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Chemistry > Unit 2a - Bonding And Calculations > Flashcards

Unit 2a - Bonding And Calculations Flashcards

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1
Q

What does the mass number tell you?

A

Total number of protons and neutrons (bigger number)

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2
Q

How to get the number of neutrons in an atom?

A

Subtract the atomic number from the mass number

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3
Q

What are the masses of protons, neutrons and electrons?

A

1,1, very small

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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

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5
Q

What is carbon dioxide?

A

A compound formed from a chemical reaction between carbon and oxygen

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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

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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

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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

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9
Q

What is an ion?

A

Charged particles from ionic bonding

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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

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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

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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.

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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
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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

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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
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16
Q

What does the atomic number tell you?

A

How many protons there are (the smaller number)

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17
Q

Which groups are the ones which readily form ions?

A

1,2,6 and 7

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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-

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19
Q

What are group 6 and 7 and what do they do?

A

Non metals that gain electrons to form negative ions

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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-

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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

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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.

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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
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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.

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25
Q

How do you know if it’s - or + charged?

A
  • when electrons are gained because the ion is negatively charged and + when electrons are lost because the ion becomes positively charged
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26
Q

How you would draw the electronic structure of calcium chloride with diagrams

A

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.

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27
Q

What is covalent bonding?

A

Where atoms share electrons with each other so they’ve got a full outer shell

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28
Q

What does each covalent bond provide?

A

One extra shared electrons for each atom so each atom have to make enough covalent bonds to fill up its outer shell

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29
Q

How does hydrogen complete its shell? H2

A

Covalent bond of two of them because they only need one more to fill up their shell

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30
Q

How does chlorine fill up its shell? Cl2

A

It only needs one more electron to fill up its shell so only two are needed to form a single covalent bond

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31
Q

How does methane atoms reach a full outer shell? CH4

A

Carbon has four outer electrons so it needed to form four covalent bonds with four atoms of hydrogen

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32
Q

How does hydrogen chloride atoms form a completed outer shell? HCl

A

Both hydrogen and chlorine only need one more atom to complete their outer shells so one covalent bond

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33
Q

How does ammonia atoms complete their outer shells? NH3

A

Nitrogen has five outer electrons so it needs to form three covalent bonds with hydrogen to make up the extra three electrons needed

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34
Q

How do water atoms reach a full outer shell? H2O

A

Oxygen atoms have six outer electrons so it shares two electrons with two hydrogen atoms in two covalent bonds

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35
Q

How does oxygen reach a full outer shell?

A

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.

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36
Q

What are two other ways besides drawing the outer shells to show covalent bonds?

A

Cl-Cl
Or
Dot and cross diagrams showing electrons but no shell

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37
Q

What are the two possibilities of substances with covalent bonds being?

A

Simple molecules or giant structures

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38
Q

What are the five properties of a simple molecular substance?

A
  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
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39
Q

Why can’t simple molecular substances conduct electricity?

A

There are no ions so there’s no electrical charge

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40
Q

Why are the melting points and boiling points so low in simple molecular substances?

A

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.

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41
Q

What are examples of simple molecular substances?

A

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

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42
Q

What are giant covalent structures called?

A

Macromolecules

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43
Q

What are the properties of giant covalent structures?

A
  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
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44
Q

What are the three main examples of giant covalent structures?

A 
Diamond , graphite (both made only from carbon atoms).
Silicon dioxide (silica)
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45
Q

Structure and properties of diamond

A

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.

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46
Q

Structure of silicon dioxide

A

This is what sand is made of.

Each grain of sand is one giant structure of silicon and oxygen.

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47
Q

Structure of graphite

A

Each carbon atom only forms three covalent bonds so this creates layers which are free to slide over each other.

48
Q

What are the properties and uses of graphite?

A
  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
Q

What are metals properties all due to?

A

The sea of free electrons

50
Q

What is the structure to metallic bonding?

A
  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
Q

Why can metals conduct electricity?

A

Because the delocalised electrons are free to move through the whole structure so metals are good conductors of heat and electricity

52
Q

What is an alloy?

A

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
Q

Why are alloys harder than pure metals?

A

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
Q

What are the two new materials that have been developed?

A

Smart materials and nanoparticles

55
Q

What do smart materials do?

A

Behave differently depending on the conditions e.g temperature.

56
Q

What is a good example of a smart material?

A

Nitinol - a “shape memory alloy”

57
Q

How does nitinol work?

A

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
Q

What is nitinol used for?

A

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
Q

What are nanoparticles?

A

Really tiny particles about 1-100 nanometres across.

60
Q

What do nanoparticles contain?

A

Roughly a few hundred atoms.

They have fullerenes.

61
Q

What are fullerenes?

A

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
Q

What kind of properties do nanoparticles have compared to the bulk chemical that it’s made from?

A

Very different e.g fullerenes have different properties from big lumps of carbon

63
Q

Why are carbon nanotubes strong?

A

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
Q

What are nanotubes?

A

Very tiny hollow carbon tubes, a few manometers across

65
Q

What is using nanoparticles known as?

A

Nanoscience

66
Q

What can nanoparticles be used for? (7)

A
  • industrial catalysts
  • sensors
  • stronger, lighter building material
  • new cosmetics
  • nanomedicine
  • new lubricant coatings
  • electric circuits for computer chips
67
Q

Why can nanoparticles be used in new industrial catalysts?

A

They have a huge surface area to volume ratio

68
Q

Why can nanoparticles be used in sensors?

A

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
Q

Why can nanoparticles be used to make new cosmetics?

A

E.g suntan cream and deodorant because the small particles do the job but don’t leave white marks on the skin

70
Q

Why can nanoparticles be used in nanomedicine?

A

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
Q

Why can nanoparticles be used in lubricant coatings?

A

The coatings reduce friction a bit like ball bearings and could be used in all sorts of places like artificial joints to gears.

72
Q

Why can nanoparticles be used in electric circuits for computer chips?

A

Nanotubes conduct electricity

73
Q

What can silver nanoparticles do?

A

Kill bacteria

74
Q

What determines the properties of plastics?

A

Forces between the molecules

75
Q

What holds the atoms in polymers together in long chains?

A

Strong covalent bonds

76
Q

What are the properties of weak forces in polymers?

A

Individual tangled chains of polymers are held together by weak intermolecular forces and are free to slide over each other

77
Q

Explain thermosoftening polymers?

A

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
Q

What are the properties of strong forces in polymers?

A

Strong intermolecular forces between the polymer chains called cross links that hold the chains firmly together.

79
Q

Explain thermosetting polymers

A

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
Q

What two things affects the properties of a polymer?

A

The starting material and reaction conditions

81
Q

What conditions is low density polythene made in?

A

Heating ethene to about 200*c under high pressure. It’s flexible and used for bags and bottles.

82
Q

What condition is high density polythene made in?

A

Lower temperature and pressure with a catalyst. It’s more rigid and is used for water tanks and drainpipes.

83
Q

What is relative atomic mass usually the same as? (Ar)

A

The mass number of the element (the biggest number)

84
Q

What is the relative atomic mass when an element has more than one stable isotope?

A

The average value of all the different isotopes

85
Q

What is relative formula mass? (Mr)

A

All the relative atomic masses added together e.g MgCl2 would be 24 (Ar of Mg) + (35.5 x2) (Ar of Cl2) = 95.

86
Q

What is the relative formula mass of a substance in grand known as?

A

One mole of that substance

87
Q

How to work out number of moles

A

Mr (of element or compound)

88
Q

How to work out the percentage mass of an element in a compound

A

Mr of the whole compound

X100

89
Q

Find the percentage mass of sodium in sodium carbonate Na2Co3

A

PM = Ar x n
—— x 100
Mr

= 23 x 2
——- X 100 = 43.4%
106

90
Q

5 steps to find the empirical formula from masses or percentages

A
  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
Q

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)

A 
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
Q

How to calculate masses in reactions

A
  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
Q

How to work out the mass of magnesium oxide that is produced when 60g of magnesium is burned in the air?

A
  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
Q

What is the mass of product called?

A

Yield of a reaction

95
Q

What does percentage yield tell you?

A

The overall success of an experiment

96
Q

What is the predicted yield?

A

What you calculated the mass you should get

97
Q

What is actual yield?

A

The mass you actually get

98
Q

How to work out percentage yield?

A

Predicted yield in grams

X100

99
Q

What does a 100% yield mean?

A

You got all the product you expected to get

100
Q

What does a 0% yield mean?

A

That no reactants were converted into product

101
Q

What can predicted yield (or theoretical yield) be calculated from?

A

The balanced reaction equation

102
Q

What are 3 reasons yields are always less than 100%?

A
  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
Q

What is a reversible reaction?

A

One where the products of the reaction can themselves react to product the original reactants

104
Q

What is sustainable development?

A

Making sure that we don’t use resources faster than they can be replaced - there needs to be enough for future generations too.

105
Q

Why is product yield important for sustainable development?

A

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
Q

How would you use chromatography to separatist artificial colours?

A
  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
Q

Why might a chromatography not be the most accurate way of separating colours?

A

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
Q

What does instrumental methods mean?

A

Using machines

109
Q

What are three advantages to machines analysing unknown substances?

A
  • very sensitive so can detect even the tiniest amount of substance
  • fast and tests can be automated
  • very accurate
110
Q

What can gas chromatography be used for?

A

Superstations out a mixture of compounds to help you identify the substances present

111
Q

In gas chromatography what is the gas used to?

A

Carry substances through a column packed with a sold material

112
Q

In gas chromatography how are substances separated?

A

They travel through the tube at different speeds

113
Q

In gas chromatography what is the time takes to reach the detector called?

A

Retention time, it can be used to help identify the substances

114
Q

In gas chromatography what does the recorder do?

A

Draws a gas chromatograph. The number of peaks shows the number of different compounds in the sample.

115
Q

In gas chromatography what does the position of peaks in a gas chromagraph show?

A

The retention time of each substance

116
Q

In gas chromatography what can the column also be linked to?

A

A mass spectrometer. This is know As GC-MS and can identity the substances leaving the column very accurately.

117
Q

In gas chromatography what can you work out from the gas chromatograph and how?

A

The relative molecular mass by reading off the molecular ion peak

Chemistry (6 decks)

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