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Chemistry (Tara) > Definitions > Flashcards

Definitions Flashcards

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1
Q

Element

A

A substance that cannot be broken down into simpler substances by chemical means or produced by combining simpler substances.

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2
Q

Metal

A

Any element that loses electrons to form a positive ion (cation).

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3
Q

Atomic number

A

The number of protons present in the nucleus of an atom.

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4
Q

Mass number

A

The mass number is the number of protons plus neutrons present in the nucleus of an atom.

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5
Q

Isotopes

A

Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

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6
Q

Relative atomic mass number

A

The average mass of an atom of an element compared to 1/12 the mass of the carbon-12 isotope, taking relative abundances of the naturally occurring isotopes into account.

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7
Q

Relative molecular mass number

A

The average mass of a molecule of a compound compared to 1/12 the mass of the carbon-12 isotope, taking relative abundances of the naturally occurring isotopes into account.

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8
Q

Compound

A

A compound is a substance that is made up of two or more elements combined together chemically.

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9
Q

The octet rule

A

This rule states that when atoms bond, most atoms tend to want an electron arrangement of eight electrons in their outermost shell (energy level).

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10
Q

Valency

A

The valency of an atom tells us the number of chemical bonds an atom can form.

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11
Q

Radioactivity

A

Is the spontaneous disintegration of the nucleus with the emission of α, β or y radiation.

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12
Q

Nuclear reaction

A

A nuclear reaction involves a change in the nucleus of an atom and a new element is usually formed as a result.

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13
Q

Chemical reaction

A

A chemical reaction involves electrons being shared or transferred from one atom to another - the nucleus of the atom remains the same.

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14
Q

Half-life

A

This is the time taken for half the nucLEI in a given sample size to decay.

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15
Q

The principle of the mass spectrometer

A

The principle involved is that different ions are separated according to their masses when moving in a magnetic field.

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16
Q

Absorption spectrum

A

An absorption spectrum is a series of dark lines against a coloured background.

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17
Q

Emission spectrum

A

An emission spectrum is a series of coloured lines against a dark background.

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18
Q

Heisenberg’s uncertainty principle

A

This states that it is impossible to know both the position and the speed of an electron at the same time as electrons move in a wave motion.

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19
Q

Atomic orbital

A

An atomic orbital is a region in space around the nucleus of an atom in which there is a high probability of finding an electron.

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20
Q

Energy level

A

Is the discrete amount of energy an electron has when it is in an atom.

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21
Q

Energy sublevel

A

A group of atomic orbitals within an atom, all of which have the same energy.

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22
Q

Aufbau principle

A

Electrons occupy the lowest available energy level.

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23
Q

Hunds rule of maximum multiplicity

A

When two or more orbitals of equal energy are available (i.e 2px 2py 2pz), electron fill them singly before filling them in pairs.

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24
Q

Pauli exclusion principle

A

No more than two electrons can occupy an orbital and this they can only do if they have opposite spin.

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25
Q

A mole

A

A mole of a substance is that amount of it which contains the Avogadro’s constant number of particles.

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26
Q

Avogadro’s constant

A

Is the number of carbon atoms in exactly 12 grams of the C-12 isotope. This equals 6 x 10(23) particles.

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27
Q

Avogadro’s law

A

Equal volumes of all gases measured at the same temperature and pressure contain equal numbers of molecules.

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28
Q

Molar mass

A

The mass of one mole of a substance is its relative atomic mass (Ar) expressed in grams.

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29
Q

Molar volume

A

At s.t.p the volume of 1 mole of any gas is 22.4 litres (22,400 cm3).

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30
Q

Atomic radius (covalent radius)

A

The atomic radius is obtained by getting half the distance between the centers of singly bonded atoms of the same element.

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31
Q

Alkali

A

An alkali is a base that is soluble in water.

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32
Q

Energy sublevel

A

A group of atomic orbitals within an atom, all of which have the same energy.

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33
Q

Transition element

A

An element that forms at least one ion with a partially filled d-sublevel.

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34
Q

D-block element

A

An element whose highest energy electron enters a d-orbital.

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35
Q

Acids - Arhenius’ theory

A

An acid produces H⁺ ions in water.

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36
Q

Monobasic acid

A

A monobasic acid produces one H⁺ ion in solution eg. HCl

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37
Q

Dibasic acid

A

A dibasic acid produces two H⁺ ions in solution e.g H₂SO₄.

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38
Q

Tribasic acid

A

A tribasic acid produces three H⁺ ions in solution e.g H₃PO₄.

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39
Q

Bases - Arrhenius’ theory

A

A base produces OH- ions in water.

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40
Q

Acid - Bronsted-Lowry theory

A

An acid is a proton (H⁺) donor.

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41
Q

Base - Bronsted-Lowry theory

A

A base is a proton (H⁺) acceptor.

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42
Q

Amphoteric

A

A substance that can act as both an acid and a base.

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43
Q

Conjugate pairs

A

Two substances that differ by one proton.

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44
Q

Salts

A

A salt is formed when the H⁺ of the acid is replaced by a metal or NH₄⁺.

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45
Q

Strong acid

A

A strong acid is an acid that fully dissociates in solution and is a good proton donor.

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46
Q

Weak acid

A

A weak acid is a poor proton donor and only slightly dissociates in solution.

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47
Q

Conjugate acid

A

A base plus a H⁺ ion.

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48
Q

Conjugate base

A

An acid minus a H⁺ ion.

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49
Q

Ionic bond

A

An ionic bond is formed due to the electrostatic attraction between oppositely charged ions caused by the complete transfer of electrons from one atom to another.

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50
Q

Electronegativity

A

The relative power of attraction of an atom of an element for the shared pair of electrons in a covalent bond.

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51
Q

Oxidation

A

Oxidation of an element occurs when the element loses electrons.

52
Q

Reduction

A

Reduction of an element occurs when the element gains electrons.

53
Q

Oxidation number

A

The oxidation number of an element is the charge an element has or appears to have when it is in compound when certain rules are applied.

54
Q

Oxidation in terms of oxidation numbers.

A

Oxidation is an increase in oxidation number.

55
Q

Reduction in terms of oxidation numbers.

A

Reduction is a decrease in oxidation number.

56
Q

Boyles law

A

When a fixed mass of gas is kept at constant temperature, its volume multiplied by its pressure is constant.

57
Q

Charles law

A

This states that the volume of a fixed mass of gas, kept at constant pressure, is directly proportional to the absolute temperature (kelvin).

58
Q

Gay-Lussac’s Law of combining volumes

A

This states that gases always react with each other in simple whole number ratios when the volumes are measured at the same temperature and pressure.

59
Q

Avogadro’s Law

A

This states that equal volumes of gases measured under the same conditions of temperature and pressure contain equal numbers of molecules.

60
Q

An ideal gas

A

An ideal gas is defined as a gas that obeys all gas laws at all temperatures and pressures.

61
Q

First ionisation energy

A

The minimum amount of energy required to remove the first most loosely bound electron from a mole of isolated atoms of an element in its neutral gaseous ground state

62
Q

Limiting reactant

A

the reactant that is fully consumed when a reaction goes to completion

63
Q

theoretical yield

A

the quantity of product that should form when all of the limiting reactant reacts (from the molar ratio of the equation)

64
Q

compound

A

a substance that is made up of 2 or more elements combined together chemically

65
Q

sigma bonding

A

when orbitals overlap ‘head on’. can occur between 2 s orbitals, and s and a p or 2 p orbitals

66
Q

pi bonding

A

when orbitals overlap side ways. can happen between 2 p orbitals only

67
Q

pure covalent bond

A

occurs when electrons are shared equally

68
Q

polar covalent bond

A

occurs when electrons are shared unequally

69
Q

dative covalent bond

A

only one atom supplies the electrons need to make the covalent bond, one atom supplies both of the electrons

70
Q

polar molecule

A

the slight positive and slight negative poles of a molecule are separated by a distance, they do not coincide

71
Q

hydrogen bonding

A

an intermolecular force of attraction that occurs when hydrogen is bonded to a small more electronegative element such as N,O or F

72
Q

standard solution

A

a solution of known concentration

73
Q

primary standard

A

a substance that is available in 100% purity, is stable in air, has a high molecular mass for accuracy and dissolves readily in water, can be made up to a standard solition directly

74
Q

secondary standard

A

is a substance that is not available in 100% purity, is not stable in air, has a low molecular mass and does not dissolve readily in water, can not be made up to a standard solution directly

75
Q

standardise

A

to find out the concentration of a solution by titration or colorimetry

76
Q

Valence shell electron repulsion theory

A

pairs of electrons in the outer shell of an atom arrange themselves to be as far away from each other as possible to minimise the repulsions between them

77
Q

lone pairs of electrons

A

pairs of electrons in the outer shell of the atom that do not take part in bonding

78
Q

bonding pairs of electrons

A

pairs of electrons in the outer shell that are shared between atoms

79
Q

heat of reaction

A

the heat change that occurs when a reaction takes place according to the balanced chemical equation

80
Q

exothermic reaction

A

a reaction where heat is lost from the reaction to the surroundings

81
Q

endothermic reaction

A

a reaction where heat is taken in by the reaction from the surroundings

82
Q

heat of combustion

A

the heat change that occurs when 1 mole of a substance is burned in an excess of oxygen

83
Q

heat of formation

A

the heat change that occurs when 1 mole of a substance is formed from its elements in their standard states

84
Q

kilogram calorific value

A

the heat that is produced when 1 kilogram of a fuel is burned in an excess of oxygen

85
Q

Hess’ law

A

when a reaction takes place in stages the sum of the heat changes of the individual stages equals the heat change that would occur if the reaction were to take place in one stage

86
Q

hydrocarbon

A

a compound that only consists of the elements hydrogen and carbon

87
Q

saturated

A

single bonds around the carbon atoms

88
Q

unsaturated

A

a multiple bon present between two carbon atoms

89
Q

aromatic

A

contains a benzene ring in the structure

90
Q

aliphatic

A

straight or branched chained molecule

91
Q

ionic addition reaction

A

2 reactants to form one main product

92
Q

free radical substitution reaction

A

an atom or group of atoms in replaced by an atom or group of atoms to form 2 main products

93
Q

condensation reaction

A

2 different molecules combine to form a more complex molecule with the production of a smaller molecule such as water

94
Q

esterification reaction

A

an alcohol and a carboxylic acid react reversibly to form an ester and water (an example of a condensation reaction)

95
Q

elimination reaction

A

a smaller molecule is removed from a larger molecule. a double bond is formed in one of the product molecules

96
Q

dehydration reaction

A

removal of water from a molecule (an elimination reaction)

97
Q

hydrogenation reaction

A

addition of hydrogen to an alkene molecule involving a nickel catalyst and 200ºC

98
Q

heterolytic fission

A

a molecule splits up to form 2 different ions

99
Q

homolytic fission

A

a molecule splits to form 2 identical atoms using u.v light

100
Q

polymerisation reaction

A

a reaction where many small molecules called monomers combine together to form a very large molecule called a polymer

101
Q

principle of the mass spectrometer

A

separation of ions based on them having different masses when moving in an magnetic field

102
Q

principle of fractional distillation

A

separation of components of crude oil based on them having different boiling points

103
Q

principle of steam distillation

A

two immiscible liquids together have a lower boiling point than either of the liquids of their own

104
Q

principle of chromatography

A

a mobile phase carries a mixture through a stationary phase, separation happens because of some of the components of a mixture are attracted to significantly different extents to the mobile or stationary phase

105
Q

principle of recrystallisation

A

more solute is soluble in hot solvent than in a cold one

106
Q

principle of colorimetry

A

concentration of solute is proportional to colour intensity of solution

107
Q

chemical equilibrium

A

a system is said to have reached a state of equilibrium when the rate of the forward reaction equals the rate of the reverse reaction

108
Q

dynamic equilibrium

A

the forward and reverse reactions occur at the same time

109
Q

Le Chatelier’s principle

A

when a system at equilibrium is subjected to a stress such as change in temperature, pressure or concentration thy system will alter to oppose the effect of the stress

110
Q

reversible reaction

A

both forward and reverse reactions happen

111
Q

electrolyte

A

a substance that in the molten or dissolved state can conduct electricity

112
Q

electrochemical series

A

a list of elements arranged in order of their tendency to lose electrons

113
Q

displacement reaction

A

a reaction where a metal will take the place of a less reactive metal from a solution of its salts

114
Q

electrolysis

A

a process that uses electricity to bring about a chemical reaction

115
Q

rate of reaction

A

the change in concentration, per unit time of any one reactant or product

116
Q

catalyst

A

a substance that alters the rate of a reaction without itself being used up in the reaction

117
Q

heterogenous catalysts

A

the catalyst and the reactants are in different phases

118
Q

homogenous catalysts

A

the catalyst and the reactants are in the same phase

119
Q

autocatalysis

A

the catalyst is a product of the reaction

120
Q

activation energy

A

the minimum amount of energy colliding molecules must have in order for a reaction to take place

121
Q

pH

A

minus log to the base 10 of the hydrogen ion concentration (where the hydrogen ion concentration is expressed in mol per litre)

122
Q

indicator

A

a substance that changes colour depending on the pH of the solution in which it is placed

123
Q

hard water

A

water that does not form a lather easily with soap

124
Q

temporary hardness

A

hardness that can be removed by boiling, caused by calcium and magnesium hydrogencarbonates

125
Q

permanent hardness

A

hardness that cannot be removed by boiling, caused by calcium and magnesium sulphates

126
Q

biochemical oxygen demand

A

the amount of dissolved oxygen consumed by biochemical action when a sample of water was kept in the dark for 5 days at 20 deg celsius

Chemistry (Tara) (50 decks)

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