Name _____________________________ Class __________ Date __________
Electron Dot Structures
Valence Electrons
Valence electrons are the electrons in the highest occupied energy level of an element’s atoms.
The number of valence electrons is important in determining the chemical properties of an
element. The number of valence electrons in an atom of an element is related to the element’s
group number in the periodic table. For a Group A element, the number of valence electrons is
the same as its group number. For example, atoms of the Group 1A elements (including
hydrogen, lithium, and sodium) all have one valence electron. The number 1 in Group 1A means
that there is one valence electron. Atoms in Group 2A have two valence electrons. Atoms in
Group 3A have three valence electrons, and so on. Helium is the only exception to the rule.
Helium is in Group 8A, but helium atoms have two valence electrons.
Electron Dot Structures
Valence electrons are usually the only electrons involved in chemical bonds. Therefore, as a
general rule, only the valence electrons are shown in electron dot structures. Electron dot
structures are diagrams that show an atom’s valence electrons as dots. In general, only valence
electrons are involved in chemical bonds. Electrons in lower energy levels are usually not
involved in bonds. The table below shows electron dot structures for atoms of some Group A
elements. Notice that all of the elements in a group (with the exception of helium) have the same
number of electron dots in their structures.
Name _____________________________ Class __________ Date __________
Electron Dot Structures and Electron Configurations
Recall the shorthand method for expressing electron configurations of atoms. For example, the
electron configuration of a nitrogen atom is 1s22s22p3. To convert an electron configuration to an
electron dot structure, identify the electrons in the highest occupied energy level. For nitrogen,
the highest occupied energy level is the second energy level. The part of the electron
configuration that corresponds to the second energy level is 2s22p3. The 2s2 means there are two
electrons in the 2s sublevel, and the 2p3 means there are three electrons in the 2p sublevel. In
total, there are five electrons in the highest occupied energy level for nitrogen. To draw the
electron dot structure for nitrogen, write the chemical symbol for nitrogen surrounded by five
dots as shown below.
Concept Practice
Use the periodic table to complete the following table.
Element
name
Element
symbol
Group in the
periodic table
Number of
valence
electrons
Electron dot
structure
iodine
bismuth
strontium
cesium
tin