Atom Notes

Pre-test
(answer at the top of your paper)
4.
5.
1.
2.
3.
How many protons, neutrons, & electrons does Magnesium have?
What is the Atomic Number of
Aluminum?
What is the Mass Number of
Uranium?
What is an Isotope?
What is an Ion?

What is in an atom?
The Three Primary
Subatomic Particles ...
 Protons
 Neutrons
 Electrons

Which Particle is Where?
 Nucleus
• Protons
• Neutrons
 Electron clouds
– Swarm around the nucleus like bees
– Not in nice clear orbitals

Protons are the identity.
 # of protons = the atomic number
 Atomic number = # of protons
 # of protons determines which element it is!
 What is element # 15?
 How many protons does lithium have?
 What is the atomic number of tin?

Neutrons provide mass.
 Number of neutrons can vary, even for the same element.
 Isotopes
– same # of protons
– different # of neutrons
 Elements have many different isotopes
– Carbon-14, Uranium-238
 Neutrons affect the atomic mass

Atomic Mass
 Sum of the protons and neutrons
 Electrons are not included
– Too small
 What is the atomic mass of this atom?

What about the electrons?
 A neutral atom has no charge.
 positive charges = negative charges.
 A neutral atom has the same # of electrons as protons
 How many electrons does this atom have?

What if the atom isn’t neutral?
 If an atom is not neutral, then it has a charge.
 Ion
– Charge particle
 This atom has:
3 protons (+++)
2 electrons (--)
 It is written as Li +

Your Periodic Table has the answers
 How many protons?
 How many neutrons?
 How many electrons (if the atom is neutral?)

SUMMING UP…
 How many protons?
– The atomic number
 How many neutrons?
– Atomic mass minus atomic number
 How many electrons (if the atom is neutral?)
– Same as # of protons

Make sure you have these definitions in your notes!!
 Ion:
 Isotope:
 Atomic number:
 Atomic mass:

Post-test
(complete the Pre-test)
4.
5.
1.
2.
3.
How many protons, neutrons, & electrons does Magnesium have?
What is the Atomic Number of
Aluminum?
What is the Mass Number of
Uranium?
What is an Isotope?
What is an Ion?