1. The Structure of an Atom

2. Atomic Structure Atoms are composed of 2 regions:
Nucleus: center of atom that contains mass of atom
Electron cloud: region that surrounds nucleus that contains most of space in atom
Nucleus
Electron
Cloud

3. What’s in the Nucleus? Nucleus contains 2 of 3 subatomic particles:
Protons: subatomic particle w/ 1+ charge (p+)
Rutherford
Neutrons: subatomic particle w/ no charge (no)

4. What’s in the Electron Cloud?
The 3rd subatomic particle resides outside nucleus in electron cloud
Electron: subatomic particle w/ 1- charge (e-) and virtually no mass

5. How do these particles interact?
Protons and neutrons live compacted in tiny nucleus
most atom’s mass
electrons small and reside outside nucleus
small mass (2000 e- = 1 p+ or no)
occupy large volume of space outside nucleus

6. How do we know the number of subatomic particles in an atom?
Atomic #: indicates # of protons in atom
Ex: Hydrogen’s atomic # is 1
hydrogen has 1 proton
Ex: Carbon’s atomic # is 6
carbon has 6 protons
**Number of protons identifies element
similar to how your fingerprint ID’s you.
Ex. 2 protons = He, 29 protons = Cu
ALWAYS!!

7. How do we know the number of subatomic particles in an atom?
Mass number: number of protons and neutrons in nucleus (p+ + no)
Ex: hydrogen can have a mass # of 3.
Since it has 1 proton it must have 2 neutrons
# of neutrons = mass # - atomic #

8. What are Isotopes? Atoms of same element with different # of neutrons
Same atomic #
Different mass # (b/c neutrons are different)
Ex. Carbon 12, Carbon 13, and Carbon 14 all naturally occurring isotopes of Carbon.
Each has 6 p+ and 6 e-, but each has different # of neutrons (therefore, different mass#)

9. Determining the number of protons and neutrons
Li has mass # of 7 and atomic # of 3
Protons = 3 (same as atomic #)
Neutrons= 7-3 = 4 (mass # - atomic #)
Ne has a mass # of 20 and an atomic # of 10
Protons = 10
Neutrons = = 10

10. What about the electrons?
electrons are equal to protons
So e- = p+ = atomic #
Ex: He has mass # of 4 and atomic # of 2
p+ = 2
no = 2
e- = 2
Basic Atomic Structure 1:57

11. Determine the number of subatomic particles in the following:
Chlorine has a mass # of 35 and an atomic # of 17
p+ = 17, no = 18, e- = 17
Potassium has a mass # of 39 and an atomic # of 19
P+ = 19, no = 20 e- = 19

12. Candy Atoms Atom #1 - mass # of 5 and an atomic # of 3.
Atom #2 – 5 protons and 7 neutrons.
Atom #3 – Atomic # of 7 and 8 neutrons.

13. Candy Atoms Atom #4 – mass # 18 and 9 electrons
Atom #5 – build your own candy atom using the candies that you have. You should be able to accurately determine:
Atomic #
Mass #
# of protons, neutrons, and electrons