2.3 Atomic Structure and Symbolism - OpenStax Chemistry (Vocabulary Flashcards)

Vocabulary-style flashcards covering key terms from atomic structure, isotopes, ions, mass units, and mass spectrometry as presented in OpenStax Chemistry section 2.3.

Nucleus

The tiny center of an atom that contains protons and neutrons and accounts for most of the atom’s mass.

Proton

A positively charged subatomic particle in the nucleus with a mass of about 1.0073 amu and a +1 charge.

Neutron

A neutral subatomic particle in the nucleus with a mass of about 1.0087 amu and a 0 charge.

Electron

A negatively charged subatomic particle surrounding the nucleus with a mass of about 0.00055 amu and a −1 charge.

Atomic Number (Z)

The number of protons in the nucleus; defines the element and, in a neutral atom, equals the number of electrons.

Mass Number (A)

The total number of protons and neutrons in the nucleus.

Isotope

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

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.

Atomic Mass Unit (amu)

A unit of mass defined as 1/12 the mass of a carbon-12 atom; 1 amu = 1.6605×10^-24 g; equivalent to Da or u.

Elementary Charge (e)

The magnitude of the charge of a single electron; e = 1.602×10^-19 C.

Mass Defect

The difference between the sum of the masses of protons, neutrons, and electrons and the actual mass of the atom (the “missing” mass).

Isotope Notation

Notation showing the isotope with the mass number to the left of the element symbol (e.g., Mg-24); atomic number may be a subscript (often omitted since Z is implied).

Hydrogen Isotopes

Protium (1H, 1 proton, 0 neutrons); Deuterium (2H or D, 1 proton, 1 neutron); Tritium (3H or T, 1 proton, 2 neutrons).

Average Atomic Mass

The weighted average of all isotopic masses based on their natural abundances; not a whole number.

Isotopic Abundance

The fraction of a particular isotope present in a naturally occurring sample.

Mass Spectrometry (MS)

An analytical technique that measures mass-to-charge ratios of ions to identify and quantify substances and determine isotopes and abundances.

Mass Spectrum

A plot from a mass spectrometer showing ion abundance versus mass-to-charge ratio.

Symbol Capitalization Rule

Element symbols use only the first letter capitalized (e.g., Co); CO represents the molecule carbon monoxide, not the element cobalt.

Isotope Notation Practice (Examples)

Magnesium-24 (Mg-24), Magnesium-25 (Mg-25), Magnesium-26 (Mg-26) illustrate how isotopes are identified by mass number paired with the element symbol.