Chemistry is the study of matter and how it reacts. What is Chemistry? matter The “stuff” in the universe is made of “building blocks” formed in stars. atoms/elements Chemistry is the study of matter and how it reacts. To study matter and its reactions, we’re going to need to make a lot of measurements… To study matter, we’ll need to make a lot of measurements…

unit Measurement number 42.5 g 1.05 mL 16 cm measurement: quantity with _______ and a _____. 42.5 g 1.05 mL 16 cm number unit

Scientific Notation = 1 x 1014 atoms = 1 x 10–11 meters a really big number: 100,000,000,000,000 (atoms in a cell) or really small number: 0.000 000 000 01 meter (size of one atom) numbers without placeholder zeroes by using powers of 10. = 1 x 1014 atoms Expressing very large numbers, such as the estimated number of stars in a galaxy, is easier if scientific notation is used. Do some on the board as examples of moving decimal back and forth (10 min) = 1 x 10–11 meters

Accurate and Precise but not Neither Precise Nor Accurate _______ Yes good acc poor prec is possible with average Accurate and Precise but not Neither Precise Nor Accurate _______ Precise ________ Accurate

Accuracy, Precision, and % Error Accurate: close to the accepted or true value Precise: (repeatable) close to each other (last digit varies little) Acc Neither Prec

Accuracy, Precision, and % Error (difference) % Error = (________) x 100% acc exp – acc exp – experimental value acc – accepted value (Is being off by 9 cm a lot or a little? It depends on whether you are measuring the length of a piece of paper or the distance to here to Philly for the X Games.

% Error Calculation: % Error = |exp – acc| x 100% acc What is the % error if a measurement of 96.8oC is made, but the accepted (true) temperature is 99.1oC? % Error = |exp – acc| x 100% acc % Error = |96.8 – 99.1| x 100% 99.1 % Error = 2.32%

Quick Quiz! 1. What is one reason to study chemistry? to pass the test you need it before driver’s ed to be the coolest kid in school to explain the natural world around you

Quick Quiz. 2. Which of the following expressions has NOT been correctly changed to sci. not.? 0.00456 = 4.56  10–3 0.0000254 = 2.54  10–5 8,426,000 = 8.426  106 45,200 = 4.52  103 (Do these on board)

Quick Quiz. 3. Which set of measurements of a 2.00 g object is the most precise? 2.0 g , 2.1 g , 2.0 g 2.10 g, 2.00 g, 2.20 g 2.05 g, 2.04 g, 2.03 g 1.50 g, 2.00 g, 2.50 g