1. Atoms & Elements Biology 137/ RR

2. Definitions Atom –The smallest part of an element that upholds the chemical properties of that element Element –A substance that can’t be broken down into simpler chemical substances. –What’s smaller: an atom or element?

3. Period Table of Elements Locate the Periodic Table in the classroom. What information can you find on the periodic table? –Element Name.... Hydrogen –Element Symbol.....H –Atomic Mass.......1.008 –Atomic Number.....1 1 H Hydrogen 1.008

4. Now you try it! Use your periodic table handout. 1.Calcium = Element Name = Element Symbol = Atomic Mass = Atomic Number 2. = Element Name = Element Symbol = Atomic Mass 7 = Atomic Number 3. = Element Name = Element Symbol 12.001= Atomic Mass = Atomic Number Ca 40.08 20 Carbon C 6 Nitrogen N 14.007

5. What does an atom look like? Atoms have a nucleus. The nucleus is located in the center of the atom. The nucleus is composed of protons and neutrons. ATOM

6. Let’s take a closer look at the nucleus of an atom... The nucleus is composed of 2 particles. 1. Protons: positively charged particles - depicted in diagrams as: p+ or + or + 2. Neutrons: particles with no charge - depicted in diagrams as: n or The nucleus is positively charged

7. ATOM PROTONS NEUTRONS

8. Clouds form around the nucleus Electrons- form “clouds” around the nucleus –They are negatively charged particles –Move very rapidly around the nucleus –Depicted in diagrams as: e- or - Terminology: –Electron “clouds” are the same as electron “energy levels” and “rings”

9. How many electrons can a energy level hold? 1.First energy level Closest to the nucleus Smallest Holds a maximum of 2 electrons 2.Second energy level Next one out after first energy level Bigger: Holds a maximum of 8 electrons 3.Third energy level Next one out after 2 nd energy level Larger yet – holds a maximum of 18 electrons

10. What’s an Isotope? Sometimes, atoms contain a different numbers of neutrons in the nucleus Isotopes are atoms of the same element that have different numbers of neutrons For ex., different types of Carbon isotopes Carbon-12 Carbon- 13 Carbon-14

11. Important Information From the Periodic Table Atomic # = # protons Mass # = # protons + # neutrons # neutrons = Mass # - Atomic # On the periodic table, Atomic # can also equal # of electrons. But, in real life, you typically will get a ions (loss or gain of electrons)

12. # of electrons = # of protons Atoms contain equal numbers of electrons and protons Therefore they typically have no charge But...in nature, elements are always bonding with other elements to make important biological molecules: –If an atom loses an electron, it becomes positively charged –If an atom gains an electron, it becomes negatively charged