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a-level chem (aqa) > 3.2: Periodicity > Flashcards

3.2: Periodicity Flashcards

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1
Q

What is periodicity?

A

a regular repeating pattern of atomic physical and chemical properties

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2
Q

What is the trend in melting points across period 3?

A
  • increases
  • due to increase in nuclear charge
  • more delocalised eolectrons to increase metallic bond strength
  • more energy needed to break these bonds
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3
Q

Na, Mg, Al

What are the trends in melting and boiling point across Period 3?

A

1.Na, Mg, Al
- giant metallic latice with positive metal ions surrounded by a sea of delocalised electrons
- strong electrostatic forces, increasing nuclear charge
- Mp- 371,922,933 l Bp- 1156,1380,2740

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4
Q

Si

What are the trends in melting and boiling point across Period 3?

A

2.Si
- giant covalent/ macromolecular molecule
- many strong covalent bonds
- Mp- 1683 l BP- 2628

melting and boiling point fluctuate

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5
Q

P4, S8, Cl2

What are the trends in melting and boiling point across Period 3?

A

3.P4,S8,Cl2
- simple molecular
- weak intermolecular forces, VDW forces, more molecules, stronger forces as larger molecule
- Mp- 317, 392, 172 l Bp- 553, 718, 238

melting and boiling point fluctuate

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6
Q

Ar

What are the trends in melting and boiling point across Period 3?

A

4.Ar
- atomic
- very weak forces between atoms
- Mp- 84 l Bp- 87

melting and boiling point fluctuate

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7
Q

What is the trend in ionisation energies across Group 2?

A
  • Melting point decreases down the group (Mg has anomalylously low b.p. due to differnt crystal structure)
  • Atomic radius increases
  • Solubility of salts increases
  • Reactivity with water increases
  • Ionisation energy decreases
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8
Q

What is the trend in melting points across Group 2?

A
  • Size of the atoms increase
  • Distance between the nucleus and “sea” of delocalised electrons increases
  • Strength of metallic bond decreases
  • Energy required to overcome the bond decreases
  • Melting points decrease down the group
  • Magnesium has an unexpectedly low melting point
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9
Q

Why does reactivity increases down Group 2?

A
  • Increased atomic radius/ size of atoms/ number of electron shells
  • Greater distance between nucleus and outer shell electrons
  • Weaker attraction between outer electrons and nucleus / more shielding
  • Easier to remove outer electrons
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10
Q

What happend when you react Group 2 metals with water?

A

By reacting group 2 metal with water, metal hydroxides and hydrogen are formed.
M(s) + 2H2O (l) → M(OH)2 (aq) + H2 (g)
Metal is oxidised
Hydrogen is reduced

Magnesium also reacts with steam at high temperatures to produce magnesium oxide:
Mg(s) + H2O(g) → MgO(s) + H2(g)

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11
Q

What is the pattern in solubility in Group 2 hydroxides?

A

Group 2 hydroxides, X(OH)2, are all white solids that become more soluble down the group.
- Magnesium hydroxide- almost insoluble
- Calcium hydroxide- sparingly soluble
- Strontium hydroxide- more soluble
- Barium hydroxide-dissolves to produce strong alkaline solution (because of the OH- ions)

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12
Q

What is the pattern in solubility in Group 2 sulfates?

A

By reacting group 2 metal with sulphuric acid, metal sulphates are formed.

Reaction equation:
Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g)

The group 2 sulphates get less soluble down the group (Mg-Ba).
BaSO4 is insoluble.

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13
Q

Acidified BaCl2 solution

How do you test for sulphate ions?

A
  • Sulphate ions in solution, (SO4^2-), are detected using acidified barium chloride solution.
  • The test solution is acidified using a few drops of dilute hydrochloric acid, and then a few drops of barium chloride solution are added.
  • A white precipitate of barium sulfate forms if sulfate ions are present:
    BaCl2(aq) + Na2SO4(aq) → 2NaCl(aq) + BaSO4(s)
  • The hydrochloric acid is added first to remove any carbonate ions that might be present - they would also produce a white precipitate, giving a false positive result.
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14
Q

What are different uses of Group 2 in medicine, agricuture and titanium extraction?

A
  • Magnesium hydroxide (Mg(OH)2), milk of magnesia, acts as an “antacid”- neutralises excess stomach acid- as a treatment for indigestion.
  • Barium sulphate (BaSO4) is used in x-rays to image a patient’s stomach and intestines as it is opaque to x-rays.
  • Calcium hydroxide (Ca(OH)2) can be added to solid to raise the pH level to 6-7, the optimum for most plants.
  • Magnesium: TiO2 is converted into TiCl4 by heating with carbon and chlorine, TiCl4 is then reduced by Mg
    ** TiCl4(g) + 2Mg(l) -> Ti(s) + 2MgCl2(l)**
  • titanium is reduced, magnesium is oxidised
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15
Q

What are Group 7 elements?

A
  • halogens
  • highly reactive non-metals of group 7
  • Flourine- pale yellow
  • Chlorine- green
  • Bromine- red-brown
  • Iodine- grey
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16
Q

What is the pattern in electronic configuration, melting and boiling points and ionisation energies across Group 7?

A
  • boiling points increase down the group due to increase in strength in VDW forces
  • electronegativty decreases down the group
  • reactivity decreases down the group as it’s harder to gain an electron as there’s more shielding and a larger atomic radius so further from electrosatic forces and opposing charge.
17
Q

When will a halogen displace a halide from solution?

A

if the halide is below it in the periodic table

  • add Cl2 (aq) (colourless)- no reaction in KCl (colourless) water l forms orange solution (Br2) in KBr (colourless) water l forms brown solution in KI (colourless water)
  • add Br2 (aq) (orange)- no reaction in KCl (colourless) water l no reaction in KBr (colourless) water l forms brown solution in KI (colourless water)
  • add l2 (aq) (brown)- no reaction in KCl (colourless) water no reaction in KBr (colourless) water l no reaction in KBr (colourless) water l no reaction in KI (colourless) water
18
Q

What happens when you mix cold, dilute, aqueous sodium hydroxide with chlorine gas?

A
  • makes sodium chlorate (I) solution NaClO(aq)
  • bleach
19
Q

What is disproportionation and an example?

A

A reaction where the same element is both reduced and oxidised
e.g. Chlorine and water:
Cl2 + H2O 🡪 2H+ + ClO- + Cl-
Chlorate ions, ClO- , kill bacteria so chlorine is added to water to make it safe.

20
Q

Why is chlorine water added to water (benefits and disadvantages)?

A

chlorate (I) ions kill bacteria so adding chlorine to water can make it safe to drink or swim in
advantages:
- kills disease-causing microorganisms
- some chlorine persists in water, preventing reinfection down the supply
- prevent algae growth eliminating bad tastes, smells and discolouration caused by organic compounds
disadvantages:
- irritates the respiratory system
- liquid chlorine causes chemical burns
- any organic compounds in water can form chlorinated
hydrocarbons which are carcinogenic

however, cancer risk small compare to untreated water (e.g. cholera)

21
Q

How do you test for Halides?

A
  • Halogens (group 7) can be tested for using silver nitrate solution with nitric acid.
  • Ag + (aq) + X-(aq) 🡪 AgX(s)
  • Silver Flouride- no precipitate
  • Silver Chloride- white precipitate (forms slowest l most soluble in NH3 (dilute))
  • Silver Bromide- cream preciptate (2nd most soluble in NH3 (concentrated))
  • Silver Iodide- yellow precipitate (forms fastest l least soluble in NH3 (dilute)))
22
Q

What is the reducing power of the halides?

A
  • The reducing power of a species is related to the reactivity.
  • Reducing power increases across the group
  • As reduction is gain of electrons, the reducing power of a species is how easily it can reduce (add electrons to) another species.
  • The reducing power of the halides increases down the group as they are more easily able to lose electrons to another species and reduce them.
23
Q

NaF or NaCl

What occurs in the reaction of the halides with sulphuric acid?

A

NaF(s) + H2SO4(aq) 🡪 NaHSO4(s) + HF(g)

NaCl(s) + H2SO4(aq) 🡪 NaHSO4(s) + HCl(g)

  • Misty fumes will be seen.
  • HF and HCl not strong enough reducing agents so reaction stops there.
24
Q

NaBr

What occurs in the reaction of the halides with sulphuric acid?

A

NaBr(s) + H2SO4(aq) 🡪 NaHSO4(s) + HBr(g)

2HBr(g) + H2SO4(aq) 🡪2H2O(l) + Br2(g) + SO2(g)

  • Misty fumes will be seen.
  • HBr is a stronger reducing agent so reacts in a redox reaction.
  • Choking fumes
  • Orange fumes
25
Q

NaI

What occurs in the reaction of the halides with sulphuric acid?

A

NaI(s) + H2SO4(aq) 🡪 NaHSO4(s) + HI(g)

2HI(g) + H2SO4(aq) 🡪 2H2O(l) + I2(s) + SO2(g)

6HI(g) + SO2(g) 🡪 2H2S(g) + 3I2(s) + 2H2O(l)

  • Misty fumes will be seen.
  • HI is a strong reducing agent so reacts with the sulphuric acid, and then also reduces the SO2.
  • H2S- toxic smells of bad eggs

a-level chem (aqa) (15 decks)

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