Unit 5: Materials and cycles on
Earth
5.1 – The structure of an atom
• Describe the structure of the atom
• List the particles found in an atom
• Describe some of the properties of the particles found in an atom
What is an Atom?
• An atom is the basic building block of matter.
• It is the smallest unit into which matter can be divided
https://www.youtube.com/watch?v=Cs87qH6-QTk
What is in an Atom?
uAtoms are made up of three main subatomic particles
1. Protons
2. Neutrons
3. Electrons
What is in an Atom?
uAt the center of each atom there is a small and dense nucleus that
consist of protons and neutrons
uProtons have a positive charge
uNeutrons have no charge
uProtons and neutrons form the nucleus of
an atom
What is in an Atom?
uAround the nucleus, there are electrons that move in shells
uElectrons have a negative charge
What is in an Atom?
What is in an Atom?
- Protons & nuetrons have a higher mass than electrons
- Electrons have almost no mass
- Protons & neutrons have the same mass as one
another
Electrostatic attraction
why can’t the electrons escape from the atom?
• There is an attraction between the positively charged
protons and the negatively charged electrons.
• This is known as electrostatic attraction
à This attraction is what holds the atom together
Atoms have no overall charge
uMost atoms do not have a charge (neutral) Why?
Because it has an equal number of protons and electrons, so equal charges cancel
each other.
uIf an atom gains or loses electrons, it becomes charged.
uA charged atom is called an ion.
Virtual Lab – Building an atom
https://phet.colorado.edu/sims/html/build-an-
atom/latest/build-an-atom_en.html
Atomic
Atomic Number Number
Each element has a unique number of protons, we call
this number “Atomic Number”
Atomic number (mass of protons)
Element’s symbol
Element’s name
Mass number (number of protons and neutrons in a nucleus)
• Elements name = ___lithium_____
• Protons = ___3_____
• Electrons = ___3_____
• Neutrons = __7-3=4____
Represent the atoms of Lithium
electron
proton
1 nucleus
0 1
-1
neutron
Practice
5
19
28
33
Scientists and the structure of atom
- for your information
• 3 very important scientist have helped build the idea of the atoms and what
they look like; J.J. Thompson, Rutherford and James Chadwick.
J.J Thompson
• J.J (Joseph John) Thompson is an English physicist. In 1897, he created
some tests to figure out what is an atom.
• He discovered the electron based on his experiments and research.
• He believed the atom was a sphere with evenly spread negative and
positive charges.
Ernest Rutherford
• Ernest Rutherford created experiments to
learn what the atom looked like a couple of
years later.
• He discovered that the atom had a proton (in
year 1908) and a nucleus (in year 1911).
How did he discover this?
Gold foil experiment
• Rutherford worked to understand the distribution
of electrons in an atom.
• He performed an experiment using alpha particles.
• An alpha particle is a positively charged particle emitted
by a ray
Gold foil experiment
https://www.youtube.com/watch?v=XBqHkraf8iE
Gold foil experiment
• Rutherford made the following observations:
• Most of the alpha particles passed straight through the gold foil.
• There was a deflection (a change in direction) of the alpha
particles by a small angle.
• Very small amount of alpha particles rebounded.
Rutherford nuclear model
• The Rutherford atomic model has the following features:
• The positive charge of an atom is confined to a dense region at the center of the atom.
• The center of an atom is called the nucleus.
• The nucleus is positively charged.
• Electrons spin around the nucleus in a circular path.
• Comparatively, the size of the nucleus is smaller than
the size of the atom.
Rutherford nuclear model
• Rutherford developed the nuclear model of the atom
• He discovered that the protons and neutrons (which make up nearly all of the mass
of the atom) are located in the nucleus at the center of the atom.
• He discovered that the electrons are distributed around the nucleus
James Chadwick
• In 1932, Chadwick discovered a third type of
subatomic particle, which he named the neutron.
• Neutrons help to reduce the repulsion between protons and
stabilize the atom's nucleus.
• Neutrons are in the nucleus of atoms and they are around
the same size as protons.
• Neutrons do not have any electrical charge; they are
electrically neutral
Summary of the scientists’ discoveries
• JJ Thompson:
• Positive and negative charges are evenly spread
• Discovered the electrons
• Earnest Rutherford:
• Discovered the proton (and that the proton is at the center)
• Discovered the nucleus
• Discovered the distribution of electrons (that electrons spin on
the orbits)
• James Chadwick:
• Discovered the neutron (the neutron is in the nucleus and it has
no charge)
A or B or C or F
D or E
G
nucleus mass
positive
electrons
orbits
Keywords
• Atoms
• Deflected
• Electrical charge
• Electrons
• Electrostatic attraction
• Neutrons
• Nucleus
• Protons
• Sub-atomic particles
LB questions page 154
Answers
LB questions page 156
Answers
