Counting atoms

atomic number - # of protons in atom of an element identifies element tells also # of e- Au, K, C, V

remember atoms of the same element ALWAYS HAVE the same number of protons, but may have different number of neutrons if atom is neutral, then it has same # of p & e-

protiumdeuterium tritium

-the total number of protons and neutrons in nucleus always whole number

H isotopes have special names; all other elements are indicated by their mass number hyphen notation - name written followed by mass # chlorine-37hydrogen-3 nuclear symbol - name of element written w/ mass number as superscript & atomic number as subscript

average atomic mass - the weighted average of the atomic masses of the naturally occurring isotopes of an element usually reported on p. table round to nearest whole number to become mass number

mass #- atomic # = # neutrons Lip ___ e-___ n ___ find for Ag, F, H

atomic masses are VERY SMALL O atoms have a mass of x scientists use relative atomic masses one atom was arbitrarily chosen to be the STANDARD by which all other atoms are measured carbon-12 atom it’s been assigned a mass of 12 amu, atomic mass units

atomic mass unit- is exactly 1/12 the mass of a carbon-12 atom most elements occur as a mixture of isotopes some isotopes are more prevalent than others

average atomic mass – the weighted average of the atomic masses of the naturally occurring isotopes of an element at mass = (mass of isotope x abundance) + (any others) total abundance ex: Copper-63 makes up 69.15% and copper-65 has an abundance of 30.85%. What is its avg at mass?

ALL ATOMIC MASSES ARE GOING TO BE ROUNDED TO TWO DECIMAL PLACES BEFORE USED IN CALCULATIONS! for ex: N is Ar= 39.95

atoms too small to weigh individually will use a unit to describe a particular # of objects SI unit chosen is mole, mol it is the amount of sub that contains as many elementary particles as there are atoms in 12 g of C-12

the mass of 1 mol of atoms of a pure element in grams is numerically equal to the atomic weight of that element in amu for ex: 47.88g of Ti= 1 mol Ti atoms

1 mol = x particles (atoms, molecules, ions) aka Avogadro’s number named in honor of Italian chemist Lorenzo Romano Amedeo Carlo Avogadro de Quaregna e di Cerreto

the mass of 1 mol of molecules, atoms, ions, or formula units used to RELATE MASS IN Grams TO # ATOMS, MOLECULES, ETC set it up as a conversion factor in calculations molar mass = # grams of substance 1 mol of sub

How many g of oxygen contains Avogadro’s # of O atoms? Au? K? Cu

How many grams in 2.25 mol of Fe? Use Avogadro’s # to show # of atoms in a given amount of a substance: Avogadro’s constant = 1 mol of any substance x particles

# grams of substance 1 mol of sub and 1 mol of any substance x particles

How many mol of lead are equal to 1.57 x atoms of Pb? How many atoms of Na are in 3.80 mol of Na? What is the mass in grams of 5.0 x 10 9 atoms of Ne?

1. What is the mass in grams of 17.8 mol of Li? 2. How many mol of Ag are found in 351g? 3. If you have 25.3 mol of Ga, how many atoms are there?

calculate mol/mass/#molecules of compounds H 2 O