Topic 1 - Key Concepts in Chemistry Flashcards

1
Q

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
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2
Q

What discovery caused Dalton’s model to change?

A

The discovery of sub-atomic particles

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3
Q

Who discovered the electron?

A

JJ Thomson

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4
Q

What did JJ Thomson discover?

A

The electron

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5
Q

How was the electron discovered?

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.
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6
Q

What model was proposed by JJ Thomson?

A
  • Plum pudding model
  • Negatively charged electrons scattered through a positively charged metal
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7
Q

Who discovered the Plum Pudding Model?

A

JJ Thomson

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8
Q

What was the plum pudding model?

A

Negatively charged electrons scattered through a positively charged metal

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9
Q

Who conducted the gold foil experiment?

A

JJ Thomson

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10
Q

What was the gold foil experiment?

A
  • JJ Thomson shot a beam of positively charged particles at sheet of gold foil.
  • Most particles passed straight through suggesting atoms are mostly empty space.
  • A few particles were deflected and a few bounced back showing there must be a tiny, dense, positively charged nucleus.
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11
Q

Rutherford’s model of the atom:

A
  • Mass is concentrated in the central nucleus
  • The atom is mostly empty space.
  • Electrons travel in random paths around the nucleus
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12
Q

Structure of the atom

A
  • Small central nucleus made up of protons and neutrons.
  • Electrons orbit the nucleus in shells.
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13
Q

The radius of the nucleus

A

1x10^-14 metres. This is 1/10,000 of the atomic radius.

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14
Q

Relative masses of sub-atomic particles

A

Proton - 1
Neutron - 1
Electron - 1/1840

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15
Q

Relative charges -

A

Proton: +1
Neutron: 0
Electron: -1

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16
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 so for charges to balance the number of protons and electrons must be equal.
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17
Q

Where is the mass of an atom concentrated?

A

In the nucleus

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18
Q

Atomic number represents

A

Number of protons.

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19
Q

Mass number -

A

Number of protons + number of neutrons

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20
Q

Fill in the blank:
‘Atoms of the same element have the same number of ______ in the nucleus and this is unique to that element’

A

Protons

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21
Q

What’s 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 numbers.
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22
Q

Exam Question - Boron has the atomic number 5 and the mass number 11. How many protons, electrons and neutrons does Boron have?

A

5 Protons
6 Neutrons
5 Electrons

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23
Q

Why is relative atomic mass not always whole?

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.
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24
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.

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25
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.
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26
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 undiscovered elements.
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27
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 not yet been discovered.
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28
Q

How are elements arranged in the modern periodic table?

A

In order of increasing atomic number

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29
Q

Fill in the blank: ‘Elements in the same group (column) have similar _______ ______’

A

Chemical properties

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30
Q

Why do elements in the same column have similar chemical properties?

A
  • Same number of outer shell electrons.
  • Number of outer shell electrons determines how an atom reacts.
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31
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 shells of electrons.
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32
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
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33
Q

Where on the periodic table are metals?

A

Left hand side

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34
Q

What determines whether something is metal or non-metal?

A

Atomic structures of elements

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35
Q

What is the maximum number of electrons allowed in each of the first 3 shells?

A

1st Shell - 2
2nd Shell - 8
3rd Shell - 8

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36
Q

When are atoms most stable?

A

When they have full electron shells

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37
Q

The atomic number of Na is 11. What is the electron configuration of Na?

A

2, 8, 1

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38
Q

How is the electron configuration of an element related to its position in the periodic table?

A
  • The number of shells is the period.
  • The number of electrons in the outer shells is the group.
  • The total number of electrons is the atomic number.
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39
Q

What is an ionic bond?

A

A bond between a metal and non-metal involving the transfer of electrons.

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40
Q

In terms of electrons, describe what happens to the metal and non-metal when an ionic bond forms

A
  • The metal atom loses electrons to become a positively charged ion (cation).
  • The non-metal gains electrons to become a negatively charged ion (anion).
41
Q

What is an ion?

A

An ion is an atom or group of atoms with a positive or negative charge.

42
Q

If an ion is positively charged, has it lost or gained electrons?

A
  • 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
43
Q

O^2- has the atomic number 8 and the mass number 16. How many protons, neutrons and electrons are in this ion?

A

8 Protons
8 Neutrons
10 Electrons

44
Q

Why do elements in groups 1, 2, 6 and 7 readily form ions?

A

So they become more stable and achieve the electron structure of the noble gases (group 8).

45
Q

What type of ions do elements in group 1 and 2 form?

A

Cations (positive)
- Group 1 metals will form 1+ ions.
- Group 2 metals will form 2+ ions

46
Q

What type of ions do elements in groups 6 and 7 form?

A

They are non-metals so form anions (negative)
- Group 6 will form 2- ions
- Group 7 will form 1- ions

47
Q

What does it mean if an ionic compound ends in -ide?

A

Compound contains 2 elements

48
Q

What does it mean if an ionic compound ends in -ate?

A

The compound contains at least three elements, one of which is oxygen.

49
Q

Describe the structure of an ionic compound

A
  • Lattice structure.
  • Regular arrangement of ions.
  • Ions held together by strong electrostatic forces between ions with opposite charges.
50
Q

What is the chemical formula of sodium oxide, formed from Na+ and O^2-?

A
  • NA2O.
  • Charges must balance so 2 sodium ions are required.
51
Q

What is the chemical formula of magnesium hydroxide, formed from Mg2+ and OH-?

A
  • Mg(OH)2
  • Charges must balance so 2 hydroxide ions are required.
52
Q

What is a covalent bond?

A

A bond formed when an electron pair is shared between two atoms.

53
Q

What forms as a result of covalent bonding?

A

A molecule.

54
Q

Are covalent bonds weak?

A

No, the bonds are strong

55
Q

Which is smaller, an atom or a molecule?

A
  • An atom.
  • Simple molecules consist of atoms joined by strong covalent bonds within the molecule.
56
Q

Why do ionic compounds have high melting points?

A

Strong electrostatic attraction between the positive and negative ions requires a lot of energy to overcome.

57
Q

When do ionic compounds electricity? Why?

A
  • 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.
58
Q

Why do simple molecular compounds have low melting and boiling points?

A

They have weak intermolecular forces (forces between molecules) which only require a little energy to overcome.

59
Q

Do simple molecular compounds conduct electricity? Why / why not?

A

No, there are no charged particles

60
Q

Do giant covalent structures have a high melting point? Explain your answer.

A

Yes, because they have lots of strong covalent bonds which require a lot of energy to break

61
Q

How do metals conduct electricity and heat?

A
  • The positive ions are fixed in a sea of delocalised electrons.
  • These electrons are free to move and carry charge / energy
62
Q

True or false?
‘Metals are insoluble in water’

A

TRUE

63
Q

Name two giant covalent structures formed from carbon atoms

A

Graphite, Diamond

64
Q

Describe the structure and properties relating to graphite

A
  • Each carbon atom bonded to 3 other carbon atoms.
  • Layers of hexagonal rings of carbon atoms.
  • Weak intermolecular forces between layers.
  • One delocalised electron per carbon atom.
65
Q

Describe and explain the properties of graphite

A
  • Graphite is soft / slippery because there are only weak intermolecular forces between layers which allow the layers to slide over one another.
  • Graphite conducts electricity because there is one
    delocalised electron per carbon atom.
  • The delocalised
    electrons are mobile charges.
66
Q

Describe the structure of diamond

A
  • All carbon atom are covalently bonded to four other carbon atoms.
  • No delocalised electrons.
67
Q

Describe the properties of diamond

A
  • Very hard.
  • Very high melting point.
  • Doesn’t conduct electricity as there are no charged particles.
68
Q

What are the uses of graphite? Why?

A
  • Electrodes because graphite conducts electricity and has a high melting point.
  • Lubricant because it’s slippery (the layers in graphite can slide over each other).
69
Q

Why is diamond used in cutting tools?

A

It’s very hard

70
Q

What is a fullerene?

A

A fullerene is a molecule made of carbon, shaped like a closed tube or hollow ball.

71
Q

Name two fullerenes

A
  • Graphene
  • C60 (buckminsterfullerene)
72
Q

What are the properties of the fullerene C60? (Buckminster…)

A
  • Slippery due to weak intermolecular forces.
  • Low melting point.
  • Spherical.
  • Strong covalent bonds between carbon atoms
    in a molecule.
  • Large surface area.
73
Q

What are the properties of graphene?

A
  • High melting point due to covalent bonding between carbon atoms.
  • Conducts electricity because it has delocalised electrons.
74
Q

Why is graphene useful in electronics?

A
  • It is extremely strong and has delocalised electrons which are free to move and carry charge.
  • It is only one atom thick as it is a single layer of graphite.
75
Q

What is a polymer? Name a polymer

A
  • Long chain molecules formed from many monomers.
  • E.g. poly(ethene)
76
Q

What bond is formed between carbon atoms in polymer molecules?

A

Covalent bonds

77
Q

What are the properties of metals?

A
  • High melting point.
  • High density.
  • Good conductors of electricity.
  • Malleable and ductile.
  • Generally shiny.
78
Q

Explain why metals are malleable

A

Atoms are arranged in uniform rows which can slide over one another

79
Q

Explain why metals can conduct electricity

A

Electrons in the metal are charges that can move

80
Q

What are the general properties of non-metals?

A
  • Low boiling points.
  • Poor conductors of electricity.
  • Brittle when solid.
81
Q

List the limitations of the following models when representing ionic compounds: dot and cross, 2D diagrams and 3D diagrams

A

● 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.

82
Q

List the limitations of the following models when representing covalent molecules: dot and cross and ball and stick

A

● 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.

83
Q

How do you calculate the relative formula mass of a compound?

A

Add together all the relative atomic masses of the atoms in the compound.

84
Q

What is the empirical formula? What 2 values could be used to calculate the empirical formula of a simple compound?

A

● 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.

85
Q

What is the empirical formula for Fe2O4?

A

FeO2

86
Q

What is the molecular formula?

A

Actual number of atoms of each element in a compound.

87
Q

Describe an experiment to work out the empirical formula of magnesium oxide (6 marks)

A

● 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.

88
Q

What is the law of conservation of mass?

A

No matter is lost or gained during a chemical reaction.

89
Q

If a reaction is carried out in a closed system, what can you say about the total mass of the reaction throughout the experiment?

A

Mass stays constant

90
Q

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?

A

Mass decreases as the gas escapes.

91
Q

Exam Q: 52g of calcium reacts with oxygen to form 79g of calcium oxide. Using the law of conservation of mass, what mass of oxygen is needed?

A
  • 79 - 52 = 27
  • Mass of oxygen = 27g
92
Q

What equation links mass, moles and relative atomic mass?

A

Mass (g) = Moles x Relative atomic mass (Mr)

93
Q

How can you calculate concentration in g/dm3?

A

Concentration(g/dm3) = Mass(g)/Volume(dm3)

94
Q

What is the Avogadro constant?

A
  • The number of atoms, molecules or ions in one mole of a given substance.
  • The value of the constant is 6.02 x 1023.
95
Q

What is the mass of 20 moles of calcium carbonate, CaCO3?

A
  • Mass (g) = Moles x Relative atomic - - mass (Mr) Mr = 100
  • 20 x 100 = 2000 g
96
Q

What formula links the Avogadro constant, moles and number of particles?

A

Number of particles = avogadro constant x moles

97
Q

Exam Q: How many atoms are in 3 moles of copper?

A
  • (6.02 x 10^23) x 3

= 1.81 x 10^24

98
Q

What is a limiting reagent in a chemical reaction?

A

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.