Atoms Notes

Basic Parts

1.

Protons—positive (+), in nucleus, identifies element

2.

Neutrons—neutral, in nucleus

3.

Electrons—negative (-), orbits nucleus, smallest,

most of atoms volume, used in bonding

4. Nucleus—positive (+), contains protons & neutrons,

most of atoms mass

Atomic Number

•# of protons in an atom of an element

•Same as # of electrons to keep atom neutral

•Unique, used to identify each element,
found on periodic table

Atomic Mass

•sum of the number of protons & neutrons
A=P=E M-A=N

•all the different isotopes are averaged to give
the average atomic mass

• found on the periodic table as decimal

Isotope

•atoms of the same element w/ diff # of
neutrons (but same # protons)

•can happen naturally or during radioactive decay

•if unstable = radioactive elements
(ex: carbon-14, uranium-238)
Calculate: Mass - atomic number = neutrons

Ions

•atom that has a charge & is no longer neutral

•has gained an electron & become a negative ion
called an anion (ex: Cl-)

•has lost electrons and become a positive ion
called a cation (ex: Na+)

Do the opposite of the charge to the number of electrons (+3 means to
-3)