S1L4: Atomic Mass

Atomic Number — the top number on an element, which determines the number of protons the element has in its nucleus, helium being 2He

Isotopes — an atom that has the same number of protons but a different number of neutrons

Mass Number — the total number of protons and neutrons in the nucleus of an atom

• Therefore, if you subtract the mass number by the atomic number, you should get the amount of neutrons

Atomic Mass Unit (amu) — A mass equal to 1/12th the mass of an atom of carbon-12, the unit of measurement used for protons, neutrons, and electrons

Carbon-12 — the atom that scientists chose as the reference standard to compare all other masses

Period — a horizontal row of the periodic table, with the periodic table including 7

Group — a vertical column of the periodic table based on the organization of the outer shell electrons

Periodic Trends — the arrangement of elements on the periodic table to show different aspects and patterns

Atomic Radius — the distance from the nucleus to the outer shell

Ionization Energy — the energy required to remove an atom’s electron

• Ionization energy generally increased from bottom left to top right of the periodic table

Electron Affinity — the energy charge associated when a neutral atom gains an electron, which increases from bottom left to top right on the periodic table

Metallic Character — the reactivity of a metal based on how easily the atom can lose an electron

Electronegativity — the degree in which elements in covalent bonds attract shared electrons

• All trends generally increase from bottom left to top right of the periodic table

Percent Natural Abundance — the relative amount of an element found in nature

Average Atomic Mass — Isotope A(amu x percent abundance)amu + Isotope B(amu x percent abundance)amu. Percent abundance must be written as a decimal

Radioactivity — the spontaneous emission of radiation in the form of particles high energy photons which result from a nuclear reaction

• All unstable isotopes are radioactive

Decay Product — the final product that radioisotope makes as it is decaying or decomposing

Energy Levels (electron shells) — fixed energies associated with an average distance from the nucleus of an atoms where electrons are found, ie energy level 1(shell 1) having two electrons, etc

• EL1 holds 2 max, EL2 holds max of 8

Orbitals — regions or volumes of space where the probability of finding an electron is very high and shape differs

Electronic Configuration — a map that shows where the electrons are likely to be located and how they’re distributed in an atom

Aufbau Principle — Rule that states that an electron occupies orbitals in order from lowest energy to highest

Ground State —  the lowest energy state of a nucleus, atom, or molecule