different isotopes
85
What is relative formula mass? (Mr)
All the relative atomic masses added together e.g MgCl2 would be 24 (Ar of Mg) + (35.5 x2) (Ar of Cl2) = 95.
86
What is the relative formula mass of a substance in grand known as?
One mole of that substance
87
How to work out number of moles
Mass in g (element or compound)
------------------------
Mr (of element or compound)
88
How to work out the percentage mass of an element in a compound
Ar x No. Of atoms (of that element)
--------------------------
Mr of the whole compound
X100
89
Find the percentage mass of sodium in sodium carbonate Na2Co3
PM = Ar x n
------ x 100
Mr
= 23 x 2
------- X 100 = 43.4%
106
90
5 steps to find the empirical formula from masses or percentages
1. List all the elements in the compound
2. Underneath them write their experimental masses or percentages
3. Divide each mass or percentage by the Ar for that element
4. Turn the numbers you get into a nice simple ratio by dividing or multiplying to get to nice numbers
5. Get the ratio in its simplest form that tells you the empirical formula of the compound
91
Find the empirical formula of the Iron oxide produced when 44.8g of iron react with 19.2g of oxygen. (Ar for iron = 56 and Ar for oxygen = 16)
```
Fe O
44.8 19.2
-----= 0.8 ----- =1.2
56 16
X both by 10
8 12
Divide both by 4
2 3
So 2 atoms of iron to 3 atoms of oxygen e.g Fe2O3
```
92
How to calculate masses in reactions
1. Write out the balanced equation
2. Work out Mr (just for the two bits you want)
3. Apply the rule - divide to get one then multiply to get all.(must do this to the substance the give information about first then apply it to the other one)
93
How to work out the mass of magnesium oxide that is produced when 60g of magnesium is burned in the air?
1. 2Mg + O2 --> 2MgO
2. (Don't do oxygen as we don't need it) 2x24= 28 and 2 x(24+16) = 80
3. 48g of Mg gives 80g of Mg0 so divide by 48g to give 1g of Mg then x 60 to give the mass produced of magnesium oxide when 60g of Mg is Burnt.
4. 80g divide by 48 = 1.67g of MgO x 60 = 100g of MgO.
94
What is the mass of product called?
Yield of a reaction
95
What does percentage yield tell you?
The overall success of an experiment
96
What is the predicted yield?
What you calculated the mass you should get
97
What is actual yield?
The mass you actually get
98
How to work out percentage yield?
Actual yield in grams
----------------------
Predicted yield in grams
X100
99
What does a 100% yield mean?
You got all the product you expected to get
100
What does a 0% yield mean?
That no reactants were converted into product
101
What can predicted yield (or theoretical yield) be calculated from?
The balanced reaction equation
102
What are 3 reasons yields are always less than 100%?
1. The reaction is reversible so the reactants will never completely be converted to products bc the reaction goes Both ways. Some of the products are always reacting together to change back to original reactants so a lower yield.
2. When you filter a liquid to remove solid particles you always lose a bit of liquid or a bit of solid. Some product is lost when it's separated.
3. Sometimes unexpected reactions can occur which use up the reactants so there's not as much reactants to make the product
103
What is a reversible reaction?
One where the products of the reaction can themselves react to product the original reactants
104
What is sustainable development?
Making sure that we don't use resources faster than they can be replaced - there needs to be enough for future generations too.
105
Why is product yield important for sustainable development?
Using as little energy as possible to create the highest product yield possible means the resources are saved and a low yield means wasted chemicals which isn't sustainable. Also keeps costs down.
106
How would you use chromatography to separatist artificial colours?
1. Extract the colour from a food sample by placing it in a small cup with a few drops of solvent (water,ethanol etc)
2. Put spots of the coloured solution on a pencil baseline on filter paper
3. Roll up the sheet and put it in a beaker with some solvent but keep base line above the solvent
4. Solvent seeps up the paper taking the dyes with it. Different dye spots form at different places.
107
Why might a chromatography not be the most accurate way of separating colours?
Because 5 dyes could be present but two of them making spots in the same places. So four dots means at least four but not exactly four.
It can't be three dyes though because one dye can't split in two.
108
What does instrumental methods mean?
Using machines
109
What are three advantages to machines analysing unknown substances?
- very sensitive so can detect even the tiniest amount of substance
- fast and tests can be automated
- very accurate
110
What can gas chromatography be used for?
Superstations out a mixture of compounds to help you identify the substances present
111
In gas chromatography what is the gas used to?
Carry substances through a column packed with a sold material
112
In gas chromatography how are substances separated?
They travel through the tube at different speeds
113
In gas chromatography what is the time takes to reach the detector called?
Retention time, it can be used to help identify the substances
114
In gas chromatography what does the recorder do?
Draws a gas chromatograph. The number of peaks shows the number of different compounds in the sample.
115
In gas chromatography what does the position of peaks in a gas chromagraph show?
The retention time of each substance
116
In gas chromatography what can the column also be linked to?
A mass spectrometer. This is know As GC-MS and can identity the substances leaving the column very accurately.
117
In gas chromatography what can you work out from the gas chromatograph and how?
The relative molecular mass by reading off the molecular ion peak
