Atomic Structure
1.1 Fundamental Particles
1.1 Fundamental Particles
- Greek philosophers thought matter was made up of a 1.2 Mass number, atomic number and isotopes
single continuous substance that produced the elements 1.3 The arrangement of electrons
(earth, fire, water and air).
- 1661 ~ Robert Boyle proposed that some substances can’t 1.4 The mass spectrometer
be simpler – these are elements. 1.5 More about electron arrangements
- 1803 ~ John Dalton said elements are composed of
1.6 Electron arrangements and ionisation
atoms, all atoms of the same element have the same
mass, different elements have different masses. Atoms
can’t be broken down.
- 1896 ~ Henri Becquerel discovered radioactivity particles could come from inside the atom and it was
not indivisible.
- 1897 ~ J. J. Thomson found electrons. Electrons negatively charged and all electrons from all elements
are the same. Electrons are light and negative so something must have the rest if the mass and be
positive. Plum pudding model.
- 1911 ~ Ernest Rutherford found most of the mass and the positive charge is in the nucleus.
- 1913 ~ Neils Bohr atoms consisted of tiny positive nucleus orbited by negative electrons. Electrons orbit
in shells of fixed size and movement of electrons from one shell to the next explained how atoms
absorbed and gave out light. Beginning of quantum theory.
- 1926 ~ Erwin Schrödinger worked out an equations that electrons have some properties of waves as
well as properties of particles. This led to quantum mechanics which can be used to predict behaviour of
sub-atomic particles.
- 1932 ~ James Chadwick discovered neutrons.
- Atoms are made from protons neutrons and
electrons. The protons and neutrons are in Property Proton Neutron Electron
-27 -27
the nucleus and are sometimes called Mass/kg 1.673 x 10 1.675 x 10 0.91 x 10-30
nucleons. Electrons surround the nucleus. Charge/C +1.602 x 10-19 0 -1.602 x 10-19
- Protons and neutrons are held together by a Relative mass 1 1 1/1836
strong nuclear force, this is much stronger Relative charge +1 0 -1
than electrostatic forces holding electrons
and protons together, so it overcomes the repulsion from the protons.
- The nucleus is surrounded by electrons found in levels (shells) which get further away from the nucleus.
1.2 Mass number, atomic number and isotopes
- The atomic number is equal to the number of protons, and the mass number is number of protons plus
the number of neutrons.
- Atoms with the same number of protons but different numbers of neutrons are called isotopes.
- Isotopes react the same chemically as they have the same electron configuration. They vary in mass
number because of the different number of neutrons.
- Relative isotopic mass – the mass of an isotope relative to 1/12th of the mass of an atom of carbon-
12.
- Relative atomic mass – the weighted mean mass of an atom of an element relative to 1/12th the
mass of an atom of carbon-12.
1.3 The arrangement of the electrons
- The number of electrons in each shell = 2n2 where n is the number of the shell, so:
o The first shell holds 2 electrons
o The second shell holds 8 electrons
1.1 Fundamental Particles
1.1 Fundamental Particles
- Greek philosophers thought matter was made up of a 1.2 Mass number, atomic number and isotopes
single continuous substance that produced the elements 1.3 The arrangement of electrons
(earth, fire, water and air).
- 1661 ~ Robert Boyle proposed that some substances can’t 1.4 The mass spectrometer
be simpler – these are elements. 1.5 More about electron arrangements
- 1803 ~ John Dalton said elements are composed of
1.6 Electron arrangements and ionisation
atoms, all atoms of the same element have the same
mass, different elements have different masses. Atoms
can’t be broken down.
- 1896 ~ Henri Becquerel discovered radioactivity particles could come from inside the atom and it was
not indivisible.
- 1897 ~ J. J. Thomson found electrons. Electrons negatively charged and all electrons from all elements
are the same. Electrons are light and negative so something must have the rest if the mass and be
positive. Plum pudding model.
- 1911 ~ Ernest Rutherford found most of the mass and the positive charge is in the nucleus.
- 1913 ~ Neils Bohr atoms consisted of tiny positive nucleus orbited by negative electrons. Electrons orbit
in shells of fixed size and movement of electrons from one shell to the next explained how atoms
absorbed and gave out light. Beginning of quantum theory.
- 1926 ~ Erwin Schrödinger worked out an equations that electrons have some properties of waves as
well as properties of particles. This led to quantum mechanics which can be used to predict behaviour of
sub-atomic particles.
- 1932 ~ James Chadwick discovered neutrons.
- Atoms are made from protons neutrons and
electrons. The protons and neutrons are in Property Proton Neutron Electron
-27 -27
the nucleus and are sometimes called Mass/kg 1.673 x 10 1.675 x 10 0.91 x 10-30
nucleons. Electrons surround the nucleus. Charge/C +1.602 x 10-19 0 -1.602 x 10-19
- Protons and neutrons are held together by a Relative mass 1 1 1/1836
strong nuclear force, this is much stronger Relative charge +1 0 -1
than electrostatic forces holding electrons
and protons together, so it overcomes the repulsion from the protons.
- The nucleus is surrounded by electrons found in levels (shells) which get further away from the nucleus.
1.2 Mass number, atomic number and isotopes
- The atomic number is equal to the number of protons, and the mass number is number of protons plus
the number of neutrons.
- Atoms with the same number of protons but different numbers of neutrons are called isotopes.
- Isotopes react the same chemically as they have the same electron configuration. They vary in mass
number because of the different number of neutrons.
- Relative isotopic mass – the mass of an isotope relative to 1/12th of the mass of an atom of carbon-
12.
- Relative atomic mass – the weighted mean mass of an atom of an element relative to 1/12th the
mass of an atom of carbon-12.
1.3 The arrangement of the electrons
- The number of electrons in each shell = 2n2 where n is the number of the shell, so:
o The first shell holds 2 electrons
o The second shell holds 8 electrons
