Why isn’t the world made only of elements? • How do the atoms of different elements combine to form compounds? • The answers to these questions are related to electrons and their energy levels. • And the roadmap to understanding how electrons determine the properties of elements is the periodic table.
Valence Electrons and Bonding • You already learned that electrons exist in energy levels. • An atom’s valence electrons (vay luns) are those electrons that are in the highest energy level and held most loosely. • The number of valence electrons in an atom of an element determines many properties of that element, including the ways in which the atom can bond with other atoms.
Valence Electrons Skydivers in the outer ring are less securely held to the group than are members of the inner ring. Similarly, valence electrons are more loosely held by an atom than are electrons in lower energy levels.
Electron Dot Diagrams • Each element has a specific number of valence electrons, ranging from 1 to 8. • Figure 9 shows one way to depict the number of valence electrons in an element. • An electron dot diagram includes the symbol for the element surrounded by dots. • Each dot stands for one valence electron.
Can hold up to 8 electrons • In order to find the number of valence electrons you must fill in each energy level with the maximum amount of electrons that it can hold, and then only show the electrons in the outermost level. • The first energy level can hold 2 electrons and the next two levels can hold 8 electrons each.
For example, the element Carbon has 6 electrons total. • This means that 2 electrons will fill the first level and 4 will go in the second level. • Because 4 electrons will be in the outermost level, Carbon has 4 valence electrons which should be shown on the dot diagram. • Atoms will always strive to fill their outermost level. • In order to fill their energy levels, they must gain, lose or share electrons with other elements. • Elements that have filled outermost levels do not easily react with other elements.
Figure 9 Electron Dot DiagramsAn atom’s valence electrons are shown as dots around the symbol of the element. Notice that oxygen atoms have 6 valence electrons. Predicting How many more electrons are needed to make an oxygen atom stable?