Chemistry

1. Chemistry Why do you think we have to learn about Chemistry in a Biology class?

2. A Brief History: Ahem… Er, Mr. Democritus, I don’t believe this is a laughing matter. • Democritus (Fourth Century BC) • First named the “atom” • From Greek word “atomos” meaning unable to cut • An atom is the basic unit of matter • Lacked evidence • John Dalton (1766-1844) • Performed experiments to discover: • Dalton’s Atomic Theory Would you kindly remove yourself? You’re blocking my information.

3. Dalton’s Atomic Theory Um, who is this? He looks pretty different from you and me, Carbon. I’m Oxygen. I am different from you, but I’m sure we could find some way to bond! It sure is nice hanging out with you, Carbon. • All elements composed of tiny indivisible particles called atoms. • Atoms of the same element are identical Tell me about it, Carbon!

4. Still more of Dalton’s Atomic Theory… • Atoms of different elements can physically mix together or can chemically combine to form compounds. • Chemical reactions occur when: • atoms are separated, joined or rearranged; • however, they are never changed into atoms of another element.

5. Reflecting on Dalton’s Theory Most of Dalton’s theory is still accepted. Which part do you think has been rejected? The Atom is Divisible! Return to Theory #1 and cross out the word “indivisible”

6. The three kinds of subatomic particles 1. Protons (p+) • Discovered in 1886, Eugen Goldstein saw cathode rays traveling against the flow. • What do you think the proton’s mass is in relation to the electron? ________________ • Actual mass = 1.67 x 10-24 grams • One unit of positive charge 2. Neutrons (n0) • Discovered by James Chadwick in 1932. • Actual mass = 1.67 x 10-24 grams • No charge 1,840 times as big

7. The three kinds of subatomic particles 3. Electrons (e-) • Discovered by J.J. Thomson in 1897. • He used a cathode ray tube • In 1916, Robert Millikan discovered the mass was 1/1840 H, and the charge was one unit of negative charge. • Actual mass: 9.11 x 10-28 __________ grams

8. So how are all these parts put together? In 1911, Rutherford performed an experiment: What did this prove? Source of alpha particles Thin sheet of gold foil

9. Atoms are mostly empty space • Rutherford proposed that the atomic structure was like “planets around the sun” • This did not account for very specific traits that atoms possessed.

10. Atomic Structure Protons and Neutrons make up the nucleus Electrons spin around in orbitals surrounding the nucleus

11. The Bohr Model • In 1915, Neils Bohr modified Rutherford’s “planetary” model of the atom • He added the new discovery of orbitals Outer orbitals = Max out at 8 Innermost Orbital = Maxes out at 2

12. What makes atoms different from each other, if they have the same basic parts? The Atomic Number Definition: The number of protons in the nucleus of an atom of that element.

13. Why protons?Why not neutrons?Or electrons? • Oxygen’s Atomic Number is 8. • How many protons does it have? _______ • How many neutrons does it have? ________ • How many electrons does it have? ________ • Wait a minute, how do we know we have that many of each atomic component? 8 8 8

14. Atomic Mass (AMU) • The total number of protons and neutrons is called the atomic mass. Based on this nucleus, what is the atomic mass? What element is it? 4 + Helium +

15. What about those special cases? • Sometimes there are more or less neutrons in a nucleus, these are called isotopes.

16. The Atomic Number B 5 5 P = _____ 6 Element’s Name N = _____ Boron 5 E = _____ Atomic Mass 10.81 Bohr Diagram Lewis Structure B

17. Welcome! • Please pick up your folder and go to your Science group! • Clean out your folder, leaving only your “Periodic Table Basics” worksheet in there.

18. Hi there! I’m Nitrogen. Am I an atom or a compound? You were right! I am now Ammonia! But, am I an atom or a compound now? Greetings, Nitrogen. We are Hydrogen atoms. Perhaps we will change the way you think about yourself. Bonding and Chemical Reactions • Chemical Bonding: Combining Atoms of Elements to form Chemical Compounds Oh, you can’t be serious!

19. Bonding To achieve stability, an atom will either gain, lose or share electrons. Ionic Bonds: A bond that involves a transfer of electrons

20. Ionic Bonds Sodium Chlorine Chloride Sodium Chloride = Salt! Ion (+1) Ion (-1)

21. Covalent Bonds Can you guess which element I am? What will complete my valence shell? • A covalent bond is a chemical bond formed by sharing electrons.

22. Different types of Covalent Bonds Single Bond: One pair of shared electrons Double Bond: Two pairs of shared electrons Triple Bond: Three pairs of shared electrons Hydrogen Cyanide (HCN) can form this. Can you? = H – H H H O=C=O C O O Lone pairs: Electron pairs not shared between atoms H N H H

23. Bonding Basics Practice 1- 2+ 1- Ionic Bonds • Mg + Br • Pb + S • Al + Cl Br Mg Br MgBr2 2- 4+ 2- S Pb S PbS2 1- Cl Cl Al Cl AlCl3 1- 3+ 1-

24. O Bonding Basics Practice Covalent Bonds • H + Cl • C + Cl • Si + O H Cl H – Cl HCl Cl Cl Cl C Cl Cl C Cl CCl4 Cl Cl Si O O = Si = O SiO2

25. Bond with your classmate! • Each of you will have an element. • The charge – or oxidation number – is on the element. • Your goal is to bond with as many of your classmates as possible. • Balance your equations! • i.e., Magnesium (Mg) and Bromine (Br) must make… MgBr2 Bond!