Glossary
Atomic Mass
The weighted average mass of all naturally occurring isotopes of an element, typically found below the element symbol on the periodic table.
Example:
The atomic mass of chlorine is about 35.45 amu, reflecting the natural abundance of its two main isotopes, Cl-35 and Cl-37.
Atomic Number
The number of protons in an atom's nucleus, which uniquely identifies an element. In a neutral atom, it also equals the number of electrons.
Example:
Oxygen has an atomic number of 8, meaning every oxygen atom contains exactly 8 protons.
Average Atomic Mass (AAM)
The weighted average of the masses of all naturally occurring isotopes of an element, calculated based on their relative abundances.
Example:
To calculate the average atomic mass of silicon, you'd multiply the mass of each silicon isotope by its natural abundance and sum the results.
Electrons
Negatively charged subatomic particles that orbit the nucleus. They determine an atom's chemical behavior and reactivity.
Example:
When sodium loses an electron to chlorine, it forms an ionic bond, creating table salt.
Element Symbol
A unique one- or two-letter abbreviation used to represent a chemical element.
Example:
The element symbol 'Au' instantly tells chemists worldwide that we are referring to gold.
Isotopes
Atoms of the same element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses.
Example:
Hydrogen has three isotopes: protium (no neutrons), deuterium (one neutron), and tritium (two neutrons), all of which are still hydrogen.
Mass Spectrometry
An analytical technique used to measure the mass-to-charge ratio of ions, providing information about the elemental composition and isotopic abundances of a sample.
Example:
Mass spectrometry can be used in forensics to identify unknown substances by analyzing their unique mass fingerprints.
Mass Spectrum
A graph produced by mass spectrometry that displays the mass-to-charge ratio (m/z) of ions on the x-axis and their relative abundance on the y-axis.
Example:
A chemist analyzing a sample of bromine would observe two distinct peaks on its mass spectrum, corresponding to its two common isotopes, Br-79 and Br-81.
Neutrons
Neutral subatomic particles located in the nucleus of an atom. They contribute to the atom's mass but not its charge.
Example:
Carbon-14 has 8 neutrons, making it heavier and radioactive compared to the more common Carbon-12, which has 6 neutrons.
Protons
Positively charged subatomic particles found in the nucleus of an atom. The number of protons determines the element's identity.
Example:
A carbon atom always has 6 protons, which is why it's carbon and not oxygen.