3.1 The Periodic Table Flashcards
How is the periodic table arranged?
In order of increasing atomic number
Periods - horizontal row - increase from left to right - trends in chemical and physical properties (periodicity)
Groups - vertical column - elements with same chemical and physical properties due to same number of electrons in outer shell and same orbitals (same electron configuration)
What is the periodic trend in electron configurations?
Moving across a period, you can see that the number of occupied energy levels is the same as the period number
What is meant by the ‘classification of elements into s-, p- and d- blocks’?
The periodic table is structured into blocks that are linked to its sub-shells
The pattern mirrors the sub-shells that are being filled
What is first ionisation energy?
The energy required to remove one electron from each atom in one mole of gaseous element to form one mole of gaseous 1+ atoms
X (g) –> X+ (g) + e-
What is the trend in first ionisation energies in periods 2 and 3?
Moving across a period…
the number of protons increase so the nuclear charge is greater
shielding remains the same
attraction between the nuclei and electrons increase
more energy required to remove an electron - 1st ionisation energy increases
What is the trend in first ionisation energies down a group?
Moving down a group…
nuclear charge increases
shielding increases therefore distance between nuclei and outermost electron increases
attraction between nuclei and outermost electron decreases
less energy required to remove one electron - 1st ionisation energy decreases
Why are there small decreases in the first ionisation energy between group 2 and 13 elements?
Group 13 elements have outermost electrons in a p- orbital
Group 2 have theirs in an s- orbital
P- orbitals have slightly higher energy than s- orbitals - further away from nucleus
…electrons in p-orbitals are easier to remove
Why is there a decrease in first ionisation energy between group 15 and 16?
Group 15 contains only one electron in its p-orbital
In group 16 the outermost electron is spin-paired in the p-orbital - experience repulsion making it easier to remove an electron
What are successive ionisation energies?
A measure of how much energy is required to remove each electron in turn
Why is each successive ionisation energy higher than the one before?
As each electron is removed…
there is less repulsion between the remaining electrons
each shell is drawn closer to the nucleus
higher nuclear attraction - more energy required to remove each successive electron
What is metallic bonding?
The strong electrostatic attraction between cations and delocalised electrons
What is a giant metallic lattice structure?
The delocalised electrons are spread throughout the structure and can move
Over the whole structure the charges balance
A lattice of positive ions fixed in position with a sea of delocalised electrons that are mobile
What are the properties of giant metallic lattices?
High melting/boiling points - strong attractions between cations and delocalised electrons
Good electrical conductivity - delocalised electrons are mobile in a solid state
Malleable (hammered into different shapes) - mobile electrons means layers can slide past each other
Ductile (drawn out or stretched) - mobile electrons means layers can slide past each other
What are giant covalent lattices and the different types?
Strong covalent bonds making up a giant structure
Diamond - each Carbon atom forms four other Carbons around it - very hard
Graphene - 2D giant lattice, one carbon atom thick, of interlocking hexagonal Carbon rings - strong, light, conductor
Graphite - layered structure with delocalised electrons between layers - conductor
Silicon - networks of atoms bonded by strong covalent bonds
Why is there a variation in melting points across periods 2 and 3 (in terms of structure and bonding)?
As you move across periods 2 and 3 the elements change from metals to non-metals and from solids to gases
What are the trends in melting points in the groups?
Group 1 - 14
…melting points increase steadily as all are giant structures
Group 14 - 15
…sharp decrease in melting point because elements have simple molecular structures (weak intermolecular forces)
Group 15 - 18
…low melting point as it has simple molecular structure
Why does reactivity increase down group 2 elements?
To achieve the electron configuration of a noble gas, 2 electrons must be lost
Two outer electrons are easier to lose down the group
Therefore reactivity increases due to the fact that…
each successive element has its outer electrons at higher energy levels;
a larger atomic radius and increased shielding
What happens when a group 2 element reacts with oxygen?
Reacts vigorously with oxygen - a redox reaction
2[Group 2 element] + Oxygen –> 2XO (s)
What happens when a group 2 element reacts with water?
All react with water except beryllium
Moving down the group, each metal reacts more vigorously with water
metal + 2Water (l) –> X-hydroxide + hydrogen
Redox - metal oxidised and hydrogen reduced
Metal hydroxide soluble in water and form alkaline solutions because they release OH- ions (pH 10-12)
Solubility increases down group
What happens when a group 2 element reacts with dilute acid?
All elements except beryllium react with dilute acid
Becomes more vigorous moving down the group
metal + 2HCl (aq) –> X chloride + hydrogen
What are the uses of group 2 compounds?
Oxides, carbonates and hydroxides of group 2 elements react with acid to form a salt and water - solid oxide or hydroxide ‘dissolves’
Calcium hydroxide is used to neutralise acidic soils in agriculture
Magnesium hydroxide neutralises excess acid in stomachs to produce a salt and water to cure indigestion
Calcium carbonate is in limestone and marble - manufacture of glass and steel…drawback is that they react with acid so erodes with rainwater
What is the trend in boiling points for the halogens?
Moving down the group…
boiling point increases and physical states change from gas to liquid to solid
because each successive element has an extra shell of electrons - more London forces between molecules
How reactive are the halogens?
Very reactive and highly electronegative
Very good at attracting and capturing electrons - good oxidising agents
During reactions each atoms gains an electron to form a 1- ion and obtain noble gas configuration
Why does the reactivity decrease down the group?
The atomic radius increases
Shielding increases
Ability to gain an electron in p sub-shell and form 1- ions decreases
What is a displacement reaction in terms of halogens?
A more reactive halogen oxidising and displacing a halide of a less reactive halogen
What are the colours of solutions of chlorine, bromine and iodine?
Chlorine
water - pale green
cyclohexane - pale green
Bromine
water - orange
cyclohexane - orange
Iodine
water - brown
cyclohexane - violet
Why is the mixture of a halogen and water usually shaken with an organic solvent, such as cyclohexane?
To help distinguish between bromine and iodine since they are similar colours in water
Which ions can chlorine oxidise?
Both bromide and iodide ions
Cl2 + 2Br- –> 2Cl- + Br2
All in aqueous state
Which ions can bromine oxidise?
Only iodide ions
Br2 + 2I- –> 2Br- + I2
All in aqueous state
Which ions can iodine oxidise?
Neither chlorine nor bromide
What is disproportionation?
A reaction where the same element is both oxidised and reduced
What is the reaction for water purification?
Cl2 + H2O –> HClO + HCl
Chlorine is oxidised and reduced
What are the advantages of using chlorine to purify water?
Chlorine kills bacteria which virtually eradicates some water-carried diseases such as cholera and dysentery
What are the disadvantages of purifying water with chlorine?
Chlorine gas is toxic chlorinated hydrocarbons could form which are toxic
What are alternatives to purifying water with chlorine?
Filtration
Aeration
Coagulation
Treatment with UV light
What is periodicity?
The trend in properties that is repeated across each period
Predictions can be made about the likely properties of an element and its compounds
What are qualitative tests and precipitation reactions?
Qualitative tests tell you which ions are present but not how much of it
A precipitation reaction produces an insoluble solid from two aqueous solutions and many qualitative tests involve this
How do you test for carbonate anions?
Method
- add a dilute strong acid to the sample
- collect any gas for,ed and pass it through limewater
Positive test
- fizzing/colourless gas is produced
- the gas turns limewater cloudy
CO32- + 2H+ –> H2O + CO2
How do you test for sulfate anions?
Method
1. add dilute Hydrochloric acid and barium chloride to the sample
Positive test
- white precipitate of barium sulfate is formed
Ba2+ + SO42- –> BaSO4
How do you test for halide anions?
Method
- dissolve sample in water
- add aqueous silver nitrate solution
- note colour of precipitate
- if colour is hard to distinguish add aqueous ammonia (first dilute then concentrated)
- note solubility of aqueous ammonia
Positive result
- AgCl - white precipitate, soluble in dilute ammonia
- AgBr - cream precipitate, soluble in concentrated ammonia only
- AgI - yellow precipitate - insoluble in ammonia
What is the reaction for bleach formation?
Cl2 + 2NaOH –> NaCl + NaClO + H2O
Chlorine is both oxidised and reduced
Household bleach is formed when chlorine and sodium hydroxide react at room temperature
What is the sequence of tests for anions?
- carbonate test
- sulfate test
- halide test
because BaCO3 and Ag2SO4 are insoluble
How do you test for ammonium cations?
Method
- add sodium hydroxide solution to the sample and warm very gently
- test any gas evolved with red litmus paper
Positive test
- red litmus paper turns blue
- ammonia gas has a distinctive smell
