Describe the structure of an atom (in terms of nucleus and electrons)
State where most of the mass of an atom is found.
: nucleus as it has 2 subatomic particles and a positive charge.
State the sizes of atoms and small molecules.
: size of atom = 1 × 10 -10 m
: size of small molecule = 0.1 nm or 1 × 10 -10 m
Describe an early model of the atom
: JJ Thomson - ‘plum pudding’ model.
Large positively charged circle full of smaller negatively charged particles to balance out the atom and
make it neutral.
Describe how and why our model of the atom has changed over time, including the plum pudding model
and the Rutherford alpha particle scattering
: During Rutherford's golden tinfoil experiment, it was found out that atoms are mostly empty space and
that positively charged subatomic alpha particles can pass through various substances but some would
bounce back. The ‘plum pudding’ model couldn’t explain this experiment so the atom was updated into
Rutherford's atom.
State what is meant by an isotope
: An isotope is an element that has the same amount of protons in the nucleus but a different amount of
neutrons.
Represent an isotope using a symbol + Explain how atoms of different elements are different ( in terms of
numbers of electrons and protons )
: Carbon originally has a mass number of 12 and an atomic number of 6. An isotope of carbon (shown
below) has a mass number of 13 and an atomic number of 6. The atomic number must always stay the
same for it to be the same element. The mass number is the only number that can change in an isotope
as the number of protons must remain the same !
, Recall the charges and masses of the three subatomic particles
Subatomic Particle : Mass : Charge :
Proton 1 +1
Neutron 1 0
Electron 1/1835 -1
Explain why all atoms have no overall charge
: Atoms have no overall charge because in the nucleus there are protons which have a positive (+1)
charge and neutrons with no charge, this makes the nucleus positive charged. The electrons on the
energy levels / outer shells are negatively (-1) charged, because of these charges of -1 and +1 the
charges cancel each other out and make the atom have overall no charge.
Describe where electrons are found inside atoms (in terms of shells)
: Electrons are found on the outer shells inside of the atom. On the first shell only 2 electrons can be
found and on the following shells 8 electrons can be found.
Describe when electrons can change orbit
: Electrons can change energy levels or shells when energy is emitted or absorbed. When an electron
absorbs electromagnetic energy, the electron gains enough energy to move up one energy level. On the
other side, when an electron emits electromagnetic energy (gives out) it loses its energy so it moves
down closer to the nucleus.
Recall what an ion is + Describe how ionisation occurs
: An ion is an atom that has lost or gained an electron due to the electron absorbing enough
electromagnetic energy to escape or an atom not having enough energy to be stable, having to take in an
electron. When an atom loses an electron it becomes positively charged and when an atom gains an
electron it becomes negatively charged. They become + or - charged because an atoms overall charge in
neutral so when an electron leaves or comes in it adds or takes away one.
Describe some of the evidence for Bohr model of the atom
: Bohr suggested that electrons can only travel in a certain successively larger orbit around the nucleus.
He thought the outer orbit could hold more electrons than the inner ones. Bohr also suggested that the
outer electron shells should determine the atom's chemical properties. Therefore, the current atom
model has a small nucleus surrounded by many outer electron shells.
Explain what background radiation is
Background radiation is a type of radiation that is around us all the time, it can be both natural and man
made and it causes little harm.
Describe how radiation measurements need to be corrected for background radiation
: When scientists measure the radioactivity of a source, they need to measure the background radiation
first by taking several readings and finding the mean. This mean value is then subtracted from
measurements.
List some sources of background radiation
: Cosmic rays (high energy, charged particles from the sun, many are stopped by atmosphere but some
come down)
Radon gas (causes most background radiation, is produced when uranium in certain rocks decays)
Ground and Buildings
Food and Drink (radioactive compounds in soil that are taken up by plants and eaten by animals, most
commonly potassium)
Medical (gamma rays in x-rays)
State where most of the mass of an atom is found.
: nucleus as it has 2 subatomic particles and a positive charge.
State the sizes of atoms and small molecules.
: size of atom = 1 × 10 -10 m
: size of small molecule = 0.1 nm or 1 × 10 -10 m
Describe an early model of the atom
: JJ Thomson - ‘plum pudding’ model.
Large positively charged circle full of smaller negatively charged particles to balance out the atom and
make it neutral.
Describe how and why our model of the atom has changed over time, including the plum pudding model
and the Rutherford alpha particle scattering
: During Rutherford's golden tinfoil experiment, it was found out that atoms are mostly empty space and
that positively charged subatomic alpha particles can pass through various substances but some would
bounce back. The ‘plum pudding’ model couldn’t explain this experiment so the atom was updated into
Rutherford's atom.
State what is meant by an isotope
: An isotope is an element that has the same amount of protons in the nucleus but a different amount of
neutrons.
Represent an isotope using a symbol + Explain how atoms of different elements are different ( in terms of
numbers of electrons and protons )
: Carbon originally has a mass number of 12 and an atomic number of 6. An isotope of carbon (shown
below) has a mass number of 13 and an atomic number of 6. The atomic number must always stay the
same for it to be the same element. The mass number is the only number that can change in an isotope
as the number of protons must remain the same !
, Recall the charges and masses of the three subatomic particles
Subatomic Particle : Mass : Charge :
Proton 1 +1
Neutron 1 0
Electron 1/1835 -1
Explain why all atoms have no overall charge
: Atoms have no overall charge because in the nucleus there are protons which have a positive (+1)
charge and neutrons with no charge, this makes the nucleus positive charged. The electrons on the
energy levels / outer shells are negatively (-1) charged, because of these charges of -1 and +1 the
charges cancel each other out and make the atom have overall no charge.
Describe where electrons are found inside atoms (in terms of shells)
: Electrons are found on the outer shells inside of the atom. On the first shell only 2 electrons can be
found and on the following shells 8 electrons can be found.
Describe when electrons can change orbit
: Electrons can change energy levels or shells when energy is emitted or absorbed. When an electron
absorbs electromagnetic energy, the electron gains enough energy to move up one energy level. On the
other side, when an electron emits electromagnetic energy (gives out) it loses its energy so it moves
down closer to the nucleus.
Recall what an ion is + Describe how ionisation occurs
: An ion is an atom that has lost or gained an electron due to the electron absorbing enough
electromagnetic energy to escape or an atom not having enough energy to be stable, having to take in an
electron. When an atom loses an electron it becomes positively charged and when an atom gains an
electron it becomes negatively charged. They become + or - charged because an atoms overall charge in
neutral so when an electron leaves or comes in it adds or takes away one.
Describe some of the evidence for Bohr model of the atom
: Bohr suggested that electrons can only travel in a certain successively larger orbit around the nucleus.
He thought the outer orbit could hold more electrons than the inner ones. Bohr also suggested that the
outer electron shells should determine the atom's chemical properties. Therefore, the current atom
model has a small nucleus surrounded by many outer electron shells.
Explain what background radiation is
Background radiation is a type of radiation that is around us all the time, it can be both natural and man
made and it causes little harm.
Describe how radiation measurements need to be corrected for background radiation
: When scientists measure the radioactivity of a source, they need to measure the background radiation
first by taking several readings and finding the mean. This mean value is then subtracted from
measurements.
List some sources of background radiation
: Cosmic rays (high energy, charged particles from the sun, many are stopped by atmosphere but some
come down)
Radon gas (causes most background radiation, is produced when uranium in certain rocks decays)
Ground and Buildings
Food and Drink (radioactive compounds in soil that are taken up by plants and eaten by animals, most
commonly potassium)
Medical (gamma rays in x-rays)
