Chapter 1: The Foundations Of Chemistry Key Terms

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Accuracy

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How closely a measured value agrees with the correct value (see Appendix A-4).

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Atom

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The smallest particle of an element that maintains its chemical identity through all chemical and physical changes.

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Atomic number

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The number of protons in the nucleus of an atom.

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Calorie

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Defined as exactly 4.184 joules. Originally defined as the amount of heat required to raise the temperature of one gram of water from 14.5ºC to 15.5ºC.

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Chemical change

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A change in which one or more new substances are formed; also known as chemical reaction or just reaction.

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Chemical property

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See Properties. Page 10.

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Compound

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A substance composed of two or more elements in fixed proportions. Compounds can be decomposed into their constituent elements.

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Density

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Density is the amount of mass per unit volume of a given object. It canbe calculated using the following equation.

d=m/v

If the density of the object and either mass or volume is known, by rearranging the above equation.

m=d*v

v=m/d

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Element

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A substance that cannot be decomposed into simpler substances by chemical means.

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Endothermic

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Describes processes that absorb heat energy.

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Energy

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The capacity to do work or transfer heat.

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Exothermic

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Describes processes that release heat energy.

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Extensive property

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A property that depends on the amount of material in a sample.

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Heat

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A form of energy that flows between two samples of matter because of their difference in temperature.

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Heat capacity

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The amount of heat required to raise the temperature of a body one degree Celsius.

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Heterogeneous mixture

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A mixture that does not have uniform composition and properties throughout.

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Homogeneous mixture

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A mixture that has uniform composition and properties throughout.

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Intensive property

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A property that is independent of the amount of material in a sample.

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Joule

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Definition of Joule. A unit of energy in the SI system. One joule is 1 kg*m2/s2 which is also 0.2390 calorie.

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Kinetic energy

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Energy that matter possesses by virtue of its motion.

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Law of Conservation of Energy

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Energy cannot be created or destroyed in a chemical reaction or in a physical change; it may be changed from one form to another.

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Law of Conservation of Matter

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No detectable change occurs in the total quantity of matter during a chemical reaction or during a physical change.

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Law of Conservation of Matter and Energy

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The combined amount of matter and energy in the universe is fixed.

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Law of Constant Composition

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See Law of Definite Proportions.

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Law of Definite Proportions

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Different samples of any pure compound contain the same elements in the same proportions by mass; also known as the Law of Constant Composition.

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Mass

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A measure of the amount of matter in an object. Mass is usually measured in grams or kilograms.

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Matter

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Anything that has mass and occupies space.

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Mixture

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A sample of matter composed of variable amounts of two or more substances, each of which retains its identity and properties.

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Molecule

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The smallest particle of an element or compound that can have a stable independent existence.

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Physical change

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A change in which a substance changes from one physical state to another, but no substances with different compositions are formed.

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Physical property

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See Properties. Page 10.

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Potential energy

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Energy that matter possesses by virtue of its position, condition, or composition.

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Precision

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How closely repeated measurements of the same quantity agree with one another (Appendix A-4)

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Properties

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Characteristics that describe samples of matter. Chemical properties are exhibited as matter undergoes chemical changes. Physical properties are exhibited by matter with no changes in chemical composition.

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Scientific (nature) law

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A general statement based on the observed behavior of matter, to which no exceptions are known.

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Significant figures

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Digits that indicate the precision of measurements -- digits of a measured number that have uncertainty only in the last digit (see Appendix A-4).

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Specific gravity

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The ratio of the density of a substance to the density of water at the same temperature.

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Specific heat

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The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

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Substance

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Any kind of matter all specimens of which have the same chemical composition and physical properties.

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Symbol (of an element)

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A letter or group of letters that represents (identifies) an element.

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Temperature

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A measure of the intensity of heat, that is , the hotness or coldness of a sample or object.

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Unit factor

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A factor in which the numerator and denominator are expressed in different units but represent the same or equivalent amounts. Multiplying by a unit factor is the same as multiplying by one.

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Weight

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A measure of the gravitational attraction of the earth for a body.