1. ATOMS

2. All matter is made up of atoms.
An atom is the smallest unit of an element that has all the properties of the element.
Atoms are made up of protons, neutrons, and electrons.

3. Protons Positive charge Located in the nucleus
Elements are organized on the Periodic Table based on their atomic number (number of protons)
Ex: Neon has 10 protons so its atomic number is 10, and it is the 10th element on the Periodic Table.

4. Neutral charge (no charge) Located in the nucleus
Neutrons
Neutral charge (no charge)
Located in the nucleus
Similar in size to protons

5. Electrons Negative charge Located in “clouds” outside of the nucleus
Smaller than protons and neutrons
A neutral atom has the same number of electrons as it has protons.

8. This pinhead represents the size of the nucleus of an atom, and the stadium represents the size of an entire atom.

9. Atomic Theory
Began in ancient Greece and continues today.
As technology has improved, we know more about atoms.

10. Democritus (Greek philosopher (440 B.C.) believed:
1. If you keep cutting something in half, eventually you will have a particle that can’t be cut.
2. Atom (atomos)- “unable to be divided”
3. thought atoms were small and hard

11. Dalton (1700s chemist/teacher) believed:
1. Everything is made of atoms.
2. Atoms can’t be created, destroyed, or divided.
3. Atoms of the same element are exactly alike and atoms of different elements are different.
4. Atoms combine to make new substances.

12. 2. thought atoms were a positive sphere with negative dots
J.J. Thomson (1897 British scientist):
1. discovered electrons
2. thought atoms were a positive sphere with negative dots

13. This is the “plum pudding” model.
Thomson thought atoms looked like this:
This is the “plum pudding” model.

14. Rutherford. 1. There is a positive, dense nucleus in the
Rutherford There is a positive, dense nucleus in the middle of the atom with electrons on the outside.
2. empty space in the atom

15. Bohr believed:
1. Electrons move in circular paths
2. Electrons could jump from one path to another.

16. Current theory:
1. Electrons do not travel in a specific path.
2. There are areas were electrons are likely to be but no exact spot (electron clouds).

17. Isotopes same number of protons but different number of neutrons
We tell isotopes apart based on their mass number (the number of protons plus the number of neutrons).
Mass number – atomic number = number of neutrons
Isotopes are named based on mass number Ex: Boron-10 has 5 protons and 5 neutrons Boron-11 has 5 protons and 6 neutrons

18. Example:
Carbon has 6 protons
How many electrons?
Carbon-12 has a mass number of 12. How many protons? How many neutrons?
Carbon-13 has a mass number of 13. How many protons? How many neutrons?

19. Atomic number? Mass number? Protons? Electrons? Neutrons?