BELL RINGER Consider the burning of gasoline and the evaporation of gasoline. Which process represents a chemical change and which represents a physical change? Explain your answer.

TOPIC II Review

Atoms and Molecules Element Atom: smallest part of an element that is still that element. Molecule: Two or more atoms joined and acting as a unit. Element A substance that cannot be broken down into other substances by chemical methods. All of the matter in the world around us contains elements. Copyright © Cengage Learning. All rights reserved

Periodic Table Vertical columns: groups, or families. Elements with similar chemical properties. Horizontal rows: Periods. Physical and chemical properties change.

Compound Pure Substances Mixtures It can be broken down into original elements by chemical methods. It always has the same composition. Pure Substances They always have the same composition and are formed by chemical processes. Mixtures Can be separated into pure substances: elements and/or compounds using physical processes. Copyright © Cengage Learning. All rights reserved

Heterogeneous Mixture Homogeneous Mixture Same throughout. Having visibly indistinguishable parts. A solution. Heterogeneous Mixture It has visibly distinguishable parts. Contains regions that have different properties from those of other regions.

Classification of Matter Physically Chemically

Properties and Changes in Matter Intensive properties do not depend on the amount of matter present. melting point boiling point density ability to conduct electricity ability to transfer energy as heat

Properties and Changes in Matter Extensive properties depend on the amount of matter that is present. volume mass the amount of energy in a substance.

Physical and chemical properties Physical property: Characteristic that can be observed or measured without changing the identity of the substance. Chemical property: Substance’s ability to undergo changes that transform it into different substances.

Methods of Separating Mixtures Magnet: separate a magnetic substance from a non-magnetic substance. Filtration: separate an insoluble substance from a soluble substance. Chromatography: separation of complex mixtures that rely on the differential affinities of substances. Distillation: Separate substances that have different boiling points

Accuracy and Precision Reliability of measurements is expressed in terms of precision and accuracy. Accuracy refers to the closeness of measurements to the correct or accepted value of the quantity measured. Precision refers to the closeness of a set of measurements of the same quantity made in the same way.

If less than 5%, then measurement is accurate Accuracy can be expressed as Percentage Error   If less than 5%, then measurement is accurate

Uncertainty in measurements A digit that must be estimated in a measurement. It depends on the precision of the measuring device. Significant Figures Measured values are reported in terms of significant figures. Consist of all the digits known with certainty plus one final digit, which is estimated. Insignificant digits are never reported.

Rules for determining significant figures The Digits Digits That Count Example # of Sig Figs Non-zero digits ALL          4.337 4 Leading zeros (zeros at the BEGINNING) NONE          0.00065 2 Captive zeros (zeros BETWEEN non-zero digits)          1.000023 7 Trailing zeros (zeros at the END) ONLY IF they follow a non zero AND there is a decimal point in the number 89.00 but 8900 Leading, Captive AND Trailing Zeros Combine the rules above 0.003020 but 3020 3 Scientific Notation         7.78 x 103

Calculating With Sig Figs Type of Problem Example MULTIPLICATION/DIVISION: Find the number that has the fewest sig figs. That's how many sig figs should be in your answer. 3.35 x 4.669 mL = 15.571115 mL rounded to 15.6 mL 3.35 has only 3 significant figures, so that's how many should be in the answer.  Round it off to 15.6 mL ADDITION/SUBTRACTION: Find the number that has the fewest digits to the right of the decimal point. The answer must contain no more digits to the RIGHT of the decimal point than the number in the problem. 64.25 cm + 5.333 cm = 69.583 cm rounded to 69.58 cm 64.25 has only two digits to the right of the decimal, so that's how many should be to the right of the decimal in the answer. Drop the last digit so the answer is 69.58 cm.