Chemistry is the study of Elements When you change the number of protons of any atom, you get a different element! Chemistry is the study of Elements Elements are the specific examples of different atoms. Ex: Hydrogen, Oxygen, Gold Atoms are the smallest piece of matter. All things we know are made of trillions of atoms in different combinations (including us). No two different elements have the same atom. What makes each different are the numbers of their parts. The type of atom is determined by the number of Protons called: “Atomic Number” (this is found on the periodic Table) For example: Lithium is an element with 3 protons in its nucleus. If it lost one, it would no longer be Lithium, it would be called Helium! If Lithium got a new proton (added to it’s original 3), it would now be called Beryllium! Every element is identified by the number of protons in it’s nucleus. It is IMPOSSIBLE to have two different elements with the same number of protons!!!

Quick review of the parts of an atom: Atoms will usually have the same number of Protons & Electrons Quick review of the parts of an atom: Electrons: Negative charge This shaded area includes the protons and neutrons. And we call it the nucleus! Neutrons: No charge Protons: Positive Charge (“Atomic Number”) If there are 4 + charges (protons), then there will usually be 4 – charges (electrons) and the charge will be “neutral” Think: What Element is this? 2 Protons = Helium Atom!!!

Bohr Models Shell 1: 2 e- Shell 2: 8 e- Shell 3: 8 e- Shell 4: 18 e- - Neils Bohr was able to discover that electrons (e-) are located in different “shells” (like a ring) around the nucleus. Each shell can only hold a certain number of electrons before it is “full” “Valence” Rule: All atoms want a full outer shell of e- Shell 1: 2 e- Shell 2: 8 e- Shell 3: 8 e- Shell 4: 18 e- Etc…(7 total shells possible) Element: Nitrogen A: 3! 5+3=8 Q: How many more e- COULD fit on the outer shell?

Li Lewis Dot models Li Li Lewis realized that the most important e- for modeling are the “Valence” electrons. These are the e- that are available for bonding! (they are found on the outer shell!) The Li atom is considered “full” with 10 e-. The final product looks like this: Li Valence electron Valence electron Li Li +1 valence Rule: Imagine an invisible square Bohr Model Rule: Only 2 e- at most are drawn on each side of the “square”

Lewis Dot Models Valence Electrons To help you see it, we need to learn the Period Table of Elements You can see all these different Elements “Dot” models It may look like chaos, but there really is a pattern here:

First, get to know this key. It explains all the symbols on the P.T.E. The periodic table of elements is an organized chart of all known elements. There are tons of great patterns that explain how chemistry works once you get the hang of it!

Periods: There are seven total! The horizontal “rows” are called “periods” 1 2 3 Periods: There are seven total! 4 5 6 7

1 The vertical “columns” are called “Groups” 8 2 3 4 5 6 7 Groups: We need to know 8 total

EX: The elements in group I all react the same with water!!! The P.T. is also separated into the types of Elements: The “types” of elements are determined by their chemical and physical properties!!! = Metal Elements = Semi-Metal Elements =Non-Metal Elements (usually gases) EX: The elements in group I all react the same with water!!! Metals (+ valences) Get Rid of Electrons “+” extra e-

You can use the P.T. to make your atomic models: +1 Full Shell One +2 +3 +/-4 -3 -2 -1 Shell Two Shell Three Shell Four Shell Five Shell Six Shell Seven