Atomic Structure

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Atomic Structure
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Subatomic Particles(Particles that make up an
atom)
? Proton (p) - Positively charged - Found
in the nucleus - Large mass ? Neutron
(n0) - A neutral particle - Found in the
nucleus - Large mass ? Electron (e-) -
Negatively charged particle - Found outside of
the nucleus in the electron cloud - Very small
mass
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Summary
? The nucleus has almost all of the mass it
has a charge ? The electron cloud has a
charge creates the atoms volume
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How to read a box on the periodic table
11 Na 22.98
Atomic
Symbol
? Atomic Number - above symbol - Always
determines of protons (can never change!) -
Determines of electrons if atom is neutral (0
charge) - We assume the periodic table is
neutral (same of p e-) ? Summary -
Sodiums atomic number is 11 - Sodium has 11
protons 11 electrons
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11 Na 22.98
Average atomic mass
? Average atomic mass - below the symbol in
decimal form - The average mass of an atom -
Not all sodiums have the same mass due to
different number of neutrons (isotope)
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11 Na 22.98
Mass (23)
? Mass Number rounding the a.a.m. to a whole
number - Mass of protons number
of neutrons - Therefore, use to find number of
neutrons mass - of p of n ?
Summary - Nas ave. atomic mass 22.98 amu
(atomic mass units) - Nas mass 23 -
Number of neutrons in Na 23 11 12 neutrons
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You just have to try one!
Determine 1. Atomic 2. of protons
3. of electrons 4. Ave. atomic mass
5. Mass number 6. of neutrons
47 Ag 107.87
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Isotopes
? Atoms of the same element can have different
numbers of neutrons, therefore, different masses
- Remember, neutrons have mass! - Changing the
number of neutrons, changes the mass ? Lets
look at 2 isotopes of carbon as an example -
Carbon ALWAYS has 6 protons - But it can have a
mass of 12 amu (6p 6n) C or C-12 -
and it can have a mass of 14 amu (6p
8n) C or C-14
12
6
14
6
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Perfect practice makes perfect!
? Here is an isotope of oxygen O - How
many protons are present? __________ - What is
the mass number? __________ - How many neutrons
are present? __________ - How many electrons
are present? __________ ? Write the shorthand
form of a nitrogen isotope that has 13 neutrons.
_ N or N - __
18
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_
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Mole Conversions
? Moles (mol) are a unit of measurement ? 1
mole 6.02 x 1023 units (atoms, molecules,
formula units, ions, etc) ? 6.02 x 1023 is
Avogadros number ? Mole Conversions 1 mole
6.02 x 1023 units formula weight (grams)
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What is formula weight?
? Formula weight is the weight of an element or
compound in grams ? How is formula weight
determined? - Use your periodic table and find
the ave. atomic mass - Formula weight of H2O -
Hs ave. atomic mass 1.01 g (x 2) 2.02 g -
Os ave. atomic mass 16.00 g 2.02 g 16.00
g 18.02 g H2O
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What is the formula weight of

• Al
• Br2
• MgF2
• CH4
• Ca3(AsO4)2

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Conversions
1. Moles to grams of moles x formula
weight (g) _____ grams 1
1 mole ? Example How many grams are in 5.00
moles of CaCl2? Formula weight of CaCl2 ?
Ca 40.08 g Cl 35.45 g (x2) 70.90 g ?
40.08 g 70.90 g 110.98 g CaCl2 5.00
moles x 110.98 g CaCl2 554.9
1 1 mole
555 g CaCl2
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• Grams to moles
• of grams x ___1 mole _ _______
  moles 1 formula wt (g)
• ? Example How many moles are in 25.00 g of
  NaCl?
• 25.00 g of NaCl x _ 1 mole___ 1
  58.44 g NaCl

0.4278 moles of NaCl
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• Moles to units (atoms, molecules, formula units,
  ions, etc.)
• of moles x 6.02 x 1023 units ____
  units 1 1 mole
• ? Example How many atoms are in 0.250 moles
  of neon?
• 0.250 moles of Ne x 6.02 x 1023 atoms
  1 1 mole

1.51 x 1023 atoms of Ne
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4. Units to moles of units x ___1
mole____ ____ moles 1 6.02 x
1023 units ? Example How many moles are in
4.23 x 1024 molecules of H2O? 4.23 x
1024 molecules x ______1 mole______
1 6.02 x 1023 molecules
7.03 moles of H2O
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5. Grams to units of grams x 6.02 x
1023 units ____ units 1
formula wt (g) ? Example How many formula
units are in 35.0 g of K2O? 35.0 g K2O x
6.02 x 1023 formula units 1
94.20 g K2O
2.24 x 1023 formula units of K2O
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6. Units to grams of units x _formula
wt (g)_ ____ grams 1
6.02 x 1023 units ? Example How many grams
are in 9.75 x 1025 atoms of Ag? 9.75 x 1025
atoms x __107.87 g Ag__ 1 6.02 x
1023 atoms
17500 g Ag
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Mass Percent Composition
? Determining what percentage of each element is
in a specific formula ? Example Find the mass
of each element in NaHCO3. - Step 1 Find
their individual ave. atomic masses from the PT
multiply by the number of atoms of each
(subscript) Na 22.99 g (1) 22.99 g H
1.01 g (1) 1.01 g C 12.01 g (1) 12.01
g O 16.00 g (3) 48.00 g 84.01 g
NaHCO3 - Step 2 Add them to get the
total weight of the formula.
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• Step 3 Find the mass of each!
• Remember Na 22.99 g (1) 22.99 g
• H 1.01 g (1) 1.01 g
• C 12.01 g (1) 12.01 g
• O 16.00 g (3) 48.00 g
• 84.01 g of NaHCO3
• - Take the elements individual total weight and
  divide by the total weight of the formula.
  Then Multiply by 100.
• - Mass of Na 22.99g /84.01 (100) 27.36
• - Mass of H 1.01g /84.01 (100) 1.20
• - Mass of C 12.01g /84.01 (100) 14.30
• - Mass of O 48.00g /84.01 (100) 57.14
• - Add s to make sure they add up to 100

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Getting the formula from mass
? Do the opposite of finding the mass ?
Example What is the formula of a substance that
is made of 27.29 C 72.71 O. The
total weight of the substance is 44.01
g. - Step 1 Divide each by 100 then multiply
by the total weight C 27.29/100 0.2729
(44.01 g) 12.01 g C O 72.71/100 0.7271
(44.01 g) 32.00 g O - Step 2 Divide the
totals by their average atomic mass (from
PT) 12.01 g C/12.01 g C 1 32.00 g O/16.00 g
O 2 - Step 3 Put the formula together ?
CO2
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Finding the relative atomic mass
? Where does the periodic table get its average
atomic masses from? ? Heres an example There
are two isotopes of chlorine which consists of
atoms of relative isotopic masses 35.0 (75.0 )
and 37.0 (25.0 ). abundance
Isotope mass Cl-35 75.0 35.0
amu Cl-37 25.0 37.0 amu
(75.0/100) x 35.0 amu (25.0/100) x 37.0 amu

35.5 amu
The answer matches Cl on the periodic table!