AS Physical Flashcards
Isotope
-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.
Four sub-shells
-S- max 2
-P- max 6
-D- max 10
-F- max 14
First ionisation energy
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.
Second ionisation energy
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.
Factors affecting ionisation energy
-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)
4 stages of mass spectrometry:
-Ionisation
-Acceleration
-Flight tube
-Detection
Ionisation
Two ways:
-Electron impact.
-Electrospray ionisation.
Electron impact
-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).
Electrospray ionisation
-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.
Acceleration
-Positive ions are accelerated by an electric field.
-To a constant kinetic energy (KE=1/2xmxv^2).
Flight tube
-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.
Detection
-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.
Relative atomic mass
The average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.
Relative molecular mass
The average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12.
Avogadro constant
There are 6.022 x 10^23 atoms in 12 grams of carbon-12.
Mole
The amount of substance in grams that has the same number of particles as there are in atoms in 12 grams of carbon-12.
Concentration
Ideal gas equation
PV=nRT
Pressure(Pa) x Volume(m^3)= No. of moles x Gas constant x Temperature(K)
Empirical formula
An empirical formula is the simplest ratio of atoms of each element in the compound.
Molecular formula
A molecular formula is the actual number of atoms of each element in the compound.
Atom economy and equation
-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.
Percentage yield
-Actual yield/ Theoretical yield x 100
-High yield- efficient conversion of products to reactants.
Ionic bonding
The electrostatic force of attraction between oppositely charged ions formed by electron transfer.
Metals in ionic bonding
Metals lose electrons and form positive ions.
Non-metals in ionic bonding
Non-metals gain electrons and form negative electrons.
Ionic bonding strength
Bonding is stronger and melting point is higher when the ions are smaller and have higher charges.
Ionic radii
-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.
Properties of ionically bonded compounds
-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.
Covalent bonding
A shared pair of electrons.
Coordinate bonding
-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.
Properties of simple covalently bonded compounds
-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.
Properties of macromolecular covalently bonded compounds
-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.
Metallic bonding
The electrostatic force of attraction between the positive metal ions and delocalised electrons.
3 factors that affect strength of metallic bond
-Number of protons/ nuclear strength.
-Number of delocalised electrons per atom.
-Size of ion (smaller ion- stronger bond).
Properties of metallic compounds
-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.
Shapes of molecules
Draw table!
Below Top Valley SS Teacher Lives
How to explain shape
-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.
Linear
BP-2
LP-0
Angle(s)- 180
Trigonal Planar
BP-3
LP-0
Angle(s)-120
Tetrahedral
BP-4
LP-0
Angle(s)- 109.5
Trigonal Pyramidal
BP-3
LP-1
Angle(s)- 107
Bent
BP-2
LP-2
Angle(s)- 104.5
Trigonal Bipyramidal
BP-5
LP-0
Angle(s)- 120, 90
Octohedral
BP-6
LP-0
Angle(s)- 90
Electronegativity
The relative tendency of an atom in a covalent bond to attract a pair of electrons to itself.
Factors affecting electronegativity
-Number of protons
-Atomic radius
-Distance
Trends in electronegativity
-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.
Intermediate bonding
Symmetric molecule
Van der Waals forces
Main factor affecting size of VDW forces
Permanent dipole-dipole forces
Hydrogen bonding
Enthalpy change
The amount of heat energy given out or taken in during any change in a system provided the pressure is constant.
Exothermic reaction
-Energy is transferred from the system to surroundings.
-Products have less energy than reactants.
Endothermic reaction
-Energy is transferred from the surroundings to the system.
-Require input of heat energy.
-Products have more energy than reactants.
Standard enthalpy of formation
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.
Standard enthalpy change of combustion
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.
Standard conditions
-100kPa pressure
-298K
-Solutions at 1moldm-3
-All substances should have their standard state at 298K
Energy change=
Mass of solution x Specific heat capacity x Temperature change
Hess’s law
States that the total enthalpy change for a reaction is independent of the route by which the chemical change takes place.
Mean bond energies
The enthalpy needed to break the covalent bond into gaseous atoms, averaged over different molecules.
Enthalpy of combustion in a homologous series
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.
Collision theory
-Reactions can only occur when collisions take place between particles with sufficient energy.
-Minimum energy is called activation energy.
Activation energy
The minimum energy which particles need to collide to start a reaction.
Maxwell-Boltzman Distribution
-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.
Increasing temperature- effect on Maxwell-Boltzman Distribution
-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.
Rate of reaction
-Change in concentration of a substance in unit time.
-Gradient of curve- ROR.
Increasing concentration and increasing pressure- effect on Maxwell-Boltzmann Distribution
-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.
Increasing surface area- effect on Maxwell-Boltzmann Distribution
-Causes successful collisions to occur more frequently between reactant particles.
-Increases ROR.
Catalyst- effect on Maxwell-Boltzmann Distribution
-Catalysts increase ROR without getting used up.
-Provide an alternative route or mechanism with a lower activation energy.
Dynamic equilibrium
-Both forward and backward reactions are happening at the same time.
-Reversible reaction.
2 features of dynamic equilibrium
-Forward and backward reactions occurring at equal rates.
-Concentrations of reactants and products stay constant.
Le Chatelier’s Principle
-If an external condition is changed, the equilibrium will shift to oppose the change and try to reverse it.
Effect of temperature on equilibrium
-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.
Effect of pressure on equilibrium
-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.
Effect of concentration on equilibrium
-Increasing one of the reactants will cause the equilibrium to shift to oppose this and move in the forward direction to decrease concentration.
Effect of catalyst on equilibrium
-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.
Haber process
-N2 +3H2 <–> 2NH3 -ve (exo).
-T=450C, P=200-1000 atm, catalyst=iron.
Production of methanol from CO
-CO + 2H2 <–> CH3OH -ve (exo).
-T=400C, P=50 atm, catalyst=chromium and zinc oxides.
Contact process
-Stage 1- S +O2 —> SO2
-Stage 2- SO2 + 1/2O2 <–> SO3 -98 (exo).
-T=450C, P=1/2 atm, catalyst=V2O5.
Hydration of ethene to produce ethanol
-CH2=CH2 +H2O <–> CH3CH2OH -ve(exo).
-T=300C, P=70 atm, catalyst= conc H3PO4.
Carbon neutral
-An activity that has no net annual carbon emissions to the atmosphere.
Equilibrium constant
