1.2 Basic ideas about atoms Flashcards
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.
What are the four types of radioactive emission?
- Alpha (α)
- Beta (β)
- Positrons/beta plus (β+)
- Gamma (γ) (electron capture)
What are alpha particles?
Two protons and two neutrons ejected from the nucleus at high speed. (42He2+).
What are beta particles?
electrons that are ejected from the nucleus at high speed. (0-1e)
What are positrons/beta plus?
Positrons are anti-electrons (01e) that are ejected from the nucleus at high speed. An anti-electron has the same mass as an electron but a different electrical charge: positive.
What is Gamma radiation? and describe electron capture
High speed electromagnetic wave. Electron capture occurs when a proton-rich nucleus absorbs an inner electron. This electron combines with a proton to form a neutron.
What is the penetrating power and ionisation level of alpha particles?
Low penetration stopped by a single sheet of paper. Highly ionising if inside the body.
What is the penetrating power and ionisation level of beta particles?
Relatively penetrating stopped by 5mm of aluminium. Also relatively ionising.
What is the penetrating power and ionisation level of gamma waves?
Highly penetrating and only partially stopped by a thick layer of lead. Very low ionisation level
What is the definition of half life?
the time taken for the radioactivity of an atom to decay by half its original value
How do TRACERS use radiation?
radioactive materials injected or ingested by medical patients, are used to scan for abnormalities like tumours.
How does RADIOTHERAPY use radiation?
Radiation can cause cancer, but it can also be used to treat it by focusing gamma beams precisely onto tumours, killing cancerous cells.
How does RADIO-DATING use radiation?
Carbon-14, with a half-life of 5570 years, can be used to determine the age of plants and animals, with a dating period of 50,000-70,000 years.
How does MONITORING METAL THICKNESS use radiation?
Metal is rolled between rollers to achieve desired thickness, with a β-source on one side and a detector on the other, adjusting the rollers as needed.
What is an ionisation energy?
It is a measure of the energy required to remove one or more electrons from an atom.
What is the definition of first ionisation energy?
the energy required to remove one mole of electrons from one mole of gaseous ions
Why is there a large jump in ionisation energy between each shell?
Because there is greater effective nuclear charge and electrons are removed from an increasingly positive ion.
What is the nature of first ionisation energy down a group?
The value decreases due to an increasing atomic radius and increasing shielding. Greater shielding outweighs the greater nuclear charge
What is the nature of first ionisation energy across a period?
The value increases due to greater positive charge of the nucleus and no change in shielding.
Explain the group 2 - group 3 ΔH1e1 dip in ionisation energy across a period.
Less energy is needed to remove the 2p electron than the 2s electron because the 2p subshell is at a higher energy than the 2s
Explain the group 5 - group 6 ΔH1e1 dip in ionisation energy across a period.
Paired electrons require less energy to remove because they repel.
What is the general trend of ΔH1e1?
Increases across periods
How many electrons can one orbital hold?
2
What are the four different types of orbital?
s, p, d and f
What is an orbital?
A volume of space where electrons of a certain energy are most likely to be found.
What is the order of the subshells?
1s 2s 2p 3s 3p 4s 3d 4p
How many electrons can fit into an s subshell?
2
How many electrons can fit into a p subshell?
6
How many electrons can fit into a d subshell?
10
Why is the 4s subshell filled before the 3d?
Because 4s has a lower energy level than 3d
What are the two exceptions to the ‘filling rule’ of subshells and what makes them different?
Chromium and Copper: the 3d orbital fills before the 4s
Does charge have an effect on how subshells are filled?
Yes. A positive charge removes electrons and a negative charge adds them. When removing electrons they are removed from the 4s subshell first.
What equation combines energy and frequency?
E = hf
What equation combines energy and wavelength?
E = hc / λ
What happens when electrons fall from their excited state?
Frequencies of light are emitted. These frequencies can be seen on an emission spectrum.
What happens when white light shines through gaseous atoms?
Photons of certain energy may be absorbed causing an electron to move from a lower energy level (n = 1) to a higher energy level (n = >1)
Where does the Lyman series occur?
in the ultraviolet region of the electromagnetic spectrum
What happens to the lines on the Lymen series?
As they fall from each energy level down to n = 1 the lines get closer and closer together as the frequency of the radiation increases
What is the Balmer series?
The visible region of the spectrum where four prominent lines fall from each energy to n = 2
