1. Atoms

2. Atoms are the main building block of all matter All chemical and physical properties of matter are a result of how the atoms in the matter behave All atoms are made of the same three subatomic particles. What makes one atom different than another is the number of each subatomic particle it has. Different types of atoms are called elements

3. Bohr Model of Atom

4. Subatomic Particles Atoms are made of the three subatomic particles ChargeLocation P roton +In nucleus E lectron -Orbiting nucleus N eutron 0In nucleus

5. Atomic Number Indicates the number of protons The number of protons in the nucleus is called the atomic number. Electrons will always equal the same number of protons. (in the atom!) What makes atoms unique? The number of protons they contain. E x. A lithium atom has 3 protons, so its atomic number is 3. 3 Li Lithium 6.9 Atomic Number

6. Atomic Mass Mass of an atom Measured in atomic mass units (u) Found on the periodic table below each element symbol 3 Li Lithium 6.9 Atomic Mass

7. Mass Number represents the contents of its nucleus (protons + neutrons). The mass of electrons is so small it is “negligible” This value is called the mass number. (round mass to the nearest whole number) # of Neutrons = Mass # – Atomic # # of Neutrons in Lithium = 7 - 3 = 4 3 Li Lithium 6.9 Atomic Number Mass Number 3 Li Lithium 7

8. Isotopes Atoms of different elements have different numbers of protons Atoms with the same number of protons but different numbers of neutrons are called isotopes For example: Lithium can have 3 or 4 neutrons  Li-6 and Li-7 Mass number is used to distinguish between the two isotopes of Lithium

9. Nuclear Notation 6.9 Li 3 Atomic Number Mass Number 6.9 Li Li-6.9

10. Homework Subatomic Particles Worksheet Pencil only please Read p. 234-235