Basic Ideas about Atoms

  • Created by: V-elo
  • Created on: 24-03-18 15:56

Atomic Structure 

Mass number: the number of protons and number of neutrons in the nucleus of an atom. (top number)

Atomic number: number of. protons in the nucleus of an atom. (bottom number)

Isotopes: atoms having the same number of protons but different numbers of neutrons. 

Proton number = Electron number

Image result for atom labelled

A particle where the number of electrons does not equal the number of protons is an ION.

Na goes to Na+ + e-  (Ionised) REDOX Reduction is gain, Oxidation is loss


Some isotopes are unstable and split up to form smaller atoms. The nucleus divides and sometimes protons, electrons, and neytrons fly out. This is RADIOACTIVE DECAY.

Radioactive isotopes have unstable nuclei and give off 3 radiation types: ALPHA, BETA, and GAMMA.

Alpha particles:

  • 2 protons and 2 neutrons (Helium nuclei).
  • Least penetrating 
  • Stopped by a thin sheet of paper
  • +vely charged

Beta particles:

  • High energy electrons 
  • More penetrating
  • Stopped by a 5mm thick sheet of Al
  • -vely chraged

Gamma particles:

  • High energy electromagnetic waves
  • Most penetrating
  • Passes through several cm of Pb
  • No charge

When alpha, beta, gamma radiation pass through matter, they knock electrons out of atoms ionising them. ALPHA is strong ionising (large in size and slow moving and carries 2 positive charges) GAMMA is the least ionising.

Since alpha is the most strongly ionising, transfer of energy happens most rapidle so it is the least penetrating. Vice versa for GAMMA.

Image result for effect of electric field on radiation (

Alpha and Beta emissions 

Alpha's effect when an element emits an alpha particle

= mass number-4 and atomic number-2

Beta's effect when an element emits a Beta particle

= Mass number-0 and atomic number+1

Inverse beta decay...Electron Capture

One of the orbital electrons is captured by a proton in the nucleus, forming a neutron and emitting an electron neutrino.

Positron emission or B+ decay

A proton is converted into a neutron whilst releasing a positron and an electron neutrino

Half life: time taken for half the atoms in a radioisotope to decay. (1 to 1/2 to 1/4 to 1/8 to 1/16...) 

The longer the half life the greater the concern because the longer the radioisotope can exist.

Consequences for living cells

Ionising radiation can damage DNA of a cell can lead to mutations and the formation of cancerous cells. 

Ingesting alpha particles is more dangerous than beta or gamma (less penetrating but least ionising to stays in the body).

Beneficial uses of radioactivity


Cobalt-60 in radiotherapy for Cancer treatment

Technetium-99m for medical radioisotope as a tracer to study tissue.


Carbon-14 used to calculate the age of plants and animal'  remains. All living organsims absorb carbon (part of which is C-14). Rate of its decay decreases over the years and the activity that remains is used to calculate the age. 

Potassium-40 for age of rocks


Dilution analysis: use of isotopically labelled substances to find the mass of a substance in a mixture (helps to extract in quantitatively).

Measuring thickness of metal *****: Metal placed between 2…


No comments have yet been made