Unit 1 –Atomic Structure
The Atom
The atom is made up of 3 types of sub-atomic
particles:
- Protons
- Neutrons
- Electrons
The nucleus contains protons and neutrons, surrounded by
electrons in shells on the outside.
Most of the mass is concentrated in the centre of the nucleus.
The protons and neutrons found in the nucleus are collectively
called nucleons.
The diameter of the nucleus is rather small compared to the
whole atom in which it is mostly empty space.
The electrons travel around the nucleus in orbitals. The
orbitals take up most of the volume of the atom.
Relative Mass and Relative Charge
Subatomic Particle Relative Mass Relative Charge
Proton 1 +1
Neutron 1 0
Electron 1/2000 -1
Nuclear Symbols
Mass Number = The total number of protons and neutrons in the
nucleus
Atomic Number = The number of protons in the nucleus - All atoms
of the same element have the same number of protons.
For a neutral atom, which has no overall charge, the number
of electrons is the same as the number of protons.
, The number of neutrons = Mass number – Atomic number
Nuclear Atomic Mass Protons Neutrons Electrons
Symbol Number Number
7 3 7 3 3 7-3 = 4
Li
3
Ions have different numbers of protons and electrons.
Atoms form ions by gaining or loosing electrons.
Negative ions have more electrons than protons.
Positive ions have fewer electrons than protons.
-
E.G Br = The negative charge means that there is 1 more electron
than there are protons.
E.G Mg2+ = The 2+ charge means that there are fewer electrons
than protons.
Isotopes
Isotopes are atoms of the same element which have the same
number of protons but a different number of neutrons.
E.G Chlorine 35 and Chlorine 37
The different mass numbers mean different numbers of neutrons
The atomic numbers are the same therefore they both have 17
protons and 17 electrons.
1. It’s the number and arrangement of electrons that decides the
chemical properties of an element. Isotopes have the same
configuration of electrons, so they’ve got the same chemical
properties.
2. Isotopes of an element do have slightly different physical
properties however, such as different densities and rates of
diffusion. This is as the physical properties tend to depend on
the mass of an atom.
Models of Atomic Structure
The accepted models of the atom have changed throughout history.
1. John Dalton described the atoms as solid spheres and
suggested that different spheres make up the different
elements.
The Atom
The atom is made up of 3 types of sub-atomic
particles:
- Protons
- Neutrons
- Electrons
The nucleus contains protons and neutrons, surrounded by
electrons in shells on the outside.
Most of the mass is concentrated in the centre of the nucleus.
The protons and neutrons found in the nucleus are collectively
called nucleons.
The diameter of the nucleus is rather small compared to the
whole atom in which it is mostly empty space.
The electrons travel around the nucleus in orbitals. The
orbitals take up most of the volume of the atom.
Relative Mass and Relative Charge
Subatomic Particle Relative Mass Relative Charge
Proton 1 +1
Neutron 1 0
Electron 1/2000 -1
Nuclear Symbols
Mass Number = The total number of protons and neutrons in the
nucleus
Atomic Number = The number of protons in the nucleus - All atoms
of the same element have the same number of protons.
For a neutral atom, which has no overall charge, the number
of electrons is the same as the number of protons.
, The number of neutrons = Mass number – Atomic number
Nuclear Atomic Mass Protons Neutrons Electrons
Symbol Number Number
7 3 7 3 3 7-3 = 4
Li
3
Ions have different numbers of protons and electrons.
Atoms form ions by gaining or loosing electrons.
Negative ions have more electrons than protons.
Positive ions have fewer electrons than protons.
-
E.G Br = The negative charge means that there is 1 more electron
than there are protons.
E.G Mg2+ = The 2+ charge means that there are fewer electrons
than protons.
Isotopes
Isotopes are atoms of the same element which have the same
number of protons but a different number of neutrons.
E.G Chlorine 35 and Chlorine 37
The different mass numbers mean different numbers of neutrons
The atomic numbers are the same therefore they both have 17
protons and 17 electrons.
1. It’s the number and arrangement of electrons that decides the
chemical properties of an element. Isotopes have the same
configuration of electrons, so they’ve got the same chemical
properties.
2. Isotopes of an element do have slightly different physical
properties however, such as different densities and rates of
diffusion. This is as the physical properties tend to depend on
the mass of an atom.
Models of Atomic Structure
The accepted models of the atom have changed throughout history.
1. John Dalton described the atoms as solid spheres and
suggested that different spheres make up the different
elements.
