Chemistry Dictionary
Essential Chemical Definitions

Atom

The smallest component of an element. Each element is made up of identical atoms each with a unique number of Protons and and equal number of Electrons. The number of Protons is referred to as the Atomic Number (Z).

Atomic Mass

The total mass of an element. The sum of the masses of the protons, neutrons and electrons of an element. Since the mass of protons and neutrons are very near 1 unit, and the mass of an electron is negligible, the atomic mass rounded to the nearest whole number is the sum of the number of protons and neutrons of an element.

Atomic Number

The unique number of protons and electrons in each atom of a specific element. Since each element has an equal number of Protons and Electrons, the Atomic Number is also equal to the number of electrons in an atom of an element.

Atomic Structure

The structural components of an atom and how they work together. Atoms are made up of protons, neutrons and electrons. The structure of an atom can be thought of as having a ball-shaped center called the nucleus, which contains the protons and neutrons. Around this nucleus, the electrons orbit like planets around our sun.

C

Cation

Cation - Atoms of elements that while keeping the same number of protons, have lost electrons and thus have a net positive charge.

E

Electron

Electron - The smallest negatively charged unit of matter. Electrons (e-) orbit around the Nucleus of the atom in various orbits. Each orbit has a different energy level.

Electrostatic Attraction

Electrostatic Attraction - The force which holds the electrons (negatively charged) in orbit around the nucleus (positively charged due to protons). This force would be like th gravitational force that holds our planets in orbit around the sun. When you rub an inflated baloon on your hair and then stick it to the wall the force that holds the balloon on the wall is electrostatic force.

Element

Element - A unique chemical substance found in nature that is made up of specific, identical atoms. Atoms of the same element all have the same number of protons. Each element has an equal number of protons and electrons. Since protons have a +1 charge and electrons have a -1 charge all elements are non-charged and are called "electrically neutral".

I

Ion

Ion - An atom of an element which contains the same number of protons, but which has either lost or gained electrons. Since electrons are negatively charged and protons are positively charged, atoms that have gained electrons will be negatively charged ions (anions) and ions that have lost electrons will be positively charged ions (cations).

Isotope

Isotope - An atom on an element which contains the same number of protons and electrons but which has additional neutrons. Sometimes isotopes are unstable and loose their "extra" neutrons. These isotopes are called "radio-active" isotopes.

N

Neutron

Neutron - The smallest neutral unit of matter. Neutrons (N) are in the nucleus of the atom.

Nucleus

Nucleus - The center, ball-shaped element of the atomic structure of the atom, which contains the protons and neutrons.

O

Orbitals

Orbitals - The electrons of an element can be in any of several types of orbitals or Sub-shells. There are four main types of orbitals or Sub- shells based on shape and energy level. The four types of orbitals listed in increasing energy order are: s orbitals-spherical-shaped, p orbitals-dumbell-shaped, d orbitals-X-shaped and f-orbitals which are complex in shape.

Orbitals-d

Orbitals-d - The X-shaped electron orbitals. The d-orbitals have the next higher energy level after the p-orbitals. There are always five d-orbitals per Shell. Each d-orbital can hold two electrons for a total of 10 in the d-type orbitals of a Shell.

Orbitals-f

Orbitals-f - The f-orbitals have a variety of complex shapes. The f- orbitals have the next higher energy level after the d-orbitals. There are always seven f-orbitals per Shell. Each f-orbital can hold two electrons for a total of 14 in the d-type orbitals of a Shell.

Orbitals-p

Orbitals-p - The dumbell-shaped electron orbitals. The p-orbitals have the next higher energy level after the s-orbitals. There are always three p-orbitals per Shell. Each p-orbital can hold two electrons for a total of 6 in the p-type orbitals of a Shell.

Orbitals-s

Orbitals-s - The spherical shaped, lowest energy level of electron orbitals. There is always one s-orbital per Shell. Each s-orbital can hold two electrons.

P

Proton

Proton - The smallest positively charged unit of matter. Protons (P+) are in the nucleus of the atom.

Q

Quantum Levels

Quantum Levels - A "fancier", more scientific term for the Shell of an element. The Quantum Level is simply the energy level of the orbit that a specific electron of the element occupies. Each element has a number of different Shells or energy levels that its electrons orbit in.

S

Shells

Shells - A more common term for Quantum Levels. The Shell of an element is simply the energy level of the orbit that a specific electron of the element occupies. Each element has a number of different Shells or energy levels that its electrons orbit in.

Sub-shells

Sub-shells - The Sub-shells of an element refer to the grouping of electron orbitals by shape. Each Shell or Quantum Level has between one and four different Sub-shells of different energies.

Click here for a tutorial on Atomic Structure.

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