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Chemistry
The study of matter
Matter
It is anything that has mass and occupies space.
Elements
Substances that cannot be divided into other elements.
Atoms
The basic building block of matter, the smallest unit that still retains distinct characteristics.
Molecules
Chemicals that result from two or more atoms linking together
The states of matter
Solid - The particles are packed closely together. The forces between particles are strong so that the particles cannot move freely but can vibrate. Solids have a stable, definite shape and volume.
• Crystalline solids, the particles are packed in a regularly ordered, repeating pattern.
Liquid -
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. The volume is definite if the temperature and pressure are constant
Gas -
A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container.
In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small (or zero for an ideal gas), and the typical distance between neighboring molecules is much greater than the molecular size.
Plasma
Like a gas, plasma does not have definite shape or volume. Unlike gases, plasmas are electrically conductive, produce magnetic fields and electric currents, and respond strongly to electromagnetic forces. Positively charged nuclei swim in a "sea" of freely-moving disassociated electrons, similar to the way such charges exist in conductive metal. In fact it is this electron "sea" that allows matter in the plasma state to conduct electricity
Pure Substance
A pure substance (usually referred to
simply as a substance) is matter that has distinct properties and a composition that does not vary from sample to sample.
Compounds
Compounds are substances composed of two or more elements that require chemical means to be separated; they contain two or more kinds of atoms
Mixtures
Mixtures are combinations of two or more substances in which each substance retains its chemical identity; substances that vary with composition.
The Law of Constant Composition (or the law of definite proportions)
The observation that the elemental composition of a compound is always the same. French chemist Joseph Louis Proust (1754-1826) first stated the law in about 1800.
Heterogeneous Mixture
Mixtures that are not uniform in composition and appearence.
Homogeneous Mixture
Solutions which have a uniform and constant composition throughout. Examples: Sugar in water
Physical Properties
Physical properties can be observed without changing the identity and composition of the substance. These properties include color, odor, density, melting point, boiling point, and hardness.
Chemical Properties
Chemical properties describe the way a substance may change, or react, to form other substances. A common chemical property is flammability, the ability of a substance to burn in the presence of oxygen.
Intensive Properties
They are properties, like temperature or melting point, do not depend on the amount of sample being examined and are particularly useful in chemistry because many intensive properties can be used to identify substances.
Extensive Properties
Extensive properties depend on the amount of sample, with two examples being mass and volume. Extensive properties relate to the amount of substance present.
Physical Change
During a physical change, a substance changes its physical appearance but not its composition. (That is, it
is the same substance before and after the change.)
Chemical Change
In a chemical change (also called a chemical reaction), a substance is transformed into a chemically different substance. When hydrogen burns in air, for example, it under-
goes a chemical change because it combines with oxygen to form water
Metric System
Petra - 10^15
Tera - 10^12
Giga - 10^9
Mega - 10^6
Kilo - 10^3
Deca - 10^1
Deci - 10^-1
Centi - 10^-2
Mili - 10^-3
Micro - 10^-6
Nano - 10^-9
Pico - 10^-12
Femto - 10^-15
Atto - 10^-18
Zepto - 10^-21
Temperature
The measure of the average amount of kinetic energy in a body of matter
Celsius Scale
0 to 100
Kelvin to Celsius
K = C + 273.15
Fahrenheit to Celsius
C = 5/9(F - 32)
The Degree Interval Comparison between Temperature Scales
1 Celsius = 1 Kelvin
1 Celsius = 1/18
Derived Unit
A unit that is the combination of metric units.
Example: Speed = meters per second.
Density
Mass/Volume and expressed in grams per cubic centimeter or grams per milliliter.
Because most substances change volume when they are heated or cooled, densities are temperature dependent, and so temperature should be specified when reporting densities. If no temperature is reported, we assume 25 °C, close to normal
room temperature.
Precision
The consistency of data to the other data
Accuracy
Accuracy refers to how closely individual measurements agree with the correct value.
Significant Figures
All digits of a measured quantity, including the uncertain one, are called significant
figures.
Significant Figure Laws Zeroes
1. Zeros between nonzero digits are always significant—1005 kg (four significant
figures);
2. Zeros at the beginning of a number are never significant; they merely indicate
the position of the decimal point—0.02 g (one significant figure)
3. Zeros at the end of a number are significant if the number contains a decimal point
Significant Figure Laws Adding and Subtracting
For addition and subtraction, the result has the same number of decimal places as
the measurement with the fewest decimal places
Significant Figure Laws Multiplying & Dividing
For multiplication and division, the result contains the same number of significant
figures as the measurement with the fewest significant figures.
Dimensional Analysis
In this approach,
units and conversions are multiplied together, divided into each other, or "canceled" making the resulting number in the desired unit.
Conversion Factor
A conversion factor is a fraction whose numerator and denominator are the same quantity expressed in different units
The form is
Given Unit x Desired Unit/Given Unit = Desired Unit
How many elements are there?
118
How do the elements hydrogen and oxygen exist naturally as?
Diatomic (two-atom) molecules.
What are homogenous mixtures called?
Solutions
Filtration
The process whereby fluids pass through a filter or a filtering medium, separating elements.
Distillation
The process of purifying a liquid by boiling it and condensing its vapors
Chromatography
A process used for separating mixtures by virtue of differences in absorbency
SI Base Units
Length - Meter
Time - Second
Mass - Kilogram
Temperature - Kelvin
Amount of a Substance - Mole
Electric Current - Amperes
Luminous Intensity - Candela
Volume
Its length cubed
What are numbers obtained by measurement?
They are always inexact.
Law of Definite Proportions
Joseph Proust 1797
The law of constant composition is a chemistry law which states samples of a pure compound always contain the same elements in the same mass proportion, despite the source.
