EP Chemistry Unit 3 Terms

Democritus

(born c. 460 — died c. 370 BC) Greek philosopher. Though only a few fragments of his work survive, he was apparently the first to describe invisible “atoms” as the basis of all matter. His atoms — indestructible, indivisible, incompressible, uniform, and differing only in size, shape, and motion — anticipated with surprising accuracy those discovered by 20th century scientists

Atom

a unit of matter, the smallest unit of an element having all the characteristics of that element and consisting of a dense central, positively charged nucleus surrounded by a system of electrons

Atomos

Greek word meaning indivisible or not able to cut

Aristotle

Greek philosopher who did not follow the teachings of Democritus. He believed in the four earthly elements (fire, earth, air, and water), and proposed a fifth heavenly element (aether)

Dalton

(born 1766 - died 1844) English scientist who was one of the first to decide that all matter is made up of small particles, or atoms

Law of Conservation of Mass

The notion that mass, or matter, can be neither created nor destroyed. According to conservation of mass, reactions and interactions which change the properties of substances leave unchanged their total mass; for instance when charcoal burns the mass of all of the products of combustion, such as ashes, soot, and gases, equals the original mass of charcoal and the oxygen with which it reacted

Law of Definite Proportions

elements composing a compound are always present in the same proportions by mass

Law of Multiple Proportions

law stating that when two elements can combine to form more than one compound the amounts of one of them that combines with a fixed amount of the other will exhibit a simple multiple reaction

Rutherford

(born 1871 - died 1937) New Zealand physicist who named the nucleus and proton and won the 1908 Nobel prize in chemistry

Nucleon

a proton or a neutron, especially as part of an atomic nucleus

Proton

a stable, positively charged subatomic particle having a mass 1,836 times that of the electron

Neutron

An electrically neutral subatomic particle having a mass 1,839 times that of the electron

Electron

a stable subatomic particle having a rest mass of 9.1066 × 10-28 grams and a unit negative electric charge of approximately 1.602 × 10-19 coulombs

Isotope

One of two or more atoms having the same atomic number, but different mass numbers due to a different number of neutrons in the nucleus

Mass number

the sum of the number of neutrons and protons in an atomic nucleus

Photon

The quantum of electromagnetic energy, regarded as a discrete particle having zero mass, no electric charge, and an indefinitely long lifetime

Spectroscopy

Study of spectra, especially experimental observation of optical spectra

Quantum Number

a set of real numbers assigned to a physical system that individually characterize the properties and collectively specify the state of a particle or of the system

Orbital

The wave function of an electron in an atom or molecule, indicating the electron’s probable location

Sublevel

One or more orbitals in the electron shell of an atom

Hund’s Rule

If two or more orbitals of equal energy are available, electrons will occupy them singly before filling them in pairs

Pauli Exclusion Principle

No two electrons may simultaneously occupy the same quantum state

Aufbau Principle

Used to determine the electron configuration of an atom, molecule, or ion. The principle postulates a hypothetical process in which an atom is “built up” by progressively adding electrons. As they are added, they assume their stable conditions (electron orbitals) with respect to the nucleus and those electrons already there. According to the principle, electrons fill orbitals starting at the lowest available (possible) energy states before filling higher states (e.g. 1s before 2s).