module 3: periodic table and energy Flashcards
what is periodicity?
a repeating trend in properties of the elements across each period of the periodic table
what is the first ionisation energy?
the energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
what are the factors affection ionisation energy?
- atomic radius
- nuclear charge
- electron shielding
explain how atomic radius affects ionisation energy
- the greater the distance between the nucleus and the outer electrons, the less the nuclear attraction
- the larger the radius, the smaller the amount of energy required to remove the electron from the outermost orbital, so first ionisation energy decreases
explain how nuclear charge affects ionisation energy
- the more protons there are in a nucleus of an atom, the greater the attraction between the nucleus and the outer electrons
- therefore, as the nuclear charge increases, so does the ionisation energy
explain how electron shielding affects ionisation energy
- the greater the shielding effect, the weaker the attraction between the nucleus and the outer electrons
- the higher the shielding effect, the lower the ionisation energy
what is the second ionisation energy?
the energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions
explain the trend in first ionisation energy down a group
first ionisation energies decrease down a group, because:
- atomic radius increases
- more inner shells so shielding increases
- nuclear attraction on outer electrons decreases
- first ionisation energy decreases
explain the trend in first ionisation energy across a period
first ionisation energies increase across a period, because:
- nuclear charge increases
- same shell: similar shielding
- nuclear attraction increases
- atomic radius decreases
- first ionisation energy increases
explain the fall in ionisation energy between beryllium and boron
- the fall in the first ionisation energy between beryllium and boron marks the start of filling the 2p sub-shell
- the 2p sub-shell in boron has a higher energy than the 2s sub-shell in beryllium
- therefore, in boron, the 2p electron is easier to remove than one of the 2s electrons in beryllium
- the first ionisation energy of boron is less than the first ionisation energy of beryllium
explain the fall in ionisation energy between nitrogen and oxygen
- the fall in the first ionisation energy between nitrogen and oxygen marks the start of electron pairing in the p-orbitals of the 2p sub-shell
- in nitrogen and oxygen, the highest energy electrons are in a 2p sub-shell
- in oxygen, the paired electrons in one of the 2p orbitals repel one another, making it easier to remove an electron from an oxygen atom than a nitrogen atom
- therefore, the first ionisation energy of oxygen is less than the first ionisation energy of nitrogen
what is metallic bonding?
the strong electrostatic attraction between cations and delocalised electrons
what are the properties of metals?
- strong metallic bonds
- high electrical conductivity
- high melting and boiling points
the reaction of barium with bromine is more vigorous than the reaction of calcium with bromine, explain why
- barium has a larger atomic radius than calcium
- therefore, outer electrons experience less shielding
- so the nuclear attraction in barium is weaker than in calcium
- so it is easier to remove outer electrons in barium than calcium
explain which block in the periodic table sodium and magnesium belong to
s-block, outer electron is in a s-orbital
the reactivity of the Group 2 elements Mg–Ba increases down the group, explain why
- atomic radius increases
- shielding increases
- nuclear attraction decreases
- easier to remove an electron
explain the differences in the melting points of sodium and magnesium, using the model of metallic bonding
- magnesium has a higher melting point than sodium
- magnesium has more outer electrons
- magnesium ions have a greater positive charge
- magnesium has a greater attraction between ions and delocalised electrons
what is the name given to this repeating pattern of properties?
periodicity
explain the differences in the melting points of phosphorus (P4) and chlorine (Cl2)
- phosphorus has more electrons
- therefore stronger London forces
- more energy required to overcome the intermolecular forces
describe the bonding in magnesium and silicon
- magnesium has metallic bonds
- cations with a +2 charge and delocalised electrons
- silicon has covalent bonds
- between atoms
explain why the first ionisation energy of strontium is less than the first ionisation energy of calcium
- strontium has a larger atomic radius
- increased nuclear charge is outweighed by increased shielding
- less nuclear attraction
- so it is easier to remove an electron
state the structure and bonding in silicon dioxide
giant covalent lattice
which groups are classified as the s-block in the periodic table?
groups 1 and 2
which groups are classified as the p-block in the periodic table?
groups 3 to 0
which group is classified as the d-block in the periodic table?
transition metals
what is the correct order to carry out the tests for anions?
- carbonate
- sulfate
- halides
why does the carbonate test need to be carried out before the sulfate test?
- in the sulfate test, you add a solution containing barium ions and are looking for a white precipitate of barium sulfate
- barium carbonate is white and insoluble in water, so if you carry out a sulphate test on a carbonate, you will get a white precipitate too
- therefore, it is important to carry out the carbonate test first and only proceed to the sulfate test when you know that no carbonate ions are present
state and explain the trend in atomic radius from Li to F
- atomic radius decreases
- because the nuclear charge increases
- outer electrons are in the same shell
- so there is a greater nuclear attraction on the outer electrons
what is the most common type of reaction for group 2 elements?
redox reactions
are group 2 elements oxidising or reducing agents and why?
reducing agents, because it loses two electrons and reduces another species
explain the trend in reactivity down group 2
- reactivity increases going down the group
- because the ionisation energies decrease down the group
- due to the decreased nuclear attraction on the outer electrons
- as a result of increasing atomic radius and increasing shielding
what is the trend in solubility of the metal hydroxides going down group 2?
- solubility of the hydroxides in water increases down the group
- so the resulting solution has more hydroxide ions and are more alkaline
explain the trend in boiling points down group 7
- going down the group, the halogen molecules have more electrons
- stronger london forces
- more energy required to overcome these intermolecular forces
- so boiling point increases
why are metals good electrical conductors?
the delocalised electrons can move throughout the structure and carry charge, in both solid and liquid states
are giant covalent structures soluble or insoluble, and why?
insoluble, because the covalent bonds holding together the atoms in the lattice are too strong to be broken down by interaction with solvents
what is the trend in melting points across period 2 and 3
- the melting point increases from group 1 to group 4
- there is a sharp decrease in melting point between group 4 and group 5
- the melting points are comparatively low from group 5 to group 0
why are silicon, carbon, oxygen and chlorine all classified as p-block elements?
their highest energy electron is in a p-orbital
explain how to carry out the test for carbonates
- in a test tube, add dilute nitric acid to the solid or solution to be tested
- if bubbles are produced, the unknown compound could be a carbonate
- to prove the gas is carbon dioxide, bubble the gas through lime water
- if the limewater turns cloudy, carbon dioxide is present and the compound is a carbonate
explain how to carry out the sulfate test
- first, add dilute hydrochloric acid to the solid or solution to be tested
- then add aqueous barium chloride
- if a sulfate is present, a white precipitate of barium sulfate will form
explain how to carry out the halide tests
- add aqueous silver nitrate to an aqueous solution of a halide
- the silver halide precipitates are different colours: silver chloride is white, silver bromide is cream, and silver iodide is yellow
- add aqueous ammonia to test the solubility of the precipitate: silver chloride is soluble in dilute aqueous ammonia, silver bromide is soluble in concentrated aqueous ammonia, and silver iodide is insoluble in concentrated aqueous ammonia
first ionisation energies decrease down groups in the periodic table, explain this trend and the effect on the reactivity of groups containing metals
- going down groups, the atomic radius increases
- there are more inner shells so increased shielding
- nuclear attraction on outer electrons decreases
- so the first ionisation energies decrease
- for groups containing metals, this means that the reactivity increases going down the group
- as it is easier to remove an outer electron due to the decreased nuclear attraction
what is the name given to this repeating pattern of properties?
periodicity
state how and explain why the attraction between nuclei and outermost electrons in gaseous atoms varies across period 3
- the attraction increases across the period
- because, the nuclear charge increases and the atomic radius decreases
describe and explain the electrical conductivity of sodium oxide, and sodium in their solid and molten states
sodium:
- can conduct in both its solid and molten states
- because the delocalised electrons are free to move
sodium oxide:
- cannot conduct in its solid state as the ions are fixed in place in an ionic lattice
- can conduct in its molten state as the ions are mobile
state and explain the trend in atomic radius from Li to F
- atomic radius decreases from Li to F
- this is because the nuclear charge increases
- and they have the same number of shells
- so there is greater nuclear attraction on outer electrons
what is the activation energy?
the minimum energy required to start a reaction by the breaking of bonds
what is enthalpy?
a measure of the heat energy in a chemical system
what is the enthalpy change?
the difference between the enthalpy of the products and the enthalpy of the reactants
what is the law of conservation of energy?
energy cannot be created or destroyed
what does “standard state” mean?
the physical state of a substance under the standard conditions of 100kPa and 298K
what is the standard enthalpy change of reaction?
the enthalpy change that accompanies a reaction in the molar quantities stated in the equation under standard conditions, all reactants and products being in their standard states
what is the standard enthalpy change of formation?
the enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions
what is the standard enthalpy change of combustion?
the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states
what are the standard conditions for enthalpy change?
100kPa pressure, 298K temperature and 1.0 mol per cubic decimetre concentration of aqueous solutions
what is the average bond enthalpy?
the energy required to break one mole of a specified type of bond in a gaseous molecule
what are the two conditions that are always true for bond enthalpies?
- bond enthalpies are always endothermic
- bond enthalpies always have a positive enthalpy value
what are the limitations of average bond enthalpies?
the actual bond enthalpy can vary depending on the chemical environment of the bond e.g. the composition of the given molecule
what is Hess’ Law?
the enthalpy change accompanying a chemical reaction is independent of the route by which the change occurs
what is the role of a catalyst?
- lowers the activation energy by providing an alternate pathway
- they increase the rate of reaction, and are not used up during the reaction
what is the difference between the activation energy in exothermic and endothermic reactions?
the activation energy is endothermic reactions is relatively larger than in exothermic reactions
what is a heterogeneous catalyst?
a catalyst that is in a different physical state to the reactant
what is the Boltzmann distribution?
the spread of molecular energies in gases
what are the key features of the Boltzmann distribution?
- no molecules have zero energy, it starts at the origin
- the area under the curve is equal to the total number of molecules
- there is no maximum energy for a molecule, the curve does not meet the x-axis at high energy
what is Le Chatelier’s principle?
states that when a system in equilibrium is subjected to an external change the system readjusts itself, the position of equilibrium shifts, to minimise the effect of that change
what does dynamic equilibrium mean?
- the rate of the forward reaction is equal to the rate of the reverse reaction
- the concentration of reactants and products do not change
what does the value of the equilibrium constant tell us?
- the exact position of equilibrium
- indicates the relative proportions of reactants and products in the equilibrium system
describe the effect of a catalyst on the position of equilibrium
- a catalyst does not change the position of equilibrium
- it merely speeds up the rates of the forward and reverse reactions equally
- but it will increase the rate at which an equilibrium is established
describe and explain the effect of decreasing the pressure on the rate of reaction
- concentration is reduced
- fewer collisions per second
- and the rate of reaction decreases
what are the factors affecting equilibrium position?
- temperature
- pressure
- concentration
how do you convert cm³ to m³?
times ten to the minus 6
how do you convert dm³ to m³?
times ten to the minus 3
