Valence Electrons and Electron Dot Structures
Valence electrons are the electrons in the atom’s outermost orbitals
 Generally the orbitals associated with the highest principal energy level
 Found in the s orbitals and p orbitals
 Determine the chemical properties of an element
 Involved in forming chemical bonds
 Can contain no more than 8 electrons
Electron Dot Structures consist of the element’s symbol representing the nucleus, surrounded by
dots representing the element’s valence electrons
 Devised by American chemist, G. N. Lewis
 Dots representing the valence electrons are placed one at a time on the four sides of
the symbol, then paired up until all are used
Organizing the Elements by Electron Configuration
Writing out electron configurations can be tedious. However, you can determine tan atom’s electron
configuration and its number of valence electrons from its position on the periodic table.
The modern periodic table consists of boxes, each containing an element name, symbol, atomic
number, and atomic mass.
The boxes are arranged in order of increasing atomic number into a series of columns called groups
or families, and rows called periods. There are seven periods and 18 groups.
Each of the group 1 elements has one valence electron. Therefore, the group 1 elements have similar
chemical properties.
Periodic Trends
Trends among elements in the periodic table include their size and their ability to lose or attract
electrons
Atomic size is a periodic trend influenced by electron configuration.
Sizes of atoms are denoted by their atomic radius which is defined as half the distance between two
bonded atoms of the same element.
As you move left to right across the period table, the atomic radii of the element decreases
 The nuclei of these elements pick up more protons as you move across the table, while
the energy of the electrons stays the same
The atomic radius of the elements increase as you move down a group in the periodic table
 The electrons are in higher energy levels, which put them in bigger orbitals
If you add electrons to an atom it makes it bigger, while taking away electrons makes it smaller
 Adding or removing an electron results in an ion
 Cations are ions with a positive charge (more protons than electrons)
 Anions are ions with a negative charge (more electrons than protons)
The Octet Rule
The octet rule states that the atoms tend to gain or lose electrons so they can have the same
number of electrons as the nearest noble gas. Here are some things that you might want to keep in
mind about this unbelievably important rule:
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The nearest noble gas may be either before the element (just as neon is before
aluminum) or after the element (as argon is after phosphorus).
If the nearest noble gas is before the element of interest, the element will lose valence
electrons until it has the same number of valence electrons as that noble gas. This will
give it a positive charge. As a result, aluminum will lose three electrons to become like
neon, giving it a +3 charge.
If the nearest noble gas is after the element of interest, the element will gain valence
electrons until it has the same number of valence electrons as that noble gas. This will
give it a negative charge. As a result, phosphorus will gain three electrons to become
like argon, giving it a -3 charge.
Ignore the d- and f-blocks when counting forwards and backwards. In this way, gallium
(Ga) wants to lose three electrons to become like argon – we just ignore all of the
transition elements that are between them.