Elements and Measurements

Periods: 7 horizontal rows.

Groups: 18 vertical columns.International standard: 1-18US system: 1A-8A, 1B-8B

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.

Alkali Metals

Some Chemical Properties of the Elements

Intensive Properties: Independent of sample size.temperaturemelting point

Extensive Properties: Dependent on sample size.lengthvolume

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.

Experimentation and Measurement

All other units are derived from these fundamental units

Système Internationale d´Unités

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.

K = °C + 273.15

TF = 1.8 TC + 32

TC = (TF – 32)

1.8

density =volume

mass

solids- cm3

liquids- mLgases- L

Typical volume units

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.

good accuracygood precision

Mass of a Tennis Ball

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.

length = 1.74 cm

0 1 2 43cm

1.7 cm < length < 1.8 cm

What is the reading on the graduated cylinder?

Accuracy, Precision, and Significant Figures

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

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

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

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

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

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

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

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

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

1 m = 39.37 in

Conversion factor:

Equivalent:

1 m

39.37 inor

39.37 in

1 m

convertsm to in

convertsin to m

39.37 in

1 m69.5 in = 1.77 mx

equivalent quantitystarting quantity

conversion factor

E.g Convert 69.5 in to m

ExampleHow many centimeters are in 2.00 ft?

Convert 2.00 in2 to cm2

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?

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