Elements and Measurements

Chemistry and the Elements

Periods: 7 horizontal rows. Groups: 18 vertical columns. International standard: 1-18 US system: 1A-8A, 1B-8B

Elements and the Periodic Table 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.

Elements and the Periodic Table Alkali Metals

Elements and the Periodic Table

Some Chemical Properties of the Elements Intensive Properties: Independent of sample size. temperature melting point Extensive Properties: Dependent on sample size. length volume

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 Mass Mass: 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.

Measuring Temperature K = °C T F = 1.8 T C + 32 T C = (T F – 32) 1.8

Derived Units: Measuring Volume

Derived Units: Measuring Density density = volume mass solids- cm 3 liquids- mL gases- L Typical volume units

Accuracy, Precision, and Significant Figures Accuracy: How close to the true value a given measurement is. Single measurement: percent error Series of measurements: average Precision: How well a number of independent measurements agree with each other. Characterized by the standard deviation.

Accuracy, Precision, and Significant Figures good accuracy good 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.

Accuracy, Precision, and Significant Figures length = 1.74 cm cm 1.7 cm < length < 1.8 cm

What is the reading on the graduated cylinder? 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 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) g 3 sfor 6.61 x 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 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 Numbers Math rules for keeping track of significant figures: Multiplication or division: The answer can’t have more significant figures than any of the original numbers gal 278 mi = 23.8 mi/gal 4 SF 3 SF

Rounding Numbers Multiplication 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 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 = If the first digit you remove is 6 or greater, round up by adding 1 to the digit on the left = 5.7

Rounding Numbers 3.If the first digit you remove is 5 and there are more nonzero digits following, round up = If the digit you remove is a 5 with nothing following, round down =

Calculations: Converting from One Unit to Another Dimensional 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

Calculations: Converting from One Unit to Another 1 m = in Conversion factor: Equivalent: 1 m in or in 1 m converts m to in converts in to m

Calculations: Converting from One Unit to Another in 1 m 69.5 in = 1.77 mx equivalent quantitystarting quantity conversion factor E.g Convert 69.5 in to m

Example How many centimeters are in 2.00 ft? Convert 2.00 in 2 to cm 2

Examples A 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/cm 3 ) are obtained from the cans? 34