IONIC BONDING

Chemical Bonding  Chemical Bond—a strong attractive force between atoms or ions in a compound.  In almost all of the stable compounds, the atoms have acquired an electron configuration that is isoelectronic with the other element.  Law of definite composition—the proportion of elements in a given compound is fixed.

 The structure of a compound is very important!  Chemical reactions happen when atoms, molecules, or ions come in contact with one another.  The shape can determine whether a reaction will occur.  Bond energy—the energy involved in the process of bond formation and breaking.

Ionic Bonds  Cation= + (positive charge)  Metals form cations  Anion= - (negative charge)  Nonmetals form anions * Each atom wants to have an octet!

How can we tell what charge a particular ion will have? Oxidation number  Tells you the charge of the ion that will form.  Example: sodium’s oxidation number is +1. It will form an ion with 1 positive charge. That is because it will lose 1 electron.

 Electrostatic attraction—opposite charges attract one another (static electricity)  Ionic bond—a chemical bond formed by the electrostatic attraction between a cation and an anion (charges must be equal)

Properties of Ionic Compounds 1. At room temperature, crystals of ionic compounds exist as regular, 3-D arrangements called crystal lattices. 2. As a liquid, conducts electricity (electrolyte) 3. High melting points, brittle, dissolve in water

Forming Ionic Compounds  React a metal with a nonmetal!  Metals transfer one or more electrons to the nonmetal.  Na 1s 2 2s 2 2p 6 3s 1 + Cl 1s 2 2s 2 2p 6 3s 2 3p 5   Na + 1s 2 2s 2 2p 6 + Cl - 1s 2 2s 2 2p 6 3s 2 3p 6  Both now are stable configurations!

Ionic Bonds: One Big Greedy Thief Dog!

 Formula unit—the simplest unit indicated by the formula of any compound. The number of ions in one formula unit depends on the charges of the ions combined.  EX: Na + Cl -  NaCl Mg +2 Cl -  MgCl 2  Shows the ratio of the ions present in a sample of the compound of any size. Al +3 Br -  ?

Determining Oxidation States  Multiply the number of atoms of that element by it’s oxidation #.  Add the elements charges up.  EX: NO 3 -1 N: 1 atom x _____ = _____ O: 3 atoms x ____ = _____ total = _____

NAMING AND WRITING IONICS

Chemical Formulas  Chemical formula—tells you what kind of atoms and how many of each kind are combined together. * consists of symbols of the elements and subscripts.  Subscript—indicates the number of atoms of the elements to its left.  Formula unit—indicates the smallest whole- number ratio of each element.

Types of Ions 1. Monatomic cations—positive ions formed from 1 atom. 2. Monatomic anions—negative ions formed from 1 atom. 3. Polyatomic ions—ions that consist of more than 1 atom. EX: NH 4 +, OH - 4. Binary Compounds—contains the ions of only 2 elements.

Predicting Ion charge Ions in group 1 have a +1 charge Ions in group 2 have a +2 charge Ions in group 13 have a +3 charge (with some exceptions) Ions in group 14 have a +4/-4 charge Ions in group 15 have a -3 charge Ions in group 16 have a -2 charge Ions in group 17 have a -1 charge

Writing Formulas 1. Make sure that you have the correct symbols. 2. The metallic element goes first! 3. Write the symbol of the cation. 4. Write the symbol of the anion. 5. Do the charges equal zero? 6. If not, criss-cross applesauce!

Examples 1. Calcium and chlorine Ca +2 and Cl -1 *must have 2 Cl ions to equal zero! CaCl 2 2. Magnesium and oxygen 3. Potassium and Nitrogen

More examples…. 4. Calcium and hydroxide 5. Ammonium phosphate

Writing Names 1. Write the name of the cation first. 2. Make sure if it has more than one oxidation number that you put a roman numeral. 3. Write the name of the anion. 4. Change the anion’s ending to “-ide” IF it’s not a polyatomic ion!

Examples 1. Na 2 O = sodium oxide 2. Al(NO 3 ) 3 3. FeCl 2 4. FeCl 3