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Edexcel Chemsitry > Topic 1: Key Concepts in Chemistry > Flashcards

Topic 1: Key Concepts in Chemistry Flashcards

1
Q

how to use word equation

A
  • molecules on left hand side of arrow are reactants
  • molecules on right hand side of arrow are products
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2
Q

how to use symbol equation

A
  • shows symobls or formulas of reactants and prodcuts
    e.g. 2Mg + O2 -> 2MgO
  • need to be balanced by putting numbers in front of formulas where needed
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3
Q

how to balance symbol equations

A
  • find element that doesnt balance in the equation and pencil in a number to try and sort it out.
  • if that creates another imbalance then pencil in another number
  • carry on doing this until becomes balanced
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4
Q

what does state symbol (s) mean

A

solid

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5
Q

what does the state symbol (l) mean

A

liquid

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6
Q

what does the state symbol (g) mean

A

gas

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7
Q

what does the state symbol (aq) mean

A

aqueous
(means dissolved in water)

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8
Q

chemical formulae for water

A

H₂O

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9
Q

chemical formulae for carbon dioxide

A

CO₂

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10
Q

chemical formulae for chlorine

A

Cl₂

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11
Q

chemical formulae for ammonia

A

NH3

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12
Q

chemical formulae for hydrogen

A

H2

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13
Q

chemical formulae for oxygen

A

O2

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14
Q

chemical formulae for ammonium ion

A

NH4 ^+

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15
Q

chemical formulae for nitrate ion

A

NO3 ^-

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16
Q

chemical formulae for sulfate ion

A

SO4 ^2-

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17
Q

chemical fomrulae for hydroxide ion

A

OH ^-

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18
Q

chemical formuale for carbonate ion

A

CO3 ^2-

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19
Q

how to use ionic equation

A
  • make sure symbol equation is balanced
  • if anything in the equation can be broken down into ions and is aqueous then can break ions into solution. so rewrite equation but with the ions
  • to get to ionic equation, cross out anything thats the same on both sides of the arrow
  • reqrite equation using remaining ions.
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20
Q

what does this symbol mean

A
  • oxidising
  • provides oxygen which allows other materials to burn more fiercely e.g. liquid oxygen
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21
Q

what does this hazard symbol mean

A

Environmental Hazard
- harmful to organsims and to the environment.g. mercury

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22
Q

what does this hazard symbol mean

A

Toxic
- can cause death by swallowing, breathing in, absorption through skin e.g. hydrogen cyanide

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23
Q

what does this hazard symbol mean

A

Harmful
- can cause irritation, reddening or blistering of the skin e.g. bleach

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24
Q

what does this hazard symbol mean

A

Highly Flammable
- catches fire easily e.g. petrol

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25
Q

what does this hazard symbol mean

A

Corrosive
- destroys materials inluding living tissues e.g. concentrated sulfuric acid

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26
Q

describe how the theory of the atomic structure has changed.

A

At the start of the 19th century, John Dalton described atoms as solid spheres, and said the different fears made up different elements. In 1897, JJ Thompson concluded from his experiments. The atoms weren’t solid, spheres. His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles called electrons. The “solid sphere” idea of atomic structure had to be changed. The new theory was known as the plum pudding model.

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27
Q

describe how Ritherford showed that the plumb pudding model was wrong

A
  • Rutherford and his students conducted the gold foil experiment.
  • They fired positively, charged alpha particles at an extremely thin sheet of gold.
  • From the plant from the plum pudding method, they were expecting particles to pass straight through the sheets or be spread out through the through the atom.
  • more particles were deflected than expected and some were deflected backwards so the plum pudding model couldn’t be right.
  • Rutherford came up with a new theory of the nuclear atom to explain this evidence.
    -This means there’s a tiny positively charge nucleus at the centre, surrounded by a cloud of negative electrons and most of the atom is empty space
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28
Q

describe the refined Bohr Model of the atomic structure

A
  • Scientists realised that electrons in a cloud around the nucleus of the atom would be attracted to the nucleus, causing the atom to collapse.
  • Bohr proposed a new model of the atom where all the electrons were contained in shells.
  • Bohr suggested that electrons can exist in fixed orbit or shells and not anywhere in between and each shell has a fixed energy.
  • Bohr’s theory of atomic structure was supported by many experiments, and it helps explain a lot of other scientist observations at the time.
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29
Q

relative mass of a proton

A

1

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30
Q

relative charge of proton

A

+1

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31
Q

relative charge of neutron

A

0

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32
Q

relative mass of neutron

A

1

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33
Q

relative charge of electron

A

-1

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34
Q

relative mass of electron

A

1/1837

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35
Q

describe the nucleus of an atom

A
  • in the middle of the atom
  • contains protons and neutrons
  • has a positive charge due to protons
  • almost whole mass of atom concentrated in the nucleus
  • compared to the overall size of the atom, the nucleus is tiny
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36
Q

describe electrons in an atom

A
  • move around the nucleus in electron shells
  • negatively charged
  • shells of electrons occupy a lot of space
  • size of shells determine size of the atom
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37
Q

why do atoms have a neutral charge

A

number of protons equals the number of electrons so the charges cancel each other out

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38
Q

what does the atomic number of an atom tell you

A

how many protons an atom has

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39
Q

what does the mass number tell you about an atom

A

the total number of protons and neutrons in the atom

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40
Q

how do you work out the number of neutrons in an atom

A

subtract atomic number from mass number

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41
Q

define isotope

A

different forms of the same element which have the same number of protons but a different number of neutrons

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42
Q

what is the relative atomic mass of an atom

A

the relative atomic mass of an element is the average mass of one atom of the element, compared to 1/12th of the mass of an atom of carbon-12

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43
Q

what symbol is used for relative atomic mass

A

Ar

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44
Q

if an element only has 1 isotope what happens to the value of Ar

A

will be the same as it’s mass number

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45
Q

if an element has more than one isotope what happens to the value of Ar

A

Ar is the avereage of the mass numbers of all the different isotopes.

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46
Q

how can you work out the relative atomic mass of an element using isotopic abundances

A

sum of (isotope mass x % abundance)
_______________________________________
100

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47
Q

how did Mendeleev arrange the elements known at the time in the periodic table

A
  • sorted elements into groups based on thier properties
  • if elements were put in order of atomic mass then a pattern appeared so he put elements with similar chemical properties in columns
  • some elements ended up in wrong columns (due to presence of isotopes). if this happened the orders of elements were switched so they were kept with the same spoperties in the same columns.
  • he also left gaps in the table and used properties of other elements in the columns to predict properties of undiscovered elements. when they were found they fit the pattern.
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48
Q

how is the periodic table arranged

A
  • elements are arranged in order of increasing atomic number in rows called periods
  • elements with similar properties are placed in the same vertical clumn called groups
49
Q

how can poisiton in the periodic table of an element show the electronic configuration of the element

A
  • the group in which the elemnt is corresponds to the number of electrons in the outer shell
  • the period to which the element belongs to corresponds to the number of shells of electrons that it has
50
Q

what are the electron shell rules when it comes to electron configurations

A
  • electrons always occupy shells (sometimes called energy levels)
  • the lowest energy levels are always filled first
  • only a certain number of electrons are allowed in each shell
    1st shell = 2 electrons
    2nd shell = 8 electrons
    3rd shell = 8 electrons
51
Q

how to work out electron configuration of an atom

A

Method 1: using argon
- argon has 18 protons so must have 18 electrons.
- first shell must have 2 electrons, second shell must have 8, 3rd shell has 8 as well
- configuration = 2.8.8.

Method 2: using sodium
- the number of shells whihc contain electrons is the same as the period of the element
- the group number tells you how many electrons occupy the outer shell of the element.
e.g. sodium is in period 3 so has 3 shells. the first 2 shells must be full. It’s in group 1 so has 1 electron in outer shell. so configuration = 2.8.1.

52
Q

how are simple ions formed

A

when an atom gains or loses electrons

53
Q

what is a negative ion called

A

anion

54
Q

what is a positive ion formed

A

cation

55
Q

how do you work out the charge of the ion

A

the number of electrons lost or gained corresponds to the charge

e.g. gain 2 electrons, 2-

56
Q

what is an ion

A

an atom/ group of atoms with a positive or negative charge

57
Q

which groups are most likely to form ions

A

1,2,6,7

58
Q

why are group 1 and 2 elements most likely to form ions

A
  • they are metals and lose electrons to form positive ions
59
Q

why are group 6 and 7 elements most likely to form ions

A

they are non-metals and gain electrons to form negative ions

60
Q

how do you work out the formula of an ionic compound

A
  • overall charge of ionic compound is zero
  • the charge of positive ions is the number of negative ions you need and vice versa

e.g.
Ca ^2+. NO3 ^-

= 1. = 2
becuase Ca has a charge of 2+ you need 2 NO3- ions

61
Q

define ionic bonding

A

oppositely charged ions are strongly attracted to eachother by electrostatic forces

62
Q

how do you show how ionic compounds are formed

A

dot and cross diagrams

63
Q

describe ionic compounds

A

ions form a closely packed regular lattice held together by a very strong electrostatic force of attraction between oppositely charged ions in all directions.

64
Q

draw ball and stick model of sodium chloride ionic compound

A
65
Q

draw 3D model of sodium chloride

A
66
Q

describe and explain properties of ionic compounds

A
  • high meltiing and boiling point = due to the strong attraction between ions, it takes a lot of energy to overcome this attraction
  • cannot conduct electricity when solid = the ions are fixed in place and cannot move, but they can move when the ionic compound melts so can carry an electric current
  • dissolve easily in water = ions separate and are free to move in solution (can also carry electric current)
67
Q

advantages and disadvnatges of 2D representations or substances e.g. displayed formula

A
  • simple
  • good at showing what atoms something contains and how they are connected

BUT

  • dont show the shape or size of the substance/ atoms
68
Q

advantages and disadvantges of dot and cross diagrams

A
  • useful for showing how compounds or molecules are formed and where the electrons in the bonds or ions came from.
  • BUT they dont usually show the size of atoms or how they are arranged
69
Q

advanatges and disadvantages of 3D models of ionic solids

A
  • show arrangement of ions
  • BUT only shows outer layer of substance
70
Q

advantages and disadvantages of ball and stick models

A
  • shows how the atoms in a substance are connected
  • great for helping visualise structures, as they show the shape of the lattice or molecule in 3D
  • more realistic than 2D drawings, but still a bit misleading as it makes it look like there are big gaps between the atoms - in reality this is where the electron clounds react.
  • also dont show correct scales of the atoms or ions.
71
Q

define covalent bond

A

a storng bond that forms when a pair of electron is shared between 2 atoms

72
Q

draw dot and cross for hydrogen molecule

A
73
Q

what are simple molecular substances

A

made of molecules containing a few atoms joined by covalent bonds

74
Q

draw a dot and cross diagram for hydrogen chloride molecule

A
75
Q

draw dot and cross diagram for water

A
76
Q

draw dot and cross diagram for oxygen molecule

A
77
Q

dot and cross diagram for methane molecule

A
78
Q

dot and cross diagram for carbon diagram

A
79
Q

what are properties of simple molecular substances

A
  • have simple molecule structures
  • held together by storng covalent bonds
  • weak forces of attraction between molecules
  • melting and boiling points are quite low as not a lot of energy is needed to break the weak intermolecular forces
  • most are gasses or liquids at room temp
  • as molecules get bigger, the strength of intermolecular forces increases so more energy is needed to break them and melting and boiling points increase
  • dont conduct electricity as no free electrons or ions
  • some are soluble, some aren’t
80
Q

what are polymers

A

molecules made of long chains of covalently bonded carbon atoms and are formed when monomers join together

81
Q

descibe the properites of giant covalent structures

A
  • all atoms are bonded to each other by strong covalent bonds.
  • they have very high melting and boiling points as lots of energy is needed to break the covalent bonds
  • they generally don’t contain charged particles, so they don’t conduct electricity (apart from graphite and graphene)
  • They aren’t soluble in water
82
Q

describe and explain diamond as a giant covalent structure

A
  • made up of a network of carbon atoms that form 4 covalent bonds
  • the strong covalent bonds take lots of energy to break, so diamond has a high melting point.
  • the strong covalent bonds also hold the atoms in a rigid lattice structure, making diamond really hard - it’s used to strengthen cutting tools
  • it doesnt conduct electricity because it has no free electrons or ions
83
Q

describe and explain graphite as a giant covalent struture

A
  • each carbon atom only forms 3 covalent bonds, creating sheets of carbon atoms arranged in hexagons
  • there aren’t any covalent bonds between the layers, they are only held together weakly so are free to move over each other. this makes graphite soft and slippery, so it’s ideal as a lubricant.
  • has a high melting point as the covalent bonds in the sheets need lots of energy to overcome
  • only three out of each carbon’s 4 outer electrons are used in bonds, so each carbon atom has one electron that’s delocalised and can move so graphite can conduct electricity
  • often used to make electrodes
84
Q

describe and explain graphene as a giant covalent structure

A
  • a type of fullerene which is one layer of graphite
  • it’s a sheet of carbon atoms joined together in hexagons
  • the sheet is just one atom thick, making it a two-dimensional compound
85
Q

describe buckminsterfullerene

A
  • has molecular formula C60 and forms a hollow sphere made up of 20 hexagons and 12 pentagons.
  • a stable molecule that forms soft brownish-black crystals
86
Q

what are fullerenes

A

molecules of carbon, shaped like closed tubes or hollow balls
- mainly made up of carbon atoms arranged in hexagons or heptagons

87
Q

explain the use of some fullerenes

A
  • can be used to ‘cage’ other molecules - fullerene structure forms around another atom or molecules, which is then trapped inside so can be used to help deliver a drug directly to cells in the body
  • they have a huge surface area, so they could help make great industrial catalysts - individual catalyst molecules could be attached to the fullerenes
88
Q

describe and explain nanotubes as a fullerene

A
  • they are tiny cylinders of graphene - so they can conduct electricity.
  • they also have a high tensile strength (they dont break when stretched) so can be used to strengthen materials without adding much weight. e.g. strengthen sports equipment so it can be strong but lightweight (tennis rackets)
89
Q

describe and explain metallic bonding

A
  • metals also consist of a giant structure
  • the electrons in the outer shell of the metal atoms are delocalised. There are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons.
  • these forces of attraction hold the atoms together in a regular structure and are known as metallic bonding. Metallic bonding is very strong
  • compounds that are held together by metallic bonding include metallic elements and alloys.
  • delocalised electrons in the metallic bonds which produce all the properties of metals
90
Q

draw diagram of metallic bonding

A
91
Q

describe and explain the physical properties of metallic bonding

A
  • electrostatic forces of attraction between metal ions and delocalised electrons are very strong so need a lot of energy to overcome them, so very high melting and boiling point.
  • shiny solids at room temp
  • not soluble in water
  • layers of atoms in a pure metal can slide over each other making metals malleable - can be hammered/ rolled in flat sheets
  • delocalised electrons carry electrical current and thermal energy through the material so metals are good conductors of electicity and heat.
92
Q

physical properties of non-metals

A
  • have different structures so have a wide range of physical properties
  • tend to be dull looking, more brittle, lower boiling points (not generally solids at room temp) don’t conduct electricity and have a lower density.
93
Q

why do metals and non-metals have different chemical properties

A
  • non-metals gain electrons to form full outer shells whereas metals lose electrons to gain full outer shells.
94
Q

define conservation of mass

A

no atoms are created or destoryed during a chemical reaction

95
Q

reaction to show conservation of mass

A
96
Q

explain the reasons for mass inreasing in an unsealed chemical reaction

A
  • if mass increases, at least one of the reactants is a gas found in the air e.g. oxygen
  • before the reaction, the gas is floating around in the air. it is there, but not contained in the reaction vessel, so you cannot measure its mass
  • when then gas reacts to form part of the product, it becomes contained inside the reaction vessel
  • so total mass of the stuff inside the reaction vessel increases
97
Q

explain the reasons for mass decreasing in an unsealed chemical reaction

A
  • if mass decreases, it’s due to some or all of the reactant are slids and at least one of the products is a gas
  • before the reaction, any solid/ liquid/ aq reactant are cnotained in the reaction vessel
  • if the vessel ins’t enclosed, then the gas can escape from the reaction vessel as it’s formed. It’s no longer contained in the reaction vessel, so you cannot measure it’s mass
  • so the total mass of the stuff inside the reaction vessel decreases
98
Q

how to find out the relative formula mass Mr) of a compound

A

sum of relative atomic masses of all the atoms in its formula

99
Q

THE Mr OF A COMPOUND IS EQUAL TO THE MASS IN GRAMS OF 1 MOLE OF THE COMPOUND

A
100
Q

what is the empirical formula

A

smallest whole number ratio of atoms in the compound

101
Q

how to work out empirical formula of a compound

A
  1. write out atoms in the compound
  2. write numbers in the molecular formula
  3. divide them by the largest number that goes into them exactly.
102
Q

how to find out the molecular formula for a compound

A
  1. find Mr of the empirical formula.
  2. divide Mr or the compound by the Mr of the empirical formula
  3. multiply everything in empirical formula by the result
103
Q

1.46 Describe an experiment to determine the empirical formula of a simple compound such as magnesium oxide

A
  1. weigh crucible and lid
  2. weigh crucible lid and magnesium
  3. heat magnesium over Bunsen burner
  4. once reaction complete, weight crucible, lid and magnesium oxide
  5. mass of magnesium = step 2 - step 1
  6. mass of oxygen = step 4 - step 2
  7. use relative masses to find empirical formula using 1.44
104
Q

Calculate masses of reactants and products from balanced equations, given the mass of one substance

A
  • EMMA method
  • E - equation - write a balanced chemical equation for the reaction
  • M - moles - calculate the mole of known reactant / product (the one you have the mass of) using Moles = Mass/Mr
  • M - moles - calculate the moles of unknown reactant / product using ratio of balanced equation e.g. if 2:3 and you want to find the 2 then divide by the other number and times by the number you want
105
Q

what is the value of a mole

A

6.02 x10 ^23

106
Q

why is avogadro’s constant useful

A

when you get that number of atoms or molecules, of any element or compound, and they weigh exactly the same number of grams as the relative atomic mass of the element or compound
e.g. one mole of carbon weight exactly 12 grams

107
Q

how to use avogadros contant to calculate the number of particles

A
  • multiply avogadro’s constant by the number of moles you have
  • if you are using a diatomic molecule like oxygen then multiply the answer by 2.
108
Q

formula for calculating moles

A

moles = mass (g)/ Mr of compound

109
Q

formula for calculating concentration using mass

A

concentration (gdm^3) = mass (g)/ volume (dm^3)

110
Q

Recall that one mole of particles of a substance is defined as:

A
  • the Avogadro constant number of particles (6.02 × 10²³ atoms, molecules, formulae or ions) of that substance
  • the mass of ‘relative particle mass’ - the mass of 1 mole of atoms in any element or compound is the same number of grams as the relative atomic (Ar) / formula mass (Mr)
  • e.g. nitrogen gas (N₂) has an Mr of 28 - so 1 mole of nitrogen gas weighs exactly 28g
111
Q

Calculate the number of: moles of particles of a substance in a given mass of that substance and vice versa

A
  • moles = mass/Mr
  • mass = Mr x moles
112
Q

Calculate the number of particles of a substance in a given number of moles of that substance and vice versa

A
  1. multiply Avogadro’s constant by the number of moles you have to find number of particles
  2. multiply by number of atoms in each molecule
113
Q

Calculate the number of particles of a substance in a given mass of that substance and vice versa

A
  1. moles = mass / Ar
  2. then Avogadro’s constant x moles
114
Q

Explain why, in a reaction, the mass of product formed is controlled by the mass of the reactant which is not in excess

A
  • a reactions tops when all of one of the reactants is used up
  • called the limiting reactant
  • all of the other reactants are in excess
  • therefore mass of product formed controlled by mass of reactant not in excess
115
Q

Deduce the stoichiometry of a reaction from the masses of the reactants and products

A
  • stoichiometry = the calculation of relative quantities of reactants and products in chemical equations - based on the law of conservation of matter (basically ratio of products and reactions to make sure equation is balanced)
  • if you know the masses of the reactants and products you can work out balanced symbol equation for the reation
    1. calculate Mr of all substances involved
    2. calculate number of moles in each substance using moles = mass / Mr
    3. divide each number of moles by smallest number of moles
    4. write balanced equation using ratio
116
Q

how can you calculate the amount of product from the imiting reactant

A
  1. write out balanced equation
  2. work out relative formula masses of the reactant and product you’re interested in
  3. find out how many moles there are of the substance you know the mass of
  4. use the balanced equation to work out how many moles there’ll be of the other substane
  5. use the number of moles to calculate the mass
117
Q

how to balance equations using reacting masses

A
  1. divide the mass of each substance by its relative formula mass to find the number of moles
  2. divide the number of moles of each substance by the smallest number of moles in the reaction
  3. if needed, multiply all the numbers by the same amount to make them all whole numbers
  4. write the balanced symbol equation for the reaction by putting these numbers in front of the formulas
118
Q

how to work out limiting reactants

A

Edexcel Chemsitry (9 decks)

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