Chapter 2: Atoms and Molecules – CHEM 107

Vocabulary flashcards covering key concepts from Chapter 2: Atoms and Molecules, including atomic structure, isotopes, bonding, polymers, and nomenclature.

Atom

The basic unit of an element that retains its identity in chemical reactions; composed of a nucleus (protons and neutrons) surrounded by electrons in a cloud.

Nucleus

The tiny, dense center of an atom that contains protons and neutrons.

Proton

A positively charged particle in the nucleus with mass ≈1 amu.

Neutron

A neutrally charged particle in the nucleus with mass ≈1 amu.

Electron

A negatively charged particle that orbits the nucleus in a cloud and has negligible mass compared with protons and neutrons.

Atomic Number (Z)

The number of protons in an atom’s nucleus; identifies the element.

Mass Number (A)

The total number of protons and neutrons in an atom’s nucleus.

Isotope

Atoms of the same element (same Z) that have different numbers of neutrons (different A).

Isotopic abundance

The mass percentage of a specific isotope in a naturally occurring element.

Ion

An atom with a different number of protons and electrons, giving it a net electric charge.

Cation

An ion with more protons than electrons; carries a positive charge.

Anion

An ion with more electrons than protons; carries a negative charge.

Atomic Mass Unit (amu)

A unit used to express atomic masses; 1 amu ≈ 1/12 the mass of a carbon-12 atom.

Atomic weight

The weighted average mass of an element’s naturally occurring isotopes.

Mass spectrometry

A technique that measures masses of atoms, isotopes, and molecules by analyzing ion deflection in electric and magnetic fields.

Molecular formula

The actual number of atoms of each element present in a discrete molecule.

Empirical formula

The simplest whole-number ratio of atoms in a compound.

Monomer

A small molecule that can join with others to form a polymer.

Polymer

A very large molecule made by linking together many monomer units.

Polymer backbone

The long chain of bonded atoms forming the main chain of a polymer.

Functional group

A specific arrangement of atoms that imparts characteristic chemical properties to a molecule.

Covalent bond

A bond formed by sharing electron pairs between atoms.

Ionic bond

A bond formed by electrostatic attraction between oppositely charged ions in a lattice.

Metallic bond

A bond in which valence electrons are shared in a ‘sea’ of electrons that moves freely, allowing conductivity.

Polyethylene

A polymer made from the monomer ethylene (C2H4); repeating unit [CH2CH2]n.

HDPE vs LDPE vs UHMWPE

HDPE: linear, less branching; LDPE: highly branched; UHMWPE: extremely long chains with very high molecular weight.

Initiator

A substance that generates free radicals to start polymerization.

Free radical

An atom or molecule with an unpaired electron, making it highly reactive.

Polymerization

The chemical process of linking monomers to form a polymer, often via initiator and terminator steps.

Nomenclature: covalent binary compounds

Name by giving full name of the first element, then the second element with -ide; prefixes indicate numbers (unless only one atom of the first element).

Periodic table

A chart organizing elements by increasing atomic number, showing periodic trends in properties.

Period

A horizontal row in the periodic table.

Group

A vertical column in the periodic table; elements in a group share similar properties.

Metals, nonmetals, metalloids

Categories in the periodic table: metals (left/bottom), nonmetals (top/right), metalloids along a diagonal line between them.

Hydrate

A compound that includes water molecules as part of its crystalline structure.