What is Chemistry The science that deals with matter, and the changes that matter undergoes.
Dec 30, 2015
Physical Change• Physical state is altered, but composition is the
same.• SOLID LIQUID Melting• LIQUID GAS Boiling• GAS LIQUID Condensing• SOLID GAS Sublimation• GAS SOLID Reverse
sublimation or deposition
• LIQUID SOLID Freezing
Wolpa/Advanced Placement Chemistry 3
Physical Change: the composition of the substance remains the same but the state changes.
Chemical Change
• Exhibited when a substance reacts with other substances
• Atoms are rearranged to form a new substance
• Often observable such as color change or change in energy
Wolpa/Advanced Placement Chemistry 7
An extensive property of a material depends upon how much matter is is being considered.
An intensive property of a material does not depend upon how much matter is is being considered.
• mass
• length
• volume
• density
• malleability
• color
Extensive and Intensive Properties
1.6
Wolpa/Advanced Placement Chemistry 8
Elements and the Periodic Table
• Each element is represented by a name and a symbol. (Periods/groups - alkali metals, alkaline earth metals, halogens, noble gases)
• The first letter is always capitalized the second (and third) are never capitalized.
Wolpa/Advanced Placement Chemistry 9
Compound
• A unique substance composed of two or more elements that are chemically combined (i.e. joined intimately, not just mixed together)
• Pure compounds have definite compositions and properties
• Require complex chemical procedures to separate into simpler substances (elements)
• Compounds include water, table salt, sugar, etc
Wolpa/Advanced Placement Chemistry 10
Density
• ratio of the mass of a substance to the volume of that mass
• usually measure in g/mL for solids and liquids; g/L for gases
• also a conversion factor relating the mass of a substance to it’s volume
• Specific gravity is the ratio of the mass of a substance to the mass of an equal volume of water
Wolpa/Advanced Placement Chemistry 11
A mixture is a combination of two or more substances in which the substances retain their distinct identities.
1. Homogenous mixture – composition of the mixture is the same throughout.
2. Heterogeneous mixture – composition is not uniform throughout.
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Wolpa/Advanced Placement Chemistry 12
Mixtures
• Combinations of two or more substances• Can be separated by exploiting different physical
properties (filtration, distillation, crystallization, chromatography)
• Have chemical and physical properties that are different from the substances that make them up
• The percentages by mass of the components of a mixture can be varied continuously
No Calculator Vomit!!
• We want to use the correct number of Significant Figures!
• On the AP exam, you have to be within 1 sig fig in order to receive credit!
Counting Significant FiguresAtlantic / Pacific Method a. Absent Decimal- Start on “atlantic” side of
number & cross out all zeroes until 1st nonzero digit is reached, remaining digits are significant
b. Present decimal- start on the “pacific” side of the number & cross out all zeros until the 1st nonzero digit Is reached, remaining digits are significant
SI Units
Measurement Unit Symbol
Mass Kilogram kg
Length Meter M
Time Second s
Temperature Kelvin K
Quantity Mole mol
Energy Joule J
Pressure Pascal Pa
Wolpa/Advanced Placement Chemistry 16
Converting between units
• The standard method to convert between two different units is the factor-label or dimensional analysis method
• Dimensional analysis converts a measurement in one unit to another by the use of a conversion factor
• Conversion factors are developed from relationships between units
Wolpa/Advanced Placement Chemistry 17
The speed of sound in air is about 343 m/s. What is this speed in miles per hour?
1 mi = 1609 m 1 min = 60 s 1 hour = 60 min
343ms
x1 mi
1609 m
60 s
1 minx
60 min
1 hourx = 767
mihour
meters to miles
seconds to hours
Wolpa/Advanced Placement Chemistry 18
Temperature and its Measurement
• Temperature - measure of the intensity of the heat of a substance
• Thermometer - device to measure temperature
• Kelvin - K - SI unit of temperature• Celsius - °C - commonly used unit• Fahrenheit - °F - only used in USA
Temperature conversion factors
Celsius to Kelvin K = T in oC + 273
Kelvin to Celsius oC = T in K - 273
Celsius to Fahrenheit
oF = (1.8 (T in oC)) + 32
Fahrenheit to Celsius
(T in oF - 32)/1.8
Measurements and Units
Measurement - determines the quantity, dimensions or extent of something1.Consist of two parts
a. a numerical quantity (1.23)b. a specific unit (meters)
Unit - a definite quantity adapted to as a standard of measurement
Features of Measured Quantities
When we measure a number, there are physical constraints to the measurement
Instruments and scientists are not perfect, so the measurement is not perfect (i. e., it has error)
The error in the measurement is related to the accuracy and the precision of the measurement
Accuracy and Precision
Accuracy – how close the measurement is to the “true” value (of course we have to know what the “true” value is)
Precision – is a measure of how closely individual measurements agree with one another.