How Atoms DifferMr. E Chemistry

Atomic Number = number of protons in the nucleus of an atom

- It really is the identity of the element. What did you discover yesterday when you changes the amount of protons in an atom?

- The atomic number identifies the element.

C

The # of electrons equals the number of protons in an atom.

If the number of protons does not equal the number of electrons we call it an ion.

Not all atoms of an element are identical. The different versions of an element are called isotopes.

6

Isotope = atoms of the same element with different numbers of neutrons

Ex: Carbon

~95%

C12

6BUT

~5%

C14

6

Protons =

Neutrons =

Protons =

Neutrons =

Mass Number = # of protons + # of neutrons in a single atom

- Different isotopes have different mass numbers

Ex:

K19

39Mass Number

Atomic Number

Protons =

Neutrons =

Mass Number =

- NOT on the periodic table!

Atomic Mass Unit (amu) = defined as 1/12 the mass of a carbon-12 atom

Composed of 2 particles:

1) Proton = positive charge

- mass of 1.673 x 10-24 g = 1 amu (atomic mass unit)

2)Neutron = neutral, no charge

- 1 amu

Average Atomic Mass (or Atomic Mass) = weighted average of all the isotopes of an element

How to calculate it:

Chlorine-35Chlorine-37

Atomic Mass = 34.969 amu Atomic Mass = 36.966 amu75.770% abundance 24.230% abundance

The average atomic mass of chlorine is closer to the mass of chlorine-35 because chlorine-35 is much more abundant in nature.

% Abundance Equation

Electrons = negatively charged particle

- mass = amu … basically no mass!

1

1678

- Charge = # of protons - # of electrons

Ex:

Li3

7Mass Number

Atomic Number

Charge

If there is nothing in the charge position, the atom has 0 charge = neutral!

Protons =

Neutrons =

Electrons=

Ex:

Mg12

24 +2 Protons =

Neutrons =

Electrons=

Cl17

36 -1 Protons =

Neutrons =

Electrons=

Ex:

Na24 Protons =

Neutrons =

Electrons= 10

SProtons =

Neutrons = 16

Electrons= 18