Atomic Structure Flashcards
Define atom
The smallest part of an element that can exist.
All substances are made up of…?
atoms
The radius of an atom is …?
0.1 nm (1 x 1010 m)
The overall charge on an atom is…
zero/neutral
Define element
Contains only one type of atom
Substances found in the periodic table are…?
elements
Approximately how many elements are there?
100
Define isotope
An atom of the same element with different numbers of neutrons
Define radioactive decay
An unstable nucleus changes to become more stabe and gives out radiation
We cannot predict when a given atom will decay, this means that radioactive deacy is ….?
random
Define activity
Rate at which decay occurs
What are the units of activity?
Becquerels (Bq)
Define count rate
Number of decays recorded each second by a Geiger-Muller tube
Defne half life
The time taken for number of radioactive nuclei in a sample to halve OR time taken for count rate (or activity) from a sample to fall to half its initial value
Define contamination
The unwanted presence of materials containing radioactive atoms
Define irradiation
When an object is exposed to radiation
Does an irradiatied object become radioactive itself?
no
The process of radiation removing electrons from atoms to form ions is called…?
ionisation
If ionisation happens in DNA it can cause ___________ which may result in ____________
mutations, cancer
Define peer review
Checking of scientific results by other scientific experts
Define mass number
The total number of protons and neutrons in an atom
Define atomic number
The number of protons in an atom (number of electrons is the same in a neutral atom)
Electrons in atoms are located in ___________
energy levels
Absorption of radiation by an atom may result in ____________ moving to a ________________ energy level
electrons, higher
Emission of radiation from an atom may lead to _____________ moving to a ______________ energy level
electrons, lower
Who came up with the Plumb Pudding model of the atom
J J Thompson
Describe the Plumb Pudding model of the atom
A ball of positive charge with negative electrons embedded in it
Was the Plumb Pudding model correct?
no
What experiment did Rutherford do?
Alpha particle scattering
What did Rutherford’s experiment reveal?
Atoms have a central area of positive charge with electrons surrounding it
Who discovered that electrons are located in energy levels?
Niels Bohr
What did Jame Chadwick discover about the atom?
That the nucleus contains neutrons as well as protons
What did John Dalton contribute to our understanding of atomic theory?
Matter is made up of descrete, spherical particles, known as atoms
Name the three subatomic particles
proton, neutron, electron
Which particles are located in the atoms nucleus
protons, neutrons
What is the charge of each subatomic particle?
proton +1, neutron 0, electron -1
What is the mass of each subatomic particle?
proton 1, neutron 1, elecrton ≈ 0
Name the three types of radiation
alpha, beta and gamma
What is an alpha particle?
two protons and two neutrons
What is a beta particle?
an electron
What is gamma radiation?
electromagnetic wave (NOT a particle)
What is the range of alpha radiation in air?
short - 5 cm in air
What is the range of gamma radiation in air?
unlimited in air
What’s the range of beta radiation in air?
medium - about 1 m
What will absorb (stop) alpha radiation?
paper/skin
What will absorb (stop) beta radiation?
about 5 mm aluminium
What will absorb (stop) gamma radiation?
several centimetres of lead
What is the ionising power of alpha radiation?
very high
What is the ionising power of beta radiation?
medium
What is the ionising power of gamma radiation?
low
What is meant by the ionising power of radiation?
how likely it is to ionise atoms which it comes into contact with
How does alpha decay alter the mass number of the parent nucleus?
decreases by 4
How does alpha decay alter the atomic number of the parent nucleus?
decreases by 2
How does beta decay alter the mass number of the parent nucleus?
stays the same
How does beta decay alter the atomic number of the parent nucleus?
increases by 1
How does gamma radiation alter the mass and atomic number of the parent nucleus
unchanged (energy is released as the particles in the nucleus reorganise to a lower energy arrangement)
