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What are Ionic Compounds • Ionic compounds are compounds that are composed of cations (positively charged ions) and anions (negatively charged ions). • They usually involve a metal (forms the cation) and a nonmetal (anion)
What causes atoms to form ions? • Every element wants to be like a noble gas and have 8 valance electrons (Rule of octet). • Elements will form chemical bonds to have 8 by either sharing or transferring electrons. • Ionic bonds deal with the transfer of electrons and the attractive forces between the opposite charged ions that form. • Every element that is close to having 8 valance electrons will steal or give away electrons to get to 8.
So, it boils down to stability • Atoms can form multiple ions based on the stability of their electron configurations. • The charges are known as the ion’s oxidation numbers. • Remember, only ions have oxidation numbers. All atoms, elements, molecules, and compounds have an oxidation number of zero. • Ions can have oxidation numbers ranging from -4 to +7.
What are the most stable electron configurations? • Most stable is a full or empty energy level. • Next is a full or empty sublevel (s,p,d,f) • Next is a half-filled sublevel • After that, it is considered unstable.
What column does every element want to be like? Most Common Predicted Oxidation Numbers 0 +4 -4 +1 +2 +3 -3 -2 -1 vary
Let’s look at Na and Cl • What is the electron configuration of Na? • How can Na become like a noble gas? • It can lose an electron. • What is the electron configuration of Cl? • How can Cl become like a noble gas? • It can gain an electron 1s2 2s2 2p6 3s1 or [Ne] 3s1 1s2 2s2 2p6 3s2 3p5 or [Ne] 3s2 3p5
Let’s look at Na and Cl Na becomes Na+ and more stable • What is the electron configuration of Na? • How can Na become like a noble gas? • It can lose an electron. • What is the electron configuration of Cl? • How can Cl become like a noble gas? • It can gain an electron 1s2 2s2 2p6 3s1 or [Ne] 1s2 2s2 2p6 3s2 3p5 or [Ne] 3s2 3p6 [Ar] Cl becomes Cl- and more stable
This can also be done with Lewis Dot Formulas So, let’s practice that… (back of homework from Friday)
To find the oxidation number of the ions that compose an ionic compound, remember… • When dealing with two atoms, the first atom listed will have a positive number, the second will have a negative number. • The majority of the time, the elements from group 1 will be +1, the elements from group 2 will be +2, the elements from group 16 will be -2, and the elements from group 17 will be -1 • The sum of the charges times their subscripts must equal zero.
NaCl MgO WS3 AlN ZnBr2 PCl5 HgS +1 -1 +2 -2 +6 -2 +3 -3 +2 -1 +5 -1 +2 -2 Find the oxidation number for each atom in the following molecules
Homework • Page 165: 6,7,10,11,13 • Page 183: 7,9,12,13,16