Chemistry Concepts: Energy Levels and Orbitals
A lot of chemistry is explained by the sharing and trading of electrons between atoms. Understanding how electrons are arranged in an atom is a building block of Chem I.
Electrons in an atom are contained in specific energy levels (1, 2, 3, and so on) that are different distances from the nucleus. The larger the number of the energy level, the farther it is from the nucleus. Electrons that are in the highest energy level are called valence electrons. Within each energy level is a volume of space where specific electrons are likely to be located. These spaces, called orbitals, are of different shapes, denoted by a letter (s, p, d, f, g). (In most cases, only the electrons contained in the s and p orbitals are considered valence electrons.) Electrons seek the lowest energy level possible.
The following electron-filling pattern indicates how the electrons fill into the energy levels. Knowing this pattern is useful in many aspects of chemistry, including predicting the bonding situation of a particular atom and in the prediction of the geometry of a covalent compound.
Electron filling pattern: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f
Chemistry Glossary
Archimedes Principle
A principle discovered by the Greek mathematician Archimedes which states that the volume of a solid is equal to the volume of water it displaces.
Chemistry Glossary
atomic number
The number of protons in the nucleus of an atom.
Chemistry Glossary
Bohr model
A model of atomic structure developed by Niels Bohr, a Danish scientist. In this model, electrons occur in orbits of differing energy levels around the nucleus of an atom.
Chemistry Glossary
condensation
The change in the physical state of matter from a gaseous state to a liquid state.
Chemistry Glossary
deposition
The change in the physical state of matter from a gaseous state to a solid state without ever becoming a liquid. The reverse of sublimation.
Chemistry Glossary
electrolytes
Substances that can conduct electricity either in the molten state or when dissolved in water.
Chemistry Glossary
electron configuration notation
A method used by chemists to represent electrons in bonding and chemical reactions.
Chemistry Glossary
electronegativity
A measure of an atom’s strength to attract a bonding pair of electrons to itself.
Chemistry Glossary
energy level diagram
A method used by chemists to diagram the electrons for an atom (including orbitals and subshells) in bonding and chemical reactions.
Chemistry Glossary
heterogeneous mixture
A mixture whose composition varies from position to position within a sample.
Chemistry Glossary
homogeneous mixture
A mixture whose composition is the same from position to position within a sample.
Chemistry Glossary
isotopes
Atoms of the same element that have varying numbers of neutrons.
Chemistry Glossary
mass number
The sum of the protons and neutrons in a particular isotope; also called atomic weight.
Chemistry Glossary
nonelectrolytes
Substances that do not conduct electricity in the molten state or when dissolved in water.
Chemistry Glossary
nuclear fission
A nuclear reaction in which an atom’s nucleus splits into smaller parts.
Chemistry Glossary
nuclear fusion
A process in which lighter nuclei of atoms join together into a heavier nucleus; essentially the opposite of nuclear fission.
Chemistry Glossary
nuclear reaction
Any reaction that involves a change in nuclear structure.
Chemistry Glossary
periodic table
A table that displays all known chemical elements in an arrangement that is based on the properties of the elements; changes over time as new elements are discovered.
Chemistry Glossary
quantum mechanical model
A model of atomic structure that is based on mathematics and can be used to explain observations made on complex atoms.
Chemistry Glossary
radioactivity
The spontaneous decay of an unstable nucleus in an atom.
Chemistry Glossary
SI system
A worldwide measurement system that is based on the older metric system. The SI comes from the French Systeme International.
Chemistry Glossary
sublimation
The change in the physical state of matter from a solid state to a gaseous state without ever becoming a liquid (such as dry ice).
Chemistry Glossary
valence electrons
The electrons in the outermost energy level of an atom, the farthest away from the nucleus.
