Unit 1: Atoms and Molecules

A vocabulary-style set of flashcards covering core terms from Unit 1: Elements, Compounds, Atoms, Molecules, and Chemical Bonds.

Matter

Anything that occupies space and has mass ( contrasts with non-matter such as light or heat).

Pure substance

A substance with uniform composition, either an element or a compound.

Element

Matter of one type; cannot be created or broken down by ordinary chemical means.

Atom

The smallest unit of an element; the basic unit of matter.

Molecule

Two or more atoms covalently bonded together; may be the same or different elements.

Covalent bond

A bond formed when atoms share electrons, filling their valence shells; can be single, double, etc.; strong.

Ionic bond

A bond formed by the electrical attraction between oppositely charged ions (cations and anions).

Ion

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

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Compound

A substance composed of two or more different elements bonded together; may be covalently or ionically bonded.

Polar covalent bond

A covalent bond with unequal sharing of electrons, creating partial charges (dipoles).

Nonpolar covalent bond

A covalent bond with equal sharing of electrons.

Hydrogen bond

A weak bond between a partially positive hydrogen atom and an electronegative atom in another molecule.

Dipole interaction

Interactions involving partial charges on polar molecules; includes dipole-ion effects and dissolution phenomena.

Inorganic compound

A compound that does not contain both carbon and hydrogen (e.g., water).

Organic compound

A compound that contains both carbon and hydrogen (e.g., glucose).

Carbon backbone

Carbon atoms form the structural framework of many large, complex organic molecules.

Triglyceride

A common fat; a lipid formed from glycerol and three fatty acids.

ATP

Adenosine triphosphate; energy-storage molecule that transfers energy when hydrolyzed to ADP + phosphate.

Electron shell

Regions around the nucleus where electrons reside; first shell holds up to 2 electrons, second up to 8, third up to 18.

Valence shell

Outermost electron shell; a complete valence shell makes an atom non-reactive (e.g., neon).

Atomic number

The number of protons in the nucleus of an atom.

Mass number

The sum of protons and neutrons in the nucleus.

Helium

Element with atomic number 2; noble gas with a complete electron shell.

Oxygen

Element with atomic number 8; essential for life; forms covalent bonds by sharing electrons.

Water (H2O)

Inorganic molecule with two hydrogens and one oxygen; forms hydrogen bonds.

Glucose (C6H12O6)

Organic molecule containing carbon, hydrogen, and oxygen; energy source in biology.

Sodium chloride (NaCl)

Ionic compound (table salt) composed of Na+ and Cl- ions; dissolves in water.

Carbon dioxide (CO2)

Molecule and compound with one carbon and two oxygens; CO2 is both a molecule and a compound.

Oxygen molecule (O2)

Diatomic molecule of oxygen; a molecule but not a compound (elemental form).