Download Basic Atomic Structure and Isotope Symbols

BASIC ATOMIC STRUCTURE AND ISOTOPE SYMBOLS
There are three key particles that make up atoms. These are called sub-atomic particles.
proton - p+
protons are found
in the nucleus
electron - eelectrons are found
in the electron shells
neutron - no
neutrons are found
in the nucleus
There are four key numbers that describe the composition of atoms.
Atomic Number - is the number of protons in the atom. If the atom is neutral the
atomic number is also the number of electrons in the atom.
Mass Number - is the number of protons + neutrons in the atom.
Both of these numbers will be parts of the Isotope Symbol.
Both of these numbers are found by counting so they are pure numbers
and will NOT have any decimals.
The Atomic Number is found in the element's box on the Periodic Table.
The Mass Number depends on which isotope it is and is NOT found on the
Periodic Table.
Atomic Mass - is the weight of a particle as compared to Carbon - 12.
Atomic Weight - is the average weight of all the atoms of all the isotopes of an element.
Neither of these numbers will be part of the Isotope Symbol.
Both of these numbers are calculated, will have decimals and are bound by the rules
of significant figures.
The Atomic Weight is found in the element's box on the Periodic Table.
The Atomic Mass is found in the Handbook of Chemistry and Physics.
The atomic mass unit - is 1/12 of the mass of a Carbon - 12 atom.
Francis Aston built a device known as a mass spectrometer.
This device measured the charge to mass ratio of charged particles.
With this device, Aston determined that there were actually more than one type of atom
for some elements. He called these different atoms of the same element - isotopes.
Isotopes are atoms of the same element that have different masses because they have
different numbers of neutrons.
The Isotope Symbol will have the same letters as the element symbol.
The Isotope Symbol will have two numbers - the Atomic Number and the Mass Number.
This is the format:
Sy
Atomic Number
Mass Number
These are ALWAYS true:
#p+ = atomic number
#no = mass number - atomic number
IFF the atom is neutral: #e- = atomic number
If the atom is NOT neutral - it is an ion.
Ions are charged particles that are made by either adding extra electrons to an atom or
taking electrons away from an atom.
Cations are positive ions that are made by taking electrons away from an atom.
Anions are negative ions that are made by adding extra electrons to an atom.
We will learn HOW both are made later in Unit 2.
If the particle is a cation: #e- = atomic number - charge of particle
If the particle is an anion: #e- = atomic + ! charge of particle !
We can calculate the atomic weight of an element by using the following equation:
Atomic = Atomic Mass1 x Percent Abundance1 + AM2 x %2 + AM3 x %3 + ........
Weight
100
The units for your answer will be: g/mole or amu
Iff you have only two isotopes for the element; you can find the Percent Abundance of the
heavier isotope by using this equation:
%2 =
100 ( Atomic Weight - Atomic Mass1 )
( Atomic Mass2 - Atomic Mass1 )
You can find the Percent Abundance of the lighter isotope by using this equation:
%1 = 100 - %2