Valence Electrons, Ions, and the Periodic Table Valence Electrons • Valence electrons are electrons in the outer energy level of an atom. • Find the number of valence electrons for: 1.Li 2.P 3.I 4.Ar 5.Ca 6.O Practice! 7. He Check It! 1. Li = 1 2. P = 5 3. I = 7 4. Ar = 8 5. Ca = 2 6. O = 6 7.. He = 2 (not 8)! Now For Lewis Dot Structures! (Also called Electron Dot Structures) • Step 1: Write the symbol for the element. • Step 2: Put ‘dots’ around the symbol to represent valence electrons. See It In Action! • Let’s do Carbon. The symbol for carbon is C • Carbon is in Group 4 • 4 valance electrons • Put one on each side! You do some! • Draw the Lewis Dot Structures for the following atoms: 1.Oxygen 2.Sodium 3.Fluorine 4.Nitrogen 5.Beryllium Check it! 1. 2. 3. 4. 5. Across Period 2 Electron Dot, or Lewis Dot Symbols for the “Representative” Elements Since elements in the same family have the same number of valence electrons, their dot structures will look the same, too! ION: an atom that has gained or lost one or more electrons **atoms with the same atomic number (protons), but different number of electrons §An atom that has LOST one or more electrons (has an overall positive charge) 19 11 Na 11 Protons 8 Neutrons 19 11 Na 11 Protons 8 Neutrons +1 19 11 Na 11 Protons 8 Neutrons Na+1 +1 19 11 Na 11 Protons 8 Neutrons +1 Na Sodium Ion If a neutral Magnesium atom loses two electrons, what will its overall charge be? A. -2 B. +1 C. +2 C D. -1 How many electrons are in an ion of K +1 ? A. 39 B. 18 B C. 19 D. 20 §An atom that has gained one or more electrons (has an overall negative charge). 17 9 F 9 Protons 8 Neutrons 17 9 F 9 Protons 8 Neutrons 17 -1 9 F 9 Protons 8 Neutrons F -1 17 -1 9 F 9 Protons 8 Neutrons -1 F Fluoride Ion If a neutral oxygen atom gains two electrons, what will its overall charge be? A. -2 B. +1 C. +2 D. -1 A How many electrons are in an ion of Br -1 ? A. 35 B. 34 C. 36 D. 79 C Learning Check Give the ionic charge for each of the following: 1. 12 p+ and 10 e- A) 0 B) 2+ C) 2- 2. 50 p+ and 46 e- A) 2+ B) 4+ C) 4- 3. 15 p+ and 18e- A) 3+ B) 3- C) 5- Now What Do I Do With That? • We can use number of valence electrons to predict which charge they make when we turn them into an ion. • Review: what’s an ion?? –An atom that has gained or lost electrons. • Atoms can become more stable if they have FULL outer energy levels PREDICTING ION CHARGES In general •metals (like Mg) lose electrons ---> cations •nonmetals (like F) gain electrons ---> anions How So? • For atoms with LESS than 4 valence electrons, they’re going to lose/give up electrons to form positive cations. • For atoms with MORE than 4 valence electrons, they’re going to gain/steal electrons to form negative anions. • For atoms with 4 valence electrons, it can go either way. • For atoms with 8 valence electrons, there is no change. Example • I need to know what ion Aluminum forms. • I know that it has 3 valence electrons. • Is 3 closer to 0 or 8? Closer to 0 • So will it gain or lose electrons? Lose • How many will it lose to be 0? All 3 • If it loses electrons, will it be + or -? + • So I end up with… Al+3 More Practice! • Predict the ion formed by the following elements: Write the symbol with the charge. 1.Cl 2.B 3.K 4.Ca 5.O 6.Ne Check It! 1.Cl = Cl- 2.B = B+3 3.K = K+ 4.Ca = Ca+2 5.O = O-2 6.Ne = Ne (no change) Ion Formation Summary n Atoms gain or lose electrons to become more stable. –They achieve the same number of valence electrons as the Noble Gases (in the last column) 1 2 3 4 5 6 7 .