Chemistry

Chemistry

The study of matter and the changes that matter undergoes.

Matter

Anything that has mass and occupies space.

Quantitative property

A property that can be measured and expressed with a number.

Qualitative property

A property that does not require measurement and is usually based on observation.

SI units

The International System of Units used universally by scientists.

Length

SI base quantity measured in meters (m).

Mass

SI base quantity measured in kilograms (kg); commonly measured in grams (g) in chemistry.

Time

SI base quantity measured in seconds (s).

Temperature

SI base quantity measured in kelvin (K).

Amount of substance

SI base quantity measured in moles (mol).

Electric current

SI base quantity measured in amperes (A).

Luminous intensity

SI base quantity measured in candela (cd).

Atomic mass unit (amu)

A unit used to express the masses of atoms and similar particles.

Celsius (°C)

A temperature scale where water freezes at 0°C and boils at 100°C.

Kelvin (K)

The absolute temperature scale; 0 K is absolute zero.

Kelvin conversion

K = °C + 273.15

Volume

The amount of three-dimensional space occupied by matter.

Density

The ratio of mass to volume; d = m/V.

Exact number

A number with a defined value or a number obtained by counting.

Inexact number

A measured number that contains some uncertainty.

Uncertainty

The unavoidable lack of complete certainty in a measured value.

Significant figures

The meaningful digits in a reported measurement.

Uncertain digit

The last digit of a measured number; it is the estimated digit.

Significant-figure rule: nonzero digits

All nonzero digits are significant.

Significant-figure rule: captive zeros

Zeros between nonzero digits are significant.

Significant-figure rule: leading zeros

Zeros before the first nonzero digit are not significant.

Significant-figure rule: trailing zeros

Trailing zeros are significant when a decimal point is present.

Scientific notation

A way to write numbers that makes the number of significant figures clear.

Addition/subtraction sig fig rule

The answer cannot have more digits to the right of the decimal point than the measurement with the fewest decimal places.

Multiplication/division sig fig rule

The answer has the same number of significant figures as the measurement with the fewest significant figures.

Exact numbers and sig figs

Exact numbers have an unlimited number of significant figures and do not limit the answer.

Rounding rule

If the first digit dropped is less than 5, round down; if it is 5 or greater, round up.

Accuracy

How close a measurement is to the true value.

Precision

How close repeated measurements are to one another; how repeatable they are.

Conversion factor

A fraction that expresses the same quantity in two different units.

Dimensional analysis

A problem-solving method that uses conversion factors to track and cancel units.

Factor-label method

Another name for dimensional analysis.

Substance

Matter with a definite composition and distinct properties.

Mixture

A physical combination of two or more substances.

Homogeneous mixture

A mixture that is uniform throughout; also called a solution.

Heterogeneous mixture

A mixture that is not uniform throughout.

Solid

A state of matter with particles held closely together in an ordered arrangement.

Liquid

A state of matter whose particles are close together but not rigidly fixed.

Gas

A state of matter whose particles are far apart and move freely.

Physical change

A change that does not change the identity of a substance.

Physical property

A property that can be observed or measured without changing a substance's identity.

Chemical property

A property describing how a substance can undergo a chemical change.

Extensive property

A property that depends on the amount of matter present.

Intensive property

A property that does not depend on the amount of matter present.

CHAPTER 2 — ATOMS AND THE PERIODIC TABLE

Atom

The smallest quantity of an element that retains the properties of that element.

Element

A substance that cannot be broken down into simpler substances by ordinary means.

Subatomic particle

A particle that makes up an atom.

Electron

A negatively charged subatomic particle.

Proton

A positively charged subatomic particle found in the nucleus.

Neutron

A neutral subatomic particle found in the nucleus.

Nucleus

The small, dense center of an atom containing protons and neutrons.

Cathode ray

A beam of particles produced in a cathode-ray tube that helped lead to the discovery of electrons.

J. J. Thomson

Scientist whose cathode-ray experiments provided evidence for the electron.

Millikan

Scientist whose oil-drop experiment determined the charge of the electron.

Atomic number (Z)

The number of protons in an atom.

Mass number (A)

The total number of protons plus neutrons in an atom.

Neutrons

The number of neutrons equals mass number minus atomic number: A − Z.

Neutral atom

An atom with equal numbers of protons and electrons.

Ion

An atom or group of atoms with a net electric charge.

Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons.

Atomic mass

The mass of an individual atom expressed in atomic mass units (amu).

Average atomic mass

The weighted average of the masses of naturally occurring isotopes.

Fractional abundance

An isotope's percent abundance written as a decimal.

Average atomic mass formula

Average atomic mass = Σ(isotope mass × fractional abundance).

Nuclear stability

The tendency of an atomic nucleus to remain stable rather than undergo radioactive decay.

Neutron-to-proton ratio (n/p)

The ratio of neutrons to protons in a nucleus; an important factor in nuclear stability.

Belt of stability

The region of neutron-to-proton ratios where stable nuclei are found.

Magic numbers

The nuclear numbers 2, 8, 20, 28, 50, 82, and 126 associated with increased nuclear stability.

Radioactive nucleus

A nucleus that is unstable and undergoes radioactive decay.

Periodic table

A chart in which elements with similar chemical and physical properties are grouped together.

Atomic number arrangement

The periodic table is arranged by increasing atomic number.

Period

A horizontal row of the periodic table.

Group

A vertical column of the periodic table.

Metal

An element that generally conducts heat and electricity well.

Nonmetal

An element that generally conducts heat and electricity poorly.

Metalloid

An element with properties intermediate between metals and nonmetals.

Alkali metals

Group 1 elements; highly reactive metals.

Alkaline earth metals

Group 2 elements.

Chalcogens

Group 16 elements.

Halogens

Group 17 elements; highly reactive nonmetals.

Noble gases

Group 18 elements; generally very unreactive gases.

Mole

A counting unit used for extremely large numbers of particles.

Molar mass

The mass of one mole of a substance.

Protons and atomic number

The number of protons identifies the element and equals its atomic number.

Protons and electrons in a neutral atom

A neutral atom has the same number of protons and electrons.

Mass number relationship

Mass number = protons + neutrons.

Isotope notation

The mass number is written above the atomic symbol and the atomic number below it.

Energy

The capacity to do work or transfer heat.

Kinetic energy

The energy associated with motion.

Potential energy

Energy associated with position.

Thermal energy

Energy associated with the random motion of atoms and molecules.

Chemical energy

Potential energy associated with chemical substances and their arrangements.