DE_Chem_2.3_ElectronRepresentations

The valence electrons, electrons in the atom’s shell, determine how the element will react to other elements. These electrons can be represented by an and/or diagram.

To study the of an element, scientists consider where the electrons are located within an atom. theory uses specific to describe the locations of the electrons. Scientists must know how to write electron configurations to apply these rules. They use a method to describe the configurations, using a system of quantum numbers. The system uses the quantum number (n) and the quantum number (l) to describe the configuration of electrons in an atom.

An Orbital diagram is used to illustrate the configuration of within the orbitals in an atom; electrons are represented by pointing up or down (denoting each electron's spin) in a box representing each

Within an energy level, the higher the quantum number, the more energy in the orbital. The 2p orbitals (azimuthal number 1) are slightly in energy than the 2s orbitals (azimuthal number 0). Quantum numbers are a unique set of numbers that describes the location of each electron in an atom or ion and include the , azimuthal, magnetic orbital, and magnetic spin quantum numbers.

In most elements, electrons in the outermost energy level of an atom are electrons. They reside in the occupied energy level of the atom. The number of valence electrons in an atom can be determined from the electron configuration of the element. The total number of electrons at the highest energy level dictates the number of valence electrons. For example, carbon (C) has four electrons in its outermost energy level: two in the 2s orbital and two in the 2p orbital. Carbon, therefore, has valence electrons.

Lewis structures follow trends in the Periodic Table. Moving across a period, a dot is for each additional electron in an atom of the element. The number and pattern of dots is the same moving a group, making Lewis structures convenient representations of both the elements and their valence electrons.

Gilbert Lewis studied the electron configurations of the various elements in the periodic table and derived the rule. The octet rule states that atoms react with one another in ways that make their electron configurations the same as that of a gas. In a noble gas, orbitals within an energy level are filled. In other elements, filling an energy level the arrangement of the electrons.

Consider the halogens, the elements in Group 17. They have valence electrons and are one short of the noble gas configuration. Halogens readily form ions by acquiring an electron from other atoms or molecules. The ions formed in this way, known as halides, have a charge of . This charge is indicated by a superscript minus sign next to an atomic symbol, such as F–. Similarly, the Group 1 alkali metals have valence electron. If an atom of sodium loses its valence electron, it forms a sodium ion, Na+, with a charge.