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chemistry A - level > periodicity > Flashcards

periodicity Flashcards

1
Q

across a period

A
  • extra electrons are added to the same electron shell
  • there’s a similar amount of electron shielding of the nuclear charge, as electrons are being added to the same electron shell
  • the nuclear charge increases
  • the atomic radii decreases as electrons are being added to the same shell & the nuclear charge increases which pulls the outer electrons closer to the nucleus
  • therefore the overall the attraction between nucleus and outer electrons increase
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2
Q

down a group

A
  • extra electrons shells are added that are further from the nucleus
  • there’s more shells between the outer electrons and the nucleus leading to the greater shielding of the nuclear charge
  • the nuclear charge increases
  • the atomic radii increases as the nuclear charge increases the outer electron is in a new shell much further away
  • therefore the overall the attraction between nucleus and outer electrons decrease
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3
Q

melting points across period 3
metals
silicon
simple covalent

A

metals - more outer shell electrons to delocalise gives stronger bonds
silicon - giant covalent so many strong bonds to break
simple covalent - van der wall forces so weak , slightly stronger forces when more electrons are in the molecule

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4
Q

period 3 - first ionisation energy

A

general trend - increase
(same reason as across the period)
group 3 & 6 - decrease, due to sub-shell filling

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5
Q

group 2 - trend in atomic radius

A

the radius of group 2 elements increased down the group as
- more shells
-more shielding
- less attraction of e- to nucleus
- (despite increase in nuclear charge)

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6
Q

group 2
first ionisation energy

A

the first ionisation energy of group 2 elements decreases down the group because
- more shells
-more shielding
- less attraction from e- to nucleus

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7
Q

group 2
melting points

A

melting points generally decreases because
- more shells
- large ionic size
- same number of electrons delocalised (2 from each atom)
- so attraction is reduced

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8
Q

group 2, what is the reactivity when you go down the group

A

the elements become more reactive because outer electrons are held less strongly

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9
Q

group 2 reacting with water equation

A

group 2 metal + water -> metal hydroxide + hydrogen

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10
Q

what happens when magnesium reacts with water

A

with steam, the oxide is formed instead as the heat makes the magnesium hydroxide unstable and decomposes to oxide

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11
Q

group 2 hydroxides solubility

A

solubility increase down a group. Ba(OH)2 is more soluble so more of it dissolves. therefore there are more OH- ions are released into the solution, making it a higher pH, (more alkaline)

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12
Q

solubility of sulphates

A

solubility of sulphates decrease down the group with barium sulphate being insoluble

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13
Q

testing for metal ions

A

adding sodium hydroxide to a solution continuing group 2 metal ions give a white precipitate

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14
Q

using barium salts as a test for a sulphate
method

A

to 1cm3 of the unknown solution
1) add 1cm3 of dilute HCL
2) add 1cm3 of aq barium chloride
3) white thick precipitate is formed then sulphate ions are present

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15
Q

why do you use BaSO4, to test for sulphates

A

its the least soluble so the precipitate would be the most visible

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16
Q

why is Hcl added during the BaSO4 experiment

A

it would remove any other ions e.g. carbonate ions which may affect the test

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17
Q

use of group 2 elements and their compounds:
magnesium

A
  • used in the extraction of titanium
  • aerospace
  • marine
  • motor vehicle industries ( extremely high corrosion resistance)
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18
Q

use of group 2 elements and their compounds:
magnesium hydorxide and barium sulphate

A

medicine

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19
Q

use of group 2 elements and their compounds:
calcium hydroxide

A

agriculture

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20
Q

use of group 2 elements and their compounds:
calcium oxide

A

remove SO2 from fule gases

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21
Q

use of group 2 elements and their compounds:
barium chloride

A

tests for sulphate ions

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22
Q

oxidation definition

A

gain of oxygen or loss of electrons or loss of hydrogen

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23
Q

reduction definition

A

loss of oxygen or gain of electrons

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24
Q

redox definition

A

reaction where oxidation and reduction occurs

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25
Q

oxidation state definition

A

number of electrons which are involved in bonding

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26
Q

metals oxidation state

A
  • have positive values in compounds
  • value is usually that of the group number
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27
Q

oxidation number rule
uncombined element (not in a compound)

A

0

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28
Q

oxidation number rule:
monoatomic ions

A

charge on ion

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29
Q

oxidation number rule
group 1 element

A

+1

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30
Q

oxidation number rule
group 2 element

A

+2

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31
Q

oxidation number rule
aluminium

A

+3

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32
Q

oxidation number rule
hydrogen

A

0

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33
Q

oxidation number rule
oxygen

A

-2
for F2O it will be +2

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34
Q

oxidation number rule
fluorine

A

-1
always

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35
Q

oxidation number rule
halogens except fluorine (Cl, Br, I)

A

-1
except when bonded to O, N, F - +1

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36
Q

oxidation number rule
polyatomic ions

A

sum of oxidation numbers in the ions charge

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37
Q

whats an oxidising agent

A

a reagent that oxidises (takes electrons from) another species

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38
Q

whats a reducing agent

A

a reagent that reduce (adds electrons to) another species

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39
Q

what is a disproportionation

A

when an elements has been oxidised and reduced

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40
Q

what is an ionic equation

A

without spectator ions (just ions/atoms reacting)

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41
Q

what is a half equation

A

only species being oxidised /reduced is shown

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42
Q

reaction of solid halides with H2SO4
F

A

NaF + H2SO4 -> NaHSO4 + HF
(HF - misty fumes)

43
Q

reaction of solid halides with H2SO4
Cl

A

NaCl + H2SO4 -> NaHSO4 + HCl
(HCL - colourless gas)

44
Q

reaction of solid halides with H2SO4
Br

A

NaBr + H2SO4 -> NaHSO4 + HBr
(HBr - acidic gas)
2HBr + H2SO4 -> Br2 + SO2 + 2H2O

45
Q

reaction of solid halides with H2SO4
I

A

NaI + H2SO4 -> NaHSO4 + HI
(HI - acidic litmus)
2HI + H2SO4 -> I2 + SO2 + 2H2O
(I2 - brown aq solution when water is added, purple gas/ black solid)
6HI + H2SO4 -> 3I2 + S + 4H2O
(S - yellow)
8HI + H2SO4 -> 4I2 + H2S + 4H2O
(H2S - eggy smell, test with lead ethanoate/ bromide paper)

46
Q

what are halides

A

reducing agents. down a group they have stronger reducing agents

47
Q

Testing for halides - AgNO3, method

A
  1. make a solution of the halide
  2. acidify with dilute nitric acid - to prevent the precipitation of other salts
  3. add a few drops of silver nitrate solution
  4. treat any precipitate with dilute ammonia solution
  5. if a precipitate still exists, add concentrated ammonia solution
48
Q

Testing for halides - AgNO3
why can’t this test, test for fluoride ions

A

as silver fluoride dissolves in water

49
Q

Testing for halides - AgNO3
colours of precipitate

A
  • white precipitate- silver chloride AgCl
  • cream precipitate - silver bromide, AgBr
  • yellow precipitate - silver iodide, AgI
50
Q

Testing for halides - AgNO3
add dilute ammonia

A
  • soluble - silver chloride AgCl
  • insoluble - silver bromide, AgBr
  • insoluble - silver iodide, AgI
51
Q

Testing for halides - AgNO3
add concentrated ammonia

A
  • soluble - silver chloride AgCl
  • soluble - silver bromide, AgBr
  • insoluble - silver iodide, AgI
52
Q

halide precipitate equations

A

Ag+(aq) + X-(aq) -> Ag+X-(s)
when they dissolve in ammonia a colourless diamine complex is formed [Ag(NH3)2]+(aq)

53
Q

OH-
Test for hydroxide ions: AQ solution

A
  1. Test a 1cm depth of solution in a test tube with red litmus paper or universal indicator paper
  2. record your observations. dispose of the test tube contents
  3. sodium hydroxide will turn damp red litmus paper blue
54
Q

OH-
Test for hydroxide ions: ammonia (OH- ions forms in contact with water)

A
  1. take 5 drops of 1.0 moldm-3 ammonia solution and place on a filter paper and place inside a petri dish with lid
  2. dampen a piece of red litmus paper with distilled water and place on the other side of the petri dish
  3. replace the lid and observe over a few minuets
  4. ammonia solution vapours will turn damp red litmus paper blue
55
Q

OH-
Test for hydroxide ions: ammonia
equation

A

NH3 + H20 -> NH4+ + OH-
this is alkali in aq solution it makes an OH- ions

56
Q

SO4-2
testing for sulfate ions

A
  1. acidify the sample dilute HCL and then add a few drops of aqueous barium chloride
  2. if a sulfate is present then a white precipitate of barium sulfate is formed:
    Ba2+(aq) + SO42-(aq) -> BaSO4(s)
    BaSO4 is an insoluble precipitate
57
Q

CO3 -
method for carbonate ions

A
  1. react carbonate with acid first. then test for CO2 product
  2. test CO2 in limewater
  3. if Co2 is present CaCO3. precipitate formed
58
Q

define the term RAM

A

the average mass of an atom ofan element
compared to 1/12th of the mass of at atom of carbon 12

59
Q

why the melting point of magnesium is higher than the melting point of sodium

A
  • mg has more electrons than Na
  • stronger attraction due to the delocalised sea of electrons
60
Q

why is chlorine added to water even though its toxic
give an equation chlorine and cold water

A
  • disinfects water
  • health benefits outweigh the risks
    Cl2 + H20 <=> HCL + HCLO
61
Q

equation for the extraction of titanium using magnesium and what’s the role of magnesium

A

2Mg + TiCl4 -> 2MgCl2 + Ti
reducing agent, via a displacement reaction

62
Q

equation for Cr2O72-

A

Cr2O72- + 6e- + 14H+ -> 2Cr3+ + 7H2O

63
Q

giant covalent structures

A
  • graphite
  • diamond
  • silicon
  • silicon dioxide
    these all have high melting points due to the strong covalent bonds
64
Q

household bleach

A

chlorine reacts with cold aq sodium hydroxide
2NaOH(aq) + Cl2 -> NaCl(aq) + NaOCl(aq) + H20

65
Q

medical use for magnesium hydroxide

A

indigestion relief

66
Q

observation and equation when magnesium reacts with steam

A

bright white light
Mg (s) + H2O -> MgO(s) + H2(g)

67
Q

equation for the reaction of drinking water with chlorine

A

Cl2 + 2H2O -> 2HCL + HClO
kills bacteria

68
Q

effect of student rinsing the burette with deionised water before filling with sodium hydroxide

A
  • increase final titre volume
  • because sodium hydroxide solution would be more dilute
69
Q

which element period 3 has the highest melting point
Aluminium
silicon
Sodium
Sulfur

A

silicon

70
Q

which ion has the largest radius
F-
Mg2+
Na+
O2-

A

O2-

71
Q

what is barium sulphate used for

A

medical tracer that allow internal organs to be traced

72
Q

fule gas removal

A

calcium oxide reacts with sulphur dioxide to remove it from factory pollutant
CaO + 2H2O + SO2 -> CaSO3 + 2H2O

73
Q

what will chlorine Cl2 displace

A

Br-
I-

74
Q

what will bromine Br displace

A

I-

75
Q

what will iodine displace

A

nothing

76
Q

chlorine reacting with cold water

A

Cl2 + H2O -> ClO- + Cl- + 2H+

77
Q

what happens to chlorine infront of UV light

A

2Cl2 + 2H2O -> 4HCL + O2

78
Q

flame test for group 2
Ca2+

A

brick red

79
Q

flame test for group 2
Sr2+

A

red

80
Q

flame test for group 2
Ba2+

A

pale green

81
Q

which is the best technique to remove the silver chloride that forms when aq solutions of silver nitrate and NaCl react
1. refluxing
2. evaporation
3. filtration
4. distillation

A

filtration

82
Q

which statement about Astatine is correct
1. At has a greater electronegativity than BR
2. At is a better oxidsing agent than Br
3. At has a greater boiling point than Br
4. At has a greater first ionisation energy than Br

A
  1. At has a greater boiling point than Br
83
Q

What is the reducing agent ni this reaction?
A. H+
B. C2O42-
C. K+
D. Cr2O72-

A

B. C2O42-

84
Q

which molecule has the largest dipole
A. ClF3
B. BF3
C. SF6
D. CF4

A

A. ClF3

85
Q

which species contain bonds that have different polarities
1. NH4+
2. CCl4
3. CH3Cl
4. H3O+

A
  1. CH3Cl
86
Q

which compound has hydrogen bonding
1. NaH
2. NH3
3. HI
4. SiH4

A
  1. NH3
87
Q

which compound contains a co-ordinate bond
1. HF
2. NH3
3. CHCl3
4. NH4Cl

A
  1. NH4Cl
88
Q

which molecule has a permanent dipole
1. CF4
2. PCl5
3. CO2
4. Cl2O

A
  1. Cl2O
89
Q

which change occurs when water is vaporised
1. an exothermic change occurs
2. covalent bonds are broken
3. intermolecular forces are overcome
4. the total energy of the molecule decreases

A
  1. intermolecular forces are overcome
90
Q

which property would you expect the element Ra to possess
1. it forms a soluble sulfate
2. it does not react with water
3. it is a good conductor of electricity
4. it forms a covalent fluoride

A
  1. it is a good conductor of electricity
91
Q

what is the best oxidising agent
1. F2
2. F-
3. I2
4. I-

A
  1. F2
92
Q

which statement is correct about reaction involving halides
1. NaCl forms Cl2 when added to conc sulfuric acid
2. NaCl forms Cl2 when added to Br
3. NaBr forms Br2 when added to conc sulfuric acid
4. NaBr forms bromine when added to chlorine

A
  1. NaBr forms Br2 when added to conc sulfuric acid
93
Q

which atom contains only two unpaired electrons?
1. Helium
2. beryllium
3. Oxygen
4. Iron

A
  1. oxygen
94
Q

which of these ions have the largest atomic radius
1. S2-
2. Cl-
3. K+
4. Ca2+

A

S2-

95
Q

which statement is correct
1. Cl- reduce conc sulfuric acid to form SO2
2. Br- reduc conc sulfuric acid to form sulphur
3. Br- ions reduce iodine to form iodide ions
4. I- reduce chlorine to form chloride ions

A
  1. I- reduce chlorine to form chloride ions
96
Q

which compound is used to treat the symptoms of indigestion
1. MgO
2. Mg(OH)2
3. CaO
4. Ca(OH)2

A
  1. Mg(OH)2
97
Q

which element has the highest first ionisation energy
1. Aluminium
2. Phosphorous
3. Silicon
4. Sulfur

A
  1. Phosphorous
98
Q

which suggestion would reduce the overall measurement uncertainty in the titration
1. Use less concentrated alkali in the burette
2. Use phenolphthalein indicator instead of methyl orange
3. use smaller samples of the diluted acid in each titration
4. begin each titration with the burette filled to the 0.00cm3 mark

A
  1. Use less concentrated alkali in the burette
99
Q

which of these is important in ensuring that the students experiment is safe
1. do the titration in a fume cupboard
2. wear gloves when measuring out the battery acid
3. wash hands before titration
4. carry the burette horizontally when collecting the apparatus

A
  1. wear gloves when measuring out the battery acid
100
Q

which colour change is observed at the end point in each titration
1. yellow to red
2. red to orange
3. yellow to orange
4. red to yellow

A
  1. red to orange
101
Q

which suggestion about rinsing the conical flask between each titration would improve the accuracy of the titrations
1. rinsing with acid
2. rinsing with alkali
3. rinsing with water
4. no rinsing with any liquid

A
  1. rinsing with water
102
Q

which suggestion would improve the chances of obtaining concordant titres
1. invert the volumetric flask several times after adding the distilled water
2. wash the pipette with distilled water between each titration
3. add extra drops of indicator to the sample when nearing the end point in each titration
4. use a more concentrated solution of sodium hydroxide in he burette

A
  1. invert the volumetric flask several times after adding the distilled water
103
Q

what happens when sodium chlorate is added to colourless solution of potassium iodide

A
  • goes brown
  • due to iodine
  • because I- is oxidised
104
Q

explain why CBr4 is not a polar molecule

A
  • its symmetrical
  • so dipoles cancel out

chemistry A - level (16 decks)

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