Isotopesmolespre-ap2008

Isotope Definition • Isotope – atoms that have the same number of protons, but different number of neutrons. Nuclide is the term for an isotope of an element. • Average Atomic Mass – the weighted average of all the isotopes of an element. • Atomic Number – the number of protons in the nucleus of an atom of an element. • Atomic Mass – the weighted average of the masses of the isotopes of an element. • Mass Number – the total number of protons and neutrons in the nucleus of an atom.

Visual Atomic Number

Atomic Mass

Mass Number

Visual

How many? • Neutrons in: –

16

–

O?

16 - 8 = 8

108

Ag?

108 - 47= 61

–

207

Pb?

207 - 82= 125

–

80

Br?

80 - 35= 45

Calculating Avg. Atomic Mass • A sample of bromine is 50.69% 78.92Br and 49.31% 80.92Br. What is it’s average atomic mass? Answer: 0.5069 x 78.92 = 40.00 0.4931 x 80.92 = 39.90 Avg. Atomic Mass = 40.00 + 39.90 = 79.90 amu

Let’s try another one! • A sample of magnesium is 78.99% 24Mg and 10.00% 25Mg and 11.01% 26Mg What is it’s average atomic mass? = 18.96 • Answer: 0.7899 x 24 = 2.500 0.1000 x 25 0.1101 x 26

Avg. Atomic Mass =

= 2.863

18.96+2.500+2.863= 24.32 amu

• One mole of rice grains is greater than the total amount of rice grown since the beginning of time! • A mole of marshmallows would cover the US to a depth of 600 miles! • A mole of basketballs would just about fit perfectly into a ball bag the size of the earth!

• Mole - 6.02 x 1023 representative particles.(Also called Avogadro’s Number) • The mole is based on Carbon-12. (Mole = amount of a substance w/ same # particles as 12g of C-12). • Representative Particles can be: – atoms – molecules – formula units – ions

• How many moles is 3.80 x 1022 atoms of carbon?

3.80 x 1022atoms 1

1 mole 6.02 x 1023 atoms

ANSWER: 0.0631 moles of carbon

=

How many molecules are there in 2.35 moles of water? 2.35 moles 1

6.02 x 1023 molecules = 1 mole

ANSWER: 1.41 x 1024molecules

Last One (of this type)! How many moles are there in 7.21 x 1025 molecules of Sulfuric acid? 7.21 x 1025 molecules 1

1 mole = 6.02 x 1023 molecules

Answer: 120. moles

Calculating Between Moles & Mass • You can convert mass of a substance into moles of a substance by using the gram formula mass of the compound. – Ex. 1 mole of NaCl = (23.00 + 35.45) = 58.45 g

Calculate the Mass • Calculate the Mass of 1 mole (aka Molar Mass) of these substances: – MgS – Li3N – H2O

24.31 + 32.07 = 56.38 g 3(6.941) + 14.01 = 34.83 g 2(1.008) + 16.00 = 18.02 g

Sample Problem • How many moles of potassium fluoride are there in 87.35 grams? – KF = 39.10 + 19.00 = 58.10 g 87.35 g 1

1 mole = 58.10 g

1.504 moles KF

Another One! • How many grams of PCl5 are there in 3.21 moles? – PCl5 = 30.97 + (5)35.45 = 208.22 g 3.21 moles 208.22 g = 1 1 mole

668 grams PCl5

Last One (seriously)! • How many moles of water are there in 63.21 grams? – H2O = 16.00 + (2)1.01 = 18.02 g 63.21 g 1

1 mole = 18.02 g

3.508 moles H2O

What is the only sports team in America with a foreign name for the city and team?

San Diego Padres