Everything Science Grade 10

CHAPTER 4. THE ATOM 4.4

See video: VPaln at http://www.everythingscience.co.za

So far, we have discussed that atoms are made up of a positively chargednucleussur-
rounded by one or more negatively chargedelectrons. These electrons orbit the nucleus.
Before we look at some useful concepts we first need to understand what electrons, protons
and neutrons are.

The Electron ESABA

The electron is a very tiny particle. It has a mass of 9 , 11 × 10 −^31 kg. The electron carries
one unit of negative electric charge (i.e.− 1 , 6 × 10 −^19 C).

The Nucleus ESABB

Unlike the electron, the nucleuscanbe broken up into smaller building blocks called
protonsandneutrons. Together, the protons and neutrons are callednucleons.

The Proton

FACT

Scientists believe that

the electron can be

treated as apoint par-

ticle or elementary

particlemeaning that

it cannot be broken

down into anything

smaller.

The electron carries one unit ofnegativeelectric charge (i.e.− 1 , 6 × 10 −^19 C, C is Coulombs).
Each proton carries one unit ofpositiveelectric charge (i.e.+1, 6 × 10 −^19 C). Since we
know that atoms areelectrically neutral, i.e. do not carry any extra charge, then the num-
ber of protons in an atom has to be the same as the number of electrons to balance out the
positive and negative charge to zero. The total positive charge of a nucleus is equal to the
number of protons in the nucleus. The proton is much heavier than the electron (10 000
times heavier!) and has a mass of 1 , 6726 × 10 −^27 kg. When we talk about the atomic mass
of an atom, we are mostly referring to the combined mass of the protons and neutrons, i.e.
the nucleons.

The Neutron

The neutron is electrically neutral i.e. it carries no charge at all. Like the proton, it is
much heavier than the electron and its mass is 1 , 6749 × 10 −^27 kg (slightly heavier than the
proton).

Chemistry: Matter and Materials 71