1.2 - Basic Ideas About Atoms Flashcards
Atomic Number
The number of protons in the nucleus of an atom
Mass Number
The number of protons and neutrons in the nucleus of an atom
Isotope
Atoms having the same number of protons but a different number of neutrons
Ions
A particle where the number of electrons does not equal the number of protons. Has an electrical charge due to loss or gain of electrons.
Alpha-particle
A helium nucleus (Two protons and two neutrons). Positively charged.
Beta-particle
A stream of fast moving, high-energy electrons - negatively charged
Gamma-particle
A high energy EM wave
Define Radioactive decay
The process of emitting radiation by unstable isotopes when their nucleu divides.
Penetrating power of each radiation
MOST -
Gamma - Several cm of lead or M of concrete
Beta - Stopped by mm of aluminium
Alpha - Stopped by paper / air
Effect of an electric field on radiation?
- Gamma rays are unaffected
- Beta particles are negatively charged and so are deflected toward the positive plate
-Alpha particles are positively charge and so deflect toward the negative plate.
-Alpha is LARGER and SLOW MOVING so deflects slower than beta
Alpha Emission effect on element
Mass = -4
Atomic No. = -2
4
2 α
Define Electron Capture
Also called Inverse Beta
An orbital electron is captured by a proton in the nucleus
This forms a neutron and emits a neutrino
Beta Emission effect on element
Mass = 0
Atomic No. = +1
0
-1 β
Electron Capture effect on element
Mass = 0
Atomic No. = -1 (Lost a proton)
Electron is on LHS of equation
40 0 40
19 K + -1 e- —-> 18 Ar
Positron Emission effect on element
(β+ decay)
Mass = 0
Atomic No. = -1
0
1 β ON RHS
Define Positron Emission
β+ decay
A proton is converted into a neutron while releasing a positron
Gamma Emission effect on element
No affect on mass or atomic no.
Just and Y symbol on the end of equation
Which is the only emission that affects mass?
Alpha - Mass number -4
Because 4 is the mass number of a helium nucleus
Which emission type adds one to the atomic number?
Beta Emission
Difference between electron capture and positron emission in equations
Both -1 on atomic number
Electron capture is on LHS and written with electron symbol
Positron emission uses Beta symbol and is on RHS
0 0
-1 e- 1β
Define Half Life
The time taken for half the atoms in a radioisotope to decay
Health Hazard of radiation
Ionisation radiation can damage DNA
This can cause cancerous mutations
Changes in cell function or cell death in high doses
What is the most dangerous type of radiation to the body?
-Gamma is the most dangerous outside the body - Only one with penetrating power
-Alpha is the most dangerous inside the body - Most ionising
Three areas where radiation is used
Health & Medicine
Carbon dating
Industry
Uses of radiation in Health and medicine
Radiotherapy - killing cancer cells (Cobalt-60)
PET Scans - Injecting a radioactive tracer )(Technetium-99)
Uses of radiation in Carbon dating
Carbon-14 used to calculate the age of plant and animal remains
All organisms absorb carbon. When the organism dies it stops absorbing Carbon-14 and it decays. The C-14 levels can be used to calculate the age of the remains. (When it stopped absorbing CO2)
Uses of radiation in Industry
Ionising radiation can be used to sterilise equipment
Thickness of metal - Metal is placed between rollers, with the radioactive source and detector on each side - The amount of radiation detected controls if the rollers roll the metal thicker or thinner.
How do electrons behave in an orbital?
Electrons have opposite spins in an orbital to reduce repulsion.
Drawn as opposite arrows
How many electrons in an S-Orbital?
2 Max
How many electrons in a P-Orbital?
6 Max
How many electrons in a D-Orbital?
10 Max
How do electrons fill a subshells? (Hund’s Rule)
Each orbital will fill first with one electron before a second is added.
Electrons prefer to be alone.
In which order to electron shells fill?
1s 2s 2p 3s 3p 4s 3d 4p 5s
How can electron configuration be written quicker?
For convenience, you can use the previous Noble gas and work from that point on.
Exceptions to subshell filling order?
Copper and Chromium
How does Chromium fill its subshells?
Only 1 electron in all on 4s and 3d
How does Copper fill its subshells?
1 Electron in 4s
And 10 in 3d
What is ionisation?
The process of removing electrons from an atom.
Define First Ionisation Energy?
The energy required to remove one mole of electrons from one mole of gaseous atoms, under standard conditions.
Equation for Ionising
X(g) —-> X+(g) + e-
Trends in successive ionisation - Why?
-Every time you remove an electron the proton/electron ratio increases, meaning more energy is required to remove an electron
As each electron is removed there is less electron-electron repulsion, so each shell will be drawn slightly closer to the nucleus.
When electrons become closer to the nucleus, the nuclear attraction increases, therefore more energy is needed to remove an electron.
Emission Spectra explanation
When an atom gains energy, electrons are excited and jump to a higher energy level/ shell further from the nucleus.
When electrons fall back down to a lower energy level quantised radiation is emitted.
The colourful lines occur when electrons fall the n=2, emitting energy which in the form of visible waves.
Explain Absorption Spectra
-All atoms and molecules absorb lights of certain wavelengths, the black lines occur where wavelengths have been absorbed.
Wavelengths of these lines correspond to energy taken in by atoms to promote electrons.
Equations for wavelength?
E =hf
C = fλ
What is the convergence limit?
n = infinity
The point at which the energy of an electron is no longer quantised.
The atom has been ionised
