1. Parts of the Atom & The Periodic Table

2. History of the Atom
Democritus – first person to think of what matter is made of around 400 BC. Theory was that matter was made up of substances.
Aristotle – disputed Democritus and came up with his own theory that matter was uniform throughout and NOT made of smaller particles. Theory was accepted for 2000 years!!! UNTIL…
John Dalton – proved that smaller “atoms” existed proving Democritus right and Aristotle wrong.

3. Parts of the Atom
Protons (p+)
Electrons (e-)
Neutrons (no)

4. History of the Periodic Table
The periodic table was discovered by Dmitri Mendeleev in the late 1800s. He arranged the elements in order by their atomic masses. The first periodic table was written on paper!!
In 1913, Henry Moseley rearranged the periodic table by their atomic numbers instead of the atomic masses.

5. Periodic Table Practice Sheet Atomic # = electrons and protons
Mass # = protons plus neutrons (average atomic mass)
Isotopes - atoms with the same number of protons but different number of neutrons
Practice Sheet

6. Half – Life
Def: the time it takes for half of the radioactive atoms to change into another element due to a change in protons
p. 552: Problem-Solving Activity
Look at the table.
How long does it take uranium-238 to turn to lead-206?
How long would it take for 75% to change?
Solutions: 1. 4,460 years 2. 3,345 years

7. Families on the Periodic Table
Group 1 = Alkali Metals
Group 2 = Alkaline Earth Metals
Group 3-12 = Transition Metals
Bottom groups= Inner Transition Metals
Group 13 = Boron Group
Group 14 = Carbon Group
Group 15 = Nitrogen Group
Group 16 = Oxygen Group
Group 17 = Halogens
Group 18 = Noble Gases
Metalloids

8. Masses of Atoms mass of protons and neutrons are about the same
mass of an electron is very, very close to zero (like a cloud)
# of neutrons = mass # - atomic #
average atomic mass – the weighted average mass of the mixture of isotopes (like grades done by %)

9. Electron Energy Levels
There are a possible 7 energy levels for the periodic table.
There are enough known elements to occupy only 4 of these energy levels.
level 1 = 2 e-
level 2 = 8 e-
level 3 = 18 e-
level 4 = 32 e-

10. Electron Dot Diagrams
Valence electrons – outer energy level electrons that can make chemical bonds
Valence electrons are the ONLY electrons used in dot diagrams.
Once dot diagrams are made, then electrons are paired to make compounds.
Compounds are made by two ways: Covalent bonding = sharing e- OR Ionic bonding = transferring e- (taking them).

11. Electron Dot Diagrams
The Bohr model shows ALL electrons in their orbitals or paths
The Lewis Dot Diagram shows just the valence electrons

12. Valence Electrons Across PT
Notice that the transition metals (3-12) are skipped!!