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A Level Chemistry > AS Physical > Flashcards

AS Physical Flashcards

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1
Q

Isotope

A

-Atoms with the same number of protons, but different number of neutrons.
-Isotopes have similar chemical properties because of the same electronic structure.
-They may have slightly varying physical properties because they have different masses.

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2
Q

Four sub-shells

A

-S- max 2
-P- max 6
-D- max 10
-F- max 14

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3
Q

First ionisation energy

A

The first ionisation energy is the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge.

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4
Q

Second ionisation energy

A

The second ionisation energy is the enthalpy change when one mole of gaseous ions with a positive charge forms one mole of gaseous ions with a double positive charge.

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5
Q

Factors affecting ionisation energy

A

-Attraction of the nucleus (protons)
-The distance of the electrons from the nucleus (bigger atom- weaker attraction)
-Shielding of the attraction of the nucleus (weakened attraction)

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6
Q

4 stages of mass spectrometry:

A

-Ionisation
-Acceleration
-Flight tube
-Detection

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7
Q

Ionisation

A

Two ways:
-Electron impact.
-Electrospray ionisation.

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8
Q

Electron impact

A

-A vapourised sample is injected at low pressure.
-An electron gun fires high energy electrons at the sample.
-Knocks out an outer shell electron.
-Forming positive ions with different charges.
(Used for elements and substances with low formula mass and fragments them).

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9
Q

Electrospray ionisation

A

-The sample is dissolved in a volatile, polar solvent.
-Injected through a fine hypodermic needle creating a fine mist or aerosol.
-Tip of the needle has high voltage.
-At the tip of the needle, the sample molecules, M, gains a proton, H+, from the solvent forming MH+
-M(g)+H+ –> MH+(g)
-The solvent evaporates away while the MH+ ions move towards a negative plate.

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10
Q

Acceleration

A

-Positive ions are accelerated by an electric field.
-To a constant kinetic energy (KE=1/2xmxv^2).

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11
Q

Flight tube

A

-The positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster.
-The heavier particles will take longer to move through the drift area.
-The ions are distinguished by different flight times.

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12
Q

Detection

A

-Ions reach detector and generate a small current, which is fed into a computer for analysis.
-Current is produced by electrons transferring from the detector to the positive ions.
-Size of the current is proportional to the abundance of the species.
-For each isotope the mass spectrometer can measure a m/z (mass/charge ratio) and abundance.

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13
Q

Relative atomic mass

A

The average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.

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14
Q

Relative molecular mass

A

The average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12.

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15
Q

Avogadro constant

A

There are 6.022 x 10^23 atoms in 12 grams of carbon-12.

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16
Q

Mole

A

The amount of substance in grams that has the same number of particles as there are in atoms in 12 grams of carbon-12.

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17
Q

Concentration

A
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18
Q

Ideal gas equation

A

PV=nRT
Pressure(Pa) x Volume(m^3)= No. of moles x Gas constant x Temperature(K)

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19
Q

Empirical formula

A

An empirical formula is the simplest ratio of atoms of each element in the compound.

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20
Q

Molecular formula

A

A molecular formula is the actual number of atoms of each element in the compound.

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21
Q

Atom economy and equation

A

-Found directly from the balanced equation.
-Theoretical.
-Mass of desired product/ total mass of reactants x 100
-High atom economy- maximum mass of reactants ends up in the desired product.

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22
Q

Percentage yield

A

-Actual yield/ Theoretical yield x 100
-High yield- efficient conversion of products to reactants.

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23
Q

Ionic bonding

A

The electrostatic force of attraction between oppositely charged ions formed by electron transfer.

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24
Q

Metals in ionic bonding

A

Metals lose electrons and form positive ions.

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25
Q

Non-metals in ionic bonding

A

Non-metals gain electrons and form negative electrons.

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26
Q

Ionic bonding strength

A

Bonding is stronger and melting point is higher when the ions are smaller and have higher charges.

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27
Q

Ionic radii

A

-Positive ions are smaller as they have one less shell and higher ratio of protons- increased strength holding ion closer together.
-Negative ions are bigger as they have one more shell but same number of protons- attraction is less making ion bigger.

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28
Q

Properties of ionically bonded compounds

A

-Melting and boiling points- high because of high electrostatic forces of attraction between oppositely charged electrons.
-Solubility in water- generally good.
-Conductivity when solid- poor, ions can’t move, fixed in lattice.
-Conductivity when molten- good, ions can move.
-General description- crystalline solids.

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29
Q

Covalent bonding

A

A shared pair of electrons.

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30
Q

Coordinate bonding

A

-When the shared pair of electrons in a covalent bond come from only one of the bonding atoms. Also known as dative bond.
-Common examples: NH4+, H3O+, NH3BF3.
-Direction of arrow goes from the atom that is providing the lone pair to the atom that is deficient.

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31
Q

Properties of simple covalently bonded compounds

A

-Melting and boiling points- low, weak IMF.
-Solubility in water- generally poor.
-Conductivity when solid- poor, no ions to conduct and electrons are localised.
-Conductivity when molten- poor, no ions.
-General description- mostly gases and liquids.

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32
Q

Properties of macromolecular covalently bonded compounds

A

-Melting and boiling points- high, strong covalent bonds in macromolecule structure.
-Solubility in water- insoluble.
-Conductivity when solid- some are, electrons can’t move but some have delocalised electrons.
-Conductivity when molten- poor.
-General description- solids.

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33
Q

Metallic bonding

A

The electrostatic force of attraction between the positive metal ions and delocalised electrons.

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34
Q

3 factors that affect strength of metallic bond

A

-Number of protons/ nuclear strength.
-Number of delocalised electrons per atom.
-Size of ion (smaller ion- stronger bond).

35
Q

Properties of metallic compounds

A

-Melting and boiling points- high, strong electrostatic forces between positive ions and delocalised electrons.
-Solubility in water- insoluble.
-Conductivity when solid- good, delocalised electrons carry current.
-Conductivity when molten- good.
-General description- shiny metal, malleable as layers slide over one another.

36
Q

Shapes of molecules

A

Draw table!
Below Top Valley SS Teacher Lives

37
Q

How to explain shape

A

-State number of bonding pairs and lone pairs of electrons.
-State the electron pairs repel as far out as possible.
-No lone pairs- repel equally.
-Lone pairs- lone pairs repel more than bonding pairs.
-Shape and bond angle.

38
Q

Linear

A

BP-2
LP-0
Angle(s)- 180

39
Q

Trigonal Planar

A

BP-3
LP-0
Angle(s)-120

40
Q

Tetrahedral

A

BP-4
LP-0
Angle(s)- 109.5

41
Q

Trigonal Pyramidal

A

BP-3
LP-1
Angle(s)- 107

42
Q

Bent

A

BP-2
LP-2
Angle(s)- 104.5

43
Q

Trigonal Bipyramidal

A

BP-5
LP-0
Angle(s)- 120, 90

44
Q

Octohedral

A

BP-6
LP-0
Angle(s)- 90

45
Q

Electronegativity

A

The relative tendency of an atom in a covalent bond to attract a pair of electrons to itself.

46
Q

Factors affecting electronegativity

A

-Number of protons
-Atomic radius
-Distance

47
Q

Trends in electronegativity

A

-Going across a period- electronegativity increases, nuclear charge increases, number of energy levels remain same, same shielding, smaller atoms.
-Down a group- electronegativity decreases, more shells are added so less attraction between nucleus and outer shell electrons.

48
Q

Intermediate bonding

A
49
Q

Symmetric molecule

A
50
Q

Van der Waals forces

A
51
Q

Main factor affecting size of VDW forces

A
52
Q

Permanent dipole-dipole forces

A
53
Q

Hydrogen bonding

A
54
Q

Enthalpy change

A

The amount of heat energy given out or taken in during any change in a system provided the pressure is constant.

55
Q

Exothermic reaction

A

-Energy is transferred from the system to surroundings.
-Products have less energy than reactants.

56
Q

Endothermic reaction

A

-Energy is transferred from the surroundings to the system.
-Require input of heat energy.
-Products have more energy than reactants.

57
Q

Standard enthalpy of formation

A

The enthalpy change when 1 mole of compound is formed from its constituent elements under standard conditions, all reactants and products in their standard states.

58
Q

Standard enthalpy change of combustion

A

The enthalpy change that occurs when one mole of a substance is completely combusted in oxygen under standard conditions, all reactants and products in standard states.

59
Q

Standard conditions

A

-100kPa pressure
-298K
-Solutions at 1moldm-3
-All substances should have their standard state at 298K

60
Q

Energy change=

A

Mass of solution x Specific heat capacity x Temperature change

61
Q

Hess’s law

A

States that the total enthalpy change for a reaction is independent of the route by which the chemical change takes place.

62
Q

Mean bond energies

A

The enthalpy needed to break the covalent bond into gaseous atoms, averaged over different molecules.

63
Q

Enthalpy of combustion in a homologous series

A

For successive members of a homologous series, there is a constant rise in the size of the enthalpies of combustion as the number of carbon atoms increases.

64
Q

Collision theory

A

-Reactions can only occur when collisions take place between particles with sufficient energy.
-Minimum energy is called activation energy.

65
Q

Activation energy

A

The minimum energy which particles need to collide to start a reaction.

66
Q

Maxwell-Boltzman Distribution

A

-Draw it!
-Shows the spread of energies that molecules of a gas or liquid have at a particular temperature.
-Most probable energy, mean energy of particles, activation energy.

67
Q

Increasing temperature- effect on Maxwell-Boltzman Distribution

A

-Area under curve remains constant because number of particles are the same.
-Curve shifts towards right (more molecules with higher energies).
-Energy increases.
-Particles collide more frequently and more often with energy greater than activation energy.
-Bigger proportion of particles have energy greater than activation energy so frequency of successful collisions increases.

68
Q

Rate of reaction

A

-Change in concentration of a substance in unit time.
-Gradient of curve- ROR.

69
Q

Increasing concentration and increasing pressure- effect on Maxwell-Boltzmann Distribution

A

-At higher conc, there are more particles per unit volume- particles collide with greater frequency- higher frequency of effective collisions.
-More molecules have more energy than activation energy.

70
Q

Increasing surface area- effect on Maxwell-Boltzmann Distribution

A

-Causes successful collisions to occur more frequently between reactant particles.
-Increases ROR.

71
Q

Catalyst- effect on Maxwell-Boltzmann Distribution

A

-Catalysts increase ROR without getting used up.
-Provide an alternative route or mechanism with a lower activation energy.

72
Q

Dynamic equilibrium

A

-Both forward and backward reactions are happening at the same time.
-Reversible reaction.

73
Q

2 features of dynamic equilibrium

A

-Forward and backward reactions occurring at equal rates.
-Concentrations of reactants and products stay constant.

74
Q

Le Chatelier’s Principle

A

-If an external condition is changed, the equilibrium will shift to oppose the change and try to reverse it.

75
Q

Effect of temperature on equilibrium

A

-If temp is increased, equilibrium will shift to oppose it, move in endothermic reaction to try and reduce temp by absorbing heat.
-If temp is decreased, equilibrium will shift to oppose it, move in exothermic direction to try and increase temp by giving out heat.

76
Q

Effect of pressure on equilibrium

A

-Increasing pressure, causes equilibrium towards the side with fewer moles of gas to oppose the change and reduce pressure.
-Decreasing pressure, causes equilibrium towards the side with more moles of gas to oppose the change and increase pressure.

77
Q

Effect of concentration on equilibrium

A

-Increasing one of the reactants will cause the equilibrium to shift to oppose this and move in the forward direction to decrease concentration.

78
Q

Effect of catalyst on equilibrium

A

-Catalyst has no effect on position of equilibrium.
-It speeds up the rate at which the equilibrium is achieved.
-Speeds up the rate of the forward and backward reactions by the same amount.

79
Q

Haber process

A

-N2 +3H2 <–> 2NH3 -ve (exo).
-T=450C, P=200-1000 atm, catalyst=iron.

80
Q

Production of methanol from CO

A

-CO + 2H2 <–> CH3OH -ve (exo).
-T=400C, P=50 atm, catalyst=chromium and zinc oxides.

81
Q

Contact process

A

-Stage 1- S +O2 —> SO2
-Stage 2- SO2 + 1/2O2 <–> SO3 -98 (exo).
-T=450C, P=1/2 atm, catalyst=V2O5.

82
Q

Hydration of ethene to produce ethanol

A

-CH2=CH2 +H2O <–> CH3CH2OH -ve(exo).
-T=300C, P=70 atm, catalyst= conc H3PO4.

83
Q

Carbon neutral

A

-An activity that has no net annual carbon emissions to the atmosphere.

84
Q

Equilibrium constant

A

A Level Chemistry (6 decks)

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