Chem:4

Describe and explain how electronegativity changes as you go down group 7

Describe and explain how electronegativity changes as you go down group 7

Electronegativity decreases due to the increase in number of inner shells, and increase in distance between outer shell and the nucleus

Describe and explain how melting and boiling points change as you go down group 7

They increase due to an increase in shells and so electrons, so London forces between molecules become stronger, requiring more energy to overcome

What is the colour and state of F₂ at room temperature?

Pale yellow, gas

What is the colour and state of Br₂ at room temperature?

Red/brown, liquid

What is the colour and state of Cl₂ at room temperature?

Green, gas

What is the colour and state of I₂ at room temperature?

Grey, solid

Describe and explain the trend in reactivity of Group 7 elements as you go down the group

As you go down, atoms become larger, so valence electrons are further from the nucleus, there is also more shielding, making it harder to for the large electrons to attract electrons and so as you go down the group reactivity decreases

Describe and experiment that can show the reactivity of group 7 elements

The relative oxidising strengths of halogens can be seen in their displacement reactions with halide ions. If a reaction takes place you see a colour change (orange for Br₂, and brown for I₂), to make the colour easier to see, ass an organic solvent and shake

How do group 2 metals react with oxygen? Write and equation for O₂ + Ca

They burn in oxygen forming white oxides

2Ca_(s) + O_2(g)→ 2CaO_(s)

How do group 2 metals react with chlorine?

Write an equation for Sr

React to from soild white chlorides (salts)

Sr_(s) + Cl_2(g) → SrCl_2(g)

How do the oxides of group 2 react with water?

Write an equation for CaO

Explain any exceptions

React to form metal hydroxides which dissolve creating strongly alkaline solutions

CaO_(s) + H₂O_(l) → Ca(OH)_2(aq)

_{BeO is an exception, it doesn’t react MgO reacts very slowly}

How do group 2 bases react with dilute acids?

Write an equation for CaO and Ca(OH)₂ with HCl

They neutralise dilute acids by forming salts

CaO_(s) + 2HCl_(aq) → CaCl_2(aq) + H₂O_(l)

Ca(OH)_2(aq) + 2HCl_(aq) → CaCl_2(aq) + 2H₂O_(l)

How do compounds of group 2 metal ions with singly charged negative ions change in solubility as you go down the group?

They increase in solubility

How do compounds of group 2 metal ions with doubly charged negative ions change in solubility as you go down the group?

They decrease in solubility

Is Mg(OH)₂ or Ba(OH)₂ more soluble?

Ba(OH)₂

Is CaSO₄ or BaSO₄ more soluble?

CaSO₄

What is thermal stability?

How easily a compound can be decomposed upon heating, if a compound is more thermally stable, it is harder to decompose

Describe and explain how the thermal stability of group 1 and 2 carbonates/nitrates changes as you go down the group

Thermal stability increases, going down both groups, but stability depends on the polarising power of the metal cation, as you go across and up elements are less stable, as they have a higher charge, and are smaller, so have a higher charge density, so a stronger ability to attract electrons

Which group 1/2 carbonates decompose (thermally)?

In group 1 only Lithium, the rest are too stable, in group 2 all decompose

Write a equation for the thermal decomposition of Lithium carbonate and Calcium carbonate

Li₂CO_3(s) → Li₂O_(s) + CO_2(g)

CaCO_3(s) → CaO_(s) + CO_2(g)

Write an equation with Cl for: Group 7 + Group 1/2

Is it redox?

2Na + Cl₂ → 2NaCl

Redox

Write an equation with Cl for: Hydrogen halides + water

Is it redox?

HCl _(g)  + H₂O_(l) → H₃O⁺_(aq)  + Cl^-_(aq)

Not redox

Write an equation with Cl for: Hydrogen halides + ammonia

Is it redox?

HCl _(g)  + NH_3(g) → NH₄Cl_(s)

Not redox

Write an equation with Cl for: Group 7 + Cold alkali

Is it redox?

Cl₂ + NaOH → NaCl + NaOCl + H₂O

Disproportionation

Write an equation with Cl for: Group 7 + Hot alkali

Is it redox?

3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O

Disproportionation

Write an equation with Cl for: Group 7 + Water

Is it redox?

Cl₂ + H₂O ⇋ H⁺ + Cl^- + HOCl

Redox

What happens when hydrogen halides react with ammonia? Why?

White fumes are produced due to the formation of NH₄Cl_(s)

What is the formula of bleach?

NaOCl

How does the solubility of group 7 change as you go down the group?

As you go down the group the solubility decreases, iodine is the least soluble

What is the formula of Chlorate?

HOCl

Describe and explain how the reducing power of halides changes as you go down the group

As you go down the group it gets easier to oxidise the halides, as the ions get bigger and so valence electrons are further from the nucleus, there is also more shielding so as you go down the halides become better reducing agents

How can you test for (hydrogen) carbonates?

Add dilute HCl, which will fizz, as CO₂ is given off, then test for CO₂ using limewater

How can you test for the presence of sulfates?

Add dilute HCl, to remove any carbonate ions and then add barium chloride solution (Ba). If a white precipitate forms sulfate was present in original compound

How can you test for ammonium compounds?

Adding sodium hydroxide and gently heating will produce ammonia gas, if ammonia ions were present in original compound, ammonia gas will turn damp red litmus paper blue, as it dissolves in water.

How can chlorine be used to kill bacteria in water?

Write 2 equations

When Cl mixes it water it undergoes disproportionation, producing HCl and hypochlorous acid:

Cl_2(g) + H₂O_(l)  ⇋ HCl_(aq) + HClO_(aq)

Hypochlorous acid ionises producing chlorate (I) ions:

HClO _(aq)  + H₂O_(l) ⇋ ClO^-_(aq)  + H₃O⁺_(aq)  

Chlorate (I) ions kill bacteria