Week 3 Chemistry Vocabulary: Ionic and Covalent Bonding

Key vocabulary from Week 3 notes on bonding, valence electrons, and ionic compounds; covers ionic/covalent bonding, valence electrons, ion formation, and polyatomic ions.

Bond

A connection between two or more atoms formed by interactions involving valence electrons.

Valence electrons

Outermost electrons that interact with the world and determine an element’s bonding and chemical properties.

Valence shell

The outermost electron shell that contains the valence electrons and largely determines bonding behavior.

Octet Rule

Atoms tend to gain, lose, or share electrons to achieve eight valence electrons (stable noble gas configuration); exceptions include H, Li, Be (2 electrons) and noble gases (already stable).

Noble gases

Elements with full valence shells that generally do not form bonds.

Ionic Bond

A bond formed when atoms transfer electrons to form oppositely charged ions that attract electrostatically.

Covalent Bond

A bond formed when atoms share valence electrons, typically between nonmetals; can involve sharing 2, 4, or 6 electrons (one, two, or three pairs).

Ionic Compound

A crystalline structure of repeating cations and anions held together by electrostatic attraction.

Molecular Element

An atom bonding to another atom of the same element, usually forming a diatomic molecule (e.g., O2, H2, Cl2).

Molecular Compound

Two or more nonmetal atoms bonded together to form a molecule.

Di​atomic molecules

Molecules consisting of two atoms, often the same element (e.g., O2, H2, N2, Cl2).

Electrostatic attraction

Forces between opposite charges that hold ionic compounds together.

Lattice

A three‑dimensional array in which ions occupy regular sites in an ionic solid.

Ion

An atom with a net electric charge due to gain or loss of electrons.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Ion notation

Writing the element symbol with a superscript for the charge (e.g., Li+, P3-).

Group (Periodic Table)

Columns of the periodic table; elements in a group have the same number of valence electrons and similar chemistry.

Alkaline Earth Metals

Group 2 elements; have 2 valence electrons and form +2 cations.

Halogens

Group 17 elements; have 7 valence electrons and form -1 anions in ionic compounds.

Transition Metals

Elements with d‑orbitals that can have multiple oxidation states; charges are shown with Roman numerals in formulas/names.

Roman numerals (in names)

Used to indicate the charge of transition metal ions in ionic compounds (e.g., iron(III) = Fe3+).

Binary Ionic Compounds

Ionic compounds composed of two elements (a metal and a nonmetal) with a formula reflecting balanced charges.

Formula Unit

The simplest whole‑number ratio of ions in an ionic compound; not the actual number of atoms in the lattice.

Crossover Rule

A method to determine formulas by swapping the charges: the metal’s charge becomes the subscript of the nonmetal and vice versa.

Polyatomic Ion

A group of covalently bonded atoms that carries a net charge (e.g., NH4+, NO3−, PO43−).

Ammonium

NH4+; a common polyatomic ion with a +1 charge.

Phosphate

PO43−; a common polyatomic ion with a -3 charge.

Nitrate

NO3−; a common polyatomic ion with a -1 charge.

Sulfate

SO42−; a common polyatomic ion with a -2 charge.

Hydroxide

OH−; a common polyatomic ion with a -1 charge.

Carbonate

CO32−; a common polyatomic ion with a -2 charge.

Acetate

C2H3O2−; a common polyatomic ion with a -1 charge.

Naming Ionic Compounds

Name the metal first, then the nonmetal root with -ide; transition metals use Roman numerals to show charge.

Salt

A term often used for ionic compounds; they form a crystalline lattice of ions.

The Structure of an Ionic Compound

Ionic compounds form a 3D crystal lattice; the formula shows ion ratios, not exact numbers of atoms.