Ions, Bonding, and Polyatomic Ions (Vocabulary)

Vocabulary-style flashcards covering definitions and concepts from the lecture on ions, bonding, empirical vs molecular formulas, and polyatomic ions.

Ion

An atom that has gained or lost electrons, giving it a net positive or negative electric charge.

Cation

A positively charged ion formed when an atom loses electrons (e.g., Na+, Mg2+).

Anion

A negatively charged ion formed when an atom gains electrons (e.g., Cl−, O2−).

Ionic bond

Electrostatic attraction between oppositely charged ions in an ionic compound.

Covalent bond

A bond formed by sharing electron pairs between nonmetals, producing a molecular compound.

Empirical formula

The smallest whole-number ratio of ions in an ionic compound; used to represent the neutral unit; charges are not shown.

Molecular formula

The exact formula of a discrete molecule in covalent compounds; not reduced to the simplest ratio.

Polyatomic ion

A charged group of two or more atoms that acts as a single ion (e.g., NO3−, SO42−, PO43−).

Polyatomic cation

A positively charged polyatomic ion (e.g., NH4+).

Noble-gas electron configuration

Stable electron arrangement that resembles a noble gas; explains why atoms gain/lose electrons to look like noble gases.

Group 1A, 2A, 3A ion charges

Main-group metals in Group 1A, 2A, and 3A tend to form +1, +2, and +3 ions, respectively.

Group 5A, 6A, 7A ion charges

Nonmetals in Group 5A, 6A, and 7A tend to gain electrons to form −3, −2, and −1 ions (simplified); hydrogen is an exception (+1 or −1).

Hydrogen bonding behavior

Hydrogen is unique: it can form H+ (lose its electron) or H− (gain an electron); often behaves like a nonmetal in bonding.

Writing ionic formulas (cation first)

In ionic compounds, write the cation (metal) first and the anion second; ignore charges in the neutral formula and use the lowest whole-number ratio.

Balancing ionic formulas (Ca2+ and PO43−)

To form a neutral unit, multiply the ion charges to obtain the smallest whole-number ratio, e.g., Ca3(PO4)2 for calcium phosphate.

Parentheses in formulas

Use parentheses around a polyatomic ion when more than one unit is present (e.g., Ca3(PO4)2) to indicate multiple PO4 units.

Molecular vs Ionic compounds

Molecular compounds form between nonmetals/metalloids via covalent bonds; ionic compounds form between metals and nonmetals via ionic bonds.

Common polyatomic ions (examples)

NO3− (nitrate), CO32− (carbonate), SO42− (sulfate), PO43− (phosphate), SO32− (sulfite), NH4+ (ammonium).