Small particles

So what is a bar of Gold made from?

Can you make smaller pieces of gold from the Gold bar?

How small can you make the pieces?

Is there a difference between Iron bars and Gold bars?

What is the difference?

Where does this difference come from ?

The Story of Atoms

the structure of the atom

Bohr structure

OC39 describe the structure of the atom, state the location, relative charge, and atomic mass of the sub-atomic particles, and define atomic number and isotope

describe the structure of the atom

structure of the atom

So the Nucleus contains 2 different types of particles, the Proton and the Neutron, outside the Nucleus lie the electrons. To describe electrons as lying there is wrong, in fact the electrons go whizzing around the atoms but they do so in specific orbits often called shells.

state the location, relative charge, and atomic mass of the sub-atomic particles,

elektron, the Greek word for "amber"

define atomic number and isotope

atomic number

Each element is made up of different types of atoms,

the atoms in these elements differ because the number of protons for each element is different.

The Atomic number is equal to the number of protons in an atom.

The number of electrons is usually the same as the number of protons, as there is no net charge on an atom, they are neutral. The number of neutrons varies from element to element obviously but also differs from atom to atom, the ne

Mass number

There is another number that is always listed with the symbol for the element, this is the mass number.

The mass number is defined as the number of protons + the number of neutrons together.

To find the number of Neutrons

# neutrons = Mass Number - Atomic Number

The Mass number will be the bigger number in the atomic symbol (except for hydrogen which usually does not have a neutron attached).

Mass number


An Isotope of an element are two atoms that have the same number of protons

but have different numbers of neutrons.

Where the decimal comes from in the Mass No.

The mass numbers of elements often has a decimal in it. There can be no such thing as a fraction of a proton, this decimal is found by finding the average of all the isotopes found in nature.

More on Molecules here

OC40 draw the Bohr structure of the first 20 elements

Bohr Diagrams


How small are atoms