Basic ideas on atoms

Question 1

Radioactivity

Answer 1

Not all nuclei of elements are stable meaning Ratio of Proton and neutrons are imbalanced
Radiation is omitted to regain this balance releasing excess protons and neutrons

Question 2

Alpha decay

Answer 2

Equivalent to helium nucleus
Reduces atomic number by 2 & 4 making element more stable
Least penetrating- stopped by sheet of paper
Strongly ionising- large slow moving and carry 2+ charges
Deflected by magnetic field- therefore must carry a charge

Question 3

Beta decay

Answer 3

streams of high energy electrons
Equivalent to electron
More penetrating than alpha- stopped by sheet of Al
Deflected by magnetic field in opp direction to alpha- therefore must carry negative charge.
Eg. 14C6 = 14N7+ 0e-1

Question 4

Beta decay- positron

Answer 4

antiparticle to electron
Proton is converted in neutron while releasing positron
+1
Eg. 23Mg12 = 23Na11 + 0e+1

Question 5

electron capture

Answer 5

Inverse beta decay
one of orbital electrons are captured by a positron in neuclus- forming neutron
Eg. 40K19 + 0e-1 = 40Ar18

Question 6

Gamma decay

Answer 6

High energy Electromagnetic waves
Short wavelength high frequency
Stopped by a block of lead
Most penetrating weakly ionising
Undeflected by magnetic field- shows gamma rays are uncharged, Don experience force when passing lines of magnetic field

Question 7

Half life

Answer 7

time taken to decay to half the number of radioactive atoms.

Question 8

Cons of living cells

Answer 8

ionising radiation may cause damage to DNA of cells
Leads to changes in way self functions
May cause mutations and formation of cancerous cells
Or cell death

Question 9

uses of radioactivity- medicine

Answer 9

Colbalt 60- radiotherapy for cancer treatment. High energy of Gamma radiation is used to kill cancer cells preventing tumours
Technetium 44m- medical radioisotope. Tracer. Normally to label a molecule which is taken by a tissue to be studied.

Question 10

Uses of radioactivity- radiodating

Answer 10

Carbon 14- Use to calculate the age of plant and animal remains. All organisms absorb carbon 14. Rates of decay decreases over years and activity that remains can be used to calculate age

Potassium 40- Used to estimate geological age of rocks. Can change into Ar 40 by nucleus gaining inner electron.
Measuring ratio gives estimate

Question 11

uses of radioactivity- dilutionanaylsis

Answer 11

Dilution analysis- Use of isotopically labelled substances to find the mass of a substance in a mixture. Useful when a component of complex mixture can be isolated from the mixture in pure state but can’t be extracted quantivaly

Question 12

Electronic structure

Answer 12

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
4s filled before 3d
electrons fill orbitals in order of increasing energy

Question 13

First ionisation energy

Answer 13

Energy required to remove one electron from each atom in one mole of its gaseous atoms
X(g) = X+(g) + e-

Question 14

First ionisation energy along a period

Answer 14

Increases due to decreasing atomic radius and greater electrostatic forces of attraction ( due to increasing number of protons)

Question 15

First ionisation energy down a group

Answer 15

Decreases due to increasing atomic radius and increasing shielding reducing effect of electrostatic forces of attraction

Question 16

atrraction

Answer 16

Electrons are held in their shells by their attraction to positive nucleus therefore the greater the attraction the greater the ionisation energy

Question 17

what is attraction dependent on

Answer 17

size of positive nuclear charge: Greater the nuclear charge, greater the attractive force on outer electron and greater the IE

Distance of outer electron from nucleus: Greater distance, lower force of attraction, lower IE

Shielding by electrons in inner shell: Electrons in filled inner shells repel electrons in outer shells- reduce effects of positive nuclear charge. More filled subshells, smaller attractive force on outer electron, lower IE

Question 18

He>H

Answer 18

Helium has a greater nuclear charge in the same subshell so there is little shielding

Question 19

He>Li

Answer 19

Lithium’s outer electron is in a new shell which has increased shielding and is further from the nucleus

Question 20

Be>B

Answer 20

Since borons outer Electron is in a new sub shell of slightly higher energy level and is partly shielded by 2S electrons

Question 21

N>O

Answer 21

Since electron- electron repulsion between two paired electrons in P orbital in oxygen makes one of the electrons easier to remove. N doesn’t have a paired electron in its P orbital

Question 22

He>Ne

Answer 22

Neon’s outer electron has increased shielding from inner electrons and is further away from the nucleus

Question 23

Successive ionisation energies

Answer 23

Measure of energy needed to remove each electron inturn until all electrons are removed from an atom
Eg. 3rd IE is a measure of how easily 2+ ion loses to form 3+ ion
Na2+ (g) = Na3+ (g) + e-

Question 24

SIEs always increase because:

Answer 24

-greater effective nuclear charge: Same number of Protons are holding fewer and fewer electrons
-as each electron is removed: Less electron-electron and each shell will be drawn in slightly closer to nucleus
- as distance of electron decreases: Nuclear attraction increases

Question 25

Emission and absorption spectra equations

Answer 25

c(3x10~8 ms-1) = F x W

E=hxf
Energy=h(6.63 x10-34) x freq

As freq increases, energy increases
As freq increases, wavelength decreases

W=c/f E= hxc/ W

Question 26

Spectrum colours

Answer 26

energy and freq increase from infrared to visible light to UV
Blue light is higher energy than red
As frequency increases wavelength decreases therefore blue light has a shorter wavelength than red

Question 26

absorption spectra

Answer 26

Displayed with an entire spectrum with black lines for the ‘missing’ frequencies of photons that have been absorbed when an electron moves up an energy level

Question 27

Emmision spectra

lines

Answer 27

Displayed with lines at specific frequencies of emitted photons from when electron moves down and energy level

Question 27

Hydrogen spectra

Answer 27

Atomic spectrum of hydrogen consists of separate series of lines in UV, visible light and infrared regions
paschen (infrared) Balmer (visible) lyman (uv)

Question 27

Hydrogen EMMISION spectrum

Answer 27

When an atom gets excited by absorbing energy an electron jumps to a higher energy level
An electron will fall back down to a lower energy level given out energy to:
n=1(uv) n=2(visible) n=3 (infrared)

Question 27

Hydrogen ABSORPTION spectrum

Answer 27

When light with several frequencies pass through a cold low density gas
Gas absorbs photons of certain energies enabling electrons to transition to a higher energy level
This process leaves dark tracks on a bright continuous spectrum resulting in the hydrogen absorption spectrum

Question 28

ionisation energy of hydrogen atoms

Answer 28

convergence limit: when sprectral lines become So close together they have a continuous bond of radiation and separate lines can’t be distinguished.
n=1, Convergence limit represents ionisation of hydrogen atom
wavelengh a CL
Entahply E= HxF
E x 6.02 x10-23

Question 28

electronic configuration- chromium, copper

Answer 28

electron taken off 4s to fill 3d and this makes it more stable
Half filled or fully filled orbitals are more stable

Question 29

orbitals

Answer 29

An orbital is a cloud of negative charge that can hold up to two electrons.

Question 30

discrete lines

Answer 30

lines are discrete energ levels so must have fixed values

Question 31

if electron is closer to the nucleus

Answer 31

greater effective nuclear charge
less shielding on outer electron so outweighs smaller nuclear charge