Periodicity Set 1 Flashcards
What is a group?
Vertical Column in the Periodic Table
What is a period?
Horizontal Row in the Periodic Table
What is periodicity
The study of trends in the Periodic Table
Trend in 1st ionisation energy down group 2
Decreases. Despite an increase in proton number, there are more electrons, shells and shielding so less energy is needed to remove a valence electron.
Trend in atomic radius down group 2
Increases. Despite an increase in proton number, there are more electrons, shells and shielding so the atomic radius is larger.
Trend in melting point down group 2
Generally decreases. The type of bonding is metallic with each metal forming a 2+ cation in a sea of delocalised electrons. Down the group the larger cations mean the attraction between the nucleus of the cation and the delocalised electrons decreases.
Trend in electronegativity down group 2
Decreases. Despite an increase in proton number, there are more electrons, shells and shielding so the ability of the nucleus to attract a pair of electrons in a covalent bond decreases.
Products of reaction of barium in cold water
barium hydroxide + hydrogen
What happens to pH of group 2 hydroxides down group?
Increases. The hydroxides become more soluble down the group so the hydroxide ion is more easily dissociated. (Alkalinity is a measure of OH ions.)
Products of reaction of magnesium with cold water
magnesium hydroxide + hydrogen
Products of reaction of magnesium with steam
magnesium oxide + hydrogen
Observations for sodium and water
Effervescence, Na forms a ball and moves around the surface of the water. A white trail of NaOH is produced that dissolves in the water. An alkaline solution is formed
Observations for burning Mg in air
White light and white powder (MgO) formed.
How does the solubility of hydroxides change down group 2?
Increases - Mg(OH)2 insoluble, Ca(OH)2 sparingly soluble
How does the solubility of sulfates change down group 2?
Decreases
What is a use of barium sulfate?
Barium meals - a suspension of Ba(OH)2 is drunk, which coats the intestine and shows up abnormalities during an X-ray
Chemical Test for sulfates?
Add acidified barium chloride. Acid reacts with carbonate impurities (causing effervescence), barium chloride reacts with sulfate forming a white ppt of barium sulfate
What is a use of magnesium hydroxide?
Antacids/ indigestion medicine. The hydroxide reacts with excess stomach acid forming neutral salt and water
What is a use of calcium hydroxide?
Neutralising acidic soils for growing crops
Which acidic gas is produced from burning fossil fuels and how can it be dealt with? Include equations.
SO2 due to sulfur impurities in the fuel. This can cause acid rain. A calcium oxide filter is put in the flue of power stations. CaO + SO2 –> CaSO3 then CaSO3 + SO2 –> CaSO3 + CO2
Trend in atomic radius across period 3
Decreases. Despite having same number of shells and shielding, the proton number increases increasing the attraction of the nucleus to the valence electrons.
Definition of electronegativity
Ability of an atom to attract a pair of electrons in a covalent bond
Trend in electronegativity across period 3
Increases. Despite having same number of shells and shielding, the proton number increases increasing the attraction of the nucleus to a pair of electrons in a covalent bond
Type of bonding in Na
metallic
Type of bonding in Mg
metallic
Type of bonding in Al
metallic
Type of bonding in Si
giant covalent network
Type of bonding in P
P4 - simple covalent molecule
Type of bonding in S
S8 - simple covalent molecule
Type of bonding in Cl
Cl2 - simple covalent molecule
Trend in melting point from Na to Al
Increases. The cations have an increasing charge density (smaller ions with greater charge) and an increase in delocalised electrons increases the attraction between the cations and sea of delocalised electrons
Melting point of Si and reason
Very high. Si forms a giant covalent network with very strong covalent bonds between atoms requiring a lot of energy to overcome.
Trend in melting point from P to Ar
S8 > P4 > Cl2 > Ar. Larger molecules have more surface area so have stronger intermolecular forces (VdWs) between molecules
Trend in 1st ionisation energy across period 3
Generally increases. Despite having same number of shells and shielding, the proton number increases increasing the attraction to the electron being removed
Account for change in 1st ionisation energy from Mg to Al
Decreases - the electron being lost in Al is in a 3p orbital compared to a 3s orbital in Mg, which is further from the attraction of the nucleus and is more shielded
Account for change in 1st ionisation energy from P to S
Decreases - the electron being lost in S is in a doubly filled 3p orbital. There is some repulsion from the other electron so less energy is needed to remove it compared with the outer electron in P
