1. The Structure of An Atom

2. Structure of an atom Positively charged nucleus (electrically charged)
Contains almost all the mass of an atom
Small but very dense
Contains protons (+) and neutrons (0)
Protons have a relative mass of 1
Neutrons have a relative mass of 1
Neutrons are very hard to detect in an atom

3. Structure of an atom
Negatively charged cloud around the nucleus (electrically charged)
Contains electrons
Arranged in various shells and energy levels
The very outer most shell is called the valence electrons
Positive must equal Negative!!
This means the number of electrons must equal the number of protons.

4. Definition of an element
An element is defined by the number of protons it has. (This is what gives the element its identity)
Protons are smaller than electrons, but they have more mass.

5. Using the Periodic Table

6. Atomic Mass The atomic weight rounded to a whole number
The sum of protons and neutrons
Number of neutrons = mass#-atomic #
Ex: Mg
Atomic # = 12
Atomic mass = 24
24-12 = 12 Neutrons

7. Brain Break: GotCha!