Atomic MassAgenda

Review (whiteboards)Read 4.7 & 4.8 NotesHomework

Parts of Atomic Theory

How do isotopes differ?

How do ions differ?

146C

____ p+

____ e-

____ no

94Be+2

____ p+

____ e-

____ no

3617Cl-

____ p+

____ e-

____ no

READGrab bookRead section 4.7 & 4.8 w/ partner

Six inch voices

Average Atomic Massdate

Average atomic massA WEIGHTED average dependent on the

percent abundance of each isotope.If all isotopes were in a bag, how frequently

would you pull out each separate isotope.Measured in amu’s

Atomic Mass UnitAn amu is the mass of a single proton.

1 amu = 1.67*10-24 g

Determining Average MassMultiply Mass number by Percent abundance.

Add the answers.Answer should be close to most abundant isotope.

ExampleCesium is 75% 133Cs, 20% 132Cs, 5%

134Cs. What is the average atomic mass?

ExampleChromium has four istopes. 4.35% 50Cr, 83.79% 52Cr, 9.5% 53Cr, 2.36% 54Cr. What is the average atomic mass of Cr?

Determining % abundance Create an equation equaling average atomic

massMass1 * %X + Mass2 * %Y = average atomic

massCreate an equation equaling 100%

X + Y = 1Use substitution to solve for x.

Mass1 * %X + Mass2 * %(1-X) = average atomic mass

The average atomic weight of boron is 10.812amu. Boron has two isotopes: boron-10 with a mass of 10.013 and boron-11 with a mass of 11.009. What are the % abundances of each isotope?

What are the % abundances of the two isotopes of rubidium?Rb-85, 84.9918 amuRb-87, 86.9092 amu

HomeworkComplete isotopes and average atomic mass worksheet

Review scientists and discoveries.

Lab report due Rough draft WednesdayFinal draft Friday