1.2 basic ideas about atoms Flashcards
(201 cards)
1
Q
what is an isotope?
A
an atom of an element with the same number of protons, but different number of neutrons
2
Q
what makes a nuclei to become unstable?
A
when isotopes of elements are formed that contain too many neutrons, it makes the nucleus ‘heavy’ and unstable
3
Q
what happens when a nuclei becomes unstable?
A
radiation is emitted from the nucleus of that atom which results in the formation of a new atom
4
Q
the heavier the atom, the ____ likely it is to degrade/emit radiation?
A
more
5
Q
what are the 5 radiation types and decay?
A
- alpha
- beta
- gamma
- positron emission
- electron capture
6
Q
what are the properties of alpha? and why?
A
- same structure as a helium nucleus (2 protons, 2 neutrons)
- doesn’t have any electrons so has a positive charge if 2+ (so will be affected by an electric field)
- penetrating power -> easily stopped by a thin sheet of paper so pose no threat to humans when outside the body
- ionising ability -> their relatively large size makes it easy for them to knock electrons off atoms to form negatively charged ions
- electric fields -> they are attracted towards the negatively charged plate but deflection is small due to large mass
- emission -> when emitted by an unstable nucleus, the particle leaves behind a new nucleus (different element) with 2 fewer protons and 2 fewer neutrons
7
Q
what is the structure of alpha?
A
4 He
2
8
Q
why does alpha have a positive charge of 2+?
A
because it doesn’t have any electrons
9
Q
does alpha have a strong or weak penetrating power?
A
weak - it is easily stopped by a thin sheet of paper so pose no threat to humans when outside the body
10
Q
does alpha have a high or low ionising ability?
A
high - they are highly ionising
their relatively large size makes it easy for them to knock electrons off atoms to form negatively charged ions
11
Q
in an electric field, what plate is alpha attracted to?
A
towards the negatively charged plate but deflection is small due to large mads
12
Q
write an equation to represent the emission of an alpha particle from a carbon - 12 nuclei
A
12 C —> 4He + 8 Be
6 2 4
13
Q
what are the properties of beta?
A
- formed when a neutron of an unstable element decays to form a proton and an electron (the electron is propelled away at high speed from the nucleus and becomes known as a beta particles)
- it has a mass of 0 and a charge of -1
- penetrating power = stopped by a thin sheet of aluminium so are much more dangerous to humans when outside the body
- ionising ability = ionises less intensely than an alpha particle due to its smaller size
- electric fields = they are attracted towards the positively charged plate but deflection is larger due to their small mass
- emission = when a beta particle is emitted, it leaves behind a new nucleus (different element) with 1 more proton so the atomic number increases by 1 and the mass number stays the same
14
Q
what is the structure of a beta particle?
A
0 e -
-1
15
Q
how is a beta particle formed?
A
when a nucleus of an unstable element decays to form a proton and an electron. the electron is propelled away at high speed from the nucleus and becomes known as a beta particle
16
Q
what is the mass and charge of a beta particle?
A
mass 0
charge -1
17
Q
what is the penetrating power of a beta particle?
A
they are stopped by thin sheets of aluminium so are much more dangerous to humans when outside the body
(stronger than alpha, weaker than gamma)
18
Q
what is the ionising ability of a beta particle?
A
it ionises much less intensely than an alpha particle due to its size
19
Q
in an electric field, what plate is a beta particle attracted to?
A
towards the positively charged plate but deflection is large due to their small mass
20
Q
what are the properties of gamma?
A
- is emitted by unstable elements in order to release energy
- does not have a mass as it’s an electromagnetic wave with a very small wavelength and a high frequency and energy
- penetrating power = it can travel great distances and has a high penetrating power. it will pass directly through the human body. it can be stopped by very thick lead
- ionising ability = having no mass, it can only weakly ionise
- electric fields = having no charge it is not deflected by electric fields
- emission = it doesn’t change the structure of the nucleus from which it is emitted, it just reduces the amount of energy contained within
21
Q
what is the structure of gamma? (charge, mass)
A
0 Y
0
22
Q
how is gamma radiation emitted?
A
by unstable elements in order to release energy
23
Q
why doesn’t gamma have a mass?
A
bc it is an electromagnetic wave with a very small wavelength and a high frequency and energy
24
Q
what is the penetrating power of gamma?
A
it can travel great distances and has a high penetrating power. it will pass directly through the human body. it can be stopped by very thick lead
25
what is the ionising ability of gamma?
because it has no mass, it can only weakly ionise
26
in an electric field, what plate is gamma attracted to?
because it doesn’t have a charge, it is not deflected by electric fields
27
when emitted, how does gamma change the structure of the nucleus?
it doesn’t change the structure of the nucleus from which it is emitted, it just reduced the amount of energy contained within
28
what is a positron?
the opposite particle to an electron
29
what does positron emission result in?
the process of a proton turning into a neutron
(there is no change in mass number)
30
what is the structure of a positron?
0 e +
+1
31
what is electron capture?
- it pretty much uses the same principles of beta emission
- an electron can be ‘captured’ by an atom
- there is no change in mass number. a proton changes to a neutron
- beta particle add to an atom
23Na + 0 e —> 23Ne
11 -1 10
32
explain the deflection (of alpha, beta and gamma through an electric field)
- alpha radiation is deflected towards the negative plate
- beta radiation is deflected towards positive plate
- gamma radiation travels straight through as unaffected by charge
- beta radiation deflects at a greater angle and meets plate earlier than alpha
- beta particles charged and lighter, can be deflected more easily than alpha which are charged but heavier
- gamma radiation has no associated mass (electromagnetic wave)
33
why is alpha radiation deflected towards the negative plate in an electric field?
because it has a positive charge
34
why is beta deflected towards the positive plate in an electric field?
because it has a negative charge
35
why does gamma radiation travel straight through in an electric field?
is is an electromagnetic wave so is unaffected by charge
36
why does beta radiation deflect at a greater angle and meet the plate earlier than alpha in an electric field?
beta particles are charged and lighter, so can be deflected more easily than alpha which are charged but are heavier
37
half-life definition
the time taken for the mass of a radioactive isotope to decay by half
OR
the time taken for half of the atoms of a radioactive sample to decay
38
what is the relationship between the rate of decay to the number of atoms present in the sample? why?
proportional
bc since half-life is unchanging
39
why does the actual rate of decay slow down as time passes?
since it is proportional to the number of unstable nuclei in the sample
40
will the radioactivity of radioactive isotopes ever fall to zero?
no so radioactive isotopes must be disposed of with care
41
how long would it take a radioactive substance to reduce to 1/8th of its original value if its half life was 2 mins?
1 -> 1/2 -> 1/4 -> 1/8
3HL = 2mins x 3 = 6 mins
42
how long would it take a radioactive substance to reduce to 25% of its original value if its half life was 35 years?
1 -> 0.5 -> 0.25
2HL = 35 x 2 = 70 years
43
what are the two ways you can work out half life?
1. from data
2. from graphs
44
when reading half life off a graph, what is important to remember?
for it to be a true half life graph, each time you do this, the half life must remain constant between readings
45
what are the uses of radiation in industry?
only need 1 but:
- to measure the thickness of paper
- to find leaks in underground pipes
- to preserve food
- in smoke detectors
46
what is the use of radiation in carbon dating?
carbon dating is used to calculate the age of plant and animal remains
47
what are the uses of radiation in health and medicine?
only need 1 but:
- to sterilise surgical instruments
- to treat cancer - cobalt 60 is used to irradiate cancer patients
- in tracer studies - iodine 132 is used to study thyroid activity
48
up to what element do we need to know the electronic configuration?
krypton - 36
49
what are the three types of orbitals (shells) and how many can each one hold?
s, p and d
s can hold 2 electrons
p can hold 6 electrons
d can hold 10 electrons
50
what does n=1 mean?
what does n=2 mean?
n=1 is shell 1
n=2 is shell 2
(‘n’ means principal quantum number - or energy level)
51
does energy increase as you move away from the nucleus??
yes
52
do energy levels get closer or further away from each other as they get further from the nucleus?
they get closer as they get further from the nucleus
53
what is the full electronic configuration of Titanium - 22?
1s^2 2s^2 2p^6 3s^2 3p^6 4s2 3d2
54
what is the order of filling when working out the electrons of an element?
1s
2s
2p
3s
3p
4s
3d
4p
4d
55
why are electrons placed into the energy levels they are placed in?? why is the 4s sub-energy level filled before the 3d sub-energy level?
when electrons are placed into energy levels, they want to occupy those with the lowest energy first
the 4s sub-energy level is of lower energy and nearer the nucleus than the 3d sub-energy level
56
when doing the ‘arrow in the box method’ what direction do the arrows point?
1 has to point up, 1 has to point down
- in opposite directions
57
how do you fill ‘the arrow in the box method’? why?
fill all the boxes first, then pair them
bc electrons have a negative charge, they stay away from each other for as long as possible
58
what is the noble gas ‘core’/ shorthand method of electronic configuration?
find the noble gas before the element you are working out
write [‘noble gas’] then 3d^8 4s^2 etc
59
what are the two elements that are the exceptions to the rules for electronic configuration?
1. chromium
2. copper
they allow one of the 4s electrons to travel to the 3d sub level early as half filled (d^5) and fully filled (d^10) sub shells have a high stability
they are so close to having a half full d sub-energy level that it ‘takes’ one of the 4s electrons to achieve it ‘early’
60
how can you work out the electronic configuration of ions?
it can be deduced by simply adding or removing the appropriate number of electrons
61
what are the rules that deduce the order in which electrons are removed when working out the electronic configuration of ions?
1. remove outer shell electrons first
2. remove paired electrons before unpaired electrons in the same sub-level
3. 4s ELECTRONS ALWAYS GET REMOVED BEFORE 3d
4. add the appropriate number of electrons if the ion is negatively charged
62
why do atoms remain on an energy level? (why do they have fixed energy levels?)
cause they are quantised
63
what is the lowest energy level that an atom has? highest?
n=1
n= infinite
64
what do you call the energy level closest to the nucleus? (n=1)
the ground state
65
does energy increase as you go up the energy levels?
yes
66
is there a n=0 level?
no
67
what happens to the difference in energy between energy levels as you go from one level to the next?
it decreases
—————
—————
—————
—————
—————
68
what eventually happens to the energy levels as they go up towards n=infinite?
they converge - it becomes impossible to separate out the energy levels
(this limit is called the convergence limit)
69
what is the convergence limit?
the point at which the energy levels converge and become impossible to separate out
70
will each atom have a slightly different energy at which these levels reside?
yes
71
what represents ionisation of an atom?
- beyond the convergence limit
- n=1 —> n=infinite
(if an electron passes n=infinite, it looses it and it becomes an ion)
72
what must happen to the electron to move up to the higher energy level?
it must gain energy
(by absorbing light)
THE ELECTRON IS PROMOTED TO A HIGHER ENERGY LEVEL
73
how does an electron gain energy to move up to a higher energy level?
by absorbing light
74
what do you say when talking about when an electron moves up to a higher energy level by absorbing light energy?
the electron is promoted to a higher energy level
75
where does an electron reside?
in the lowest energy level possible - the n=1 level (ground state)
76
what specifically must occur for an electron to move up to a higher energy level? (more details)
- if light of the correct frequency and wavelength (and therefore energy) are shone on the atom, the electron will absorb that specific frequency and wavelength of light and become promoted to an energy level of higher energy
this is called an excited state
77
what is an excited state?
when an electron has absorbed the specific frequency and wavelength of light to be promoted to an energy level of higher energy
78
what happens to the electron that had been promoted to a higher energy level if the light source stops?
- the electron will seek once again to reside in the lowest energy level
- it must lose energy to do this
- it does this by emitting out light
79
what are the three types of transitions or ‘series’ you need to know when looking at absorption and emission spectras?
1. lyman transitions
2. balmer transitions
3. paschen transitions
80
what are lyman transitions?
- they represent transitions from higher energy levels back down to n=1 level
- often occur in the UV light region (long arrows)
81
what are balmer transitions?
- they represent transitions from higher energy levels back down to n=2 level
- they often occur in the visible light region
82
what are paschen transitions?
- they represent transitions from higher energy levels back down to the n=3 level
- they often occur in the IR region (short arrows)
83
the longer the arrow, the (more/less) energy is given out and the (lower/higher) the energy of the light emitted will be
the longer the arrow:
- the more energy is given out
- the higher the energy of the light emitted
84
why are there several series of lines that converge?
because as there are several energy levels that the promoted electrons can fall back down to and they converge as the higher energy levels also converge
85
for hydrogen, what are the first 4 colours of arrows for the balmer series?
1. red
2. green
3. blue
4. purple
86
what is the equation for energy, using planck’s constant, energy and frequency?
E = hf
E = energy
h = planck’s constant, 6.63 x10^-34 Js
f = frequency, Hz or s^-1
87
what is the equation for frequency, using wavelength, speed of light and frequency?
f = c / wavelength
f = frequency, s^-1 or Hz
y = wavelength, m
c = speed of light, m s^-1
88
what is the equation linking wavelength, frequency and light?
E = hc / y
E = energy, J
h = planck’s constant, 6.63 x10^-34 Js
c = speed of light, m s^-1
y = wavelength, m
89
what is the relationship between wavelength and energy?
they are inversely proportional
90
what is the relationship between frequency and energy?
they are directly proportional
91
what is the relationship between wavelength and frequency ?
they are inversely proportional
92
in increasing energy order, what is the order of the different types of light? (x-rays, visable light, infrared, ultra violet, radio waves)
radio waves -> infrared-> visible light -> ultra violet -> x-rays -> gamma rays
(increasing wavelengths the opposite way)
93
what happens when white light passes through a gas?
that gas absorbs certain frequencies of the light
( these frequencies correspond to the exact energy differences between the atom’s quantised levels)
94
what does the sun emit?
white light
95
what happens in the hydrogen absorption spectrum?
1. white light is shone onto hydrogen gas
2. the electrons in the hydrogen atoms absorb certain frequencies of light
3. the absorbed frequencies are now black lines and are absent from the spectrum as they have been absorbed by the hydrogen atom’s electrons
96
are all frequencies (and therefore colours) of light absorbed by the hydrogen atoms? why?
no - because the energy levels are quantised and so energy from the white light can only be absorbed if the energy it has is exactly the same as the energy difference between two energy levels
97
what is the black line on the right of the absorption spectrum of hydrogen and what does it represent?
- it is the lowest energy transition
- it represents the electron being promoted from the n=2 level to the n=3 level
98
what happens in the hydrogen emission spectrum?
1. a current is passed through hydrogen gas. this excites electrons in the atoms
2. the photons of light are collected as they drop down from the higher to lower energy levels. this will produce a series of coloured lines on a mainly black background - showing that light is only emitted at certain frequencies relating to certain jumps
99
are all frequencies (and therefore colours) of light emitted by the hydrogen atoms? why?
no - because the energy levels are quantised and so energy from the electrons jumping down from higher to lower energy levels is emitted, have certain discrete energies and therefore colours on an emission spectrum
100
what are the only transitions we can see in the visible region when looking at hydrogen’s emission spectrum?
- visible transitions (= Balmer transitions)
(this does not mean there are not any other transition such as Lyman and Paschen - as these transitions occur in the IR and UV part of the spectrum which we cannot see with the naked eye)
101
because the only transitions we can see are the Balmer transitions when looking at hydrogen’s emission spectra, does this mean there aren’t any other transitions?
no - this does not mean there are not any other transition such as Lyman and Paschen - as these transitions occur in the IR and UV part of the spectrum which we cannot see with the naked eye)
102
what is the red line on the right of the hydrogen emission spectrum and what does it represent?
- it is the lowest energy transition
- it represents the electron jumping from the n=3 to the n=2 level
103
if you have kJ but want to find kJ mol^-1, what must you do?
x by avogadro’s number
___ x avogadro’s number =___mol^-1
104
when a question asks for an appropriate number of significant figures, what do you put it to?
whatever they’ve given their numbers in
(if multiple numbers e.g 4500 and 2364, give it to whatever is the lowest number of significant figures given e.g 2 sig figs)
105
why are electrons able to take ip multiple different energies?
cause they have multiple different energy levels to move up to
106
when does ionisation occur?
when an electron gets promoted past the convergence limit
107
what is below the n=1 level?
what is above the n=infinite level?
- below the n=1 level is the nucleus
- above the n=infinite level is the outside of the atom
108
how are you able to work out the ionisation energy of the hydrogen atoms?
- if we know the frequency of wavelength of the convergence limit of the lyman series
(measuring the convergent frequency of the lyman series (difference from
n=1 to n=infinite) and usign ∆E=hf allows the ionisation energy to be calculatred. the value of ∆E is multiplied by avogadros constant to give the first ionisation energy for a mole of atoms)
109
what element is used when looking at absorption and emission spectras at AS level?
hydrogen
110
would the order of red, green, blue then purple of the arrows for the Balmer transition of hydrogen be the same for every element?
no - it would change per element
111
how is a beta particle formed?
when a neutron breaks down to form a proton and an electron
(the proton stays in the nucleus, the electron is emitted as a beta particle)
112
what does a change in atomic number mean?
a different element
113
what is the mnemonic to remember the order that the shells/orbitals fill up?
stupid people die first
s, p, d, f
114
what is the nature of the radiation of alpha?
- it is a helium nucleus if 2 protons and 2 neutrons
- has a mass of 4
- has a charge of +2
115
what is the nature of the radiation of beta?
- high kinetic energy electrons
- mass roughly 1/2000
- charge -1
116
what is the nature of the radiation of gamma?
- high frequency electromagnetic radiation
- mass of 0
- charge of 0
117
what is the penetrating power of alpha?
- low
- bc biggest mass and charge, stopped by a few cm of air or thin sheet of paper
118
what is the penetrating power of beta?
- medium
- stopped by aluminium
119
what is the penetrating power of gamma?
- very high
- bc smallest mass, most is stopped by a thick layer of steel or concrete but even a few cm of dense lead doesn’t stop all of it
120
what is the ionising power of alpha?
- very high
- bc the biggest mass and charge, has the biggest ‘punch’
121
what is the ionising power of beta?
- moderate ionising power
- bc smaller mass and charge than the alpha particle
122
what is the ionising power of gamma?
- low
- bc carries no electric charge and has virtually no mass, so not much of a ‘punch’ when colliding with an atom
123
what is the max number of electrons a s orbital can have?
2
124
what is the max number of electrons a p orbital can have?
6 electrons
125
what is the max number of electrons a d orbital can have?
10 electrons
126
why do you draw one arrow up and one arrow down in electronic configuration?
a maximum if 2 electrons can occupy any orbital, each with opposite spin
127
what do the chemical properties of an atom depend on?
the electronic configuration
(so isotopes have the same chemical properties as they have the same electronic configuration)
128
what has no affect on the chemical properties of an atom? why?
the neutron number
(they have no charge and hence exert no attractive force on the nucleus)
129
therefore, why do isotopes tend to have very similar chemical properties?
since they have the same atomic number and the same electronic configuration
(they differ only in number of neutrons, which do not directly influence the chemical properties of an element)
130
what effect does alpha decay have on the mass number and the atomic number?
mass number -4
atomic number -2
131
what effect does beta decay have on the mass number and the atomic number?
mass number = 0
atomic number +1
132
what is ionisation energy?
the energy required to remove an electron and produce an ion
133
explain the trend in ionisation energy across a period
ionisation energy generally increases as you move left to right across a period
134
explain the trend in ionisation energy down a group
ionisation energy decreases down a group
135
why does the amount of energy needed to remove electrons increase?
as you remove each electron, you are creating an ion. the attraction is now stronger
136
first ionisation energy definition
the energy required to remove the outer electron of a gaseous atom to form a +1 ion
e.g Na(g) —> Na + (g) + e -
137
what are the three factors that affect ionisation energy?
- nuclear charge (no. of protons)
- atomic radius (size of atom)
- the number of electrons between the outer electron and the nucleus (shielding)
138
how does the nuclear charge affect ionisation energy?
- the more protons in the nucleus, the more positively charged the nucleus is, and the more strongly the outer electron is attracted to it
(going across a period)
139
how does the atomic radius affect ionisation energy?
- attraction falls off very rapidly with distance
- an electron close to the nucleus will he much more strongly attracted than one further away
(going down the group)
140
how does the number of electrons between the outer electrons and the nucleus affect ionisation energy?
- the outer shell electrons are repelled by any inner shells between the electrons and the nucleus
- this repelling effect, called electron shielding or screening, reduces the overall attractive force experienced by the outer shells
- the more filled inner shells or subshells there are, the smaller the attractive force on the outer electron
141
what elements have the highest ionisation energies?
(cause the peaks on the graph)
noble gases
142
what elements have the lowest ionisation energies?
(cause the troughs on the graph)
alkali metals
143
do the ionisation energy in the troughs and peaks slowly increase or decrease?
decrease
144
what are some example of the blips in the ionisation energies?
- boron is lower than beryllium
- oxygen is lower than nitrogen
145
why does boron have a lower ionisation energy than beryllium?
it’s easier to remove the outer electron as it’s further away from the nucleus so it’s less attracted to the nucleus
(show sub-shells)
146
why does oxygen have a lower ionisation energy than nitrogen?
it’s easier to remove electron due to repulsion
(a half filled shell is more stable)
147
what isotope is used in radiotherapy for the treatment of cancer?
cobalt-60
(the high energy of gamma radiation is used to kill cancer cells)
148
what isotope is normally used as a medical tracer?
technetium-99m
149
what isotope is used in carbon dating?
carbon-14
150
what isotope is used in estimating the geological age of rocks?
potassium-40
it can change into argon-40 by the nucleus gaining an inner electron. measuring the ratio of potassium-40 to argon-40 in a rock gives an estimate of its age
151
ionisation definition
the process of removing electrons from an atom
152
what is the shielding effect/screening?
the repulsion between electrons in different shells. inner shell electrons repel outer shell electrons
153
how many ionisation energies does an element have?
as many as it has electrons
e.g the third ionisation energy:
Na 2+ (g) —> Na 3+ (g) + e -
154
why does the ionisation energy increase as you remove electrons from an atom?
- there is a greater effective nuclear charge as the same number of protons are holding fewer and fewer electrons
- as each electron is removed there is less electron-electron repulsion and each shell will be drawn in slightly closer to the nucleus
- as the distance of each electron from the nucleus decreases, the nuclear attraction increases
155
when does radioactive emission occur?
when an unstable nucleus becomes more stable by giving out energy and, in most cases, small particles such as electrons
156
other than gamma radiation, when else is gamma radiation emitted?
after a process called electron capture
electron capture occurs when a proton-rich nucleus absorbs an inner electron. this electron combines with a proton to form a neutron
157
does gamma radiation have high or low energy?
high or low frequency?
long or short wavelength?
high energy
high frequency
short wavelength
158
how does gamma radiation ionise atoms?
only if the electrons absorb the energy of the gamma radiation
however this is unlikely given that gamma radiation has such a short wavelength
159
why are positrons more strongly attracted to the negative plate than alpha particles?
because they have a lower mass
160
when using a tracer, what is important to make sure?
- it has a short half life, so that it decays quickly before it can do any permanent damage
- it emits enough radiation to be detected outside of the body
161
what is the evidence for electrons existing in shells?
the study of ionisation energies provide very clear evidence for shells of electrons
162
why is there a general increase in ionisation energy from lithium to neon?
due to the increased nuclear attraction l, since distance to the nucleus is constant, shielding is constant and the number of protons is steadily increasing
163
why does the excited state need to lose energy?
its unstable
164
what are photons?
- light can be considered as energy packets called photons
- they have both the properties of a ‘particle’ or a transverse wave
165
what is the name for when outer electrons feel less of the positive attraction of the nucleus due to inner electrons?
shielding
166
what is the type of decay that occurs when a neutron breaks down into a proton and a high energy electron?
beta
167
what is energy directly proportional to?
frequency
168
what is the name for when the energy levels of an atom get closer together?
convergence
169
the greater the frequency, the ___ the energy?
the greater the wavelength, the ___ the frequency?
the greater the frequency, the higher thr energy
the greater the wavelength, the lower the frequency
170
how are the Lyman series and ionisation energy linked?
transition from n=infinite to n=1 can be used to calculate IE using E = hv
171
the greater the nuclear charge, the ___ the ionisation energy?
greater the nuclear charge, the greater the ionisation energy
172
the greater the atomic radius, the ___ the ionisation energy?
the greater the atomic radius, the lower the ionisation energy
173
the greater the shielding, the ___ the ionisation energy?
the greater the shielding, the lower the ionisation energy
174
relative atomic mass definition
the weighed average mass of all isotopes compared to 1/12th the mass of C12
175
explain why neon has a lower first ionisation energy than helium?
although Ne has a higher nuclear charge, it also has greater shielding and atomic radius which outweighs this
176
what happens when a positron comes into contact with an electron?
they annihilate each other and create gamma radiation
177
are radioisotopes with a longer or shorter half-life more dangerous?
short half lives, because it decays very quickly and thus emits a large dose of radiation over a short period of time, causing more damage to living cells
(but radioisotopes with a long half life are more of an environmental problem as it takes a long time to decrease to a safe level)
178
what shape are s-orbitals?
spherical
179
what shape are p orbitals?
dumb-bell shaped
180
what is the name of how energy levels are split into regions of space around the nucleus where there is a high probability of finding an electron of a particular energy?
orbitals
181
what are atomic orbitals?
regions in space where electrons may be found
182
what are energy levels split into?
sub-levels (subshells) which contain orbitals of the same type
183
how many electrons can each orbital contain?
a maximum of 2 electrons
184
as there are 3 p orbitals, with each one holding __ electrons, p subshell can hold __ electrons
2
6
185
suggest why compounds containing B3+ ions are unlikely to exist?
too much energy is required to form B3+ ions
186
when do cations (positive ions) form?
when an atom loses one or more electrons
187
when do anions (negative ions) form?
when an atom gains one or more electrons
188
why is radiation bad for living cells?
high energy radioactive emissions break chemical bonds in the cell molecules giving rise to changes in DNA which can cause mutations and thr formation of cancerous cells at lower doses, or cell death at higher doses
189
how can you monitor the thickness of metal strops or foil?
- the metal is placed between two rollers to get the right thickness
- a radioactive source ( a beta emitter) is mounted on one side of the metal with a detector on the other.
- if the amount of radiation reaching the detector increases, the detector operates a mechanism for moving the rollers apart and vice versa
190
how are electrons held in their shells?
by their attraction to the positive nucleus
191
why will successive ionisation energies always increase?
- there is a greater effective nuclear charge as the same number of protons are holding fewer and fewer electrons
- as each electron is removed there is less electron-electron repulsion and each shell will be drawn in slightly closer to the nucleus
- as the distance of each electron from thr nucleus decreases, the nuclear attraction increases
- but a larger increase shows that an electron has been removed from a new shell
192
molar first ionisation energy definition
the energy required to remove one mole of electrons from one mole of gaseous atoms
193
explain why the lines become closer together at the high frequency end of the spectrum?
the (electron) energy levels of a hydrogen atom become closer
194
electron deficient definition
when the outer shell of electrons is not full
195
e.g Aluminium
why does it have a big jump in ionisation energy between it’s 3rd and 4th?
- it has 3 electrons in its outer shell
- so largest jump between 3rd and 4th IE
196
explain how the lyman series can be used to calculatr the ionisation energy of hydrogen?
- measuring the wavelength at the convergence limit
- calcuate the ionisation enrrgy using E=hf
197
what units is wavelength usually in f=c/wavelength
wavelength = meters
198
david said that sodium compounds give a yellow flame test because the heat makes the atoms move faster. he also said that the yellow flame was the sodium absorption spectrum consisting of one line because the atoms take in light of just one energy.
discuss how far you agree with david’s statement and correct any errors whcih he has made.
- not an absorption spectrum/ is an emission spectrum
- (it is not atoms) but electrons that are excited
- (electrons) go to higher energy levels
- then they fall back (to lower energy levels)
- they emit energy
- sodium spectrum has more than 1 line
- the flame colour is yellow because the energy emitted is in the yellow part of the visible spectrum
- series of lines that come closer together (wirh increase in energy involved)
199
state the relationship between energy, frequency and wavelength [2] (equations)
E = hf (1)
c = f λ (1)
200
as successive electrons are removed, the value of the ionisation energy increases due to a _____________?
greater effective nuclear charge
201
atomic orbital definition
a region in an atom that can hold up to two electrons with opposite spins
