Ionic Bonding and Ionic Formulas Vocabulary bond ionic bond electrostatic attraction subscript formula “Spiral Jetty”, Robert Smithson, American, 1970

What types of particles do you think are involved in ionic bonding? Prediction What types of particles do you think are involved in ionic bonding? What are the two types of ions? How is each type of ion formed?

Chemical Bond What is a bond? An attractive force holding two or more atoms together. How do you think ions could form a bond?

Let’s look at electron configurations We’ve already talked about how cations and anions form. Remember the octet rule? What will each of the following do as with regards to their valence electrons? K 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ Cl 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___

Let’s look at electron configurations In ionic bonding, two elements are involved: one that will lose electrons to form a cation and one that will gain electrons to form an anion. One element will lose one or more electrons to the other element. K (will lose e-) 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ Cl (will gain e-) 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___

Let’s look at electron configurations In ionic bonding, two elements are involved: one that will lose electrons to form a cation and one that will gain electrons to form an anion. One element will lose one or more electrons to the other element. K+ 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___ Cl- 4s __ 4p ___ ___ ___ 3s___3p ___ ___ ___ 2s___2p ___ ___ ___ 1s ___

Let’s look at electron configurations Now that there is a positive ion and a negative ion, they can form a bond through electrostatic attraction. Cl- K+ This attraction IS the ionic bond! The chemical formula for this compound is KCl.

Important Points about Ionic Bonding One element must lose electrons (a metal) and one element must gain electrons (a non-metal). The attraction of the resulting ions is the ionic bond. The compound MUST be neutral (the sum of the positive and negative charges MUST add up to zero.)

Example 1 Let’s look at another example. What will the formula be for a compound with calcium and fluorine? First, draw the Lewis Structures for calcium and for fluorine. Ca F

Example 1 Which element will lose electrons to form a cation? Which will gain electrons to form an anion? Ca F

Example 1 Is that it? Does either of the atoms need to lose or gain any more electrons? + - Ca F Still need to lose this electron, so we need ANOTHER fluorine atom.

Example 1 The number of atoms available to achieve a neutral compound is unlimited! + - Ca F F

Example 1 So now all atoms are following the octet rule and the overall charge is zero. The atoms will now attract each other and form ionic bonds. Ca 2+ F - F -

Example 1 So notice that the overall compound is neutral. Compounds must always be neutral! The chemical formula for this compound is CaF2. F - Ca 2+ F - When drawing the Lewis structure for the overall ionic compound, place brackets around the negative ions to indicate that the electrons belong completely to the negative ion and are not being shared with the positive ion.

Let’s try one now without drawing Lewis structures. Example 2 Let’s try one now without drawing Lewis structures. What will be the chemical formula for a compound containing lithium and phosphorus?

Example 2 First, using the periodic table find out the charge of ions of each element. + 3 - Li P

Li P Li Li + 3 - + So the formula for this compound will be Li3P. + Example 2 How many of each ion will be required to make a neutral compound? (i.e., how many lithium ions will you need to neutralize the charge of the phosphorous ion?) Li + P 3 - Li + So the formula for this compound will be Li3P. Li +

Example 2 In the formula, Li3P, the 3 is a subscript. It tells you the number of lithium ions in the formula. There is also a subscript on P, but it is an understood 1. 1 is the only subscript that is not written.

Example 3 What is the formula for compounds containing each of the following pairs of ions? rubidium and sulfur strontium and oxygen aluminum and oxygen

Example 3 What is the formula for compounds containing each of the following pairs of ions? Rb2S SrO Al2O3

That’s It!