Atoms and the Periodic Table Lecture Notes

Vocabulary practice cards covering fundamental concepts of atoms, elements, the periodic table, and electronic structure.

Element

A pure substance that cannot be broken down into simpler substances by a chemical reaction.

Metals

Elements located on the left side of the periodic table; they usually exist as shiny solids and are good conductors of heat and electricity.

Mercury (Hg)

The only metal that is a liquid at room temperature.

Nonmetals

Elements located on the right side of the periodic table that usually do not have a shiny appearance and are poor conductors of heat and electricity.

Metalloids

A group of seven elements ($B$, $Si$, $Ge$, $As$, $Sb$, $Te$, and $At$) with properties intermediate between metals and nonmetals, located on the solid line starting at boron.

Building-block elements

The four nonmetals—$O$, $C$, $H$, and $N$—that comprise $96\%$ of the mass of the human body.

Compound

A pure substance formed by chemically combining two or more elements together.

Chemical formula

Consists of element symbols and subscripts to show the identity and ratio of atoms in a compound.

Atoms

The basic building blocks of all matter, composed of protons, neutrons, and electrons.

Nucleus

The dense core of the atom where protons and neutrons are located; it contains most of the atom's mass.

Electron cloud

The location of electrons, comprising most of the atom’s volume.

Atomic number (Z)

The number of protons in the nucleus of an atom.

Mass number (A)

The sum of the number of protons ($Z$) and the number of neutrons in an atom: $A = Z + \text{neutrons}$.

Isotopes

Atoms of the same element that have a different number of neutrons.

Atomic weight

The weighted average of the masses of the naturally occurring isotopes of an element, reported in atomic mass units (amu).

Period

A horizontal row in the periodic table.

Group

A vertical column in the periodic table.

Main group elements

The elements in the two far-left columns and the six far-right columns, numbered $1A$–$8A$.

Transition metal elements

The elements contained in the $10$ short columns in the middle of the periodic table, numbered $1B$–$8B$.

Alkali metals

The elements in Group $1A$, which are soft, shiny, and react with water to form basic solutions.

Alkaline earth elements

The elements in Group $2A$, which have properties similar to alkali metals but are less reactive.

Halogens

The elements in Group $7A$, which exist as two atoms joined together and are very reactive.

Noble gases

The elements in Group $8A$, which are very stable and rarely combine with any other elements.

Principal energy levels (shells)

The regions occupied by electrons, numbered $n = 1, 2, 3, \dots$; lower numbers are closer to the nucleus.

Orbital

A region of space where the probability of finding an electron is high; each orbital can hold a maximum of $2$ electrons.

Electron configuration

A description of how the electrons are arranged in an atom’s orbitals.

Ground state

The lowest energy arrangement of an atom's electrons.

Valence shell

The outermost shell of an atom (the highest value of $n$).

Valence electrons

The electrons in the outermost shell that determine the chemical properties of an element.

Electron-dot symbols

Representations where dots corresponding to valence electrons are placed on the four sides of an element symbol.

Ionization energy

The energy needed to remove an electron from a neutral atom.