Periodicity Flashcards
trend of atomic radius across a period (2)
decreases
• Outer electrons are in the same shell so same amount of shielding
• Increase in number of protons in the nucleus so nuclear charge increases so stronger attraction between nucleus and outer shell electrons. Outer shell electrons are pulled closer to the nucleus
general trend of ionisation energies across a period (3)
generally increases
• Decrease in atomic radius
• Increase in protons increases nuclear charge
• Same shielding
why is there a decrease in ionisation energy between groups 2 -> 3
o Electron is lost from 3s orbital in Mg but in 3p orbital in Al
o 3p is higher in energy than 3s so requires less energy to remove from 3p
why is there a decrease in ionisation energy between groups 5 -> 6
o Electron is lost from an orbital containing a pair of electrons in group 6
o Extra electron-electron repulsions means less energy is required to remove the electron from p4 rather than p3
trend of electronegativity across period (2)
increases
• More protons in nucleus increases nuclear charge
• Smaller atomic radius
• Same shielding so stronger attractions between nucleus and outer shell electrons
trend of melting points across period 3
increases group 1 -> 3
greater increase group 3 -> 4
decreases group 4 -> 0
why does melting point increase from group 1 -> 3 (3)
Positive metal ions increase in charge
More delocalised electrons per positive ion
Smaller ions/ atomic radius
why does melting point increase more from group 3 -> 4 (1)
Group 4 has a giant covalent structure with millions of strong covalent bonds
why does melting point decrease from group 4 -> 0
Groups 5, 6 and 7 are simple molecules so have weak intermolecular forces between the molecules
Slight increase from P4 to S8 (S8 has higher molecular mass so stronger van der waals forces)
Cl2 has low molecular mass so less electrons so weaker van der waals
Group 0 exist as monoatomic so there are very weak forces between atoms
sodium reaction with water
Na floats, moves and fizzes with water: 2Na + H2O 2NaOH + H2
magnesium reaction with water
Mg has a very slow reaction with water and with steam it burns with a white flame and forms a white powder: Mg + H2O MgO + H2
Al, Si, P4 and S8 reaction with water
do not react with water as they are non-polar molecules so no interactions
chlorine reaction with water
Cl2 dissolves to give a pale green colour: Cl2 + H2O ↔ HCl + HClO (chloric acid)
sodium reaction with oxygen
• Na burns with a yellow flame and produces a white powder: 4Na + O2 Na2O (s)
magnesium reaction with oxygen
• Mg burns with a bright white flame and produces a white powder: 2Mg + O2 2MgO (s)
aluminium reaction with oxygen
• Al forms an oxide layer when in contact with air
o Prevents further reaction
o If pure it produces a white flame and forms a white powder
o 4Al + 3O2 2Al2O3 (s)
silicon reaction with oxygen
• Si is unable to ignite alone and will burn with a white flame and slowly form a white powder: Si + O2 SiO2 (s)
phosphorus reaction with oxygen
• P4 is spontaneously flammable in air and burns with a bright white flame and forms a white powder: P4 + 5O2 P4O10 (s)
sulphur reaction with oxygen
• S burns with a blue flame and gives off an acidic colourless choking gas: S + O2 SO2 (g)
Na2O, MgO and Al2O3 melting points
high melting points
Ionic giant lattice structures contain many strong electrostatic attractions between the oppositely charged ions which require a lot of energy to break
Large electronegativity between metal and O
why does Al2O3 have a lower melting point than Na2O and MgO
has some covalent character and Al is not as electronegative so bonding is weaker
how doe we test if metal oxides are ionic
melt the solid and test for conductivity
why does SiO2 have quite a high melting point
o Has a macromolecular structure consisting of millions of strong covalent bonds between the atoms which require a lot of energy to break
why do P4O10, SO3 and SO2 have low melting points
o Are simple molecules so have weak van der waals forces between the molecules which require little energy to break
why does P4O10 have a higher melting point than SO2
higher molecular mass so contains more electrons so van der waals forces are stronger
order of melting points of period 3 oxides
MgO > Al2O3 > Na2O > SiO2 > Na2O > P4O10 > SO3 > SO2
sodium oxide reaction with water
• Na2O is ionic so dissolves and reacts to form a alkaline solution pH 14: Na2O + H2O 2NaOH
magnesium oxide reaction with water
• MgO is slightly soluble as ionic bonding is strongest to form an alkaline pH 10 solution: MgO + H2O Mg(OH)2
aluminium oxide reaction with water
• Al2O3 is insoluble as not enough interaction and high ionic lattice enthalpy
phosphorous oxide reaction with water
• P4O10 is a big simple molecule so reacts violently to form pH 0: P4O10 + 6H2O 4H3PO4
H2O molecules attach to δ+ P atoms leading to the release of H+ ions from water molecules
P4O10 + 6H2O 4H+ + 4H2PO4-
sulphur dioxide reaction with water
• SO2 dissolves and then reacts to form a solution pH 3: SO2 + H2O H2SO3
SO2 + H2O H+ + HSO3-
sulphur trioxide reaction with water
• SO3 is a simple molecule which reacts violently to form pH 0: SO3 + H2O H2SO4
H2O molecules attach to δ+ S atoms leading to the release of H+ ions from water molecules
SO3 + H2O H+ + HSO4-
sodium oxide reacting with acid/base
• Na2O is basic so only reacts with acids: Na2O + 2H+ 2Na+ + H2O
magnesium oxide reacting with acid/base
• MgO is basic so only reacts with acids: MgO + 2H+ Mg2+ + H2O
aluminium oxide reacting with acid/base
• Al2O3 is amphoteric so will react with both acids and alkalis
Al2O3 + 6H+ 2Al3+ + 3H2O
Al2O3 + 2OH- 2Al(OH)4 + 3H2O
silicon oxide reacting with acid/base
• SiO2 is acidic so only reacts with very concentrated NaOH: SiO2 + 2NaOH Na2SiO3 + H2O
phosphorous oxide reacting with acid/base
• P4O10 is acidic: P4O10 +12OH- 4PO43- + 6H2O
sulphur dioxide reacting with acid/base
• SO2 is acidic: SO2 + 2OH- SO32- + H2O
sulphur trioxide reacting with acid/base
• SO3 is acidic: SO3 + 2OH- SO42- + H2O
Silicon dioxide reaction with water
SiO2 has a macromolecular structure consisting of strong covalent bonds so pH 7
