1. Isotopes Chapter 4, Section 3 Pg. 100 - 111

2. Review of Atoms Atoms are made of protons, neutrons, and electrons. – Protons are +, electrons are –, and neutrons have no charge. Atoms are neutral. – The # of protons and electrons is equal. Each element is identified by its atomic number. – Atomic number tells us the # of protons.

3. Mass Number Protons and neutrons are found in the nucleus (center) of the atom. The mass of an atom depends mostly on the number of protons and neutrons. The mass number tells us the total number of protons and neutrons in the nucleus. If using only the periodic table, you round the atomic mass to get the mass number. Other times the mass number will already be given to you.

4. Calculating Number of Neutrons Atomic # = Number of protons Mass # = Number of protons and neutrons We can use the atomic # and mass # to find the number of neutrons # of Neutrons = Mass number – Atomic number

5. Calculating Number of Neutrons Example: Neon Atomic # = 10 Mass # = 20 # of Neutrons = Mass # - Atomic # # of Neutrons = 20 – 10 # of Neutrons = 10

6. Isotopes Isotopes – Atoms of the same element that have different numbers of neutrons – They are the same element because they have the same number of protons. – They behave the same way because they have the same number of protons and electrons. – Having a different number of neutrons causes the mass number to change.

7. Isotopes Isotopes can be written out two different ways: 1.Element name followed by mass number: Neon – 20 2. Chemical Symbol with mass # and atomic #: Ne 20 10

8. Practice Problems Fill in the missing information for the isotopes of neon: IsotopeAtomic ## of Protons Mass ## of Neutrons Neon-20 Neon-21 Neon-22