October 23

Hi Class,
We began class today with a Quiz on Physical and Chemical Changes and Properties.


In today's lecture, we covered Unit 2 Section A.8.
Topics:
Mass number
Isotopes

Remember:
Every element has a unique number of protons, that DOES NOT CHANGE. If I change the number of protons, the element is not the same. For example an atom of Sodium always has 11 protons. If I have an atom with 10 protons, I have Neon, NOT an ion of Sodium.

Number of Protons are given by the Atomic Number

In a Neutral atom, protons are equal to electrons

Every element can have atoms with varying numbers of Neutrons. For example you could have 3 atoms of Carbon:

6 Protons, 6 Neutrons, 6 Electrons
6 Protons, 7 Neutrons, 6 Electrons
6 Protons, 8 Neutrons, 6 Electrons

All three have the same numbers of Protons (Atoms of the same element have the same number of Protons). But the number of Neutrons have changed. These are Isotopes.

If I add the Neutrons and Protons, I get the Mass Number for that Isotope.

Homework:
Page 131 #19-21
Worksheet
Hint: Atomic Number equals Protons
Protons equals Electrons
Mass Number = Protons + Neutrons

You will have a quiz next class, similar to this worksheet.