Mullis 1

Atomic Model Review(Match Theory to Scientist)

1. Atoms are solid spheres.2. Electrons move around

the nucleus in specific levels.

3. Protons are concentrated in the center.

4. Electrons move in ever-changing paths within certain energy levels.

5. Electrons are stuck in the atom’s surface.

A. Thomson

B. Dalton

C. Bohr

D. Rutherford

E. Electron cloud model

Mullis 2

• Atomic Number – Number of protons or electrons in an element– Identifies the element

• Atomic Mass– Nucleus contains most of the mass of an atom.– Protons and neutrons are each ~ 1.67 x 10-24 g.– Electrons are each ~ 9.11 x 10-28 g.– Use atomic mass unit (amu) instead of gram.– The mass of one proton is ~ 1 amu.

• Mass Number– The sum of the number of protons and number of neutrons in the nucleus– Is approximately equal to the average atomic mass shown on periodic table.– Number of neutrons = mass number – atomic number

Mullis 3

• Isotopes– Atoms of the same element with different numbers of

neutrons– Have the same number of protons– Example: Carbon-12 and Carbon-14

• Radioactive Isotopes– Unstable in nature – Can be used to date fossils and rocks– The time it takes for half of the radioactive atoms in a piece

of the fossil to change to another element is its half-life.

Mullis 4

Radioactive Isotopes

If 25% of the atoms in a rock are uranium-238, how old is the rock?• 50% changed to lead-206 in 4.510 x 109 yrs• 50% of remaining changed to lead-206 in 4.510 x 109 yrs• Total is 75% changed in 9.020 x 109 yrs• Age of rock is ~ 9,020 million years

Radioactive Element Changes to this radioactive element

Half-life

uranium-238 lead-206 4510 million years

potassium-40 argon-40, calcium-40 1350 million years

rubidium-87 strontium-87 50,000 years

carbon-14 nitrogen-14 5,730 years

Mullis 5

The Atom: Idea to Theory

• Democritus (~ 400 BC) called nature’s basic particle an atom

• Atom comes from Greek word meaning “indivisible”

• 1808: Dalton proposed a theory with several statements which were later verified, but his “model” of an atom was that of a sphere.

Mullis 6

Dalton’s Atomic Theory

1. All matter is composed of extremely small particles called atoms.

2. Atoms of a given element are identical in size, mass and other properties.

3. Atoms cannot be divided, created or destroyed.4. Atoms of different elements combine in simple

whole-number ratios to form chemical compounds.

5. In chemical reactions, atoms are combined, separated or rearranged.

Mullis 7

Modern Atomic Theory

• Democritus = Idea about an atom• Dalton = Scientific theory which could be tested

• Dalton’s concepts which have “held true:”– All matter is composed of atoms

– Atoms of any one element differ in properties from atoms of another element

Mullis 8

• Law of Conservation of Mass : Mass is neither created nor destroyed during ordinary physical or chemical changes.

•Law of Definite Proportions:

A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample.

•Law of Multiple Proportions:

If two or more different compounds are made of the same two elements, then the ratio of the masses of the 2nd element combined with a certain mass of the 1st element is always a ratio of small whole numbers.

Mullis 9

The Mole

• A mole is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12.

• A mole is the SI unit for the amount of a substance.

Mullis 10

Avogadro’s Number

• This is the number of particles in one mole.

• Avogadro was an Italian scientist who explained the relationship between mass and number of atoms.

• 12.0 g of carbon-12 contains 6.022 1367 x 1023 carbon-12 atoms.

Avogadro’s number is rounded to 6.022 x 1023

Mullis 11

Molar mass

• The mass of one mole of a pure substance• Units = __g_

mol

Molar mass of an element = atomic mass of the element in amu.

Molar mass of Al is 26.98 g/mol

Mullis 12

Relationship between mass, moles and molecules in a compound

Mass(g)

Amount(moles)

# moleculesor

Formula units

X molar mass

(__g__ mole)

X 6.022 x 1023

(units mole)

Grams moles = moles gram

moles units = units or molecules mole

moles grams = grams mole

Mullis 13

Molar mass• Molar mass of a substance = mass in grams of one

mole of the substance.• A compound’s molar mass is NUMERICALLY equal to its

formula mass.2 mol H x 1.01 g H = 2.02 g H

1 mol H1 mol O x 16.00 g O = 16.00 g O

1 mol O molar mass H2O =18.02 g/mol

• Formula mass H2O = 18.02 amu• Molar mass H2O = 18.02 g/mol

Mullis 14

Molar Mass Example

What is the molar mass of K2SO4?2 mol K x 39.10 g K = 78.20 g K

1 mol K1 mol S x 32.10 g S = 32.07 g S

1 mol S4 mol O x 16.00 g O = 64.00 g O

1 mol Omolar mass K2SO4 =

174.27 g/mol

How many moles of each element are present in this compound?

2 mol K, 1 mol S, 4 mol O

Mullis 15

What is the molar mass of C6H12O6?6 mol C x 12.01 g C = 72.06 g C

1 mol C12 mol H x 1.01 g H = 12.12 g H

1 mol H6 mol O x 16.00 g O = 96.00 g O

1 mol Omolar mass C6H12O6 =

180.18 g/mol

How many moles of each element are present in this compound?

6 mol C, 12 mol H, 6 mol O

Mullis 16

Converting to grams from molesHow many moles of glucose are in 4.15x10-3 g C6H12O6?

4.15x10-3 g x 1 mol C6H12O6 = 2.30 x 10-5 mol C6H12O6

180.18 g

How many molecules of glucose are in 4.15x10-3 g C6H12O6?

2.30 x 10-5 mol C6H12O6 x 6.022 x 10 23 molecules =1 mol

(2.30 x 6.022)(10(-5+23)) = 13.90 x 10 –18 molecules = 1.39 x 10 –19 molecules

Mullis 17

What is the mass in grams of 6.25 moles copper (II) nitrate?

Cu 2+ NO3 - : formula is Cu(NO3)2

Find molar mass of Cu(NO3)2 first.1 mol Cu x 63.55 g Cu = 63.55 g Cu

1 mol Cu2 mol N x 14.01 g N = 28.02 g N

1 mol N6 mol O x 16.00 g O = 96.00 g O

1 mol O

molar mass Cu(NO3)2 = 187.57 g/molNow find mass in grams of 6.25 moles:

6.25 moles x 187.57 g = 1172 g Ans. 1170 g Cu(NO3)2 1 mol