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.

• 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)

Review• Elements react resulting in new chemical substances. Strategy for naming

compoundsIs it one of

the 11 compounds

with a special name?

New compound

Give special name. ex. NH3

Ammonia

Is it a binary compound?

Is it a compound

with a metal and non metal?

Name the metal then the polyatomic atom. Ex.

Na2CO3, sodium carbonate

Name the metal then the non-metal with sufix –ide. Ex. CaCl2,

calcium chloride

Name first non-metal (more reactive), then the second with sufix -ide. Ex. SO3,

sulfur trioxide

yes

yes yes

no

no no

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?

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

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 reactionA+B C + D

“Substances A and B react to form substances C and D”

Reactants Products

Indications of chemical reaction

1. The reactants disappear or are diminished2. New substances appear as products which have different

chemical and physical properties3. 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 formSolid particles form in solution, heat is produced.

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

Example (for activity)

Balance the following reaction:

Hydrogen + Oxygen water

Steps:1. Decide the chemical formula of the reactants

using Lewis dot structures2. Balance the chemical equation by following the

rules of chemical balancing

Example 2

Balance the reaction

methane + oxygen carbon dioxide + water

Gas barbecue

Find your partner and write the chemical reactions

1) Copper + sulfur Copper(II) sulfide

2) Calcium oxide + water Calcium hydroxide

3) Hydrogen + nitrogen

4) Chromium + oxygen

5) Aluminum + bromide

6) Sodium + iodine

7) Hydrogen + chlorine

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?

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

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

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

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

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