Parts of the Atom & The Periodic Table

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.

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

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.

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

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

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

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 %)

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-

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).

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

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