Unit 1 Sec 2 Ions

1 shell ---- 2 e 2 shell ---- 8 e 3 shell ---- 1 e

Octet Rule Noble gases, such as neon and argon, are nonreactive in chemical reactions. -- That is, they are stable In 1916, chemist Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules. He called his explanation the octet rule.

Octet Rule The octet rule states that in forming compounds, atoms tend to achieve the electron configuration of a noble gas.

Octet Rule An octet is 8 valence electrons. is associated with the stability of the noble gases. He is stable with 2 valence electrons (duet). valence electrons He 2 2 Ne 2, 8 8 Ar 2, 8, 8 8 Kr 2, 8, 14, 8 8

1 shell ---- 2 e 2 shell ---- 8 e 3 shell ---- 1 e protons --- 11 neutrons --- 11 electrons --- 11

Na+ 1 shell ---- 2 e 2 shell ---- 8 e protons --- 11 neutrons --- 11 electrons --- 10 Na+

IONS are atoms or groups of atoms with a positive or negative charge. An ion forms when an atom or group of atoms loses or gains electrons. IONS are atoms or groups of atoms with a positive or negative charge.

Cation If a neutral atom loses one or more electrons it becomes a cation. A cation has lost an electron(s) and therefore has a positive charge ex. Mg2+ Mg - 2e-  Mg2+

Formation of a Sodium Ion, Na+ Sodium achieves an octet by losing its one valence electron. 2, 8, 1 2, 8 Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Charge of Sodium Ion, Na+ With the loss of its valence electron, the sodium ion has a +1 charge. Sodium atom Sodium ion 11p+ 11p+ 11e- 10e- 0 1+ 2, 8 Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Formation of Mg2+ Magnesium achieves an octet by losing its two valence electrons. 2, 8, 2 2, 8 Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Charge of Magnesium Ion Mg2+ With the loss of two valence Electrons, magnesium forms a positive ion with a +2 charge. Mg atom Mg2+ ion 12p+ 12p+ 12e- 10e- 0 2+ Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check A. The number of valence electrons in aluminum is 1) 1e-. 2) 2e-. 3) 3e-. B. The change in electrons for octet requires a 1) loss of 3e-. 2) gain of 3e-. 3) a gain of 5e-. C. The ionic charge of aluminum is 1) 3-. 2) 5-. 3) 3+. D. The symbol for the aluminum ion is 1) Al3+. 2) Al3-. 3) Al+.

Solution A. The number of valence electrons in aluminum is 3) 3 e-. B. The change in electrons for octet requires a 1) loss of 3e-. C. The ionic charge of aluminum is 3) 3+. D. The symbol for the aluminum ion is 1) Al3+.

Formation of Negative Ions If a neutral atom gains one or more electrons it becomes an anion. An anion has gained an electron(s) and therefore has a negative charge. ex. N3- N + 3e-  N3-

Formation of a Chloride, Cl- Chlorine achieves an octet by adding an electron to its valence electrons. 2, 8, 7 2, 8, 8 Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Charge of a Chloride Ion, Cl- By gaining one electron, the chloride ion has a -1 charge. Chlorine atom Chloride ion 17p+ 17p+ 17e- 18e- 0 1– Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Ionic Charge from Group Numbers The charge of a positive ion is equal to its Group number. Group 1A(1) = 1+ Group 2A(2) = 2+ Group 3A(3) = 3+ The charge of a negative ion is obtained by subtracting 8 or 18 from its Group number. Group 6A(16) = 6 - 8 = 2- or 16 - 18 = 2-

Some Ionic Charges I- Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

To tell the difference between an atom and an ion, look to see if there is a charge in the superscript!

Na I Ca O Which are the ions? anions? cations? elements? Learning Check Na+ I- Ca+2 O-2 Na I Ca O Which are the ions? anions? cations? elements?

Learning Check A. The number of valence electrons in sulfur is 1) 4e-. 2) 6e-. 3) 8e-. B. The change in electrons for octet requires a 1) loss of 2e-. 2) gain of 2e-. 3) a gain of 4e-. C. The ionic charge of sulfur is 1) 2+. 2) 2-. 3) 4-.

Learning Check – Counting State the number of protons, neutrons, and electrons in each of these ions. 39 K+ 16O -2 41Ca +2 19 8 20 #p+ ______ ______ _______ #no ______ ______ _______ #e- ______ ______ _______

Solution A. The number of valence electrons in sulfur is 2) 6e-. B. The change in electrons for octet requires a 2) gain of 2e-. C. The ionic charge of sulfur is 2) 2-.

Ionic and Covalent Bonds : Atoms form octets to become more stable. by losing, gaining, or sharing valence electrons. by forming ionic bonds or covalent bonds. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Bonds Forces that hold groups of atoms     together and make them function   as a unit. Ionic bonds – transfer of electrons Covalent bonds – sharing of electrons

Metals Form Positive Ions by a loss of their valence electrons. with the electron configuration of the nearest noble gas. that have fewer electrons than protons. Group 1A metals  ion 1+ Group 2A metals  ion 2+ Group 3A metals  ion 3+ Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings