Elements and Measurements. Chemistry and the Elements.
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Transcript of Elements and Measurements. Chemistry and the Elements.
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Elements and Measurements
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Periods: 7 horizontal rows.
Groups: 18 vertical columns.International standard: 1-18US system: 1A-8A, 1B-8B
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Metals: Left side of the zigzag line in the periodic table (except for hydrogen).
Nonmetals: Right side of the zigzag line in the periodic table.
Semimetals (metalloids): Tend to lie along the zigzag line in the periodic table.
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Alkali Metals
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Some Chemical Properties of the Elements
Intensive Properties: Independent of sample size.temperaturemelting point
Extensive Properties: Dependent on sample size.lengthvolume
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Some Chemical Properties of the Elements
Physical Properties: Characteristics that do not involve a change in a sample’s chemical makeup.
Chemical Properties: Characteristics that do involve a change in a sample’s chemical makeup.
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Experimentation and Measurement
All other units are derived from these fundamental units
Système Internationale d´Unités
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Measuring MassMass: Amount of matter in an object.
Matter: Describes anything with a physical presence—anything you can touch, taste, or smell.
Weight: Measures the force with which gravity pulls on an object.
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K = °C + 273.15
TF = 1.8 TC + 32
TC = (TF – 32)
1.8
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density =volume
mass
solids- cm3
liquids- mLgases- L
Typical volume units
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Accuracy, Precision, and Significant Figures
Accuracy: How close to the true value a given measurement is.Single measurement: percent errorSeries of measurements: average
Precision: How well a number of independent measurements agree with each other. Characterized by the standard deviation.
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good accuracygood precision
Mass of a Tennis Ball
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Accuracy, Precision, and Significant Figures
Significant figures: The number of meaningful digits in a measured or calculated quantity. They come from uncertainty in any measurement.
Generally the last digit in a reported measurement is uncertain (estimated).
Exact numbers and relationships (7 days in a week, 30 students in a class, etc.) effectively have an infinite number of significant figures.
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length = 1.74 cm
0 1 2 43cm
1.7 cm < length < 1.8 cm
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What is the reading on the graduated cylinder?
Accuracy, Precision, and Significant Figures
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Accuracy, Precision, and Significant Figures
Rules for counting significant figures (left-to-right):
1. Zeros in the middle of a number are like any other digit; they are always significant.
4.803 cm 4 sf
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Accuracy, Precision, and Significant Figures
Rules for counting significant figures (left-to-right):
Zeros in the middle of a number are like any other digit; they are always significant.
Zero at the beginning of a number are not significant (placeholders).
0.00661 g 3 sf or 6.61 x 10-3 g
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Accuracy, Precision, and Significant Figures
Rules for counting significant figures (left-to-right):
Zeros in the middle of a number are like any other digit; they are always significant.
Zeros at the beginning of a number are not significant (placeholders).
Zeros at the end of a number and after the decimal point are always significant.55.220 K 5 sf
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Accuracy, Precision, and Significant Figures Zeros in the middle of a number are like any
other digit; they are always significant.
Zeros at the beginning of a number are not significant (placeholders).
Zeros at the end of a number and after the decimal point are always significant.
Zeros at the end of a number and after the decimal point may or may not be significant.
34,2000 ? SF
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Rounding NumbersMath rules for keeping track of significant
figures:• Multiplication or division: The answer
can’t have more significant figures than any of the original numbers.
11.70 gal
278 mi= 23.8 mi/gal
4 SF
3 SF
3 SF
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Rounding NumbersMultiplication or division: The answer
can’t have more significant figures than any of the original numbers.
Addition or subtraction: The answer can’t have more digits to the right of the decimal point than any of the original numbers.
3.19+ 0.01315
3.18 2 decimal places
5 decimal places
2 decimal places
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Rounding Numbers Rules for rounding off numbers:
1. If the first digit you remove is less than 5, round down by dropping it and all following numbers.
5.664 525 = 5.66 2. If the first digit you remove is 6 or
greater, round up by adding 1 to the digit on the left.
5.664 525 = 5.7
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Rounding Numbers3. If the first digit you remove is 5 and there
are more nonzero digits following, round up.
5.664 525 = 5.665
4. If the digit you remove is a 5 with nothing following, round down. 5.664 525 = 5.664 52
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Calculations: Converting from One Unit to AnotherDimensional analysis: A method that
uses a conversion factor to convert a quantity expressed in one unit to an equivalent quantity in a different unit.
Conversion factor: States the relationship between two different units.
original quantity x conversion factor = equivalent quantity
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1 m = 39.37 in
Conversion factor:
Equivalent:
1 m
39.37 inor
39.37 in
1 m
convertsm to in
convertsin to m
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39.37 in
1 m69.5 in = 1.77 mx
equivalent quantitystarting quantity
conversion factor
E.g Convert 69.5 in to m
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ExampleHow many centimeters are in 2.00 ft?
Convert 2.00 in2 to cm2
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ExamplesA group of students collected 125 empty aluminum cans to take to the recycling center. If 21 cans make 1.0 lb aluminum, how many liters of aluminum (D=2.70 g/cm3) are obtained from the cans?
34