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)
James Chadwick

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
JJ Thomson

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
Atoms

6. How do the subatomic particles balance each other?
In atoms:
protons = electrons
If 20 protons are present in atom then 20 electrons balance overall charge of atom—atoms are neutral
The neutrons have no charge; therefore they do not need to (and often times don’t) equal protons or electrons

7. 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!!

8. 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 #

9. 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#)

10. 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

11. 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

12. 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

13. 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.

14. 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

15. Modern Atomic Theory

16. Electron Cloud Model Electrons travel around nucleus in random orbits.
cannot predict location at any given moment.
fast, appear to form “cloud” around nucleus.
Ex. - Airplane propeller