Presentation on theme: "Chemistry = Properties and Changes of Matter Pure substances = properties are constant; only 1 type of substance Mixtures = properties are variable; 2."— Presentation transcript:
Chemistry = Properties and Changes of Matter Pure substances = properties are constant; only 1 type of substance Mixtures = properties are variable; 2 or more different substances Elements = cannot be broken into simpler substances; only 1 type of atom Compounds = can be broken into simpler substances; 2 or more types of atom Matter Homogeneous = composition is the same throughout the mixture Heterogeneous = composition varies
Elements Element = a substance that cannot be broken down into simpler substances by chemical means.
Compounds Compound = a pure substance with atoms of two or more elements chemically united in fixed proportions.
Types of Matter Mixtures Matter Pure substances Heterogeneous mixtures Homogeneous mixtures CompoundsElements separated by physical methods separated by chemical methods
Types of Properties and Changes Properties Chemical or physicalIntensive or extensive Changes
Types of Properties and Changes Properties Chemical or physical Physical = doesn’t change type of matter Chemical = changes type of matter Intensive or extensive Changes
Types of Properties and Changes Properties Chemical or physical Physical = doesn’t change type of matter Chemical = changes type of matter Intensive or extensive Extensive = is affected by amount of matter Intensive = is not affected by amount of matter Changes
1. Smoke is an example of a(n): homogeneous mixture compound gaseous solution heterogeneous mixture element
The correct answer was "heterogeneous mixture". Smoke is a suspension of tiny particles in air, and so is a heterogeneous mixture. It is not a solution (homogeneous mixture) because the properties of the tiny particles are different from the properties of air.
Precision and Accuracy - Think of a Dart Board!!!
Precision is the closeness of a set of values obtained from identical measurements (are your darts clustered??)
Accuracy is the closeness of a single measurement to the true value (the bulls-eye!)
Precision vs. Accuracy Draw the Dart Board Showing Each of These: good precision & good accuracy poor accuracy but good precision good accuracy but poor precision poor precision & poor accuracy
The DREADED “Significant Figures” Those digits in a measured number that include all certain digits and final one have some uncertainty
Rules for assigning significance to a digit: 1. Digits other than zero are always significant. 2. Rules about zeros: Final zeros after a decimal point are always significant. Zeros between two other significant digits are always significant. Zeros used only to space the decimal are never significant.
Determine the number of significant digits in each of these: 6.751 g 0.157 kg 28.0 ml 2500 m 0.070 g 30.07 g 0.0067 cm 6.02 x 10 23 atoms Scientific notation!!!
A)Between 0 and 2 in b)Between 1 and 2 in C)Between 1.5 and 1.6 in D)Between 1.54 and 1.56 in E)Between 1.546 and 1.547 in Which of the following best describes the length of the beetle's body in the picture to the left?
Any measurement made by comparing an object to a scale should include not only the certain digits (1.5 in this case) but also one estimated (uncertain) digit. Because the ruler was marked every tenth of an inch, you must to read the measurement to the nearest hundredth of an inch. You couldn't be certain if the measurement was 1.54, 1.55, or 1.56 cm. The uncertain digit is in the hundredths place.
Sig Figs in Calculations: Division and Multiplication…. Final answer with least # of SF in the quantities you multiplied or divided Addition or Subtraction….. Final answer with the same # of decimal places as there are in the measurement with the least # of decimal places Rounding off numbers….. Hope you remember!!!!!
Le Systéme Internationale (SI) is a set of units and notations that are standard in science. Four important SI base units …. QuantitySI English Base UnitEquivalent lengthmeter (m)1 m = 39.36 in masskilogram (kg) 1 kg = 2.2 lbs timesecond (s) temperaturekelvin (K)°F = 1.8( o C)+32 K = °C + 273.15
Commonly used SI prefixes Prefix Meaning Abbreviation Exponential Notation Giga- billion G 10 9 Mega- million M 10 6 kilo- thousand k 10 3 centi- hundredths of c 10 -2 milli- thousandths of m 10 -3 micro- millionths of µ 10 -6 nano- billionths of n 10 -9 pico- trillionths of p 10 -12
Arithmetic with units addition and subtraction: units don't change 2 kg + 3 kg = 5 kg 412 m - 12 m = 400 m consequence: units must be the same before adding or subtracting! 3.001 kg + 112 g = 3.001 kg + 0.112 kg = 3.113 kg 4.314 Gm - 2 Mm = 4.314 Gm - 0.002 Gm = 4.312 Gm multiplication and division: units multiply & divide too 3 m × 3 m = 9 m 2 10 kg × 9.8 m/s 2 = 98 kg m/s 2 consequence: units may cancel 5 g / 10 g = 0.5 (no units!) 10.00 m/s × 39.37 in/m = 393.7 in/s
5 step plan for converting units identify the unknown, including units choose a starting point list the connecting conversion factors multiply starting measurement by conversion factors check the result: does the answer make sense?
Density One of the simplest equations you’ll see…. D = m /V Density = mass/volume PROBLEM: a sample of the mineral galena weighs 12.4 g and has a volume of 10 mL. What is its density?
HOMEWORK ASSIGNMENT 1 DUE WED, SEPTEMBER 5 TH READ CHAPTER 1….YOU ARE RESPONSIBLE FOR ALL OF IT!!!! 1.50, 1.54, 1.66, 1.76, 1.82, and 1.94 (Tricky but not too tricky!!)