Chemical Bond 8 Bonding, the way atoms are attracted to each other to form molecules, determines nearly all of the chemical properties we see. And, as we shall see, the number “8” is very important to chemical bonding.

What are the properties of Ionic Compounds?

Ionic compounds have strong attraction of positive and negative ions that result in a crystal lattice. The crystals that result are hard and have strong or high: a. Melting point b. Boiling point

7.1 Valence Electrons Valence Electrons How do you find the number of valence electrons in an atom of a representative element?

7.1 Valence Electrons Valence electrons are the electrons in the highest occupied energy level of an element’s atoms. The number of valence electrons largely determines the chemical properties of an element.

7.1 Valence Electrons To find the number of valence electrons in an atom of a representative element, simply look at its group number.

Find the number of valence electrons: Be I Ge 7.1 Valence Electrons Find the number of valence electrons: Be I Ge

Electron dot structures 7.1 Electron dot structures How do chemists represent valence electrons in forming chemical bonds?

7.1 Valence Electrons Chemists represent valence electrons that are involved in forming chemical bond by the atom’s electron-dot structure.

7.1 Valence Electrons Electron dot structures are diagrams that show valence electrons as dots. It consists of the element’s symbol surrounded by dots representing the atom’s valence electrons. In writing electron dot structure, dots representing valence electrons are placed one at a time on the four sides of the symbol, then paired up until all are used.

Show the electron dot structures of the following: B Sr N 7.1 Valence Electrons Show the electron dot structures of the following: B Sr N

7.1 Valence Electrons

7.1 The Octet Rule The Octet Rule Atoms of which elements tend to gain electrons? Atoms of which elements tend to lose electrons?

7.1 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 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 Formation of Cations Formation of Cations How are cations formed?

7.1 Formation of Cations An atom’s loss of valence electrons produces a cation, or a positively charged ion.

7.1 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 Formation of Cations The electron configuration of the sodium ion is the same as that of a neon atom.

7.1 Formation of Cations Using electron dot structures, you can show the ionization more simply.

The sodium atoms in a sodium-vapor lamp ionize to form sodium cations. 7.1 Formation of Cations The sodium atoms in a sodium-vapor lamp ionize to form sodium cations. The sodium atoms in a sodium-vapor lamp ionize to form sodium cations (Na+). Applying Concepts How many electrons are in the highest occupied energy level of Na+?

7.1 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 2+.

7.1 Formation of Cations Walnuts are a good dietary source of magnesium. Magnesium ions (Mg2+) aid in digestive processes. Walnuts are a good dietary source of magnesium. Magnesium ions (Mg2+) aid in digestive processes.

7.1 Formation of Cations Cations of Group 1A elements always have a charge of 1+. Cations of group 2A elements always have a charge of 2+. Cations of Group 1A elements have a charge of 1+. Cations of Group 2A elements have a charge of 2+.

7.1 Formation of Anions Formation of Anions How are anions formed?

7.1 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. Examples: Chlorine becomes Chloride Fluorine becomes Fluoride

7.1 Formation of Anions The figure shows the symbols of anions formed by some elements in Groups 5A, 6A, and 7A. Atoms of nonmetals and metalloids form anions by gaining enough valence electrons to attain the electron configuration of the nearest noble gas. Interpreting Diagrams In which group of the periodic table do the elements bromine and iodine belong?

7.1 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 Formation of Anions Both a chloride ion and the argon atom have an octet of electrons in their highest occupied energy levels.

7.1 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 Formation of Anions The negatively charged ions in seawater—the anions—are mostly chloride ions. The six most abundant ions in seawater are chloride (Cl– ), sulfate (SO42–), sodium (Na+), magnesium (Mg2+), calcium (Ca2+), and potassium (K+).

All halogen atoms have seven valence electrons. 7.1 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 Formation of Anions Oxygen is in Group 6A.

7.1 Formation of Anions

7.1 Conceptual Problem 7.1

7.1 Conceptual Problem 7.1

7.1 Conceptual Problem 7.1

Practice Problems For Conceptual Problem 7.1 Problem Solving 7.1 Solve Problem 1 with the help of an interactive guided tutorial.

7.1 Section Quiz. 7.1.

7.1 Section Quiz. 1. How many valence electrons are there in an atom of oxygen? 2 4 6 8

7.1 Section Quiz. 2. Atoms that tend to gain a noble gas configuration by losing valence electrons are metals. nonmetals. noble gases. representative elements.

7.1 Section Quiz. 3. When a magnesium atom forms a cation, it does so by losing two electrons. gaining two electrons. losing one electron. gaining one electron.

7.1 Section Quiz. 4. When a bromine atom forms an anion, it does so by losing two electrons. gaining two electrons. losing one electron. gaining one electron

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