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Chemistry Chapter 3. Counting atoms. atomic number - # of protons in atom of an element identifies element tells also # of e- Au, K, C, V. Isotopes. remember atoms of the same element ALWAYS HAVE the same number of protons, but may have different number of neutrons
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ChemistryChapter 3 Counting atoms
atomic number- # of protons in atom of an element • identifies element • tells also # of e- • Au, K, C, V
Isotopes • 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-
Isotopes of Hydrogen protium deuterium tritium
Mass Number -the total number of protons and neutrons in nucleus always whole number
Designating Isotopes • H isotopes have special names; all other elements are indicated by their mass number • hyphen notation- name written followed by mass # • chlorine-37 hydrogen-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
Find p, e-, & n • mass #- atomic # = # neutrons • Li p ___ e-___ n ___ find for Ag, F, H
atomic masses are VERY SMALL • O atoms have a mass of 2.657 x 10-23 • 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?
IMPORTANT MESSAGE FROM OUR SPONSORS! • ALL ATOMIC MASSES ARE GOING TO BE ROUNDED TO TWO DECIMAL PLACES BEFORE USED IN CALCULATIONS! • for ex: N is 14.01 • 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 = 6.022 x 1023 particles (atoms, molecules, ions) aka Avogadro’s number named in honor of Italian chemist Lorenzo Romano Amedeo Carlo Avogadro de Quaregna e diCerreto
Molar mass • 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 6.022 x 1023 particles
We’ve learned about 2 conversion factors: # grams of substance 1 mol of sub and • 1 mol of any substance 6.022 x 1023 particles
How many mol of lead are equal to 1.57 x 1042 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 109 atoms of Ne?
Molar mass, Avogadro’s constant Quiz • What is the mass in grams of 17.8 mol of Li? • How many mol of Ag are found in 351g? • If you have 25.3 mol of Ga, how many atoms are there?
