1.14 - 1.17 Atomic structure
As building blocks, they can be thought of spheres.
However, to understand how and why atoms join up with one another, a more sophisticated model is needed..
The small size of atoms give scientists a problem when trying to see them. Conventional microscopes cannot resolve particles at an atomic scale.
This short video gives an outline of how modern science is beginning to reveal the atomic world to us in a visual way.
The technique outlined involves a nanoparticle of the element platinum. This is a particle which is a few nanometres in size.
The nanometre (symbol: nm) is a unit used to measure length . It is equal to one billionth of a metre (1 m / 1,000,000,000).
1.14 Visualising atoms
Two different models of a carbon atom
The modern model of the atom was developed early in the 20th Century.
1.14 Modelling molecules
Molecules are particles made up of two or more atoms bonded together
A molecule is a particle composed of more than one atom joined together by covalent bonds.
1.15 Sub atomic particles
1.15 know the structure of an atom in terms of the positions, relative masses and relative charges of sub-atomic particles
- protons are particles with a positive charge (+1) and a mass of 1 atomic mass unit (
amu) . They are part of the nucleus of an atom.
- The number of protons is given by the atomic number of an element.
- neutrons are particles with no charge and a mass of 1(
amu) they are also part of the nucleus of an atom.
- electrons are particles with a negative charge (-1 ) and a mass of 1/2000 of an
amu, they orbit the nucleus in shells.
1.15 Into orbit
This animation shows an atom of carbon, we know it is carbon because it has six protons shown in the nucleus.
Carbon has three isotopes, Carbon 12, Carbon 13 and carbon 14. These are described in more detail in the next section:
1.16 Activity 1. Three types of carbon atom
1.16 know what is meant by the terms atomic number, mass number, isotopes and relative atomic mass (Ar)
Use this animation to explore the number and type of sub atomic particles which make up the three isotopes of carbon. Use the information to complete a copy of the table below:
|ISOTOPE||Carbon 12||Carbon 13||Carbon 14|
|no. of protons|
|no of neutrons|
|no of electrons|
1.17 Activity 2. Calculating relative atomic mass.
1.17 be able to calculate the relative atomic mass of an element (Ar) from isotopic abundances
Sorting by mass
A mass spectrometer is an instrument which can separate and sort the particles in a sample of an element according to their mass. The output from a mass spectrometer is known as a mass spectrum. For an element the mass spectrum tells us the percentage of each isotope which can be found in a naturally occurring sample. This data then allows us to calculate the relative atomic mass for the element under investigation.
Mass and abundance
We can calculate Ar values using this isotopic abundance data:
For Boron two isotopes exist, Boron 10 and Boron 11. The mass spectrum shows that 20% of boron atoms are Boron -10 and 80% are Boron -11.
The weighted mean is calculated as follows: