Basic Principles of Chemistry

Unit 2: Chemical Reactions and Their Significance

Lecture #9

Summary

• Matter...

– Is composed of atoms which...

• are composed of protons, neutrons, and electrons

• AND

• make up molecules

Classes of Pure Substances

More About Matter

• Each pure substance is characterized by its own unique set of properties.

– Physical

– Chemical

Our Business

• The study of the physical and chemical properties of matter

Our Method

• The scientific method

• Making careful measurements and other observations

• Communicating our findings to others

The Dilemma

• Atoms are very tiny

• Atoms are very numerous

Tiny Atoms

Many Atoms

Counting by Weight

Counting Units

• Pair

• Dozen

• Gross

• Score

• Magnum

• Ream

• Turkey

Is This Really Necessary?

• Why do we need to be able to account for all the atoms and molecules in a sample?

• Can we account for all of the atoms or molecules in a sample?

A New Counting Unit

• The MOLE

– One carbon (C) atom

weighs 12.0 amu

– One mole of carbon (C)

atoms weighs 12.0 g

Avogadro’s Number

• The MOLE

6.02 x 1023 items

This is HUGE!

Avogadro’s Number

• One mole of marbles could cover Earth to a depth of 50 miles.

Avogadro’s Number

• One mole of pennies could give every man, woman, and child on Earth $1,000,000,000,000!

Avogadro’s Number

• A glass of water contains about 10 moles of water.

• This is more water molecules than grains of sand in the Sahara Desert.

Extra Credit Assignment

• “How Big is a Mole” Project