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Chemistry > 3.1-3.7 > Flashcards

3.1-3.7 Flashcards

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1
Q

how many elements were discovered before 1815

A

45

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2
Q

what is the law of triads and who created it

A

Johann Dobereiner. when elements are put into groups of three (with similar chemical properties) it states that the atomic mass of the second element falls halfway between the first and third.

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3
Q

which elements did Johann Dobereiner notice had a pattern

A

calcium, strontium, barium
and
chlorine, bromine, iodine

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4
Q

what did John Newlands do?

A

he arranged the 62 elements known at his time by atomic mass. he noticed a repeating pattern every 8 elements called the law of octaves. this pattern broke when he reached the transition metals.

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5
Q

what did Dmitri Mendeleev do?

A

he ordered the elements by atomic mass. when certain elements were put in columns a pattern of properties emerged. he left gaps and predicted properties of unknown elements. he switched the positions of some elements to better group them by properties

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6
Q

what did Henrey Moseley do?

A

he noticed that when ordered by increasing atomic number the errors in Mendeleev’s table were corrected.

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7
Q

what is periodicity

A

a repeating trend in the properties of the elements across each periods in the periodic table

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8
Q

what are the properties that repeat in the periodic table

A
  1. atomic radii
  2. 1st ionisation energy
  3. electronegativity
  4. conductivity
  5. M.P and B.P
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9
Q

explain the trend in atomic radius across periods

A

it decreases. shielding stays the same but nuclear charge increases. the attraction is stronger so outer electrons are pulled closer.

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10
Q

explain the trend in 1st ionisation energy across periods

A

increases. shielding stays the same but nuclear charge increases and atomic radius decreases. stronger attraction between the nucleus and outer electron

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11
Q

explain the trend in electronegativity across periods

A

it increases. shielding stays the same. atomic radius decreases, nuclear charge increases. causes stronger attraction between nucleus and bonding pair

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12
Q

explain the trend in conductivity across periods

A

first three elements: increases. the electron cloud gets denser,

others: non-conductive cause there’s no free charge.

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13
Q

explain the trend in melting points across periods

A

first three elements: increases, electron cloud gets denser, atomic radius decreases, charge increases.

group 4: larger M.P than metals. strong covalent bonds in the giant covalent lattice

group 5-8: much lower M.P’s. intermolecular forces are weak so low energy requirement.

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14
Q

what is oxidation

A

the gain of oxygen or the loss of electrons

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15
Q

what is reduction

A

the loss of oxygen or the gain of electrons

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16
Q

whats a redox reaction

A

when oxidation and reduction take place

17
Q

what are oxidising and reducing agents

A

oxidising agent: the species that accepts the electrons

reducing agent: the species that transfers the electrons

18
Q

what are oxidation numbers

A

the hypothetical charge on an element in an ion or molecule if the bonding is considered 100% ionic.

19
Q

rules of assigning ON’s.

A
  1. always 0 in elements or diatomic molecules
  2. the most electronegative element has a negative ON
  3. in simple ions the ON is the same as the charge
    4, ON’s add to zero in neutral molecules
  4. ON’s add to equal the charge of molecular ions
20
Q

which elements usually have the same ON’s and what are there exceptions

A

Fluorine: always -1 but 0 in the diatomic molecule (F2)

oxygen: -2 but 0 in O2. -1 in H2O2. +2 in F2O

Hydrogen: +1 but 0 in the diatomic molecule (H2)

chlorine: -1 but O in Cl2. +1 to +7 with oxygen and fluorine

21
Q

how are molecule names

A

put the ON in roman numerals in brackets next to its name. ie, Lead(II) oxide. or sulphate(VI)

22
Q

how can you identify a redox reaction

A

assign ON’s to each element. any changes to the ON’s of the reactants indicate the loss or gain of electrons. this shows you what was oxidised and reduced.

23
Q

what is disproportionation

A

when the same species is oxidised and reduced in a reaction.

24
Q

how can half equations be combined to give a full redox equation

A

makes the number of electrons equal by multiplying everything in the reaction. combine the reactants and products to write a full equation. cancel out any electrons, hydrogens and waters if there on both sides.

25
Q

how can you find the half equation of a molecule such as VO^2+ –> VO2 ^+

A
  1. calc the ON’s and balance the element that changes
  2. add electrons to either side to balance the ON change
  3. if the oxygen is different add water to the opposite side
  4. add H+ ions to balance the hydrogen in the water.
  5. check if the total charge on each side is equal
26
Q

explain the trend in M.P down group 2

A

the atomic radius increases but the number of delocalised electrons remains the same. the attraction between the nucleus and electrons is weaker so less energy is needed so M.P decreases.

27
Q

explain the trend in reactivity down group 2

A

it increases. the shielding and atomic radius increase. this overrides the nuclear charge increase. the attraction to the outer electrons is weaker so they are lost more easily

28
Q

how does the solubility of group 2 hydroxides change down the group

A

it increases. this is because the atomic radius increases so the attraction between the metal ion and hydroxide ion is weaker. this allows water to more easily solvate the compound

29
Q

define solvate

A

when a solvent breaks down a substance to dissolve it

30
Q

why are insoluble group 2 substances used as antacids?

A

group 2 hydroxides are bases so they neutralise excess stomach acid. they need to be insoluble so they don’t enter your blood and harm you

31
Q

explain the trend in reactivity down group 7

A

reactivity decreases. the atomic radius and shielding increase so the attraction to the outer electrons and the nucleus is weaker. this makes it harder to gain an electron

32
Q

what is are the uses of chlorine

A

bleach: when reacted with cold, dilute sodium hydroxide it forms sodium chlorate. (chlorate ions kill micro-organism)

water treatment: chlorine reacts with water forming hydrogen chlorate. this kills any bacteria.

33
Q

risks of water treatment using chlorine

A

chlorine is an irritant

chlorine reacts with hydrocarbons to form carcinogenic compounds.

34
Q

alternative water treatment methods than chlorine

A

Ozone: powerful oxidiser that kills bacteria. doesn’t last long

UV light: damages organisms DNA. hard to set up

Chemistry (18 decks)

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