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.
Periodic Table of the Elements IA IIA IIIA IVA VA VIA VIIA VIIIA H He Li Be B C N O F Ne Na Mg IIIB IVB VB VI VIIB VIIIB IB IIB Al Si P S Cl Ar K Ca Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Ag Cd Sn Sb I Xe Cs Ba W Pt Au Hg Pb Bi
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.
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
Recall that atomic masses have two meanings:
- What is the mass of 27 atoms of oxygen
- in amu's? (27 atoms)(16.00amu/atom) = 432.0 amu
- in grams? (27atoms)(16.00amu/atom)(1g/[6.022 x x 1023amu]) = 7.174 x 10-22g
- Given 3.45 grams of copper
- how many moles of copper is this? (0.0543 mole)
- how many atoms of copper are there in this sample? (3.45g)(1mol/63.55g)(6.022 x 1023atom/mol) = 3.27 x 1022atoms
- A 2.34 mole sample of sulfur contains
- how many grams of sulfur? (2.34mol)(32.06g/mol) = 75.0 g
- how many atoms of sulfur? (4.52 x 1025)
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© R A Paselk
Last modified 4 February 2015