Download UNIT 2 – ATOMIC THEORY AND STRUCTURE

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Name: _____________________________________________________
UNIT ____
ATOMIC THEORY AND STRUCTURE
Learning Target: Describe the various atomic models according to Dalton and Rutherford
in terms of the experimental evidence that led to their proposals.
John Dalton: was a Chemist who, in 1803, performed a number of
experiments that eventually led to the acceptance of the idea of atoms
Dalton’s Atomic Theory:
In the Textbook on page 104
 Matter is composed of extremely ____________ particles called ____________
 Atoms are ___________________ and ___________________ *(later proved wrong)
 Atoms of the same element are identical
*(later proved wrong)
 Atoms of a specific element are different from those of another element
 Atoms combine in simple ___________-_______________ ratios to form compounds
 In a chemical reaction atoms are _____________, _____________ or _____________
Ernest Rutherford:
In 1911 Rutherford conducted experiments in which a stream of tiny
positively charged particles were shot at a very thin sheet of gold foil
that was only a few atoms thick.
Like charges repel each other (+ pushes away other +)
Rutherford’s Gold Foil Experiment
gold
atom
expected
results
gold
atom
actual results
Most of the positively charged particles shot straight through the gold foil.
This showed Rutherford that atoms are mostly empty space.
A very small number of the positively charged particles were deflected at
odd angles.
This showed Rutherford there must be a tiny, dense, positively charged
mass in the center of an atom.
We now call this tiny, dense, positively-charged mass in the center of an
atom the nucleus.
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An atom is the smallest particle of an element that retains the properties of that element.
All atoms are electrically neutral; all atoms have a neutral overall charge.
Atoms are made up of three subatomic particles: protons, electrons and neutrons.
THE THREE SUBATOMIC PARTICLES
AN ATOM
proton
A positively charged subatomic particle located in the atom’s nucleus.
A proton has a charge of +1
A proton has a relative mass of 1 amu (atomic mass unit)
electron
A negatively charged subatomic particle that orbits around the atom’s nucleus in what is
known as the electron cloud.
An electron has a charge of -1
An electron has an extremely small mass (effectively a mass of zero)
neutron
A neutral subatomic particle located in the atom’s nucleus.
A neutron has no charge (0)
A neutron has a mass nearly equal to the mass of a proton (1 amu)
Subatomic Particle
Location
Proton
In the nucleus
Electron
Orbiting in the
electron cloud
Neutron
In the nucleus
Charge
Mass (amu)
All atoms have a neutral overall charge, this means a stable atom must have an equal
number of protons (+1 charge) and electrons (-1 charge)
All atoms of the same element have the same number of protons in their nucleus!
The number of protons in an atom is called its Atomic Number
Every element has its own atomic number
atomic number = number of protons = number of electrons
Hydrogen is
atomic number 1
1
H
Hydrogen
1.008
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DO THIS:
The atomic number of hydrogen (H) is 1.
How many protons does a hydrogen atom have? ______ How many electrons? ______
The atomic number of carbon (C) is 6.
How many protons does a carbon atom have? ______ How many electrons? ______
The atomic number of lead (Pb) is 82.
How many protons does a lead atom have? ______ How many electrons? ______
ISOTOPES:
Atoms of the same element can have different numbers of neutrons.
These are called isotopes.
Isotopes of an element have the same atomic number (the same number of protons).
Each isotope of an element has a different number of neutrons.
Isotope
Notation
Hydrogen, for example, has three isotopes (the number indicates mass in amu):
H
Hydrogen-1 has _______ proton and _______ neutrons
(a mass of 1 amu)
1
Hydrogen-2 has _______ proton and _______ neutron
(a mass of 2 amu)
1
Hydrogen-3 has _______ proton and _______ neutrons
(a mass of 3 amu)
1
H
H
The Mass Number is the total number of protons and neutrons in the nucleus of an atom.
Remember protons and neutrons both have a mass of 1 amu (they are nearly equal in mass).
The mass of an electron is zero.
Mass Number – total number of protons & neutrons
Chemical Symbol
Atomic Number – number of protons (which is equal to the number of electrons)
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The fictional element X as shown above has ____ protons, ____ neutrons and ____ electrons
The fictional element M shown above has ____ protons, ____ neutrons and ____ electrons
1
Atomic Number
Average Atomic Mass
H
Hydrogen
1.008
Chemical Symbol
Molar Mass
Average Atomic Mass: A “weighted” average of the masses of the isotopes of the element
Average atomic mass depends on the relative abundance (amount) of each isotope
Recall the three isotopes of Hydrogen from the previous page
Most of the Hydrogen that exists is Hydrogen-1 which has a mass number of 1
A small fraction of Hydrogen is Hydrogen-2 with a mass number of 2
A very tiny fraction of Hydrogen is Hydrogen-3 with a mass number of 3
Considering the relative amount of each isotope, the weighted average mass of all
Hydrogen is 1.008
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THE MOLE
1 mole = 6.02 x 1023 particles
Particles can be atoms
or molecules!
A mole is an amount containing 6.02 x 1023 particles of a substance.
Like a dozen is 12
Like a pair is 2
Like a gross is 144
6.02 x 1023 is called Avogadro’s Number
Avogadro’s Number
6.02 x 1023
The number of particles in one mole
of a substance
The mass of one mole of any substance is its molar mass.
Yes, it is the same as the average atomic mass!
What is the mass of 1 mole of hydrogen? (Look for H on the periodic table)
1 mole of Hydrogen has a mass of 1.008 g
Hydrogen’s molar mass is 1.008 g
What is the mass of 1 mole of carbon? (Look for C on the periodic table)
What is the mass of 1 mole of oxygen? (Look for O on the periodic table)
What is the mass of 1 mole of water (H2O)? (2 hydrogens + 1 oxygen)
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The mass in grams of one mole of a substance is its molar mass.
The substance CaF2 (calcium fluoride) contains one atom of Ca and two atoms of F
To determine the molar mass of CaF2, add up the molar masses of each atom (found on the
periodic table)
Ca: 1 x 40.078 = 40.078 g
F: 2 x 18.998 = 37.996 g
78.074 g molar mass of CaF2
H2O contains two H atoms and one O atom. Determine the molar mass of H2O.
H: 2 x
=
O: 1 x
= _________
molar mass of H2O
Al2(CO3)3 contains two atoms of Al, three atoms of C and nine atoms of O.
Al: 2 x 26.982 = 53.964 g
C: 3 x 12.011 = 36.033 g
O: 9 x 15.999 = 143.991 g
233.988 g molar mass of Al2(CO3)3
PAY
ATTENTION
you will be
asking me
how to do this
(then you will
tell me how
“mean” I am)
The number after
the parentheses
only applies to what
is inside the
parentheses!
Ca(OH)2 contains one Ca atom, two O atoms and two H atoms.
Ca: 1 x
=
O: 2 x
=
H: 2 x
=
molar mass of Ca(OH)2
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MOLE CONVERSIONS
UNIT
WANT
HAVE
A mole is 6.02 x 1023 atoms of an element.
A mole is 6.02 x 1023 molecules of a compound.
Atoms/Molecules
6.02 x 1023
Moles
periodic table
Grams (mass)
Atoms/Molecules to Moles or Moles to Atoms/Molecules
FACT:
1 mole = 6.02 x 1023 atoms/molecules
We can write this fact as a ratio (conversion factor):
1 mole
6.02 x 1023 particles
6.02 x 1023 particles
1 mole
we can also write the inverse
Always set up your conversion so that the units cross-cancel down and to the right!
Example: Convert 3.04 x 1022 atoms of carbon (C) to moles of carbon.
3.04 x 1022 atoms C
1 mole C
=
0.0505 moles C
6.02 x 1023 atoms C
You Try One: Convert 3.27 x 1017 atoms of sodium (Na) to moles of sodium.
=
8
Always set up your conversion so that the units cross-cancel down and to the right!
WANT
HAVE
Example A:
Convert 3.50 moles of carbon (C) to atoms of carbon.
3.50 moles C
6.02 x 1023 atoms C
=
2.11 x 1024 atoms C
1 mole C
You Try One: Convert 2.60 moles of water to molecules of water.
=
The mass of one mole of any substance is its molar mass.
We can find the molar mass of any element on the periodic table!
1
Atomic Number
The number of protons
H
Molar Mass
Hydrogen
1.008
The mass of one mole
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For example, the molar mass of hydrogen (H):
FACT: 1 mole of H = 1.008 g H (look on the Periodic Table)
We can write this fact as a ratio (conversion factor):
1 mole H
1.008 g H
we can also write the inverse
1.008 g H
1 mole H
or maybe, the molar mass of oxygen (O):
FACT: 1 mole of O = 15.999 g O (look on the Periodic Table, you are not looking, c’mon look)
We can write this fact as a ratio (conversion factor):
1 mole O
15.999 g O
we can also write the inverse
15.999 g O
1 mole O
how about, the molar mass of water (H2O):
FACT: 1 mole of H2O = 18.015 g H2O (look on the Periodic Table; 2 H’s + 1 O)
We can write this fact as a ratio (conversion factor):
1 mole H2O
18.015 g H2O
we can also write the inverse
18.015 g H2O
1 mole H2O
or even, the molar mass of hydrogen peroxide (H2O2):
FACT: 1 mole of H2O2 = 34.014 g H2O2 (look on the Periodic Table; 2 H’s + 2 O’s)
We can write this fact as a ratio (conversion factor):
1 mole H2O2
34.014 g H2O2
we can also write the inverse
34.014 g H2O2
1 mole H2O2
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Moles to Grams or Grams to Moles
Always set up your conversion so that the units cross-cancel down and to the right!
WANT
HAVE
Example: What is the mass in grams of 3.00 moles of neon, Ne?
3.00 moles Ne
20.180 g Ne
=
60.54 g Ne
1 mole Ne
Where does one find the
molar mass (the mass of one
mole) of Ne? _____________
You Try One: What is the mass in grams of 5.50 moles of gold, Au?
=
Where does one find the
molar mass (the mass of one
mole) of Au? _____________
Always set up your conversion so that the units cross-cancel down and to the right!
WANT
HAVE
Example: Convert 625 g of aluminum to moles of aluminum, Al?
625 g Al
1 mole Al
=
23.2 moles Al
26.982 g Al
You Try One: Convert 2.00 g of water to moles of water, H2O?
=
Where does one find the
molar mass (the mass of one
mole) of Al? _____________
Where does one find the
molar mass (the mass of one
mole) of H2O?
________________________
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_
Atoms/Molecules to Grams or Grams to Atoms/Molecules
For these conversions there will be two steps, that means you must use both kinds of conversion factors!
Oh no! How horrible!
We have two kinds of conversion factors:
1 mole = 6.02 x 1023 particles -and- The molar mass of a substance (from the periodic table)
Always set up your conversion so that the units cross-cancel down and to the right!
WANT
HAVE
Example A: What is the mass in grams of 3.00 x 1024 atoms of carbon, C?
3.00 x 1024 atoms C
1 mole C
12.011 g C
6.02 x 1023 atoms C
=
59.9 g C
1 mole C
Example B: How many molecules are in 3780 g H2O (1 gallon of water)?
3780 g H2O
1 mol H2O
18.0 g H2O
6.02 x 1023 molecules H2O
1 mol H2O
= 1.26 x 1026 molecules H2O
Try It: How many atoms of copper (Cu) are in a 25.5 g piece of copper wire?
Grams
periodic table
Moles
6.02 x 1023
Atoms
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Calculating the average atomic mass of an element
Given the isotopic mass and relative abundance
1. Multiply each isotopic mass by its relative abundance
2. Add the results together
3. Divide by 100 (move the decimal two places left)
Example - The fictional element L is found to have two naturally occurring isotopes:
L-285 has an isotopic mass of 285.03 amu and a relative abundance of 54.22%
L-288 has an isotopic mass of 287.97 amu and a relative abundance of 45.78%
To calculate the average atomic mass of the element L:
285.03(54.22) + 287.97(45.78) = 28638 / 100 = 286.38 amu
Another Example - The fictional element J is found to have three naturally occurring isotopes:
J-298 has an isotopic mass of 298.01 amu and a relative abundance of 15.53%
J-300 has an isotopic mass of 299.98 amu and a relative abundance of 33.35%
J-302 has an isotopic mass of 301.99 amu and a relative abundance of 51.12%
To calculate the average atomic mass of the element J:
298.01(15.53) + 299.98(33.35) + 301.99(51.12) = 30070 = 300.70 amu
Try one (no really, try one) – Silver (Ag) has two naturally occurring isotopes:
Ag-107 has an isotopic mass of 106.905 amu and a relative abundance of 52.00%
Ag-109 has an isotopic mass of 108.905 amu and a relative abundance of 48.00%
Calculate the average atomic mass of the element Silver (DO IT!).
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ISOTOPES: Atoms with the same number of protons, but different numbers of
neutrons in the nucleus.
Average Atomic Mass: A “weighted” average of the masses of the isotopes of the element
Determining which isotope of an element is the most
abundant based on average atomic mass:
Choose the isotope with the mass that is closest to the
average atomic mass
For example, Hydrogen has three isotopes:
1H
is Hydrogen-1 with a mass of 1 (1 proton, 0 neutrons)
2H
is Hydrogen-2 with a mass of 2 (1 proton, 1 neutron)
3H
is Hydrogen-3 with a mass of 3 (1 proton, 2 neutrons)
The average atomic mass of Hydrogen is 1.008 g/mol according to the periodic table
1.008 is closest to 1. Therefore, the most abundant isotope of Hydrogen is 1H
Magnesium has three naturally occurring isotopes, 24Mg, 25Mg, and 26Mg.
The average atomic mass of magnesium is 24.305 amu.
Which of the three isotopes of magnesium is most abundant?
Aluminum has only two naturally occurring isotopes, 26Al and 27Al.
Look for the average atomic mass of Al on the periodic table.
Which of the two isotopes of Aluminum is most abundant?
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