1. Chapter 4 Notes
Atoms

2. Atomic Theories
All scientists believed that all matter consisted of extremely small particles that could not be divided called atoms.

3. All matter is made of atoms. Solid Spheres
Scientists
Evidence for Theory
Models
1. Dalton- gathered evidence by measuring masses of elements.
All matter is made of atoms.
Compounds contain atoms of more than one element.
All elements have different masses.
Atoms of different elements always combine in the same way.
Solid
Spheres

4. Scientists
Evidence for Theory
Models
2. JJ Thomson- provided the first evidence for subatomic particles
Used a sealed tube of gas and when the current was on a glowing beam appeared. The beam bent toward the positively charged plate indicating the beam was negative.
Plum pudding Or
Choc. Chip ice cream

5. Scientists
Evidence for Theory
Models
3. Rutherford- discovered the nucleus by using a gold foil experiment
Nucleus- contains the protons and neutrons in the center of an atom
Positive & dense nucleus

6. Rutherford’s Gold Foil Experiment

7. Discovered energy levels where electrons orbit around the nucleus
Scientists
Evidence for Theory
Models
4. Bohr- agrees
with Rutherford’s
model but he
focused on
electrons and
discovered 4 levels
MODERN THEORY USED TODAY
Discovered energy levels where electrons orbit around the nucleus
When they move UP a level they are in an EXCITED STATE
When they move DOWN they EMIT ENERGY AS LIGHT
Each level can only contain a certain number of electrons
Planet Model

8. Other Models
Electron Cloud Model- used to show possible location of electrons in an atom.
Electron Configuration- is an arrangement of electrons in the orbital of an atom
** Most STABLE electron configuration is when electrons are in the lowest possible energy levels. This is the GROUND STATE.

9. Structure of an Atom
Atoms consist of protons and neutrons in the nucleus and electrons in the energy levels surrounding the nucleus.

10. Particle
Symbol
Charge
Mass
Location
Proton P+ 1+ 1
Nucleus
Electron e- 1-
1/1836
Outside nucleus
Neutron N0
No Charge

11. Structure of an Atom
A. Atomic Number- equals the number of protons in an element. Found above the symbol of an element.

12. Structure of an Atom
B. Atomic Mass- is the mass of the nucleus (equals #protons + #neutrons)
*** All atoms are neutral with a ZERO CHARGE since they have the same number of negative and positive charges.
*** To find the number or neutrons:
Atomic Mass – Atomic Number = Number of neutrons

13. Structure of an Atom
C. Isotopes – Atoms of the same element with different numbers of neutrons which changes the mass number.
** The element on the periodic table is the one that occurs most readily in nature.

14. 7 N

15. Atoms Quiz Which scientist used the gold foil experiment?
Which scientist’s model was the solid sphere model?
Which scientist discovered the nucleus?
What are atoms?
Which scientist’s theory do we use today?
Opposite charges ________, and like charges __________.
What is the nucleus?
What are the 3 subatomic particles called?
What charge do electrons have?
How many protons, electrons, and neutrons does an atom of Magnesium (Mg) have?