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Chapter 6: Chemical Bonds

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1 Chapter 6: Chemical Bonds
Section 1: Ionic Bonding

2 Compounds All matter wants to exist in a stable state. Stability is formed when the outer electron energy level is full. Most elements do not have full outer electron levels. Elements readily form compounds to reach an overall stable state.

3 Atomic Stability For atoms to be stable in real life, they need to have the outermost level of electrons full. Remember that 2, 8 & 8 (18) are the stable electron configuration for the first three energy levels. The noble gases (group 18) are quite stable as each has a completely full outer energy level. Because of this they do not readily make compounds.

4 Valence electrons The outside level of electrons are what are known as valence electrons. Valence electrons determine how close an element is to being in a stable state. For example, fluorine has seven outer electrons. It needs only one more electron to fill its outer level to the stable state (8).

5 Dot Diagrams Dot diagrams are models that show the valence electrons (outside electron level only!) in an atom. Here is a dot diagram for fluorine. This shows that fluorine needs only one electron to become stable (full outer level). Dot diagrams are commonly only used for elements in groups 1, 2 and

6 Oxidation Numbers We will be placing numbers on your periodic table above groups 1, 2, and groups These numbers are called oxidation numbers. Oxidation numbers tell you how many electrons an atom will need to lose or gain to become stable. When elements lose or gain electrons they become what are known as ions.

7 Ionic Bonds When an element gains or loses an electron(s) it forms an ion. The element is called an ion as it no longer has an equal number of protons and electrons and the element takes on either a positive or a negative charge. When elements bond with ions, it is called an ionic bond.

8 What elements form an ionic bond
Ionic bonds are normally formed between metals and a nonmetals. As you may notice, these elements are on opposite sides of the periodic table from each other. For example, sodium, a metal bonds with chlorine, a non metal, to form sodium chloride (NaCl). This is an ionic bond.

9 Ionic Compounds = No Net Charge
In an ionic bond, one element gains an electron(s) and one loses an electron(s). An atom that gains electrons is called a anion (- charged). An atom that loses electrons is called a cation (+ charged). Even though they form ions, the net overall sum charge of a stable ionic compound is zero.

10 Chemical Formulas When elements combine to form compounds, these are written as chemical formulas. A chemical formula shows the elements in a compound and their exact ratio. If more than one atom of an element is present in the compound, a subscript is used to show this number. For example Li2O shows 2 lithium atoms. If there is only one atom present, no subscript is used.

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