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Chemistry A level > chap 1- elements of life > Flashcards

chap 1- elements of life Flashcards

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1
Q

what is an isotope

A

an atom of the same element with different mass number (different number of neutrons) but the same atomic number

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2
Q

what is mass spectrometry

A

the technique used to find the atomic mass of elements and compounds.
sample atoms or molecules are ionised to positively charged cations which are then separated according to their mass to charge ratios (m/z)
the separated ions are detected together with their relative abundance

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3
Q

what is nuclear fusion

A

when 2 light nuclei fuse to form a single heavier nucleus of a new atom

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4
Q

why can nuclear fusion not occur on earth

A

the temperature is not high enough so the nuclei do not have enough energy to overcome the repulsion of the 2 positive nuclei against each other

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5
Q

why can nuclear fusion occur in a star

A

temp is much higher, nuclei have more energy and are moving at much higher speeds so can overcome the repulsion

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6
Q

what is the chromosphere

A

the region outside the star’s surface (photosphere) that contains ions, atoms and small molecules

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7
Q

why are the lines black in an absorption spectra

A

the black lines on the spectrum are the missing frequencies of light that have been absorbed by particles in the chromosphere

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8
Q

what happens when atoms, molecules and ions in the chromosphere absorb energy

A

they are raised from their ground state to higher energy states called excited states then when they fall back to ground state they emit the extra energy in the form of electromagnetic radiation

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9
Q

what is an emission spectra

A

coloured lines on a black background which correspond to the frequencies of the electromagnetic radiation emitted

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10
Q

how do you calculate speed of light (ms-1)

A

wavelength (m) x frequency (s-1)

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11
Q

how to calculate energy of a photon (J)

A

planck constant (Js-1) x frequency (s-1)

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12
Q

how does bohr’s theory explain emission spectrum

A

when an atom is excited electrons jump into higher energy levels. when they drop back into lower levels they emit the extra energy as electromagnetic radiation and give off an emission spectrum

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13
Q

how does bohr’s theory explain absorption spectrum

A

when white light is passed through a relatively cool sample of a gaseous element black lines appear which correspond to light that has been absorbed by atoms in the sample

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14
Q

what is the energy of a photon equal to

A

the difference between the 2 energy levels

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15
Q

what colour is lithium in a flame test

A

bright red

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16
Q

sodium flame test colour

A

yellow

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17
Q

potassium flame test colour

A

lilac

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18
Q

calcium flame test colour

A

brick red

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19
Q

barium flame test colour

A

apple green

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20
Q

copper flame test colour

A

blue/green

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21
Q

how many electrons can the first 4 shells hold

A 
1st= 2
2nd = 8
3rd = 18
4th = 32
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22
Q

how many electrons can each sub shell hold

A

s = 2
p =6
d = 10
f = 14

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23
Q

what is the chromium exception

A

chromium electronic configuration is in the last 2 sub shells is 4s1 3d5 even though it would be expected to be 4s2 3d4 but one of the electrons from 4s is promoted to 3d to give a more stable arrangement

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24
Q

what is the copper exception

A

the last 2 sub shells of copper are 4s1 3d10 even though it would be expected to go 4s2 3d9 but to achieve a more stable arrangement of lower energy one electron is promoted to 3d

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25
Q

how do you calculate miles using concentration and volume

A

no of moles = (conc x vol)/ 1000

26
Q

what is a closed shell arrangement

A

when sub shells are fully occupied by electrons. these are particularly stable arrangements

27
Q

what is a p block element

A

where the outermost p sub shell is being filled

28
Q

why do non metallic elements form covalent bonds

A

it is not electronically favourable to form ions so electrons are shared

29
Q

what is a dative covalent bond

A

when both bonding electrons come from the same atom (shown by an arrow)

30
Q

why do elements and compounds with a simple molecular structure have relatively low melting and boiling points

A

the electrostatic attractions between different simple molecules are weak (even though the covalent intramolecular bonds are strong) so small amounts of energy are needed to separate one molecule from another

31
Q

why do covalent simple molecules not conduct electricity

A

because there are no charged particles

32
Q

what is a linear molecule

A

2 groups of electrons around the central atom. bond angle 180

33
Q

what is a planar molecule

A

3 groups (bonds) of electrons around the central atom. bond angle 120

34
Q

what is a bipyramidal molecule

A

5 groups of electrons around a central atom. bond angles approx 120 or 90 depending on position within molecule

35
Q

what is an octahedral molecule

A

6 groups of electrons around a central atom. bond angle 90

36
Q

what is a tetrahedral molecule

A

4 groups of electrons around a central atom with no lone pairs. bond angle 109.5

37
Q

what is a trigonal pyramidal molecule

A

4 groups of electrons, 3 bonded groups and one lone pair. bond angle 107

38
Q

what is a non linear or bent molecule

A

when there are 4 groups of electrons but only 2 bonded groups and then 2 lone pairs. bond angle 104.5

39
Q

what are the 4 ways of making salts

A

1) acid + alkali = salt + water
2) acid + base = salt + water
3) acid + carbonate = salt + water + carbon dioxide
4) acid + metal = salt + hydrogen

40
Q

which ionic substances are insoluble

A

1) barium, calcium, lead and silver sulfates
2) silver and lead halides (chlorides, bromides and iodides)
3) all metal carbonates
4) metal hydroxides (except group 1 and ammonium hydroxide)

41
Q

what is a precipitation

A

a suspension of solid particles produced by a chemical reaction in solution

42
Q

what are the practical applications for precipitation reactions

A

water treatment, production of coloured pigments for paints and dyes and identifying metal ions in solution

43
Q

how do electrostatic attractions hold together ionic lattice structures

A

because the electrostatic attraction of oppositely charged ions overcomes any repulsion between ions of the same charge

44
Q

what is the model of a metallic giant lattice

A

has an electron sea of delocalised electrons

structure is held together by the attraction of metal cations to the delocalised electrons

45
Q

what happens to reactivity in groups 1 and 2

A

the elements become more reactive (more readily form cations in ionic compounds) as you go down the group

46
Q

what happens to the trend of reactivity as you go across a period

A

elements become less reactive as you go across a period (left to right) so group 1 metals are more reactive than group 2 of the same period

47
Q

what are the reasons for similarities and differences in a particular group

A

there are similarities because the elements have similar arrangements of electrons in their atoms

differences because the size of the atom increases down the group

48
Q

what is first ionisation enthalpy

A

the energy required to remove the first electron from an atom

49
Q

what is the general equation for first ionisation process

A

X (g) = X+ (g) + e-

50
Q

first ionisation energy increases as you go along the periodic table. however there is a decrease between beryllium and boron. why?

A

electronic configuration of beryllium is 1s2 2s2 and boron is 1s2 2s2 2p1
the s sub shell is lower in energy than the p sub shell so less energy is needed to remove the outer electron is boron in spit of increased nuclear charge

51
Q

first ionisation energy increases as nuclear charge increases but there is a decrease between nitrogen and oxygen. why?

A

nitrogen electronic configuration is 1s2 2s2 2p3 but oxygen is 1s2 2s2 2p4 (which includes a pair) so the extra repulsion from the paired electron sub shell in oxygen means less energy is needed to remove one of the paired electrons

52
Q

why does first ionisation energy decrease going down a group

A

the attraction between the nucleus and the outermost electron decreases so it is easier for the outermost electron to be removed

53
Q

what is second ionisation energy

A

the energy needed to remove one electron from a positive ion
not the energy needed to remove 2 electrons

54
Q

what happened when carbonates are heated

A

they decompose forming the oxide and releasing carbon dioxide

55
Q

how does thermal stability change down a group

A

thermal stability increases down a group

56
Q

how can the change in thermal stability down the group be explained

A

by charge density. charge density decreases down a group so metals at the top of group 2 have a higher charge density which which distorts the negative charge cloud more making a carbonate less stable and easier to break up on heating so metal carbonates lower down the group have higher thermal stability

57
Q

what is charge density

A

measure of the concentration of charge on the cations. the smaller the +2 ion the higher the charge density

58
Q

why does emission spectra consist of bright lines on a dark background

A

when the electrons fall from the excited level to the ground level, they emit light

59
Q

why does absorption spectra consist of dark lines on a coloured background

A

when the electrons are excited to higher levels they absorb the particular frequency of light and therefore there is a black line corresponding to the missing frequency that has been absorbed

60
Q

similarities between absorption and emission spectra

A

both are line spectra

lines are in the same position for a given element

lines become closer at higher frequencies

sets of lines represent transitions to of from a particular energy level

61
Q

differences between the 2 types of spectra

A

absorption has dark lines on coloured background

emission has bright lines on a dark background

62
Q

how can you describe the visible emission spectrum of hydrogen

A

a set of lines that converge towards a high frequency value

Chemistry A level (10 decks)

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