General Chemistry Notes

1. Review on Principles
of Chemistry
Adamson University Chemical
Society
Presentation by:
Rovic Elli, 4th Year Chemistry
January 03, 2022
REFRESH

2. PG. 03
Significant Figures
Review Outline AUCS' REFRESH
Quantum Numbers and
Electron Configuration
Lewis Structure and VESPR
Stoichiometry
Concentrations
1
2
3
4
5

3. PG. 03
AUCS' REFRESH
Significant Figures
Rules
1. Nonzero digits are always significant.
2. Any zeros between two nonzero digits
are significant.
3. Zeros to the left of the first nonzero digit
are NOT significant.
4. If the number is greater than 1, all zeros
written to the right of the decimal point
are significant.
5. For numbers that do not contain
decimal points, the trailing zeros may or
may not be significant.

4. PG. 03
AUCS' REFRESH
Significant Figures
1. Addition and Subtraction
Round off the final answer to the lowest
decimal placement from the given.
2. Multiplication and Division
The final answer must have the same
number of significant digits as the given
with the smallest number of significant
figures.
Calculation Rules

5. PG. 03
AUCS' REFRESH
Quantum Numbers
Principal Quantum Number (n)
Angular Momentum (l)
Magnetic Quantum Number (ml)
Electron Spin (ms)
Quantum Numbers describe the
distribution of electrons in hydrogen and
other atoms. These are used to describe
and label electrons that reside in those
atoms.
Principal Quantum Number (n)
determines the energy of an orbital. It also
relates to the average distance of the
electron from the nucleus in a particular
orbital.
n = 1, 2, 3, 4.....

6. PG. 03
AUCS' REFRESH
Quantum Numbers
Angular Momentum (l) determines the
shape of the orbitals.
l = 0 to n - 1
Orbitals:
l = 0 = s
l = 1 = p
l = 2 = d
l = 3 = f

7. PG. 03
AUCS' REFRESH
Quantum Numbers
Magnetic Quantum Number (ml)
describes the orientation of the orbital in
space.
ml = 2l + 1

8. PG. 03
AUCS' REFRESH
Quantum Numbers
Electron Spin Quantum Number (ms)
describes the two possible spinning
motion of an electron, one clockwise and
one counter clockwise.
ml = + 1/2, -1/2

9. PG. 03
AUCS' REFRESH
Electron Configuration
Electron Configuration describes how
electrons are distributed among the
various atomic orbitals.
s - 2 electrons
p - 6 electrons
d - 10 electrons
f - 14 electrons
Example:
H - 1s1
O - 1s2 2s2 2p4

10. PG. 03
AUCS' REFRESH
Electron Configuration
A noble gas configuration of an atom
consists of the elemental symbol of the
last noble gas prior to that atom, followed
by the configuration of the remaining
electrons.
Example:
He - 1s2
O - [He] 2s2 2p4
Ne - 1s2 2s2 2p6
Mg - [Ne] 3s2

11. PG. 03
AUCS' REFRESH
Lewis Structure
The Lewis dot symbol consists of the
symbol of an element and one dot for each
valence electron in an atom of the
element.
Lewis structure is the simplified
representation of the valence shell
electrons in a molecule.

12. PG. 03
AUCS' REFRESH
VSEPR
The valence shell electron pair
repulsion (VSEPR) theory is a model used
to predict 3-D molecular geometry based
on the number of valence shell electron
bond pairs among the atoms in a molecule
or ion. This model assumes that electron
pairs will arrange themselves to minimize
repulsion effects from one another.

13. PG. 03
AUCS' REFRESH
Molecular vs Electronic
Geometry
Molecular Geometry
The arrangement of atoms in a molecule,
usually relative to a single central atom, is
known as molecular geometry.
It excludes lone pairs from determining a
molecule’s shape, though repulsion from
lone pair(s) is taken into account only in
bond angles.
Number of bonding pairs are only
calculated.
Electronic Geometry
The arrangement of electron pairs around
a central atom is known as electron
geometry.
In determining the shape, it takes into
account the presence of both bond pair(s)
and lone pair(s) of electrons.
Number of total electron pairs are
calculated.

14. PG. 03
AUCS' REFRESH
Molecular vs Electronic
Geometry

15. PG. 03
AUCS' REFRESH
Stoichiometry
Empirical vs Molecular Formula
Empirical formula tells the simplest or
most reduced ratio of
elements in a compound.
Molecular formula is the actual formula
of a molecule; tells how many
atoms of each element are in a molecule.

16. PG. 03
AUCS' REFRESH
Stoichiometry
Suppose that in one experiment the
combustion of 11.5 g of ethanol produced
22.0 g of CO2 and 13.5 g of H2O.
Calculate the empirical formula of
ethanol.

17. PG. 03
AUCS' REFRESH
Stoichiometry
A sample of a compound contains 1.52 g of
nitrogen (N) and 3.47 g of oxygen (O).
The molar mass of this compound is
between 90 g and 95 g. Determine the
molecular formula.

18. PG. 03
AUCS' REFRESH
Stoichiometry
A sample of a compound containing boron
(B) and hydrogen (H) contains 6.444 g of
B and 1.803 g of H. The molar mass of the
compound is about 30 g. What is its
molecular formula?

19. PG. 03
AUCS' REFRESH
Stoichiometry
Limiting and Excess Reagents
Limiting reagents are the reactants that
are used up first in a reaction.
Excess reagents are the reactants present
in quantities greater than the necessary to
react with the quantity of the limiting
reagent.
Let's consider the the industrial synthesis
of methanol from carbon monoxide and
hydrogen at high temperatures:
Suppose initially we have 4 moles of CO
and 6 moles of H2.

20. PG. 03
AUCS' REFRESH
Stoichiometry
Urea [(NH2)2CO] is prepared by reacting
ammonia with carbon dioxide:
In one process, 637.2 g of NH3 are treated
with 1142 g of CO2 .
(a) Which of the two reactants is the
limiting reagent?
(b) Calculate the mass of (NH2)2CO
formed.
(c) How much excess reagent (in grams) is
left at the end of the reaction?

21. The reaction between aluminum and
iron(III) oxide can generate temperatures
approaching 3000'C and is used in
welding metals:
PG. 03
AUCS' REFRESH
Stoichiometry
In one process, 124 g of Al are reacted with
601 g of Fe2O3.
(a) Calculate the mass (in grams) of Al2O3
formed.
(b) How much of the excess reagent is left
at the end of the reaction?

22. The percent yield is the proportion of the
actual yield to the theoretical yield. This
determine how efficient a given reaction
is.
PG. 03
AUCS' REFRESH
% Yield

23. Titanium is a strong, lightweight,
corrosion-resistant metal that is used in
rockets, aircraft, jet engines, and bicycle
frames. It is prepared by the reaction of
titanium(IV) chloride with molten
magnesium between 950'C and 1150'C:
PG. 03
AUCS' REFRESH
% Yield
In a certain industrial operation 3.54x10^7
g of TiCl4 are reacted with 1.13x10^7 g of
Mg.
(a) Calculate the theoretical yield of Ti in
grams.
(b) Calculate the percent yield if 7.91x10^6
g of Ti are actually obtained.

24. The concentration of a solution is the
amount of solute present in a given
amount of solvent, or a given amount of
solution.
1. %w/w = (mass of solute/mass of
solution) x100
2. Molarity (M) = moles of solute/L of
solution
3. Molality (m) = moles of solute/ mass
(in kg) of solvent
PG. 03
AUCS' REFRESH
Concentration Units

25. How many grams of potassium
dichromate (K2Cr2O7) are required to
prepare a 250-mL solution whose
concentration is 2.16 M ?
PG. 03
AUCS' REFRESH
Concentration Units

26. In a biochemical assay, a chemist needs to
add 3.81 g of glucose to a reaction mixture.
Calculate the volume in milliliters of a 2.53
M glucose solution she should use for the
addition.
PG. 03
AUCS' REFRESH
Concentration Units

27. A concentrated solution of aqueous
ammonia is 28.0%w/w NH3 and has a
density of 0.899 g/mL. What is the
concentration, in M, of NH3 in this
solution?
PG. 03
AUCS' REFRESH
Concentration Units

28. 200.0 grams of a 15.0% (w/w)
hydrochloric acid solution will contain
what mass of acid?
PG. 03
AUCS' REFRESH
Concentration Units

29. Calculate the molality of 12.5% w/w
sulfuric acid?
PG. 03
AUCS' REFRESH
Concentration Units

30. THANK YOU!