1. Atoms – The Nucleus Part 1
CHEMISTRY 11
April 26, 2010

2. The Nucleus
The atom contains a nucleus of protons and neutrons and is surrounded by electrons
Protons are charged +1
Electrons are charged -1
Neutrons are charged 0 (no charge)

3. The Atom +

4. The Nucleus & The Periodic Table
Atomic number and atomic mass describe the structure of the nucleus of each element
Atomic number tells the number of protons in the nucleus (always a whole number)
Atomic mass tells the number of protons and neutrons in the nucleus (always a decimal number)
To figure out the average number of neutrons in a particular element, subtract the atomic number from the atomic mass

5. The Nucleus & The Periodic Table

6. Element, Isotope, Ion
Atoms with different numbers of protons are called “elements”
Elements differ by the number of protons in the nucleus
Atoms with different numbers of neutrons in the nucleus are called “isotopes”
Atoms with different numbers of electrons are called “ions”

7. Elements, Isotopes, IonsNa
ISOTOPES of SODIUM
Na+

8. Writing Isotopes
The number of neutrons and protons in a particular atom (in this case, uranium) is written concisely as follows:
Number of
Protons + neutrons
Atomic Mass
Number of protons
Atomic Number

9. Summary
Each different element has a different number of protons in its nucleus
A single element has the same number of protons in its nucleus, but can have different numbers of neutrons. Each atom with different numbers of neutrons is called an isotope
The atomic number equals the number of protons in the nucleus
The atomic mass equals the number of protons + the number of neutrons in the nucleus