Chemistry Term 1 Flashcards
(130 cards)
1
Q
What are the three ideas in John Dalton’s theory about the atom?
A
- Atoms cannot be created, divided or destroyed.
- Atoms of the same element are exactly the same and atoms of different elements are different.
- Atoms join with other atoms to make new substances.
2
Q
What discovery caused the original Dalton model of an atom to change?
A
The discovery of subatomic particles.
3
Q
How did J J Thomson discover the electron?
A
Thomson experimented with a cathode ray tube.
The beam moved towards the positively charged plate so he knew that the particles must have a negative charge.
4
Q
Describe the atomic model proposed by J J Thomson.
A
Plum Pudding Model.
Negatively charged electrons scattered through a positively charged material.
5
Q
What di Ernest Rutherford discover from his gold foil experiment?
A
- Most of the particles passed straight through suggesting that atoms were mostly empty space.
- A few particles were deflected and a few bounced directly back showing that there must be a tiny, dense and positively-charged nucleus.
6
Q
Describe Rutherford’s new model of the atom.
A
- Mass is concentrated in the central nucleus.
- Mostly empty space.
- Electrons travel in random paths around the nucleus.
7
Q
Describe the structure of an atom.
A
- Small central nucleus made up of protons and neutrons.
- Electrons orbit (move around) the nucleus in shells.
8
Q
What is the radius of the nucleus? How large is it compared to the radius atom?
A
The radius of the nucleus is 1x10-14 m.
This is 1/10000 of the atomic radius.
9
Q
What is the relative masses of protons, neutrons and electrons?
A
Protons: 1
Neutrons: 1
Electrons: 1/1836
10
Q
What are the relative charges of protons, neutrons and electrons?
A
Protons: +1
Neutrons: 0
Electrons: -1
11
Q
Why do atoms contain equal numbers of protons and electrons?
A
Atoms are stable with no overall charge.
Protons are positively charged and electrons are negatively charged. For the charges of balance, the number of protons and electrons must be equal.
12
Q
Where is the mass of an atom concentrated?
A
In the nucleus.
13
Q
What does the atomic number of an atom represent?
A
The number of protons.
14
Q
What does the mass number of an atom mean?
A
The mass number is the number of protons and neutrons found in the nucleus of an atom.
15
Q
What is an isotope?
A
Isotopes are atoms with the same number of protons (so they are the same element) but a different number of neutrons.
Isotopes of an element have the same atomic number but different mass number.
16
Q
Why is the relative atomic mass not always a whole number?
A
Different isotopes of the same element have different mass numbers. The relative atomic mass is an average of the masses of all these isotopes.
17
Q
What two values would be required to calculate the relative atomic mass of chlorine?
A
Mass numbers and relative abundances of all the isotopes of chlorine.
18
Q
How did Mendeleev arrange the elements in his periodic table?
A
Elements arranged with increasing atomic masses.
Elements with similar properties put into groups (due to periodic trends in chemical properties).
Switched the position of some elements.
Gaps left for undiscovered elements.
19
Q
How was Mendeleev able to predict the properties of new elements?
A
Mendeleev left gaps in his periodic table. He used the properties of elements next to these gaps to predict the properties of undissolved elements.
20
Q
Mendeleev’s table lacked some amount of accuracy in the way he’d ordered his elements. Why was this?
A
Isotopes were poorly understood at the time.
Protons and neutrons had no yet been undiscovered.
21
Q
How are elements arranged in the modern periodic table?
A
In order of increasing atomic number.
22
Q
Why do elements in the same column have similar chemical properties?
A
Same number of outer shell electrons.
Number of outer shell electrons determined how an atom reacts.
23
Q
What does the period (row) number tell you about all the elements in that period?
A
Elements in the same period have the same number of electron shells.
e.g. all elements in period 4 have 4 electron shells.
24
Q
What does group (column) number tell you about all the elements in that group?
A
All elements in the same group have the same number of outer electrons.
e.g. all elements in group 2 have 2 electrons in their outer shell.
25
On which side of the periodic table are the metals positioned?
Left hand side.
26
What determines whether an element is a metal or non-metal?
Atomic structure of the elements.
27
What is the maximum number of electrons allowed in each of the first 3 shells?
1st shells : 2
2nd shell : 8
3rd shell : 8
28
When are atoms most stable?
When they have full electron shells.
29
How is the electron configuration of an element
related to its position in the periodic table?
Diagram:
The number of rings is the period.
The number of electrons in the outer ring is the group.
The total number of electrons is the atomic number.
Number (e.g. sodium, 2.8.1):
Sodium has 3 shells as there are 3 numbers.
The last number is the number of outer shell electrons / the group.
The sum of the digits is the atomic number.
30
What is an ionic bond?
A bond between a metal and non-metal involving the transfer of electrons.
31
In terms of electrons, describe what happens to the metal and non-metal when an ionic bond forms.
The metal atom loses electrons to become a positively charged ion (cation).
The non-metal gains electrons to become a negatively charged ion (anion).
32
What is an ion?
An ion is an atom or group of atoms with a positive or negative charge.
33
If an ion is positively charged, has it lost or gained electrons?
It has lost electrons. There are fewer negatively charged electrons to cancel out the charge of the positive protons. This means the overall charge becomes positive.
34
What does it mean if an ionic compound ends in
-ide?
The compound contains 2 elements.
35
What does it mean if an ionic compound
ends in -ate?
The compound contains at least three
elements, one of which is oxygen.
36
Describe the structure of an ionic compound.
Lattice structure.
Regular arrangement of ions.
Ions held together by strong electrostatic
forces between ions with opposite charges.
37
What is a covalent bond?
A bond formed when an electron pair is shared between two atoms.
38
What forms as a result of covalent bonding?
A molecule
39
Which is smaller, an atom or a molecule?
An atom.
Simple molecules consist of atoms
joined by strong covalent bonds within
the molecule.
40
Why do ionic compounds have high melting points?
Strong electrostatic attraction between
the positive and negative ions requires a
lot of energy to overcome.
41
When do ionic compounds electricity? Why?
When molten or aqueous (dissolved in
water) because the ions are charged and
free to move. When solid, the ions are fixed
in an ionic lattice so can’t move.
42
Why do simple molecular compounds have low
melting and boiling points?
They have weak intermolecular forces
(forces between molecules) which only
require a little energy to overcome.
43
Do simple molecular compounds conduct electricity?
Why / why not?
No because there are no charged
particles.
44
Do giant covalent structures have a high melting
point? Explain your answer.
Yes because they have lots of strong
covalent bonds which require a lot of
energy to break.
45
How do metals conduct electricity and heat?
The positive ions are fixed in a sea of
delocalised electrons. These electrons
are free to move and carry charge / energy.
46
What is a fullerene?
A fullerene is a molecule made of carbon, shaped like a closed tube or
hollow ball.
47
What are the properties of metals?
- High melting point.
- High density.
- Good conductors of electricity.
- Malleable and ductile.
- Generally shiny.
48
Explain why metals are malleable.
The atoms are arranged in uniform rows which can slide over one another.
49
Explain why metals can conduct electricity.
The electrons in the metal are charges that can move.
50
What are the general properties of non-metals?
- Low boiling points.
- Poor conductors of electricity.
- Brittle when solid.
51
List the limitations of the following models when
representing ionic compounds: dot and cross, 2D diagrams and 3D diagrams.
● Dot and cross - no lattice structure or ionic bonds.
● 2D diagrams - only shows one layer, doesn’t show
formation of ions.
● 3D diagrams - shows spaces between the ions,
doesn’t show charges.
52
List the limitations of the following models when
representing covalent molecules: dot and cross and ball and stick.
● Dot and cross - doesn’t show relative sizes of
atoms or intermolecular forces.
● Ball and stick - bonds shown as sticks rather
than forces, doesn’t show how covalent bonds
form.
53
How do you calculate the relative formula mass of a compound?
Add together all the relative atomic
masses of the atoms in the compound.
54
What is the empirical formula? What 2 values could be used to calculate the empirical formula of a
simple compound?
● The empirical formula is the smallest whole
number ratio of the atoms of each element in a
compound.
● Reacting masses or percentage composition
can be used to calculate the empirical formula.
55
What is a molecule formula?
Actual number of atoms of each element in a compound.
56
Describe an experiment to work out the empirical
formula of magnesium oxide.
● Weigh a sample of magnesium.
● Heat the sample in a crucible.
● Weigh the mass of magnesium oxide at the end.
● Calculate the mass of oxygen (this is the increase of mass).
● Calculate the moles of magnesium and oxygen using the
experimental mass and relative atomic mass.
● Work out the whole number ratio of the number of moles of
magnesium to oxygen.
57
What is the law of conservation of mass?
No matter is lost or gained during a chemical reaction.
58
If a reaction is carried out in a closed system, what
can you say about the total mass of the reaction
throughout the experiment?
Mass stays constant.
59
If a reaction is carried out in an open flask and a gas
is produced, what can you say about the total mass
of the reaction throughout the experiment?
Mass decreases as the gas escapes.
60
What equation links mass, moles and relative atomic
mass?
Mass (g) = Moles x Relative atomic mass (Mr)
61
What is the Avogadro constant?
The number of atoms, molecules or ions in
one mole of a given substance.
The value of the constant is 6.02 x 1023.
62
What formula links the Avogadro constant, moles and number of particles?
Number of particles = Avogadro constant x Moles
63
What is a limiting reagent in a chemical reaction?
The chemical that is used up first in a reaction,
preventing the formation of more product.
Typically, an excess of one of reactants is used
to ensure that the other reactant is completely
used up.
64
Describe the arrangement and movement of particles in solids.
Tightly packed together in a regular arrangement.
Vibrate in fixed positions.
65
Describe the arrangement and movement of particles in liquids.
Close together but able to move past each other.
Vibrate and move around each other.
66
Describe the arrangement and movement of particles in gases.
Well separate with no regular arrangement.
Vibrate and move freely at high speeds.
67
Compare the relative energies of particles in solids, liquids and gases.
Particles in a solid have the least amount of energy and particles in a gas have the most energy.
68
What does 'interconversion of state' mean?
When matter changes from one state to another due to changes in temperature.
69
What are the names of state changes from solid to liquid and vice versa?
Solid ---> liquid : Melting
Liquid ---> solid : Freezing
70
What are the names for the state changes from liquid to gas and vice versa?
Liquid --->gas : Evaporation
Gas ---> liquid : Condensation
71
Describe the forces between particles in solids, liquids and gases.
Solids - Strong forces of attraction between particles which keeps them in their fixed positions.
Liquids - Weaker attractive forces than in solids.
Gases - Weakest intermolecular forces so particles are in random movement.
72
How does a physical change differ from a chemical change?
A physical change involves in the forces between particles. The particles themselves remain the same and the chemical properties remain in same.
A chemical change is different as it affects the chemical properties of a substance.
73
What is the term describing when a solid changes straight into a gas?
Sublimation
74
Describe what happens, in terms of particles, when a solid is heated and melts into a liquid.
When heated the particles absorb thermal energy which is converted into kinetic energy the particles in the solid vibrate more. This causes the solid to expand until the structure breaks, and becomes a liquid.
75
Describe what happens, in terms of particles, when a liquid is heated and evaporates into a gas.
When heated, the particles in a liquid expand and some particles on the surface gain sufficient energy to overcome the intermolecular forces and evaporate. At the boiling point, all of the liquid particles gain enough energy to evaporate.
76
What is a mixture?
Contains 2 or more elements or compounds that are not chemically combined together.
The chemical properties of each substance in the mixture are unchanged.
77
What is a pure substance?
A single element or compound, not mixed with any other substance.
78
How can you use melting point data to distinguish between pure substances and mixtures?
Pure substances have a sharp exact melting point whereas mixtures melt over a range of temperatures since they consist of several elements/compounds.
79
When is simple distillation used?
Used to separate a pure liquid from a mixture of liquids. Only works when the liquids. Only works when the liquids have different boiling points.
80
How can ethanol be separated from water?
Ethanol has a lower boiling point than water so can be separated from water by simple distillation:
- Distillation apparatus set up.
- Mixture boiled.
- Ethanol evaporates first.
- Ethanol vapour cool in the condenser, condensing back to a liquid before being collected.
81
When is fractional distillation used to separate mixtures?
Fractional distillation is used to separate all the element/ compounds in a mixture. These chemicals must have different boiling points to be seperated.
81
What is the difference between fractional and simple distillation?
Simple distillation is only able to separate the liquid with the lowest boiling point from the mixture.
Fractional distillation separates all the chemicals in a mixture using their different boiling points.
81
How does fractional distillation work?
- Oil is heated until it evaporates into the fractional column.
- Vapour rise up the fractionating column and condense at the different fractions, depending on the relative boiling point of each substance.
82
What sort of mixture can filtration be used to separate?
Filtration is used to separate an insoluble substance from a solution.
83
Describe how to separate an insoluble substance from a solution.
- Place filter paper in a funnel.
- Pour the solution an insoluble substance through the funnel into a conical flask.
- The insoluble substance will collect on the filter paper and the solution will collect in the conical flask.
84
When is the process of crystallisation used to separate a mixture?
To separate a soluble solid from a solution in the solid decomposes when heated.
84
How could you separate a soluble solid from a solution, in the solid decomposes when heated?
Crystallisation
- Pour the solution into an evaporating dish and heat gently.
- When the crystals start to form, remove the dish from the heat and leave to cool.
- Once cold, filter the crystals out of the solution and leave them in a warm place to dry.
84
What process can be used to identify soluble substance in a mixture?
Chromatography
85
How does paper chromatography work to separate a mixture?
- The mobile phase (solvent) moves through the stationary phase (paper) so anything dissolved in the mobile phase will move up the paper.
- Compound interacts differently with each phase so will move different distances through the stationary phase meaning they will be separated.
86
How can chromatography show the composition of a mixture?
Different coloured substances in the mixture will separate as they have different solubilities in the solvent and will travel at different rates.
87
Why should pencil be used to draw the line along the bottom of the chromatography paper?
It will no be affect the experiment as it is insoluble in the solvent.
88
Why should the water (solvent) in the beaker for paper chromatography be no deeper than 1cm deep?
If it is deeper it will wash away from the substances placed on the line on the chromatography paper.
89
Why should you use a lid when carrying out paper chromatography?
To prevent the solvent evaporating.
90
How many spots will a pure substance produce on a chromatogram? How would this be different for an impure substance?
Pure substance produce one spot.
An impure substance contains more than one compound so will produce more spots (one spot for each chemical).
91
What is an Rf value?
The Rf value is the ratio between the distance travelled by the dissolved substance (the solute) and the distance travelled by the solvent.
92
How do you calculate Rf values?
Rf =
Distance travelled by substance
________________________________________
Distance travelled by solvent
93
When measuring the distance moved by a substance on the chromatography paper, where should you measure between?
Measure from the pencil baseline to the middle of the spot of the substance.
94
How can you use chromatography to see if a certain substance is present in a mixture?
Run a pure sample of this substance alongside the unknow mixture.
If the Rf value of the pure substance watches the value of one of the spots from the mixture, it is likely to be present.
95
How could you separate salt from a mixture of salt and sand?
- Salt is soluble in water, sand isn't.
- Add water to the mixture.
- Filter the solution to remove the insoluble sand.
- Evaporate the water to collect the salt crystals.
96
How can liquids be separated if they have different densities?
If liquids have different densities they will naturally separate into two layers.
To separate these layers, use a flask with a tap on the bottom. Open the tap to collect the bottom liquid (has the highest density) .
97
What does potable mean?
Safe to drink.
98
How can waste and groundwater be made potable?
1. Sedimentation: Large insoluble particles sink to the bottom after the water is left still for a while.
2. Filtration: Removes small insoluble particles by passing the water through layers of sand and filters.
3. Chlorination: Kills bacteria and microorganisms which are two small to be removed by filtration.
99
How can seawater be made potable?
Distillation
1. Filter to remove the insoluble particles.
2. Boil.
3. Cool and condense the water vapour.
100
What issues surround the process of making seawater potable?
- Extremely expensive as it requires a lot of energy to boil large volumes of water.
- Wastewater is toxic due to the high concentration of salt so must be disposed of carefully.
101
What is deionised water?
Water that has had metallic ions (such as copper or calcium ions) removed.
102
Why is deionised water used in experimental analysis?
Deionised water is used to prevent ions in the water interacting with the substances under analysis. If water wasn't deionised false positive results may be produced.
103
How are the elements arranged in the periodic table?
Ordered by increasing atomic number.
Elements in the same group (column) have the same number of outer shell electrons.
Elements in the same period (row) have the same number of electron shells.
104
How many electrons are in the outer shell of a group 1 element?
1
105
Why do elements in the same group have similar chemical properties?
They have the same number of electrons in the outer shell.
106
What group of the periodic table are the alkali metal?
Group 1
107
List two poperties of alkali metals.
- Relatively low melting points.
- Soft.
108
Why are group 1 elements called alkali metals?
They react with water to form alkaline solutions (pH greater than 7).
109
Why should alkali metals be stored in oil?
To prevent them reacting with water vapour and oxygen in the air.
110
What would be observed when lithium reacts with water?
- Slowest reaction of the alkali metals.
- Bubbles of hydrogen are produced.
- Doesn't melt (highest melting point of alkali metals).
111
What would be observed when sodium reacts with water?
- Faster reaction than lithium.
- Floats on the surface of water (less dense than water).
- Bubbles of hydrogen are produced which cause the sodium to whizz around the surface of the water.
- Melts as enough energy is given out to meet sodium's melting point.
112
What would be observed when potassium reacts with water?
- More violent reaction than sodium.
- Bubbles of hydrogen are produced which cause the potassium to whizz around the surface of the water.
- Melts into a shiny ball.
- Burns with a lilac flame.
113
Which group 1 element would you expect to react most violently with water?
Reactivity increases down the group so francium will react most violently wiht water.
114
What group are the halogens in? Why?
Group 7 because they have 7 outer shell electrons.
115
Why does reactivity decrease down group 7?
As you go down group 7, the outer shell is further from the nucleus and electron shielding increases. Attraction between the nucleus and outer electrons decreases so it is harder for the atom to gain an electron meaning reactivity decreases.
116
What is a redox reaction?
A reaction where oxidation and reduction take place at the same time.
117
Are halogen displacement reactions redox reactions? Explain your answer?
Yes because the halide ion is oxidised (loses an electron) to form a halogen atom and halogen is reduced (gains an electron) to form a halide ion.
118
What name is used to describe the elements in group 0 of the periodic table?
Nobel gases
119
How many electrons do the noble gases have in their outer shell?
0
They have no incomplete shells of electrons.
120
What does chemically intent mean?
Not chemically active.
121
Why are the noble gases chemically intent?
They have a full outer shell.
122
What properties of helium makes it suitable for use in ballons?
It is less dense than air and does no burn.
123
Why is argon used to fill electric light bulbs?
It is very chemically intent so will no react when the light bulb gets hot. It is non-flammable.
124
Why is argon used for welding?
It provides an inert welding atmosphere. Argon is more dense than air so keeps air away from the metal.
125
What is the trend of boiling points down group 0?
Boiling point increase down group 0 because the relative atomic mass increase so there are more intermolecular forces between the atoms.
126
