P4-Atomic Structure

Model of the Atom summary

Dalton: concept of atoms

Thomson: electrons plum pudding

Rutherford: alpha scattering nucleus is positive with a cloud of electrons

Bohr: electrons in shells

Chadwick: neutron in nucleus

Isotope

An atom with the same number of protons and a different number of neutrons from other atoms of the same element.

What happens to unstable isotopes?

They decay (break down) and emit radiation as they try to be stable (by balancing the number of protons and neutrons).

Ionising radiation

any form of radiation that has the ability to remove electrons from atoms and molecules

Ionising power

HOW easily they knock out electrons

Alpha Particles

helium nuclei

'a'

2 neutrons, 2 protons, like a helium atom

dont penetrate far, can be stopped quickly, only travel a few cm

can be absorbed by paper

due to size, strongly ionising

Beta particles

high speed electrons

B with line running down

moderately ionising and penetrative

few metres range

absorbed by aluminium

for every beta particle released, a neutron turns to a proton

gamma rays

electromagnetic waves

y thats curvy

penetrates far, long distance

weakly ionising due to range it focuses on

absorbed in lead or concrete

Alpha nuclear equation

4

He

2

Beta nuclear equatjon

0

e

-1

gamma ray nuclear equation

none.

gamma rays get rid of excesss energy, so there is no change to atomic number or mass

What can you measure radiation with?

Geiger-Muller tube and counter (records number of radiation counts hitting it per second)

is radiactive decay random?

yes

what happens to radioactivity over time?

it decreases

half-life

the time taken for the number of radioactive nuclei in an isotope to halve

ionising radiation is dangerous because...

it can enter living cells and ionise their atoms, damaging cells

irradiation

exposure to radiation

does NOT make it radioactive

contamination

radioactive particles getting onto or into objects

will decay and release radiation in body, damaging cells

What nuclear particles can penetrate human skin?

beta and gamma

most dangerous nuclear particles?

alpha as they focus ionisation on a smaller area