Chapter 1 Elements and Measurements Chemistry and the Elements Development of the Periodic Table Mendeleevs Periodic Table (1871) Until the discovery of the proton, the elements were typically organized by increasing atomic weight. The modern organization is by increasing atomic number. 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 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 samples chemical makeup. Chemical Properties: Characteristics that do involve a change in a samples chemical makeup. Elements in the same group have the similar chemical properties Experimentation and Measurement All other units are derived from these fundamental units Systme Internationale dUnits Measuring Mass Mass: Amount of matter in an object. Matter: Describes anything with a physical presenceanything 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: Volume and Its Measurement 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 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): 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 at the end of a number and after the decimal point are always significant K 5 sf Accuracy, Precision, and Significant Figures 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 cant have more significant figures than any of the original numbers gal 278 mi = 23.8 mi/gal 4 SF 3 SF Rounding Numbers Addition or subtraction: The answer cant 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 lb are in 35.5 kg? 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? Example The diameter of the nucleus of an atom is approximately 1 pm. If 1 nm is equal to 10 ngstroms, what is the diameter of the nucleus in ngstroms?