Summer Chem Atom Review

Sublevel

A subdivision of an energy level in an atom (s, p, d, f) that describes the shape of the region where electrons are likely to be found.

s-Sublevel

The lowest-energy sublevel; can hold a maximum of 2 electrons.

p-Sublevel

A sublevel that can hold up to 6 electrons and is first found in the second principal energy level.

d-Sublevel

A sublevel that can accommodate 10 electrons; begins in the third principal energy level.

f-Sublevel

The highest-capacity sublevel discussed (14 electrons); begins in the fourth principal energy level.

Principal Energy Level (n)

Major energy shells around the nucleus, labeled n = 1, 2, 3…; each can hold up to 2n² electrons.

Electron Configuration

A notation that shows the arrangement of electrons among sublevels and orbitals in an atom’s ground state.

Orbital

A three-dimensional region around the nucleus that can hold a maximum of two electrons with opposite spins.

Maximum Electrons per Orbital

Two; a consequence of the Pauli Exclusion Principle.

Electron Cloud

The region of space around a nucleus where electrons are likely to be found; accounts for most of an atom’s volume.

Nucleus

The dense, positively charged center of an atom containing protons and neutrons; holds most of the atom’s mass.

Proton

A positively charged subatomic particle found in the nucleus with a relative mass of 1 amu.

Neutron

A neutral subatomic particle in the nucleus with a mass nearly equal to that of a proton.

Electron

A negatively charged particle with a mass about 1⁄2000 that of a proton; occupies orbitals outside the nucleus.

Atomic Number (Z)

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

Mass Number (A)

The total number of protons and neutrons in an atom’s nucleus.

Isotope

Atoms of the same element (same Z) that differ in mass number because of different numbers of neutrons.

Nuclide

A specific isotope of an element, identified by its atomic number and mass number.

Mass Spectrum

A plot showing the relative abundance of isotopes of an element versus their mass-to-charge ratio.

Weighted Average Atomic Mass

The average mass of an element’s atoms, calculated using the percent abundance of each naturally occurring isotope; gives the decimal values on the Periodic Table.

Valence Electrons

Electrons in the outermost principal energy level of an atom; determine chemical properties.

Ground State

The lowest-energy arrangement of electrons in an atom.

Excited State

Any electron configuration of an atom that has higher energy than the ground state; electrons have absorbed energy to move to higher levels.

Emission (Bright-Line) Spectrum

Distinct lines of colored light produced when excited electrons return to lower energy levels, releasing photons.

Flame Test

A lab technique in which the color of flame emission identifies elements based on their characteristic spectra.

Photon

A quantum (packet) of electromagnetic radiation energy.

Wavelength (λ)

The distance between consecutive peaks of a wave; inversely related to frequency and energy.

Frequency (ν)

The number of wave cycles that pass a point per second; measured in s⁻¹ (Hz).

Planck’s Constant (h)

A proportionality constant (6.6 × 10⁻³⁴ J·s) used in the equation E = hν to relate photon energy to frequency.

Electromagnetic Spectrum (Energy Order)

Radio < Microwave < Infrared < Visible < Ultraviolet < X-ray < Gamma, with energy increasing from left to right.

Half-Life

The time required for half the nuclei in a radioactive sample to decay.

Fission

A nuclear reaction in which a heavy nucleus splits into smaller nuclei, releasing energy.

Fusion

A nuclear process where light nuclei combine to form a heavier nucleus with the release of large amounts of energy.

Gold Foil Experiment

Rutherford’s experiment that led to the discovery of the atomic nucleus by observing alpha particle scattering.

Nuclear Density

The nucleus occupies very little of an atom’s volume but contains nearly all of its mass.