halogens

i am going toexplode and combust and then implode

how reactive are the halogens in general?

fairly reactive

how does reactivity change down the group? why?

• decreases down the group

• as halogens want to gain e^- to become -ve ions so reactivity decreases down the group as shielding increases down the group

how does the bpt of the halogens change down the group? why?

• increases down the group

• as molecules get larger

• so VDWs between molecules get stronger

how does electronegativity change down group 7? why?

• decreases down group

• as nucleus is more shielded

• so weaker attraction between nucleus and bonding pair

what is a disproportionation reaction?

a substance is both oxidised and reduced

give the full and ionic eqn for making bleach. what type of reaction is this? what observations are made?

2NaOH + Cl₂ → NaClO + NaCl + H₂O

ionic: 2OH⁻ + Cl₂ → Cl⁻ + ClO⁻ + H₂O

disproportionation, yellow green gas Cl → colourless solution

give the full and ionic eqn for the reaction of chlorine w/ water. what type of reaction is this?

ionic: Cl₂ + H₂O ⇌ 2H+ + Cl^- + ClO^-

Cl₂ + H₂O ⇌ HCl + HClO

disproportionation

give the eqns for the reaction of chlorine w/ water IN SUNLIGHT:

2Cl₂ + 2H₂O ⇌ 4HCl + O₂

2HClO → 2HCl + O₂

why is Cl added to water, despite its limitations?

• ClO^- ions kill bacteria → safe to swim in/drink

• only a small amount is added/benefits outweigh risks

give the strengths of adding Cl to water:

• kills disease causing microorganisms

• prevents algae growth

• removes discolouration

give the limitations of adding Cl to water:

• Cl gas is harmful

• liquid Cl is corrosive

• Cl can react w/ organic compounds in water to make chlorinated compounds (which can be cancerous)

describe a halogen displacement reaction and give the eqn for the displacement of Br by Cl₂ in KBr:

• a solution of a more reactive halogen can displace a less reactive halide from its salt

• 2KBr + Cl₂ → 2KCl + Br₂