Structure of the Atom
Chapter 13 pg. 314-331
Chemistry-The study of matter and the transformations it can undergo
 …is the basis for understanding the entire universe
 …is used to make fuels, pesticides, herbicides and even cook.
EVERYTHING is composed of atoms
*Like only 3 colors make up every conceivable color, atoms make up everything.
*90% of atoms are Hydrogen
-Living things use 4 elements, oxygen, carbon, hydrogen, and nitrogen
-Atoms are nearly ageless
-So small they can’t be seen with visible light
I.
The Atomic Nucleus
a. Ernest Rutherford- 1909 gold foil experiment
i. Atom is mostly empty space w/ the mass at the center-Nucleus
ii. Nucleus - nearly all the Atom’s mass
iii. Nucleus composed of protons and neutrons
b. Protoni. Equal in # to the # of electrons
ii. positive charge
iii. Elements classified by the # of protons, called their atomic number.
1. Ex : H – #1- 1 proton
He – #2 - 2 protons
c. Neutroni. -Neutral charge
ii. Isotopes- different number of neutrons but same number of protons
II.
Outside the nucleus
a. Electroni. Have a negative charge
ii. Electrons - on the outer edges of atoms
iii. Dictate the properties of the material
1. Ex (taste, texture…)
2. Outermost electrons called valence electrons.
b. Atomic mass number- Total mass of an atom
i. *Electrons so small they can be ignored in mass
Ex: Be – atomic number = 4
-atomic mass = 9
(9 - 4) = 5 neutrons
Cs – atomic number = 55
- atomic mass= 133
(133 – 55) = 78 neutrons
III.
3 Models of the Atom
We will focus on one!
1)
Bohr’s Planetary Model of the atom
-Electrons orbit the nucleus like planets orbit the sun.
-Neils Bohr in 1911
-Dev. because of Atomic spectra- light emitted by atoms
- elements emit their own freq. of light (diff. colors)
- “fingerprints” of the elements
-The innermost first orbit, is called the ground state
-Bohr’s model is only a beginning
-Doesn’t explain why electrons are limited to those specific orbits