Periodic Table and Atomic Theory Vocabulary

Vocabulary flashcards covering key definitions, historical scientists, and atomic structure terms from the Periodic Table lecture notes.

Element

A substance that cannot be broken down into simpler substances by chemical means .

Sir Robert Boyle

An Irish scientist whose main contribution to the periodic table was providing a clear definition of an element as a basic substance that cannot be broken down further by chemical means.

Sir Humphry Davy

A scientist who advanced the definition of an element by isolating new elements through electrolysis (such as sodium, potassium, and calcium) and proving that some substances thought to be elements were actually compounds.

Henry Moseley

A scientist who redefined the concept of an element by showing that its identity depends on its atomic number rather than its atomic mass.

Valency

The number of chemical bonds an atom of an element can form with another atom.

Octet Rule

A useful guide stating that most atoms try to attain eight electrons in their outermost shell when they bond.

Alkali Metals

Group 1 elements with 1 electron in their outer shell and a valency of 1; they are soft, low-density, extremely reactive metals stored under oil that burn in air to form metal oxides and react vigorously with water to form metal hydroxides and hydrogen gas.

Alkaline Earth Metals

Group 2 elements with 2 electrons in their outer shell and a valency of 2; they are very reactive metals, though less reactive than group 1 metals.

Halogens

Group 7 elements with 7 electrons in their outer shell and a valency of 1; they are very reactive non-metals with low melting and boiling points.

Noble Gases

Group 0 elements with 8 electrons in their outer shell (except helium which has 2) and a valency of 0; they exist mono-atomically as gases at room temperature and are the least reactive of all elements.

Metal

Any element that loses electrons to form a positive ion (cation).

Atomic Number ($Z$)

The number of protons present in the nucleus of an atom, which is always a whole number and equals the number of electrons in a neutral atom.

Mass Number

The number of protons plus neutrons in the nucleus of an atom.

Isotopes

Atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

Relative Atomic Mass Number ($A_r$)

The average mass of an atom of an element compared to $\frac{1}{12}$ the mass of the carbon-12 isotope, taking relative abundances of the naturally occurring isotopes into account.

Relative Molecular Mass Number ($M_r$)

The average mass of a molecule of a compound compared to $\frac{1}{12}$ the mass of the carbon-12 isotope, taking relative abundances of the naturally occurring isotopes into account.

Cation

A positively charged ion formed when an atom loses one or more electrons.

Anion

A negatively charged ion formed when an atom gains one or more electrons.

Protons

Positively charged sub-atomic particles located in the central nucleus of an atom.

Neutrons

Neutral sub-atomic particles located in the central nucleus of an atom.

Electrons

Negatively charged sub-atomic particles located in orbitals (sub-levels) around the nucleus of an atom.

Francis Aston

The scientist awarded the Nobel Prize in chemistry in 1922 for detecting the existence of isotopes using the first mass spectrometer.

Isotope Abundance Calculation

A calculation method where the percentage of each isotope is multiplied by its mass number, summed to get total mass per 100 atoms, and divided by 100 to get the relative atomic mass ($A_r$).