Mr. Ramos
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Chemistry is the study of matter, and matter is the stuff things are
made of.
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Matter is anything that takes up space and has mass.
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All matter is composed of small particles known as atoms.
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Chemistry is known as the central science
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Chemistry has been divided into 5 branches
◦ Organic Chemistry is the study of all substances
that contain carbon.
◦ Inorganic Chemistry is the study of substances
that do not contain carbon.
◦ Analytical Chemistry is concerned with error and
precision, separation, identification, and quantification
of substances.
◦ Physical Chemistry is concerned with theories & experiments that describe
the behavior of chemicals. In other words, it is the physics of chemicals
and reactions.
◦ Biochemistry is the study of the chemistry of living organisms.
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SI Units, also known as System of International Units, are
used by scientists all over the words to make conversions
easier.
In chemistry we use grams for mass instead of kilograms
since we deal with very small quantities.
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There is error associated with every measurement.
Accuracy is a measure of how close a measurement comes to
the actual or true value. Keep in mind there is no way to
measure the “true” value of anything.
Precision is a measure of how close a series of measurements
are to one another; you may be precise but not accurate.
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Suppose you want to measure the boiling point of water with
a thermometer and the thermometer reads 99.1°C, but you
know that water’s boiling point is actually 100°C.
100°C, is the accepted value. An accepted value is the correct
value based on reliable references. This is also known as the
theoretical value.
99.1°C is the experimental value. This is the value measured
in the lab.
Error = experimental value – accepted value
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Suppose you estimate a temperature that lies
between 23°C and 24°C to be 24.3°C. This
estimated number has 3 digits.
The first two digits (2 & 4) are known with certainty, but the
rightmost digit has been estimated and involves some
uncertainty.
Significant figures in a measurement include all of the digits
that are known, plus a last digit that is estimated.
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1. Every nonzero digit is significant
◦ 24.7, 0.743, and 714 each have 3 sig figs
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2. Zeros between nonzero digits are significant
◦ 7003, 40.79, and 1.503 each have 4 sig figs
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3. Leftmost zeros appearing in front of nonzero digits
are not significant
◦ 0.0071, 0.42, and 0.000099 all have 2 sig figs
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4. Zeros at the end of a number and to the right of a
decimal are always significant
◦ 43.00, 1.010, and 9.000 each have 4 sig figs
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5. Zeros at the rightmost end of a measurement that
does not bare a decimal point are not significant;
however they are ambiguous.
◦ 300, 7000, and 10,000 all have 1 sig fig
◦ If written in scientific notation, more than 1 sig fig may
apply. These numbers are ambiguous
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6. Unlimited sig figs exist in two situations:
◦ Counting: 23 people in the class (this is an exact
measurement)
◦ Exactly defined quantities: 1hour = 60 minutes
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5.12500
0.0204
5.20x1013
5.0x10-3
1 ft = 12 inches
300
0.600
0.3056
0.002
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Scientific notation is a way of writing numbers that are too
big or too small to be conveniently written in decimal form.
Imagine having to write and read a number this this big:
60221.000
To write a number in scientific notation, place a decimal
between the first two digits of that number. The first digit
cannot be a zero. Then, place a x 10n.
60221.000 becomes 6.0221 x 104
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89600000
0.0056
90.80
70000
0.6080
5.26
23.5
34.65 x 102
0.065 x 103
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In multiplication or division, the solution carries
the same number of significant figures as the
factor with the fewest significant figures
5.02 x 89.665 x 0.10 = 45.0118 = 45
(3 sig figs)
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(5 sig figs)
(2 sig figs)
(2 sig figs)
The intermediate result (in blue) is rounded to two
sig figs to reflect the least precisely known number
(0.10), which has two sig figs.
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In addition or subtraction, the result carries the same number
of decimal places as the quantity carrying the fewest decimal
places.
It is sometimes helpful to draw a vertical line directly to the
right of the number with the fewest decimal places. The line
shows the number of decimal places that should be in the
answer.
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In calculations involving both multiplication/division and
addition/subtraction, do the steps in parentheses first.
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Determine the number of significant figures in the
intermediate answer; then do the remaining steps.
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3.489 x (5.67 – 2.3) Do not round until the very end
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3.489 x 3.37 A line is placed underneath the number to
(4 sig figs) (2 sig figs)
remind us that we should stop counting
sig figs at that point
11.758 will then need to be rounded to two sig figs because
of the multiplication rule = 12
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6.78 x 5.903 x (5.489 – 5.01)
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19.667 – (5.4 x 0.916)
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The first letter of all elements in the periodic table is
capitalized.
◦ Some elements contain only 1 letter
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H = hydrogen
K = potassium
C = carbon
O = oxygen
◦ Some elements contain 2 letters,
but the second letter is NOT
capitalized.
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Li = lithium
Na = sodium
Ca = calcium
He = helium
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C6H12O6
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6CO2
◦ The subscripts “6”, “12”, and “6” tell us how many atoms of
each element is in the compound.
◦ This compound contains 6 carbon atoms, 12 hydrogen atoms,
and 6 oxygen atoms
◦ The coefficient “6” tells us that there are 6 molecules of the
compound CO2.
◦ Multiply the coefficient “6” by the amount of each atom to
determine the total atoms.
 6 x 1 carbon = 6 carbons
 6 x 2 oxygen = 12 oxygen
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Ca(OH)2
◦ The subscript “2” belongs to the polyatomic anion “OH.”
Therefore, we place the “OH” in parentheses to separate it from
“Ca.”
◦ This molecule has 1 Ca atom and 2 OH atoms.
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C6H12O6
◦ Carbon’s weight is “12.01” on the periodic table
◦ Hydrogen’s weight is “1.01” on the periodic table
◦ Oxygen’s weight is “16.00” on the periodic table
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To find the molecular mass of the molecule
above, multiply the weight of each atom by the
number of atoms and add them all up.
◦ 6 Carbon x 12 grams = 72 grams of Carbon
◦ 12 Hydrogen x 1.01 grams = 12.12 grams of Hydrogen
◦ 6 Oxygen x 16.00 grams = 96 grams of Oxygen
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72g C + 12.12g H + 96 g O = 180.1 g/mol of C6H12O6
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CO2
Ca(OH)2
NaCl
H2O
H2SO4
H2O2
Na2CO3
CH4
C2H5OH
CsOH