Atoms, Ions & Periodic Trends – Vocabulary Review

A set of vocabulary flashcards covering the basic structure of atoms, sub-atomic particles, ions, and relevant periodic-table trends discussed in the lecture.

Atom

The fundamental unit of matter composed of protons, neutrons, and electrons; normally electrically neutral.

Proton

Positively charged sub-atomic particle found in the nucleus; its number is the atomic number and mass ≈ 1 amu.

Neutron

Neutral sub-atomic particle located in the nucleus; contributes to atomic mass (≈ 1 amu) and can vary in number among isotopes.

Electron

Negatively charged sub-atomic particle occupying energy levels around the nucleus; negligible mass and determines chemical behavior.

Nucleus

Dense central core of an atom containing protons and neutrons; holds nearly all the atom’s mass.

Electron Shell (Energy Level)

A specific region around the nucleus where electrons of similar energy are found; inner shells are lower in energy than outer shells.

Valence Shell

The outermost electron shell of an atom; its electrons participate in chemical reactions and bonding.

Electron Cloud

The combined region of all electron shells surrounding the nucleus where electrons are likely to be found.

Ion

An atom or molecule that has gained or lost electrons, resulting in a net electric charge.

Cation

A positively charged ion formed when an atom loses one or more electrons.

Anion

A negatively charged ion formed when an atom gains one or more electrons.

Octet (Rule)

The stable configuration of eight electrons in an atom’s valence shell; drives atoms to gain, lose, or share electrons.

Group IA Elements

Elements with one valence electron that tend to lose it to form +1 cations (e.g., Na⁺).

Group IIA Elements

Elements with two valence electrons that tend to lose both to form +2 cations.

Group VIIA Elements

Elements with seven valence electrons that typically gain one electron to form –1 anions (e.g., Cl⁻).

Group VIIIA Elements (Noble Gases)

Elements that naturally possess an octet of valence electrons, making them chemically inert.

Atomic Number

The number of protons in an atom’s nucleus, uniquely identifying the element.

Electrical Neutrality (of Atoms)

Condition where an atom has equal numbers of protons and electrons, resulting in no net charge.