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GSCI 163

GSCI 163. Lecture 6. Review. The order in the periodic table comes from the distribution of electrons in the shells. Atoms with similar shell structures have similar chemical characteristics.

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GSCI 163

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  1. GSCI 163 Lecture 6

  2. Review • The order in the periodic table comes from the distribution of electrons in the shells. Atoms with similar shell structures have similar chemical characteristics. • There are 2 major groups: Metals, which tend to loose electrons in chemical reactions and non-metals that tend to gain electrons in chemical reactions. • Octet rule: atoms are happy when they have their valence shell full (typically 8 electrons)

  3. Review • Elements react resulting in new chemical substances. Strategy for naming compounds Is it one of the 11 compounds with a special name? New compound Give special name. ex. NH3 Ammonia yes no Is it a compound with a metal and non metal? Is it a binary compound? Name the metal then the non-metal with sufix –ide. Ex. CaCl2, calcium chloride yes yes no no Name the metal then the polyatomic atom. Ex. Na2CO3, sodium carbonate Name first non-metal (more reactive), then the second with sufix -ide. Ex. SO3, sulfur trioxide

  4. Combining atoms to form new substances • Can we determine how atoms combine to make new substances? • Specifically, how many atoms of each element are involved in the chemical reaction?

  5. Chemical vs Physical properties • Chemical properties: related to ways a substance can be transformed into another • Wood burns when heated in the presence of air • Water can be decomposed into H2 and O2 electrolyze • Iron rusts in the presence of oxygen • Physical properties: no changes in chemical composition of the substances. • Water freezes at low temperatures • Salt dissolves in water • Alcohol evaporates

  6. Chemical reaction Chemical reaction: rearrangement of atoms in which some of the original chemical bonds and new bonds are formed to give different chemical structures. • Generalized chemical reaction A+B  C + D “Substances A and B react to form substances C and D” Reactants Products

  7. Indications of chemical reaction • The reactants disappear or are diminished • New substances appear as products which have different chemical and physical properties • Energy (heat, light, electricity, sound) is either released or absorbed (sometimes the energy change is hard to detect) Clues that a chemical reaction going on: Color changes, odor changes, gas bubbles form Solid particles form in solution, heat is produced.

  8. Chemical equation • Chemical equation can be written for each chemical reaction. • Chemical equations must be balanced to express the actual ratio of substances used and yielded as products. Rules: • The same number of atoms of each element must be represented on each side of the reaction arrow • Only the coefficients may be manipulated, but not the subscripts • The coefficients must be whole numbers

  9. Example (for activity) Balance the following reaction: Hydrogen + Oxygen  water Steps: • Decide the chemical formula of the reactants using Lewis dot structures • Balance the chemical equation by following the rules of chemical balancing

  10. Example 2 Balance the reaction methane + oxygen  carbon dioxide + water Gas barbecue

  11. Find your partner and write the chemical reactions • Copper + sulfur  Copper(II) sulfide • Calcium oxide + water  Calcium hydroxide • Hydrogen + nitrogen  • Chromium + oxygen  • Aluminum + bromide  • Sodium + iodine • Hydrogen + chlorine 

  12. Chemical reactions in the real world • What happens when we react 10 g of sodium with 20 g of iodine? Write the chemical equation • We need to know how many atoms of each will react to make sodium iodine. • How do we find that?

  13. Weight of a substance • The atomic unit (u) is the standard unit of mass for an atom. • The isotope 12 of carbon was chosen as the standard weight: 1/12 of 12C = 1u See atomic masses on the periodic table

  14. Concept of Mole The mole is defined as the amount of substance that contains as many elementary entities (e.g., atoms, molecules, ions, electrons) as there are atoms in 12 g of the isotope carbon-12 (12C). Two consequences: • 1 mole of any substance is the atomic weight in grams • The number of elements in 1 mole = 6.02 x 1023

  15. Avogadro’s number • This magic number (6.02 x 1023) is caled Avogadro’s number in honor to Italian Physicist Amedeo Avogadro. • How did they measured? • It takes by electrolysis 96,485 Coulombs to produce 1 mole (23g) of sodium metal from molten sodium chloride. 1 electrons = 1.6 x 10-19 C Thus 1 mole of electrons is (96,485 C/mol)  (1.6 x 10-19 C) = 6.02 x 1023

  16. Back to chemical reaction • In a chemical reaction atoms of each reactant combine to make products. A+B  C + D X moles of A reacts with X moles of B to produce X moles of C and D

  17. Next class Balancing equations and types of reactions • To prepare for the class read: • Handout pages 18 to 22 (day 5-6) • Presentation by Rebecca Cross, Acids and Bases • To prepare for the quiz read: • Handout pages 16-19 (day 4-5) • Power point for this class • Your class notes

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