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Part 1 • Atomic Theory Chemistry Warm-up: Why do you think we have to learn about Chemistry in a Biology class? A Brief History: • Democritus (Fourth Century BC) – First named the “atom” – Lacked evidence • John Dalton (1766-1844) – Performed experiments to discover: • Dalton’s Atomic Theory Dalton’s Atomic Theory Um, who I’m Oxygen. is this? It sure is 1. All composed of tiny I amindivisible different Heelements looks nice particles from you, but pretty called atoms. hanging Tell me I’m sure we different out with about it, could find from you you, Carbon! some way to and me, 2. Atoms of the same element are identical Carbon. bond! Carbon. Atoms of Element A Atoms of Element B What happens when they mix? Still more of Dalton’s Atomic Theory… 3. Atoms of different elements can physically mix together or can chemically combine to form compounds. 4. Chemical reactions occur when: – atoms are separated, joined or rearranged; – however, they are never changed into atoms of another element. 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! The three kinds of subatomic particles 1. 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 The three kinds of subatomic particles 2. 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? 1,840 ________________ times as big – Actual mass = 1.67 x 10-24 grams – One unit of positive charge 3. Neutrons (n0) – Discovered by James Chadwick in 1932. – Actual mass = 1.67 x 10-24 grams – No charge 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 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. The Bohr Model • In 1915, Neils Bohr modified Rutherford’s “planetary” model of the atom and added the new discovery of Quantum Theory: High energy orbital Low energy orbital 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. Why protons? Why not neutrons? Or electrons? • Oxygen’s Atomic Number is 8. – How many protons does it have? _______ 8 8 – How many neutrons does it have? ________ 8 – How many electrons does it have? ________ • Wait a minute, how do we know we have that many of each atomic component? Mass Number • The total number of protons and neutrons is called the mass number. Based on this nucleus, what is the mass number? 4 + + What element is it? Helium What about those special cases? • Sometimes there are more or less neutrons in a nucleus, these are called isotopes. Do page 30 now The Atomic Number Element’s Name Atomic Mass 5 5 P = _____ B 6 N = _____ Boron 10.81 5 E = _____ Bohr Diagram Lewis Structure B Part 2 • Bonding with activities Bond with your classmate! (page 37) • 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! were HiYou there! Greetings, Nitrogen. Bonding and Chemical right! I am We are Hydrogen I’mReactions now Ammonia! atoms. Perhaps we Nitrogen. But, am I an •willChemical Bonding: change the way Am I an atom or a you think about Combining Atoms of Elements to form atom or a compound yourself. Chemical Compoundscompound? now? Oh, you can’t be serious! Bonding To achieve stability, an atom will either gain, lose or share electrons. Ionic Bonds: A bond that involves a transfer of electrons Ionic Bonds Sodium Chloride = Salt!Chloride Chlorine Ion (+1) Ion (-1) Can you guess which Covalent Bonds element I am? What will complete my • A covalent bond is a chemical bond valence shell? formed by sharing electrons. Different types of Covalent Bonds Single Bond: One pair of shared electrons Double Bond: Two pairs = of H shared – H electrons Triple Bond: Three pairs of shared electrons O=C=O C Lone pairs: Cyanide Electron (HCN) pairs not shared Hydrogen can form this. between Can you? atoms H N H H Practice Exercises How many Bonds and Lone Pairs? 1. 2. 3. 4. Write Lewis structure for F2. Write Lewis structure for O2. Write Lewis structure for N2. Write Lewis structure for ammonia, NH3. 5. Write Lewis structure for CO2. Time for more Practice • Page 34-35 Making Ionic Bond Chemical Reactions • Any process in which a chemical change takes place. – Slow occurring (i.e., Iron and Oxygen Rust) – Quickly occurring (i.e., Combustion Reaction) Time to Practice Page 36 Balancing Act Bonding Basics Practice Answers (page 33) 12+ 1Ionic Bonds 1. Mg + Br Br 2. Pb + S Mg 2- 4+ S Pb Br MgBr2 2- S PbS2 1- Cl 3. Al + Cl Cl Al Cl 1- 3+ 1- AlCl3 Bonding Basics Practice Answers (page 33) Covalent Bonds 1. H + Cl Cl H – Cl H Cl 2. C + Cl Cl C Cl Cl O Si Cl C Cl CCl4 Cl Cl 3. Si + O HCl O O = Si = O SiO2