Matter, Measurement, and Problem Solving; Atoms and Elements

atom

A submicroscopic particle that constitutes the fundamental building block of ordinary matter; the smallest identifiable unit of an element.

molecule

Two or more atoms joined chemically in a specific geometrical arrangement.

chemistry

The science that seeks to understand the behavior of matter by studying the behavior of atoms and molecules.

hypothesis

A tentative interpretation or explanation of an observation; a good hypothesis is falsifiable.

experiment

A highly controlled procedure designed to generate observations that may support a hypothesis or prove it wrong.

scientific law

A brief statement or equation that summarizes past observations and predicts future ones.

law of conservation of mass

A law stating that matter is neither created nor destroyed in a chemical reaction.

theory

A proposed explanation for observations and laws, based on well established and tested hypotheses, that presents a model for the way nature is and tries to show not merely what nature does but why.

atomic theory

The theory that each element is composed of tiny indestructible particles called atoms, that all atoms of a given element have the same mass and other properties, and that atoms combine in simple, whole-number ratios to form compounds.

matter

Anything that occupies space and has mass.

substance

A specific instance of matter.

state

A classification of the physical form of matter as a solid, liquid, or gas.

composition

The basic components that make up a substance.

solid

A state of matter in which atoms or molecules are packed close to one another in fixed locations with definite volume.

liquid

A state of matter in which atoms or molecules pack about as closely as they do in solid matter but are free to move relative to each other; liquids have a fixed volume but not a fixed shape.

gas

A state of matter in which atoms or molecules have a great deal of space between them and are free to move relative to one another; lacking a definite shape or volume, gases always assume the shape and volume of their containers.

crystalline

A term that describes a solid in which atoms, molecules, or ions are arranged in patterns with long-range, repeating order.

amorphous

A term describing a solid in which atoms or molecules do not have any long-range order.

pure substance

A substance made up of only one component and having invariant composition; the particles that compose a pure substance can be individual atoms or groups of atoms joined together.

mixture

A substance composed of two or more components in proportions that can vary from one sample to another.

element

A substance that cannot be chemically broken down into simpler substances.

compound

A substance composed of two or more elements in fixed, definite proportions.

heterogenous mixture

A mixture in which the composition varies from one region to another.

homogenous mixture

A mixture with the same composition throughout.

decanting

A method of separating immiscible liquids by pouring the top layer into another container.

distillation

The process by which mixtures are heated to boil off the more volatile (easily vaporizable) liquid. The volatile liquid is then recondensed in a condenser and collected in a separate flask.

volatile

Tending to vaporize easily.

filtration

A procedure used to separate a mixture composed of an insoluble solid and a liquid by pouring the mixture through filter paper or some other porous membrane or layer.

physical change

A change that alters only the state or appearance of a substance but not its chemical composition.

chemical change

A change that alters the composition of matter.

physical property

A property that a substance displays without changing its chemical composition.

chemical property

A property that a substance displays only by changing its composition via a chemical change.

energy

The capacity to do work.

work (w)

The action of a force through a distance.

kinetic energy

The energy associated with motion of an object.

potential energy

The energy associated with the position or composition of an object.

thermal energy

A type of kinetic energy associated with the temperature of an object, arising from the motion of individual atoms or molecules in the object.

law of conservation of energy

A law stating that energy can neither be created nor destroyed, only converted from one form to another.

units

Standard quantities used to specify measurements.

metric system

The system of measurements used in most countries in which the meter is the unit of length, the kilogram is the unit of mass, and the second is the unit of time.

English system

The system of units used in the United States and various other countries in which the inch is the unit of length, the pound is the unit of force, and the ounce is the unit of mass.

International System of Units (SI)

The standard unit system used by scientists, based on the metric system.

meter (m)

The SI standard unit of length; equivalent to 39.37 inches.

kilogram (kg)

The SI standard unit of mass defined as the mass of a block of metal kept at the International Bureau of Weights and Measures at Sèvres, France.

mass

A measure of the quantity of matter making up an object.

second (s)

The SI standard unit of time, defined as the duration of 9,192,631,770 periods of the radiation emitted from a certain transition in a cesium-133 atom.

kelvin (K)

The SI standard unit of temperature.

temperature

A measure of the average kinetic energy of the atoms or molecules that compose a sample of matter.

Fahrenheit (°F) scale

The temperature scale that is most familiar in the United States, on which pure water freezes at 32 °F and boils at 212 °F at sea level.

Celsius (°C) scale

The temperature scale most often used by scientists (and by most countries other than the United States), on which pure water freezes at 0 °C and boils at 100 °C (at sea level).

Kelvin scale

The temperature scale that assigns 0 K (-273°C or -459 °F) to the coldest temperature possible, absolute zero, which is the temperature at which molecular motion virtually stops.

prefix multipliers

Multipliers that change the value of the unit by powers of ten.

derived unit

A unit that is a combination of other base units. For example, the SI unit for speed is meters per second (m/s), a derived unit.

volume (V)

A measure of space. Any unit of length, when cubed (raised to the third power), becomes a unit of volume.

liter (L)

A unit of volume equal to 1000 cm³ or 1.057 qt.

milliliter (mL)

A unit of volume equal to 10-3 L or 1 cm³.

density (d)

The ratio of an object's mass (m) to its volume (V).

intensive property

A property such as density that is independent of the amount of a given substance.

extensive property

A property that depends on the amount of a given substance, such as mass.

significant figures / digits

In any reported measurement, the non-place-holding digits (those that are not simply marking the decimal place) that indicate the precision of the measured quantity.

exact numbers

Numbers that have no uncertainty and thus do not limit the number of significant figures in any calculation.

accuracy

A term that refers to how close a measured value is to the actual value.

precision

A term that refers to how close a series of measurements are to one another or how reproducible they are.

random error

Error that has equal probability of being too high or too low.

systematic error

Error that tends to be consistently either too high or too low.

dimensional analysis

The use of units as a guide to solving problems.

conversion factor

A fractional quantity with the units we are converting from on the bottom and the units we are converting to on the top; a conversion factor can be constructed from any two quantities known to be equivalent.

law of conservation of mass

A law stating that matter is neither created nor destroyed in a chemical reaction.

law of definite proportions

A law stating that all samples of a given compound have the same proportions of their constituent elements.

law of multiple proportions

A law stating that when two elements (A and B) form two different compounds, the masses of element B that combine with one gram of element A can be expressed as a ratio of small whole numbers.

cathode ray

A stream of electrons produced when a high electrical voltage is applied between two electrodes within a partially evacuated tube.

cathode ray tube

An evacuated tube containing charged plates to accelerate and view electron beams.

electrical charge

A fundamental property of certain particles that causes them to experience a force in the presence of electric fields.

electron

A negatively charged, low-mass particle found outside the nucleus of all atoms that occupies most of the atom's volume but contributes almost none of its mass.

radioactivity

The emission of subatomic particles or high-energy electromagnetic radiation by the unstable nuclei of certain atoms.

nuclear theory

The theory that most of the atom's mass and all of its positive charge are contained in a small, dense nucleus.

nucleus

The very small, dense core of the atom that contains most of the atom's mass and all of its positive charge; composed of protons and neutrons.

proton

A positively charged subatomic particle found in the nucleus of an atom.

neutron

An electrically neutral subatomic particle found in the nucleus of an atom, with a mass almost equal to that of a proton.

atomic mass unit (amu)

A unit used to express the masses of atoms and subatomic particles, defined as 1/12 the mass of a carbon atom containing 6 protons and 6 neutrons.

atomic number (Z)

The number of protons in an atom; the atomic number defines the element.

chemical symbol

A one- or twoletter abbreviation for an element; listed directly below an element's atomic number on the periodic table.

isotopes

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

natural abundance

The relative percentage of a particular isotope in a naturally occurring sample with respect to other isotopes of the same element.

mass number (A)

The sum of the number of protons and neutrons in an atom.

ion

An atom or molecule with a net charge caused by the loss or gain of electrons.

cation

A positively charged ion.

anion

A negatively charged ion.

periodic law

A law based on the observation that when the elements are arranged in order of increasing mass, certain sets of properties recur periodically.

metal

A member of the class of elements that are generally good conductors of heat and electricity, malleable, ductile, and lustrous, and tend to lose electrons during chemical changes.

nonmetal

A member of the class of elements that tend to be poor conductors of heat and electricity and usually gain electrons during chemical reactions.

metalloid

A member of the class of elements found on the boundary between the metals and nonmetals of the periodic table, with properties intermediate between those of both groups.

semiconductor

A material with intermediate electrical conductivity that can be changed and controlled.

main-group elements

Those elements found in the s or p blocks of the periodic table, whose properties tend to be predictable based on their position in the table.

transition elements / metals

Those elements found in columns labeled with a number and the letter B in the periodic table whose properties tend to be less predictable based simply on their position in the table.

family (group)

Columns within the main-group elements in the periodic table that contain elements that exhibit similar chemical properties.

noble gases

The group 8A elements, which are largely unreactive (inert) due to their stable filled p orbitals.

alkali metals

Highly reactive metals in group 1A of the periodic table.

alkaline earth metals

Fairly reactive metals in group 2A of the periodic table.

halogen

Highly reactive nonmetals in group 7 A of the periodic table.