Lecture 2
General Chemistry Review
LEARNING OBJECTIVES = “topics covered on the exam”
•The structure of the atom, the main features of the subatomic particles, and the importance of
isotopes in determining atomic mass.
•The format of the periodic table and general location and characteristics of metals, metalloids,
and nonmetals.
•The essential features of ionic and covalent compounds and the distinction between them.
•The definition of a mole unit.
•The relationship between amount of substance (mol), mass (g), and number of chemical
entities.
•Mole-mass-number information in a chemical formula.
1
With many slides from Suzanne Bart….
General Chemistry Review
2
What is the stuff things are made of?
Page 57, your book
https://www.moneycontrol.com/news/trends/travel-trends......
Gold is made of atoms with p⁺, n⁰, e⁻.
Cotton towels are also made of atoms with p⁺, n⁰, e⁻.
Can you turn cotton towels into gold?
Atoms cannot be created or destroyed.
Law of Conservation of Mass
Know how to use the Periodic Table
Also know how to use this one !
Do not get confused by different names for
the same thing!
Page 57, your book
Might be on exams…
Inside cover, your book
The atomic number is the smaller one, the atomic mass number is the larger one.
Ionic vs. Covalent Compounds
Ionic Compounds
Often metal + non-metal
Crystalline solids (made of ions)
High melting and boiling points
Conduct electricity when melted
Many soluble in water but not in nonpolar liquid
Covalent Compounds
Often non-metal + non-metal
Gases, liquids, or solids (made of molecules)
Low melting and boiling points
Poor electrical conductors in all phases
Many soluble in nonpolar liquids but not in water
Need more help! Look for my handwritten notes posted on blackboard.
Practice – Ionic vs. Covalent Compounds
1. NaBr
2. BF3
3. CO
4. Li2S
5. P2Br4
6. MgBr2
7. Be(OH)2
8. SF6
9. NH3
10. SO3
11. N2S
12. CaO
13. PH3
14. SiO2
15. NO2
sodium bromide
boron trifluoride
carbon monoxide
lithium sulfide
diphosphorus tetrabromide
magnesium bromide
beryllium hydroxide
sulfur hexafluoride
ammonia
sulfur trioxide
dinitrogen sulfide
calcium oxide
phosphorus trihydride
silicon dioxide
nitrogen dioxide
Covalent Compounds: Molecules
Ionic Compounds and Polyatomic Ions
Isotopes and how to determine atomic mass
Page 57, your book
Sample Problem
Calculate the atomic mass of silicon given the following data:
Isotope
Abundance
Mass
Silicon - 28
92.2297%
27.9769 amu
Silicon - 29
4.6832%
28.9765 amu
Silicon - 30
3.0872%
29.9738 amu
Ans. 28.085 amu
What do you with this question?
The mass of 3He is:
a) the same as 3H
b) slightly less than that of 2 hydrogen atoms and 1 neutron
c) slightly more than that of 2 hydrogen atoms and 1 neutron
d) equal to that of 2 hydrogen atoms and 1 neutron
What do you with this question?
The mass of 3He is:
a) the same as 3H
Correct!
b) slightly less than that of 2 hydrogen atoms and 1 neutron 42% of students chose this answer
c) slightly more than that of 2 hydrogen atoms and 1 neutron 24% of students chose this answer
d) equal to that of 2 hydrogen atoms and 1 neutron 24% of students chose this answer
What were you thinking?
Is this question about mass and isotopes?
Yes, but also about nuclear chemistry…
Terminology
• Atomic mass number refers to the number of
p⁺ and n⁰ in an atom
• Molecular mass refers to the average mass of
a molecule.
• Molar mass refers to the mass per mole of
substance.
Sample Problem #1
Your text lists the following atomic masses:
Al 26.982
Br 79.904
 Calculate the molecular mass of
aluminum tribromide (AlBr3).
Ionic or covalent?
Sample Problem #1
AlBr3:
1 Al = 26.982 x 1 = 26.982
3 Br = 79.904 x 3 = 239.71
Total = 266.69
Molecular Mass
• Answer to Sample #1: 266.69
• What does this number refer to? Units!
• Unit of molecular mass:
“amu” = atomic mass units
• 1 amu = 1.661 x 10-24 g
• 1 molecule of AlBr3 = 266.69 amu
Molecular Mass and Molar Mass
Amu’s aren’t really a convenient unit to talk about…
That is Avogadro’s number
1 mole of things = 6.022 x 1023 of those things
(“things” can be atoms, molecules, or eggs…)
Relating amu, g, and moles for AlBr3
1 H atom weighs 1.008 amu = 1.677 x 10-24 g
1 mol of H atoms weighs 1.008 g
(1.677 x 10-24 g) x (6.022 x 1023/mol) = 1.008 g/mol
1 mol of AlBr3 weighs 266.69 g
*Remember: 1 molecule of AlBr3 = 266.69 amu*
Still don’t get it? Look for my handwritten notes posted on blackboard.
More on Moles and Atoms
• How many moles of sodium (Na) atoms
correspond to 1.56 x 1021 atoms of sodium?
Answer:
1.56 x 1021 atoms (1 mole / 6.02 x 1023 atoms) =
2.59 x 10-3 moles Na
• How many grams of sodium is that?
Answer:
2.59 x 10-3 moles (23.0 g /1 mole) = 0.0595 g Na
Sample Problem #2
How many pounds does 1 mole of coffee beans
weigh? (Assume each bean weighs 2 grams)
Answer to Sample Problem #2
1. 1 mol coffee beans x (6.022 x 1023 / mol) =
6.022 x 1023 coffee beans
2. 6.022 x 1023 coffee beans x (2 g / 1 coffee bean) =
1.024 x 1024 g coffee beans
3. 1.024 x 1024 g coffee beans x (1 lb / 454 g) =
2.653 x 1021 lb coffee beans
Wake Up!
Practice – Calculating Molecular Weight
Paclitaxel or Taxol (from the Pacific Yew tree)
Chemotherapy medication and anti-cancer drug
Chemical Formula: C47H51NO14
Calculate the molecular weight of Paclitaxel.
Ans. =
Pacific Yew tree
If you got this right, skip the next slide, if you got this wrong, practice more.
Practice – Calculating Molecular Weight
Catechol
(argan oil, fruit)
C6H6O2
3,4-Dihydroxy-Benzoic Acid
(acai oil, hibiscus) C7H6O4
Vanillin
(Vanilla plant)
C8H8O3
Gallic Acid
(oak, algae, fruit)
C7H6O5
(+) Catechin Hydrate
(apple, tea) C15H14O6 · H2O
Caffeic Acid
(coffee, spearmint)
C9H8O4
3,4-Dihydroxy Benzaldehyde
(mushrooms, cork oak)
C7H6O3
Juglone
(walnut)
C10H6O3
Quercetin
(fruit, vegetables) C15H10O7
Mass Conservation Again…
• Law of Conservation of Mass
– Atoms cannot be created or destroyed
– In chemical reactions, atoms of one element
cannot be converted in atoms of another element
4 H atoms, 4 O atoms and 1 C atom are present before and after the reaction.
The total mass before and after the reaction remains the same.
The total mass before and after the reaction
remains the same!
When the following equation is balanced, what
will be the Al(NO3)3 : Al2S3 mole ratio?
Al(NO3)3 + Na2S → Al2S3 + NaNO3
A.1:1
B.3:2
C.1:2
D.2:3
E.2:1
If you get this wrong, go to the next slide.
TEST DRIVE Mock Exam
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• 60-minute, timed practice exam
• Mon. Sept. 9 at 8:00 PM
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