1.2 Basic Ideas about Atoms

Question 1

what is radioactive decay?

Answer 1

Nuclear decay is a spontaneous process, unstable nuclei decay to form more stable nuclei

Question 2

where do radiations come from?

Answer 2

the nucleus of the atom

Question 3

types of radiations

Answer 3

alpha emission
beta emission
positron emission (beta plus decay)
gamma emission

Question 4

alpha emission

Answer 4

atomic number -2 left
mass number -4

Question 5

beta emission

Answer 5

mass conserved
atomic number +1 right

Question 6

what happens in electron capture

Answer 6

An electron from the closest energy level falls into the nucleus (is
‘captured’) which causes a proton to change into a neutron emitting
an electron neutrino. The atomic number of the original element
decreases by one, forming a different element (the ‘daughter’
isotope is one place to the left in the Periodic Table) and has the
same mass number.

Question 7

gamma rays

Answer 7

no mass
high energy wave

Question 8

what are the effects of a field on radiation?

Answer 8

α-particles are positive, heavy and slow-moving
and are attracted slightly to the negative plate
of an electric field.

β-particles are light and fast-moving and show
considerable deviation toward the positive
plate of an electric field.

γ-radiation is electromagnetic radiation of short
wavelength and is unaffected by an electric
field.

Question 9

charge and deflection of beta radiation

Answer 9

-1 charge
small mass so strongly deflected

Question 10

charge and deflection of gamma radiation

Answer 10

no mass or charge
no deflection

Question 11

charge and deflection of gamma radiation

Answer 11

+2 charge
high mass weak deflection

Question 12

penetrating power of alpha

Answer 12

sheet of paper

Question 13

penetrating power of gamma

Answer 13

few cm of lead

Question 14

penetrating power of beta

Answer 14

few mm of aluminium

Question 15

term radioactive half-life

Answer 15

is the time for half the radioactive nuclei in any sample to undergo radioactive decay

Question 16

what are atoms made of?

Answer 16

electron- relative mass 1/1840 charge -1
proton- relative mass 1 charge +1
neutron- relative mass 1 charge 0

Question 17

what is atomic number?

Answer 17

number of protons

Question 18

mass number

Answer 18

sum of protons and neutrons

Question 19

alpha particles

Answer 19

positively charged

Question 20

beta particles

Answer 20

negatively charged

Question 21

the half-life of a radioisotope is..

Answer 21

the time taken for its radioactivity to fall to half of its initial value

Question 22

effects of radiation

Answer 22

Ionizing radiation can damage the DNA of a cell.
Damage to the DNA may lead to changes in the way the cell functions, which can
cause mutations and the formation of cancerous cells at lower
doses or cell death at higher doses.

Exposure to high levels of radiation can cause radiation burns and death.

Question 23

beneficial uses of radioactivity

Answer 23

• Treatment of cancer – radiotherapy using gamma radiation from cobalt-60.
• Tracer – taken up by the tissue to be studied e.g. techtinium-99.
• Calculating age of plant and animal remains – carbon-14 (half-life 5570 years).
• Estimating geological age of rock potassium-40 (half-life 1300 million years).
• Production of electricity – nuclear power stations: uranium-235, plutonium-239.
• Measuring the thickness of metal foil

Question 24

what is electron shielding

Answer 24

repulsion between electrons in different shells. inner electron shells repel outer shell electrons

Question 25

explain the term molar first ionization energy

Answer 25

the energy required to remove 1 mole of electrons from one mole of atoms in the gaseous state.

Question 26

s-orbital

Answer 26

spherical can hold up to

Question 27

d-orbital

Answer 27

5 different orbitals can hold up to ten electrons

Question 28

p-orbital

Answer 28

dumbell / 8 can hold up to six electrons

Question 29

emission spectrum

Answer 29

coloured bands on a black background electrons falling from excited state to n=2

Question 30

absorption spectrum

Answer 30

black bands on a coloured background electrons being promoted to an excited state from n=2

Question 31

f-orbital

Answer 31

seven different orbitals can hold up to 14 electrons

Question 32

the way electrons are arranged

Answer 32

electron configuration electron structure

Question 33

term ionisation

Answer 33

the process of removing electrons from an atom

Question 34

Successive ionization energies always increase because:

Answer 34

* there is a greater ‘effective’ nuclear charge as the same number of protons are holding fewer and fewer electrons * as each electron is removed, each shell will be drawn slightly closer to the nucleus * as the distance of each electron from the nucleus decreases, the nuclear attraction increases.

Question 35

ionisation energy The attraction depends on three factors:

Answer 35

* the size of the positive nuclear charge * the distance of the outer electron from the nucleus * the shielding effect of electrons in fully occupied inner shells

Question 36

The equation frequency of electromagnetic radiation has the equation :

Answer 36

E = hf (h is a constant called Planck’s constant (6.63 × 10–34 J s)

Question 37

electromagnetic spectrum

Answer 37

The whole range of frequencies of electromagnetic radiation

Question 38

absorption spectra

Answer 38

The light of a frequency corresponding to the energy of the photon is removed. Black lines appear in the spectrum where the light of some wavelengths has been absorbed. The wavelengths of these lines correspond to the energy taken in by atoms to promote electrons to higher energy levels.

Question 39

emission spectra

Answer 39

When the source of energy is removed, electrons in the excited state fall to a lower energy level. Energy lost is released as a photon with a specific frequency. The spectrum consists of a number of coloured lines on a black background.

Question 40

the hydrogen spectra

Answer 40

The atomic spectrum of hydrogen consists of many separate series of lines. Transitions between different energy levels result in the emission of radiation of different frequencies and therefore produce different lines in the spectrum. As the frequency increases, the lines get closer together because the energy difference between the shells decreases

Question 41

paschen series (infrared region)

Answer 41

each line is due to electrons returning to the 3rd shell, n = 3 energy level.

Question 42

balmer series (visible region)

Answer 42

each line is due to electrons returning to the 2nd shell, n = 2 energy level.

Question 43

lyman series (ultraviolet region)

Answer 43

each line is due to electrons returning to the 1st shell, n = 1 energy level.

Question 44

convergence limit

Answer 44

The higher-frequency spectral lines eventually become a continuous band of radiation and separate lines cannot be distinguished