1.2 Basic Ideas about Atoms Flashcards
what is radioactive decay?
Nuclear decay is a spontaneous process, unstable nuclei decay to form more stable nuclei
where do radiations come from?
the nucleus of the atom
types of radiations
alpha emission
beta emission
positron emission (beta plus decay)
gamma emission
alpha emission
atomic number -2 left
mass number -4
beta emission
mass conserved
atomic number +1 right
what happens in electron capture
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.
gamma rays
no mass
high energy wave
what are the effects of a field on radiation?
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.
charge and deflection of beta radiation
-1 charge
small mass so strongly deflected
charge and deflection of gamma radiation
no mass or charge
no deflection
charge and deflection of gamma radiation
+2 charge
high mass weak deflection
penetrating power of alpha
sheet of paper
penetrating power of gamma
few cm of lead
penetrating power of beta
few mm of aluminium
term radioactive half-life
is the time for half the radioactive nuclei in any sample to undergo radioactive decay
what are atoms made of?
electron- relative mass 1/1840 charge -1
proton- relative mass 1 charge +1
neutron- relative mass 1 charge 0
what is atomic number?
number of protons
mass number
sum of protons and neutrons
alpha particles
positively charged
beta particles
negatively charged
the half-life of a radioisotope is..
the time taken for its radioactivity to fall to half of its initial value
effects of radiation
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.
beneficial uses of radioactivity
- 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
what is electron shielding
repulsion between electrons in different shells. inner electron shells repel outer shell electrons
explain the term molar first ionization energy
the energy required to remove 1 mole of electrons from one mole of atoms in the gaseous state.
s-orbital
spherical
can hold up to
d-orbital
5 different orbitals
can hold up to ten electrons
p-orbital
dumbell / 8
can hold up to six electrons
emission spectrum
coloured bands on a black background
electrons falling from excited state to n=2
absorption spectrum
black bands on a coloured background
electrons being promoted to an excited state from n=2
f-orbital
seven different orbitals
can hold up to 14 electrons
the way electrons are arranged
electron configuration
electron structure
term ionisation
the process of removing electrons from an atom
Successive ionization energies always increase because:
- 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.
ionisation energy
The attraction depends on three factors:
- 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
The equation frequency of electromagnetic radiation has the equation :
E = hf
(h is a constant called Planck’s
constant (6.63 × 10–34 J s)
electromagnetic spectrum
The whole range of frequencies of electromagnetic radiation
absorption spectra
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.
emission spectra
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.
the hydrogen spectra
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
paschen series (infrared region)
each line is due to electrons returning to the 3rd shell, n = 3 energy level.
balmer series (visible region)
each line is due to electrons returning to the 2nd shell, n = 2 energy level.
lyman series (ultraviolet region)
each line is due to electrons returning to the 1st shell, n = 1 energy level.
convergence limit
The higher-frequency spectral lines eventually become a continuous band of radiation and separate lines cannot be distinguished
