1. Section 2 Protons, neutrons, and electrons- how atoms differ
Chapter 7
Section 2
Protons, neutrons, and electrons- how atoms differ

2. The parts of the atom Electron- charge -1
Orbit in a cloud around the nucleus
Extremely small
The electrons are found in mostly empty space

3. The parts of the atom The nucleus contains protons and neutrons
Protons have a positive charge
Neutrons have no charge and are neutral

4. Elements There are about 115 different elements
Each element has the same number of protons
The number of protons in an atom of an element is the atomic number
Carbon has six protons and all carbon atoms have six protons.
Therefore, the atomic number of carbon is 6.

5. Elements cont Each element could be neutral or have a charge.
If the element is neutral then the number of electrons equals the number of protons so the positive charges equal the negative charges.
If the element has a charge then it may be positive or negative so the protons and electrons do not balance.
The element is now called an ion.

6. Neutrons and isotopes Elements can have different numbers of neutrons
For example- some atoms of carbon have 6 neutrons, some have 7 neutrons, and some have 8 neutrons.
Those 3 different forms of neutrons are called isotopes.
Isotopes – are atoms of the same element that have different numbers of neutrons.

7. Mass number
Mass number- is the sum of the protons and neutrons in an atom
Mass number= neutrons + protons

8. Average atomic mass
Average atomic mass of an element is the average mass of the elements isotopes weighted according to the abundance of each of the isotopes
It is a weighted average.