Group 2 and Group 7 Flashcards
What happens to the atomic radius as you go down group 2?
It increases as each element gets an extra main energy level.
What happens to the first ionisation energy as you go down group 2?
It decreases because the atomic radius increases, more shielding, these decrease attraction between nucleus and outer shell electrons
What happens to the melting point as you go down group 2?
Decreases because all of the metals donate two outer electrons to the delocalised sea. As you go down the group, the atomic radius increases so these electrons are further away from the nucleus so the force of attraction between them is less so the metallic bonds are weaker.
What happens to the electronegativity as you go down group 2?
Decreases because atomic radius increases and there is more shielding, this decreases attraction between electrons and nucleus so it has a weaker ability to attract electrons.
Observations and equation when Mg is reacted with water
Reacts with steam to form a white solid
Mg(s) + H2O(g) -> MgO(s) + H2(g)
Or reacts slowly with water in the general equation.
Observations and equation when Ca is reacted with water
Fizzing with bubbles given off and a white precipitate
Ca(s) + 2H2O(l) -> Ca(OH)2(s) + H2(g)
Observations and equation when Sr is reacted with water
Fizzes more in water and bubbles formed. Colourless solution
Sr + 2H2O -> Sr(OH)2 + H2
Observations and equation when Ba is reacted with water
Fizzes more in water and bubble formed. Colourless solution.
Ba + 2H2O -> Ba(OH)2 + H2
Trend for solubility of hydroxides (G2)
Mg is insoluble
Ca is partially soluble
Sr and Ba are both soluble
Trend for solubility of sulfates (G2)
Mg is soluble
Ca is partially soluble
Sr and Ba are insoluble
Uses for Mg(OH)2
Extracting titanium from TiCl4, indigestion treatment.
Uses of Ca(OH)2
Limewater to neutralise acidic soil.
Uses of BaSO4
Barium meal as it absorbs x-rays well
Why is dilute nitric or hydrochloric acid added before testing for sulfate ions?
To remove carbonate ions as CO2 because barium carbonate is also a white solid so is indistinguishable from barium sulfate.
Trend in electronegativity in group 7
Decreases down the group because atomic radius increases because the have more shells. This means more shielding so less attraction between nucleus and electrons in covalent bond
Trend in boiling point in group 7
Increases down the group because the atoms are larger and have more electrons so have more and stronger Van der Waals forces between the molecules.
Why is the F-F bond unexpectedly weak?
Goes against trend of bond enthalpy. The small size of F atom leads to repulsion between the non-bonding pairs as they are so close together.
Oxidising agent
Something that takes electrons from another substance and is itself reduced
Trend of oxidising power of halogens
Increases up the group because (same as trend in electronegativity)
Reducing agent
Something that loses electrons to reduce another substance and is itself oxidised.
Trend in reducing power of halides
Increases down the group because the ions are larger meaning the electrons in the outer shell are further from the nucleus so the attraction between them is less and the electrons are more easily lost.
Observations of reaction with chloride ions and sulfuric acid.
Steamy fumes (HCl)
Observations of reaction with bromide ions and sulfuric acid.
Steamy fumes (HBr), colourless gas (SO2), orange gas (Br2), water
Observations of reaction with iodide ions and sulfuric acid.
Steamy fumes (HI), colourless gas (SO2), purple gas (I2), bad smell H2S, yellow solid (S), water.
Method to test for halide ions
Add dilute nitric acid to remove any other ions that could form a precipitate with silver nitrate. Add silver nitrate until a precipitate forms. Add dilute ammonia to the precipitate (2cm^3). Dropwise, add concentrated ammonia.
How can you tell there were chloride ions in a sample?
White precipitate, dissolved, dissolved
How can you tell there were bromide ions in a sample?
Cream precipitate, not dissolved, dissolved
How can you tell there were iodide ions in a sample?
Yellow precipitate, not dissolved, not dissolved
Equation with chlorine reacting with cold, dilute NaOH
Cl2 + 2NaOH -> NaClO + NaCl + H2O
Equation with chlorine reacting with water (no sunlight)
Cl2(g) + H2O(l) -> HClO(aq) + HCl(aq)
Equation with chlorine reacting with water (sunlight)
2Cl2(g) + 2H2O(l) -> 4HCl(aq) + O2(g)
Equation with water reacting with sodium chlorate
NaClO(s) +H2O(l) Na+(aq) + OH-(aq) + HClO(aq)
How does chloric acid (HClO) purify water
It is an oxidising agent and kills bacteria by oxidation.
Why is swimming pool water kept slightly acidic?
So that the equilibrium for the reaction with NaClO and H2O is to the right so more chloric acid is formed. Not too acidic to corrode metal components or affect swimmers.
Test for sulfate ions
Add dilute nitric or hydrochloric acid. Then add barium chloride solution. If sulfate ions are present, a white precipitate of barium sulfate is formed.
Test for hydroxide ions
Same as test for ammonium ions only you add the ammonium compound.
Test for ammonium ions
Add sodium hydroxide solution and warm the mixture. If ammonium ions were present, ammonia gas will be formed which has a pungent smell and turns red litmus paper blue.
Test for carbonate ions
Add dilute nitric or hydrochloric acid. If carbonate ions were present, there is effervescence due to CO2 gas forming. This gas turns limewater cloudy.
