15.2 Notes: Ionic Bonds
Learning Targets Explain how the octet rule is related to bond formation Identify the location of metals and nonmetals on the periodic table. Describe how ionic bonds are formed Discuss some important properties of ionic compounds
The Octet Rule According to the octet rule, in forming compounds, atoms tend to combine with other atoms so that they each have 8 valence electrons
Formation of Ionic Bonds
Anions (negative ions) and cations (positive ions) have opposite charges. They attract one another by electrostatic forces The forces of attraction that bind these oppositely charged ions are called ionic bonds
Compounds that consist of groups of ions joined by electrostatic forces are called ionic compound
In any sample of an ionic compound, the total positive charges of the cations must equal the total negative charges of the anions
Consider the reaction between sodium and chlorine
Sodium has a single valence electron that it can easily lose Chlorine has seven valence electrons and can easily gain one When sodium and chlorine react to form a compound, the sodium atom gives up its valence electron and a chlorine ion accepts this electron
The chemical formula of sodium chloride (NaCl) represents a formula unit, or the lowest whole-number ratio of cations to anions in an ionic compound
An aluminum atom has 3 valence electrons while bromine has 7
Therefore, aluminum wants to lose its 3 electrons while bromine wants to gain one more electron This means that when aluminum and bromine react, three bromine atoms combine with each aluminum atom (AlBr3)
Properties of Ionic Compounds
Ionic compounds are always composed of one nonmetal and one metal Electrons transfer from a metal to a nonmetal Where are metals located on the periodic table? What about nonmetals? Metals = left of the stairs except hydrogen Nonmetals = right of stairs and plus hydrogen Elements never gain or lose more than 3 electrons as they form ionic compounds
When melted, ionic compounds can conduct electric current
At room temperature, most ionic compounds are solids because the forces between ions are very strong Ionic solids have a high melting point When melted, ionic compounds can conduct electric current Ionic solids are also hard and dissolve easily in water
Review: What is electronegativity???
The ability of an atom to attract electrons to itself
Write the symbol and determine the charge for the following ions?
Calcium Bromine Aluminum Magnesium Nitrogen Tellurium
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