SUBATOMIC PARTICLES
REVIEW ATOMS
Atom

An atom is the smallest particle of an element that
still has the properties of that element
 50
million atoms, lined up end-to-end = 1 cm
 An atom = proton(s) + neutron(s) + electron(s)
The Greek root
for the word
atom, "atomon,"
means "that
which cannot be
divided.”
The structure of the atom
The Ancient Greeks used to believe that everything was made up of
very small particles. Some experiments in 1808 proved this and
called these particles ATOMS:
ELECTRON –
negative, mass
nearly nothing
NEUTRON –
neutral, same mass
as proton (“1”)
PROTON – positive,
same mass as
neutron (“1”)
The Atom:
Nucleus
Shell or Orbit
Electron
The Atom Hydrogen:
Proton
Hydrogen has one proton, one electron and NO neutrons
Electron
The Atom Sodium
Valence Shell
Protons
Neutrons
Sodium has eleven electrons, eleven protons and twelve neutrons.
Electrons
Atomic Theory:

Atoms are made up of smaller particles known as sub-atomic particles.
Name

Symbo
Charge
l
Location
Relative Mass
Proton
p
1+
nucleus
1836
Neutron
n
0
nucleus
1836
Electron
e
1–
area surrounding the
nucleus
1
The nucleus is at the center of an atom.





The nucleus is composed of protons and neutrons.
Electrons exist in the space surrounding the nucleus.
# of protons = # of electrons in every atom
Nuclear charge = charge on the nucleus = # of protons
Atomic number = # of protons = # of electrons
See page 170
Mass and atomic number
Particle
Proton
Relative Mass
1
Relative Charge
1
Neutron
Electron
1
0
0
-1
MASS NUMBER = number of protons + number
of neutrons
SYMBOL
ATOMIC NUMBER = number of protons
(obviously)
Subatomic Particles
Group 1
1
Period 1
H
Hydrogen
1.001
Atomic
number
Element symbol
Element name
Atomic mass
•Atoms are split into subatomic particles (electrons, neutrons, protons)
•Nucleons are particles of the nucleus of the atom
•These include protons (1 +), neutrons (no charge)
• Number of protons in element is the atomic number (ie H has 1 proton)
• Electrons have charge (1-) are located outside of nucleus
•Neutral atom, their number of electrons equals atomic number (ie. H has 1
electron)
SUBATOMIC PARTICLES:
(think parts of atoms)
Protons(p): positively charged ions located in the nucleus.
Number of protons=atomic number
Neutrons(n): neutral particles located in the nucleus; no
charge.
• Use the formula
Atomic Mass - Atomic Number= # neutrons
Subatomic Particles Continued:
Electrons




exist in space surrounding the nucleus in invisible shells (energy levels)
electrons are transferred or shared between atoms to form chemical bonds
Carry a negative ion charge
Each energy shell has electrons.
 First shell always has 2 electrons
 Than 8 electrons on each other shell.
MUST REMEMBER:
Atomic Number=# of protons = # of electrons in every atom
Atomic Mass
Symbol
Atomic Number
Charge
(if ion)
EXAMPLE:
How many protons, neutrons and electrons are found in an
atom of
Atomic Number
133
55
Cs
How do you get the number of protons?
•Protons=Atomic #
How do you get the number of Electrons
•Electrons=Atomic #
Therefore, the
Atomic number = protons and electrons
There are 55 protons and 55 electrons in Cesium.
Mass number = sum
of protons and
neutrons
Neutrons= Mass #
(133) - atomic # (55)
= 78
•There are 78
neutrons
Calculate how many protons, neutrons and electrons the element
Hydrogen has.
1
1
H
Protons: 1
Neutrons: 0
Electrons: 1
Calculate how many protons, neutrons and electrons the element
Sodium has.
23
11
Protons: 11
Neutrons: 12
Electrons: 11
Na
Calculate how many protons, neutrons and electrons the element
Sodium has.
36
17
Cl
Protons: 17
Neutrons: 19
Electrons: 17
Calculate how many protons, neutrons and electrons the element
Sodium has.
27
13
Al
Protons: 13
Neutrons: 14
Electrons: 13
Calculate how many protons, neutrons and electrons the element
Rhenium has.
186
75
Re
Protons: 75
Neutrons: 111
Electrons: 75
REVIEW:
From your knowledge of subatomic particles, fill in the chart
below
Element
Name
Atomic #
Atomic
Mass
# Protons
# Neutrons # Electrons
Aluminum
12
19
5
Focus Questions:



How does the mass of protons compare with the mass
of electrons?
What reason could there be for the number of
protons being equal to the number of electrons in an
electrically neutral atom?
Is a particle an atom if it has no protons?