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Lecture 1

CHEM 1001 Lecture Notes - Lecture 1: Decimal Mark, Molar Mass, Significand


Department
Chemistry
Course Code
CHEM 1001
Professor
Bob Burk
Lecture
1

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Chemistry Topic 1
Measurements and Math in
Chemistry
Standard Notation (All values)
oThe standard notation includes actual numbers in its entirety.
The rest mass of an electron
0.000 000 000 000 000 000 000 000 000 000 910 9 kg
Exponential Notation
oConsidering standard deviation there are two components;
The significand (mantissa)
The non-zero portion
The exponent
The power of 10 by which you multiply the mantissa to give
the whole value
The speed of light
299 800 200 m/s
The significand: 2998
Exponent: 10^5 - Therefore the exponential notation is 2998 x 10^5
Scientific Notation
oThe significand must be >1 and <10
Only 1 digit before the decimal point but as many digits that are
required after the decimal point
oA positive exponent means the value is larger than the significand implies
(decimal jumps left)

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oA negative exponent means the value is smaller than the significand
implies (decimal jumps right)
0.000 239 = 2.39 x 10^-4  Number becomes smaller
239 0000 = 2.39 x 10^5  Number becomes larger
TRAILING ZEROS: Any zeros left behind the significand
2.99 800 000 x10^8 m/s becomes 2.998 x 10^8 m/s
The idea is to reduce all of the zeros after the significand.
The difference between the exponential and scientific notation is the placement of the
decimal point (scientific has only one digit before the decimal point).
SIGNIFICANT FIGURES: The amount of digits that are considered significant in a final
value. The number of digits that indicate precision of a measured value.
Rules for SIGFIG;
Indicate how precisely a value is measured
oPRECISION: Measure of how consistent (close) a series of measured
values are
oACCURATE: Measure of how close to the true value a series of
measured values are
Do not show accuracy
Only apply to measured values
Things to remember about SIGFIG;
All non-zero are significant
Any zeros between two SIGFIGS are significant (209 = 3 SF)
Leading zeros are not significant
Trailing zeros are significant or not depending on the placement of the decimal.
(The decimal must be present for these zeros to be significant)
21.895 = 5 2980 = 3
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0.001 244 = 4 2980. = 4
1001 = 4 6.00 = 3
3000 = 1
When rounding to SF in a completed calculation the result is different depending on the
type of calculation.
1. Multiplication and Division
Round to a number of SF equal to the input value with the fewest SF
( 24 )(8.314) = 0.021 149 386
(293)(32.2)
= 0.02
Round to the lowest number of SF
2. Addition and Subtraction
Round to the number of SF such that the lowest number of decimal places is
preserved.
112.2765 + 222.7= 334.9765 round to 1 decimal point
= 335.0
For addition and subtraction in scientific notation, all values should be converted
to all have the same exponential value, then the rule of decimal places applies.
If you make the exponent LARGER, the significand gets SMALLER
If you make the exponent SMALLER, the significand gets LARGER
3. Logarithmic
Rules;
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