Slide 1 of 39 Chemistry 7.1

© Copyright Pearson Prentice Hall Ions > Slide 2 of 39 Valence Electrons How do you find the number of valence electrons in an atom of a representative element? 7.1

Slide 3 of 39 © Copyright Pearson Prentice Hall Ions > Valence Electrons Valence electrons are the electrons in the highest occupied energy level of an element’s atoms. The number of valence electrons determines the chemical properties of an element and are usually the only electrons used in chemical bonds. 7.1

© Copyright Pearson Prentice Hall Slide 4 of 39 Ions > Valence Electrons To find the number of valence electrons in an atom of a representative element, look at its group number. For example, Group 1A elements have 1 valence electron. Group 5A elements have 5 valence electrons. 7.1

Slide 5 of 39 © Copyright Pearson Prentice Hall Ions > Valence Electrons Electron dot structures are diagrams that show valence electrons as dots. 7.1

Slide 6 of 39 © Copyright Pearson Prentice Hall Ions >

Slide 7 of 39 © Copyright Pearson Prentice Hall Ions > The Octet Rule Noble gases, such as neon and argon, are unreactive in chemical reactions. 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: In forming compounds, atoms tend to achieve the electron configuration of a noble gas. 7.1

© Copyright Pearson Prentice Hall Slide 8 of 39 Ions > The Octet Rule Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level. Atoms of some non-metals tend to gain electrons or to share electrons with another nonmetal to achieve a complete octet. 7.1

© Copyright Pearson Prentice Hall Ions > Slide 9 of 39 Formation of Cations How are cations formed? 7.1

© Copyright Pearson Prentice Hall Slide 10 of 39 Ions > Formation of Cations An atom’s loss of valence electrons produces a cation, or a positively charged ion. 7.1

Slide 11 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Cations The most common cations are those produced by the loss of valence electrons from metal atoms. You can represent the electron loss, or ionization, of the sodium atom by drawing the complete electron configuration of the atom and of the ion formed. 7.1

© Copyright Pearson Prentice Hall Slide 12 of 39 Ions > Formation of Cations The electron configuration of the sodium ion is the same as that of a neon atom. 7.1

Slide 13 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Cations Using electron dot structures, you can show the ionization more simply. 7.1

Slide 14 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Cations The sodium atoms in a sodium-vapor lamp ionize to form sodium cations. 7.1

Slide 15 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Cations A magnesium atom attains the electron configuration of neon by losing both valence electrons. The loss of valence electrons produces a magnesium cation with a charge of

Slide 16 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Cations Walnuts are a good dietary source of magnesium. Magnesium ions (Mg 2+ ) aid in digestive processes. 7.1

Slide 17 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Cations Cations of Group 1A elements always have a charge of 1+. Cations of group 2A elements always have a charge of

© Copyright Pearson Prentice Hall Slide 18 of 39 Ions > Formation of Cations A copper atom can ionize to form a 1+ cation (Cu + ). By losing its lone 4s electron, copper attains a pseudo noble-gas electron configuration. 7.1

© Copyright Pearson Prentice Hall Ions > Slide 19 of 39 Formation of Anions How are anions formed? 7.1

Slide 20 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Anions The gain of negatively charged electrons by a neutral atom produces an anion. An anion is an atom or a group of atoms with a negative charge. The name of an anion typically ends in -ide. 7.1

Slide 21 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Anions The figure shows the symbols of anions formed by some elements in Groups 5A, 6A, and 7A. 7.1

Slide 22 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Anions A gain of one electron gives chlorine an octet and converts a chlorine atom into a chloride ion. It has the same electron configuration as the noble gas argon. 7.1

© Copyright Pearson Prentice Hall Slide 23 of 39 Ions > Formation of Anions Both a chloride ion and the argon atom have an octet of electrons in their highest occupied energy levels. 7.1

Slide 24 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Anions In this equation, each dot in the electron dot structure represents an electron in the valence shell in the electron configuration diagram. 7.1

Slide 25 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Anions The negatively charged ions in seawater—the anions—are mostly chloride ions. 7.1

Slide 26 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Anions The ions that are produced when atoms of chlorine and other halogens gain electrons are called halide ions. All halogen atoms have seven valence electrons. All halogen atoms need to gain only one electron to achieve the electron configuration of a noble gas. 7.1

© Copyright Pearson Prentice Hall Slide 27 of 39 Ions > Formation of Anions Oxygen is in Group 6A. 7.1

Slide 28 of 39 © Copyright Pearson Prentice Hall Ions > Formation of Anions 7.1

© Copyright Pearson Prentice Hall Slide 29 of 39 Conceptual Problem

© Copyright Pearson Prentice Hall Slide 30 of 39 Conceptual Problem

© Copyright Pearson Prentice Hall Slide 31 of 39 Conceptual Problem

© Copyright Pearson Prentice Hall Slide 32 of 39 Practice Problems Practice Problems For Conceptual Problem 7.1 Problem Solving 7.1 Solve Problem 1 with the help of an interactive guided tutorial. for Conceptual Problem 7.1

© Copyright Pearson Prentice Hall Slide 33 of 39 Section Quiz -or- Continue to: Launch: Assess students’ understanding of the concepts in Section 7.1 Section Quiz. 7.1.

© Copyright Pearson Prentice Hall Slide 34 of Section Quiz. 1. How many valence electrons are there in an atom of oxygen? a.2 b.4 c.6 d.8

© Copyright Pearson Prentice Hall Slide 35 of Section Quiz. 2. Atoms that tend to gain a noble gas configuration by losing valence electrons are a.metals. b.nonmetals. c.noble gases. d.representative elements.

© Copyright Pearson Prentice Hall Slide 36 of When a magnesium atom forms a cation, it does so by a.losing two electrons. b.gaining two electrons. c.losing one electron. d.gaining one electron. 7.1 Section Quiz.

© Copyright Pearson Prentice Hall Slide 37 of When a bromine atom forms an anion, it does so by a.losing two electrons. b.gaining two electrons. c.losing one electron. d.gaining one electron 7.1 Section Quiz.

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