3-3:

Counting Atoms

Beaker Breaker

1. What was the name of Rutherford’s experiment?

2. What did Rutherford’s experiment discover?

3. My atomic number is 36..who am I?

Objectives

• Explain isotopes

• Define mass # and atomic #

• Given the identity of a nuclide, determine its # protons, neutrons & electrons

What is the same for all atoms on an element ?

• # protons

• Atomic number, Z = # protons in the nucleus of each atom of that element

ISOTOPES

• Atoms of the same element that differ in mass

• Have the same # protons but different # neutrons

Isotopes (con’t)

• Atomic # = # protons• # protons determines the identity of the

element• # neutrons determines the isotope of the

element• (Another revision to Dalton’s Theory)• Although isotopes differ in mass, they

do NOT significantly differ in their chemical properties

Beaker Breaker

1. The_____________of an element is the number of protons in the nucleus of each atom of that element.

2. ______________are atoms of the same element that have different masses.

3.________________number is the total number of protons and neutrons in the nucleus of an isotope.

• Mass number: total number of protons and neutrons in the nucleus of an isotope

# protons (At. #)

+ # neutrons

Mass #

Mass Number

• NUCLIDE: particular kind of atom containing a definite number of protons and neutrons

–ex. Carbon-14

Mass #, A - total # nucleons (particles that make up the nucleus --> protons and neutrons)

How many neutrons are in carbon-14?

If: # protons (At. #) then: 6

+ # neutrons + ?

Mass # 14

How can you determine the # neutrons in an isotope?

Mass # # protons + # neutrons

- Atomic # - # protons# neutrons # neutrons

Designating Isotopes

• Carbon–14 (name mass #) or……..

• 14C mass #element symbol.

6 atomic #.

Radium-226

• ID the following:

• # protons

• # neutrons

• # electrons

• atomic symbol

Radium-226• ID the following:• # protons• Atomic # = 88 88 protons• # neutrons• 226-88=138• # electrons• # protons = # electrons (neutral) 88 electrons

• atomic symbol 226Ra• 88

Beaker Breaker

1. How many protons, electrons, and neutrons are in an atom of bromine-80?

2. Write the nuclear symbol for carbon-13

3. Write the hyphen notation for the element that contains 15 electrons and 15 neutrons.

Name At. SymbolAt.# Mass # # neut. # protons

11 23136 Ba 56

Lithium-9 6

Homework

Name At. SymbolAt.# Mass # # neut. # protons

Sodium-23 23 Na 11 11 23 12 11

Barium-136 136 Ba 56 56 136 80 56

Lithium-9 9 Li 3 3 9 6 3

Atomic masses are VERY, VERY small…..too small to be measured in grams!

We need another way to express “how much”

• Electron = 9.10953 x 10-28 g

• Proton = 1.67265 x 10-24 g

• Neutron = 1.67495 x 10-24g

Scientists use a relative scale to describe atomic mass – Atomic

Mass Units

• Carbon-12 nuclide is the standard

• Carbon-12 = 12 atomic mass units (amu)

• The mass of all nuclides is determined by comparing them to carbon-12

What is the value of 1 amu ??

• If 12 amu = 1 carbon-12 atom, then…

• 1 amu = 1/12 the mass of a carbon-12 atom

• Since H = 1/12 the mass of carbon-12, then..

• H = 1/12 ( 12 amu) = 1 amu

• O = 4/3 mass of carbon-12

• = 4/3 (12amu) = 16 amu

If we round…proton = 1 amuneutron = 1 amuelectron = 0 amu

proton = 1.007276 amu

neutron = 1.008665 amu

electron = 0.0005486 amu

Atomic Mass

• Sum of subatomic masses in a atom

– Carbon-12:

• 6 protons = 6 ( 1 amu) = 6 amu

• 6 neutrons = 6 ( 1 amu) = 6 amu

• 6 electrons = 6 ( 0 amu) = 0 amu

12 amu

• Predict the atomic mass of oxygen-16

• 8 protons + 8 neutrons + 8 electrons

• = 8 amu + 8 amu + 0 amu

• = 16 amu

• How does this compare with the atomic mass value on Periodic Table?

• Predict the atomic mass of uranium-234• 92 protons + 142 neutrons + 92

electrons• = 92 amu + 142 amu + 0 amu• = 234 amu

• How does this compare with the atomic mass value on Periodic Table?

• 238 !!…why is it different?

Average Atomic Mass

• Weighted average of the atomic masses of the naturally occurring isotopes of an element

IF 40.% of the students living in Hershey have 2 telephones while

60.% of the students have 4 phones, what is the average # phones in

Hershey homes?

• (0.40 x 2 phones) + (0.60 x 4 phones)

• 3.2 phones

• “weighted” average

What is the aver. atomic mass of the chlorine?

Isotope Isotope Mass (amu) % Abundance

Chlorine-35 34.96885 75.771

Chlorine-37 36.96590 24.229

• Average Atomic Mass =

• (isotope mass)(relative abundance[dec]) +

(isotope mass)(relative abundance[dec])

• (0.75771)(34.96885amu) + (0.24229)(36.96590amu)

• = 35.453 amu

Which isotope of hydrogen is the most abundant…?

hydrogen-1 hydrogen-2

hydrogen-3

• Hydrogen-1 (1.0079 = aver. atomic mass on chart)

Complete the following:Beaker Breaker

(not in packet)

Isotope # protons #electrons #neutron

Oxygen-16

29 34

Uranium-238

Complete the following:

Isotope # protons #electrons #neutron

Oxygen-16 8 8 8

Copper-63 29 29 34

Uranium-238

92 92 146

Objectives

• Define MOLE in terms of Avogadro’s #

• Define MOLE in terms of molar mass

• Use FLM to convert between grams, moles and # atoms/molecules

Relating MASS to # ATOMS

The Mole (mol)

• Amount of substance that contains as many particles as there are atoms in exactly 12 g of carbon-12 (Avogadros #)

• Experimentally determined to 6.0221367 x 1023 atoms

6.022 x 1023

“Mole Things” Conversions

How many atoms are in 0.43 moles of copper?

• 0.43 mol Cu 6.02 x 1023 atoms Cu =

1 1 mol Cu

• 2.6 x 1023 atoms of Cu

How many moles are in 1.4 x 1022 atoms of aluminum?

• 1.4 x 1022 atoms Al 1 mole Al

1 6.02 x 1023 atoms

• = 0.023 mol Al

Beaker Breaker

• Calculate the number of molecules in 1.058mole of H2O?

Molar Mass

• Mass of 1 mole of a pure substance

• Numerically equal to the atomic mass but expressed in GRAMS

• What is the molar mass of the following:

• Potassium ?• 39.098 g (or 39.098 g/mol)

Nickel ?

• 58.693 g (or 58.693 g/mol)

• What is the atomic mass of the following:

• Potassium ?

• 39.098 amu

Nickel ?

• 58.693 amu

Gram- Mole Conversions

How many grams are needed to have 0.852 moles gold?

• 0.852 mol Au 196.97 g Au

1 1 mol Au

= 168 g Au

How many moles are in 55 g of lead?

• 55 g Pb 1 mol Pb

1 207.2 g Pb

• = 0.26 moles Pb

How many moles are in 86.1 g sodium?

• 86.1 g ? mole Na = 1 ? g

• 86.1 g 1 mole Na = 1 22.99g• 3.74 moles Na

How many atoms would be in 12.0 grams of carbon-12 ?

• If …atomic mass of carbon-12 = 12.0 amu

(chart value)

• Then…12.0 g C = 1 mole (molar mass)

• And since…..1 mole = 6.022 x 1023 atoms

• Then…12.0 g carbon contains 6.02 x 1023 C atoms

Beaker Breaker

1. How many moles are there in 5.04x103

atoms of Cu?

Gram #Atoms Conversions

How many atoms are in 54.21 g potassium?

• 54.21 g K 1 mole K 6.022 x 1023 atoms K

1 39.098g K 1 mole K

• = 8.350 x 1023 atoms K

How many grams are in 5.75 x 1021 atoms of Mg?

• 5.75 x 1021 atoms 1 mole 24.305 g

1 6.022 x 1023 atoms 1 mole

• 0.232 grams Mg

Beaker Breaker

• How many grams are there in 780atoms of nickel?

• MOLE definition movie D:\data\0030665841\student\ch07\sec03\qc02\hc207_03_q02fs.htm