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Science Spec Flaschcards > C1 > Flashcards

C1 Flashcards

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1
Q

What are all substances made of?

A
  • Atoms
  • An atom is the smallest part of an element that can exist
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2
Q

How are atoms of each element represented?

A

A chemical symbol

(E.g O represents an atom of oxygen and Na represents an atom of sodium)

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3
Q

How many elements are there and how are they shown?

A
  • There are about 100 different elements(118 to be specific).
  • Elements are shown in the periodic table
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4
Q

How are compounds formed?

A

From elements by chemical reactions

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5
Q

What do chemical reactions always involve?

A
  • The formation of one or more new substances
  • And often involve a detectable energy change
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6
Q

What do compounds contain?

A

Two or more elements chemically combined in fixed proportions

( They can be represented by formulae using the symbols of the atoms from which they were formed )

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7
Q

What is the only way compounds can be separated?

A

By chemical reactions to revert them back to elements

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8
Q

How can chemical equations be represented?

A
  • By word equations
  • By equations using symbols and formulae
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9
Q

Note:

A

AQA says students will be supplied with a periodic table for the exam and should be able to:

  • use the names and symbols of the first 20 elements in the periodic table, the elements in Groups 1 and 7, and other elements in this specification
  • name compounds of these elements from given formulae or symbol equations
  • write word equations for the reactions in this specification
  • write formulae and balanced chemical equations for the reactions in this specification
  • write balanced half equations and ionic equations where appropriate.
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10
Q

What does a mixture consist of?

A
  • Two or more elements or compounds not chemically combined together.
  • Chemical properties of each substance in the mixture are unchanged
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11
Q

How are mixtures separated?

A
  • By physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography.
  • These physical processes do not involve chemical reactions and no new substances are made
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12
Q

What do filtration and crystallisation separate?

A

Separate solids from liquids

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13
Q

What does filtration specifically separate?

A

Insoluble solids from liquids

(It can be used in purification as well.For example,solid impurities in the reaction mixture can be separated out using filtration)

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14
Q

Define soluble

A

If a solid can be dissolved

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15
Q

What are two methods to separate soluble solids from solutions?

A

Evaporation and crystallisation

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16
Q

Explain the steps for evaporation

A

1) Pour the solution into an evaporating dish

2) Slowly heat the solution.The solvent will evaporate and the solution will get more concentrated. Eventually,crystals will start to form

3) Keep heating the evaporating dish until all you have left are dry crystals

(You dont have to use a bunsen burner,you could use a water bath or an electric heater)

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17
Q

Why would you want to use crystallisation instead of evaporation?

A
  • Evaporation is a really quick way of separating a soluble salt from a solution
  • Though you can only use it if the salt doesnt decompose (break down) when its heated
  • Otherwise youll have to use crystallisation
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18
Q

Explain the steps for crystallisation

A

1) Pour the solution into an evaporating dish and gently heat the solution.Some of the solvent will evaporate and the solution will get more concentrated

2) Once some of the solvent has evaporated,or when you see crystals start to form (the point of crystallisation), remove the dish from the heat and leave the solution to cool

3) The salt should start to form crystals as it becomes insoluble in the cold,highly concentrated solution

4) Filter the crystals out of the solution, and leave them in a warm place to dry. You could also use a drying oven or a desiccator

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19
Q

What is rock salt a mixture of?

A

Salt and sand

(They spread it on the roads in winter)
(Salt and sand are both compounds - but salt dissolves in water and sand doesnt.This vital difference in their physical properties gives a great way to separate them)

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20
Q

What are the steps to separate rock salt?

A

1) Grind the mixture to make sure the salt crystals are small,so they will dissolve easily

2) Put the mixture in water and stir.The salt will dissolve,but the sand wont (You can heat the mixture to help dissolve the salt)

3) Filter the mixture.The grains of sand wont fit through the tiny holes in the filter paper,so they collect on paper instead.The salt passes through the filter paper as its part of the solution

4) Evaporate the water from the salt so that it forms dry crystals
( You could also use crystallisation here if you wanted to make nice,big crystals)

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21
Q

At the start of the 19th century what did John Dalton say about atoms?

A
  • Atoms were solid spheres
  • The different spheres made up different elements
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22
Q

In 1897,what did JJ Thompson conclude from his experiments?

A

Atoms werent solid spheres.

(His measurements of charge and mass showed that an atom must contain even smaller,negatively charged particles - electrons.The ‘solid sphere’ idea of the atomic structure had to be changed.The new theory was known as the ‘plum pudding model)

(The plum pudding model showed the atom as a ball of positive charge with electrons stuck in it)

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23
Q

What happened in 1909 with Ernest Rutherford and his student Ernest Mardsen?

A
  • They conducted the famous alpha particle scattering experiments.
  • They fired positively charged alpha particles at an extremely thin sheet of gold.
  • From the plum pudding model,they were expecting the particles to pass straight through the sheet or be slightly deflected at most.This was because the positive charge of each atom was though to be very spread out through the pudding of the atom.
  • But,whilst most of the particles did go straight through the sheet,some were deflected more than expected,and a small number were deflected backwards.
  • So the plum pudding model couldnt be right.
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24
Q

What did Rutherford come up with after the experiment?

A
  • The nuclear model of the atom.In this a tiny,positive charged nucleus at the centre,where most of the mass is concentrated.
  • A ‘cloud’ of negative electrons surrounds this nucleus - so most of the atom is empty space.

(When alpha particles came near the concentrated,positive charge of the nucleus they were deflected.If they were fired directly at thr nucleus.They were deflected backwards.Otherwise,they passed through the empty space)

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25
Q

In 1913 what did Niels Bohr discover?

A
  • All electrons were contained in shells
  • Bohr proposed that electrons orbit the nucleus in fixed shells and arent anywhere in between
  • Each shell is a fixed distance from the nucleus

(Bohrs theory of the atomic structure was supported by many experiments and it helped explain lots of other scientists observations at the time)

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26
Q

In 1932,what did James Chadwick discover?

A
  • James Chadwick carried out an experiment which provided evidence for neutral particles in the nucleus which are now called neutrons.
  • The discovery of neutrons resulted in a model of the atom which was pretty close to the modern day accepted version,known as the nuclear model

(Protons were also discovered by another person)

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27
Q

What is the difference between the plum pudding model of the atom and the nuclear model of the atom?

A
  • In the plum pudding model, there is a positive sphere with negative charge randomly placed within the sphere.
  • There is no empty space
  • In the nuclear model, there is a central positive,tiny nucleus, with mostly empty space and lots of negative charges a long way from the nucleus
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28
Q

What is the relative charge of a proton?

A

+1

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29
Q

What is the relative charge of a neutron?

A

0

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30
Q

What is the relative charge of an electron?

A

-1

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31
Q

In an atom, what is the number of electrons equal to?

A

The number of protons in the nucleus,this is why atoms have no overall electrical charge.

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32
Q

What is the number of protons make an element?

A
  • The number of protons in an atom of an element is its atomic number.
  • All atoms of a particular element have the same number of protons.
  • Atoms of different elements have different numbers of protons
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33
Q

What does the nucleur symbol in an atom tell you about an atom?

A

It tells you the atomic(proton and electron) number and mass number

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34
Q

What is the radius of an atom?

A

Around 0.1 nanometres (1x10^-10 m)

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35
Q

What is the radius of the nucleus?

A

Around 1x10^-14

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36
Q

How much as the nucleus’ mass is concentrated in the atom

A

Almost the whole mass

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37
Q

What is the relative mass of a proton?

A

+1

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38
Q

What is the relative mass of a neutron?

A

1

39
Q

What is the relative mass of an electron?

A

Very small (taken as 0 or 1/2000)

40
Q

What is the mass number?

A

The sum of the protons and neutrons in an atom

41
Q

What are isotopes?

A

Atoms of the same element can have different numbers of neutrons

42
Q

Note:

A

Check CGP page 97 to see how atoms are represented

43
Q

What does the mass number tell you about the atom?

A

The total number of protons and neutrons in an atom

44
Q

How do you calculate the number of neutrons with the atomic and mass number?

A

Subtract the atomic number from the mass number to find the amount of neutrons

45
Q

Note:

A

AQA says that students should be able to calculate the numbers of protons,neutrons and electrons in an atom or ion, given its atomic number and mass number.

46
Q

Note:

A

AQA says that students should be able to relate size and scale of atoms to objects in the physical world.

47
Q

What is the relative atomic mass of an element?

A

An average value that takes account of the abundance of the isotopes of the element.

48
Q

What is the formula to work out the relative atomic mass of an element?

A

RELATIVE sum of (isotope abundance x isotope mass number)
ATOMIC = ——————————————————————————-
MASS (Ar) sum of abundances of all the isotopes

49
Q

State an example of a pair of isotopes

A

Carbon-12 and Carbon-13

50
Q

Copper has two stable isotopes.Cu-63 has an abundance of 69.2% and Cu-65 has an abundance of 30.8%. Calculate the relative atomic mass of copper to 1 decimal place.

A

1) (69.2 x 63) + (30.8 x 65) 4359.6 + 2002
———————————– = —————————
69.2+30.8 100

2) 6361
———— = 63.616
100

3) To 1 decimal place so 63.6

51
Q

What do the electrons in an atom occupy?

A

Electrons in an atom occupy the lowest available energy levels
(innermost available shells)

52
Q

How is the electronic structure of an atom represented?

A
  • The electronic structure of an atom can be represented by numbers or by a diagram.
  • For example, the electronic structure of sodium is 2,8,1 or showing two electrons in the lowest energy level, eight in the second energy level and one in the third energy level.

(Note: Students may answer questions in terms of either energy levels or
shells)

53
Q

How are elements in the periodic table arranged?

A
  • Elements in the periodic table are arranged in order of atomic (proton) number and so that elements with similar properties are in columns, known as groups.
  • The table is called a periodic table
    because similar properties occur at regular intervals
54
Q

What are the similarities of elements in the same group?

A
  • Elements in the same group in the periodic table have the same number of electrons in their outer shell (outer electrons)
  • This gives them similar chemical properties
55
Q

Note:

A

AQA says that students should be able to:

  • explain how the position of an element in the periodic table is
    related to the arrangement of electrons in its atoms and hence
    to its atomic number
  • predict possible reactions and probable reactivity of elements
    from their positions in the periodic table.
56
Q

Before the discovery of protons, neutrons and electrons, how did scientists arrange elements?

A

In order of their atomic weights

57
Q

What were many early periodic tables like?

A
  • The early periodic tables were incomplete
  • Therefore some elements were placed in inappropriate groups if the strict order of atomic weights was followed
58
Q

How did Mendeleev overcome these problems?

A
  • By leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights.
  • Elements with properties predicted by Mendeleev were discovered and filled the gaps
  • Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct
59
Q

Note:

A

AQA says that students should be able to describe these steps in the development of the periodic table.

60
Q

What are elements that react to form positive ions?

A

Metals

61
Q

What are elements that react to form negative ions?

A

Non-metals

62
Q

What are the majority of elements and how are they arranged in the periodic table?

A
  • The majority of elements are metals.
  • Metals are found to the left and towards the bottom of the periodic table.
  • Non-metals are found towards the right and top of the periodic table
63
Q

State properties of metals

A

As all metals have metallic bonding,this cause them to have similar basic physical properties
which are:

  • They are strong(hard to break) but can be bent or hammered into different shapes (malleable)
  • Great at conducting heat and electricity
  • They have high melting and boiling points
64
Q

State common properties of non-metals

A

As non-metals dont have metallic bonding,they tend to not have the same properties as metals they are:

  • Dull looking
  • Brittle
  • Arent always solids at room temperature
  • Dont generally conduct electricity
  • Often have a lower density
65
Q

How does the atomic structure of metals and non-metals relate to their position in the periodic table?

A
  • The outer shell of a metal is less than half full of electrons.
  • For this reason, metals are more likely to lose electrons to form a full outer shell.

Non-metals are mostly found in groups 5,6 and 7. These non-metals will have 5,6 or 7 electrons in their outer shell

66
Q

Explain how the reactions of elements are related to the arrangement of electrons in their atoms and hence to their atomic number

A
  • When substances react, it is only the outer electrons in the atoms that are involved
  • The nature of the reactions which occur depend on the number of outer shell electrons in the reacting atoms
67
Q

What is group 0 called?

A

Noble gases

68
Q

What is a characteristics of group 0 electrons?

A
  • They dont react with very much
  • Cant see it (as it is a gas)
  • Monoatomic gases (single atoms not bonded with each other)
  • Non-flammable (inert)
  • Colourless gases at room temperature
69
Q

What is the electronic arrangement of group 0 elements?

A
  • The noble gases have eight electrons in their outer shell
  • Except for helium, which has only two electrons
70
Q

Why are noble gases so unreactive?

A
  • All noble gases have 8 electrons in their outer energy level apart from helium which has two,giving them a full outer shell.
  • As their outer shell is energetically stable they dont have to lose nor gain electrons to become stable.
  • This means that they are more or less inert - they dont react with much at all
71
Q

Patterns in the properties of noble gases as you go down the group

A
  • The relative atomic masses increase
  • The boiling points increase as you move down the group
72
Q

Why is there an increase in boiling point in noble gases?

A

Due to an increase in electrons in each atom leading to greater intermolecular forces between them which need to be overcome

73
Q

What is group 1 called?

A

Alkali metals

74
Q

How much electrons do group 1 metals have in their outer shell?

A

One electron in their outer shell (this leads them all to being very reactive and gives them similar properties)

75
Q

What happens when you put group 1 metals in water

A

They react very vigorously

76
Q

What happens to lithium,sodium and potassium when you react it with water?

A

They float and move around the surface,reacting furiously

77
Q

What do group 1 metals and water produce when they react with each other? (HINT GAS)

A

Produces hydrogen

(The amount of energy given out when they react increases down the group.For potassium and below,theres enough energy to ignite hydrogen)

78
Q

What do group 1 metals and water also produce when they react together?

A

Also forms hydroxides that dissolve in water to give alkaline solutions

79
Q

What happens when group 1 metals react with chlorine

A
  • React vigorously when heated in chlorine gas which form white salts called metal chlorides

(As you go down the group,as reactivity increases the reaction with chlorine gets more vigorous,like a chain reaction)

80
Q

What happens when group 1 metals react with oxygen?

A
  • Forms a metal oxide,there are different types of oxides depending on the metal
81
Q

What happens when lithium reacts with oxygen?

A

Forms Lithium oxide (Li2O)

82
Q

What happens when sodium reacts with oxygen?

A

Forms a mixture of sodium oxide (Na2O) and sodium peroxide (Na2O2)

83
Q

What happens when potassium reacts with oxygen?

A

Forms potassium peroxide (K2O2) and potassium superoxide (KO2)

84
Q

What are the trends when you go down the table for group 1 metals?

A
  • Increasing reactivity ( As the outer electron is easily lost because the electron is further away from the nucleus the further down the group you go)
  • Lower melting and boiling points
  • Higher relative atomic mass
85
Q

What are group 7 elements called?

A

Halogens

86
Q

Characteristics of group 7 elements

A
  • All have similar reactions because they all have seven electrons in their outer shell.
  • The halogens are non-metals and consist of molecules made of pairs of atoms
87
Q

Properties of chlorine

A

Fairly reactive poisonous dense green gas

88
Q

Properties of bromine

A

Dense,poisonous red brown volatile liquid

89
Q

Properties of iodine

A

Dark grey crystalline solid or a purple vapour

90
Q

What is the nature of the compounds formed when chlorine, bromine and iodine react with non-metals?

A
  • Form molecular compounds as they want to acheive a full outer shell ( HCL , PCI5 , HF and CCl4 contain covalent bonds).
  • The compounds formed all have simple molecular structures
91
Q

What is the nature of the compounds formed when chlorine, bromine and iodine react with metals?

A

The form 1- ions which are called halides ( F- , Cl- , Br- and I- ) when they bond with a metal ( Na+Cl or Fe3Br-3+)

92
Q

What are the trends as you go down the group 7 elements?

A
  • Become less reactive ( harder to gain an extra electron,because the outer shell is further from the nucleus)
  • Have higher melting and boiling points
  • Have higher relative atomic masses
93
Q

How does a displacement reaction occur in group 7 metals?

A

A displacement reaction can occur between a more reactive halogen and the salt of a less reactive one.

(E.g chlorine can displace bromine and iodine from an aqueous solution of its salt ( a bromide or iodide) Bromine can also displace iodine because of the trend in reactivity )

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