Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109 - General Chemistry - Spring 2015

Lecture Notes 7: 2 February

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Chemical Periodicity , cont.

Last time looked at the Periods (rows) in the Periodic Table, today we look a bit further and discuss the Groups or columns in the Table.

Note that elements go from metallic(Group 1) to non-metallic (Group VIII) as you proceed from left to right across the table.

Groups

Terms etc.:

 

Stoichiometry: Moles, Atoms, & Formulae

Stoichiometry is the quantitative study of the composition of compounds (e.g. determining the ratios of atoms in a molecule) and/or the ratios of substances in chemical reactions.

The Mole

This is the SI unit of amount of substance. 1 mole = the number of carbon atoms in 12 g of 12C. This number, called Avogadro's Number, has been measured as 6.022 x 1023 mol-1 (current value: 6.022 141 99 x 1023mol-1). Notice that this number can refer to anything (a mole of eagles, a mole of pennies, etc.). In each case we are talking about 6.022 x 1023 items or entities.

For chemists a mole has two common uses:

Note that Avogadro's number, 6.022 x 1023 is thus the conversion factor from amu's to grams!

Mole Samples Demo

Atomic Mass

Recall that atomic masses have two meanings:

Examples:

 

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© R A Paselk

Last modified 4 February 2015