Chemistry 7.1

Chemistry 7.1Chemistry 7.1

IonsIons

Pyrite (FeSPyrite (FeS22), a common mineral ), a common mineral

that emits sparks when struck that emits sparks when struck against steel, is often mistaken against steel, is often mistaken for gold—hence its nickname, for gold—hence its nickname, “fool’s gold.” Pyrite is an “fool’s gold.” Pyrite is an example of a crystalline solid. In example of a crystalline solid. In this chapter, you will learn about this chapter, you will learn about crystalline solids composed of crystalline solids composed of ions that are bonded together. ions that are bonded together. But first you need to understand But first you need to understand how ions form from neutral how ions form from neutral atoms.atoms.

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Valence ElectronsValence Electrons

Valence ElectronsValence Electrons How do you find the number of valence How do you find the number of valence

electrons in an atom of a representative electrons in an atom of a representative element?element?

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Valence electronsValence electrons are the electrons in the are the electrons in the highest occupied energy level of an element’s highest occupied energy level of an element’s atoms.atoms.

The number of valence electrons largely The number of valence electrons largely determines the chemical properties of an determines the chemical properties of an element.element.

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

Example: 1A = 1 valence electronExample: 1A = 1 valence electron 2A = 2 valence 2A = 2 valence

electronselectrons

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Applications of Group 4A ElementsApplications of Group 4A Elements Carbon Silicon GermaniumCarbon Silicon Germanium

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Carbon Silicon Germanium


Electron dot structuresElectron dot structures are diagrams that show are diagrams that show valence electrons as dots.valence electrons as dots.

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The Octet RuleThe Octet Rule

The Octet RuleThe Octet Rule Atoms of which elements tend to gain Atoms of which elements tend to gain

electrons? electrons? Atoms of which elements tend to lose Atoms of which elements tend to lose

electrons?electrons?

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Noble gases, such as neon and argon, are Noble gases, such as neon and argon, are unreactive in chemical reactions. In 1916, unreactive in chemical reactions. In 1916, chemist Gilbert Lewis used this fact to chemist Gilbert Lewis used this fact to explain why atoms form certain kinds of ions explain why atoms form certain kinds of ions and molecules.and molecules.

He called his explanation the octet rule: In He called his explanation the octet rule: In forming compounds, atoms tend to achieve forming compounds, atoms tend to achieve the electron configuration of a noble gas.the electron configuration of a noble gas.

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Atoms of metals tend to lose their Atoms of metals tend to lose their valence electrons, leaving a complete valence electrons, leaving a complete octet in the next-lowest energy level.octet in the next-lowest energy level.

Atoms of some non-metals tend to Atoms of some non-metals tend to gain electrons or to share electrons gain electrons or to share electrons with another nonmetal to achieve a with another nonmetal to achieve a complete octet.complete octet.

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Formation of CationsFormation of Cations

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

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An atom’s loss of valence An atom’s loss of valence electrons produces a electrons produces a cationcation, or a , or a positively charged ion.positively charged ion.

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The most common The most common cationscations are those produced are those produced by the loss of valence electrons from by the loss of valence electrons from metal metal atoms. atoms.

You can represent the electron loss, or ionization, You can represent the electron loss, or ionization, of the sodium atom by drawing the complete of the sodium atom by drawing the complete electron configuration of the atom and of the ion electron configuration of the atom and of the ion formed.formed.

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Formation of CationsFormation of Cations The electron configuration of the sodium ion is The electron configuration of the sodium ion is

the same as that of a neon atom.the same as that of a neon atom.

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Using electron dot structures, you can show the Using electron dot structures, you can show the ionization more simply.ionization more simply.

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The The sodiumsodium atoms in a sodium- atoms in a sodium-vapor lamp ionize to form sodium vapor lamp ionize to form sodium cations.cations.

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Formation of CationsFormation of Cations A A magnesiummagnesium atom attains the electron configuration atom attains the electron configuration

of neon by losing of neon by losing bothboth valence electrons. The loss of valence electrons. The loss of valence electrons produces a magnesium cation with valence electrons produces a magnesium cation with a charge of 2+.a charge of 2+.

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Walnuts are a Walnuts are a good dietary good dietary source of source of magnesium. magnesium. Magnesium ions Magnesium ions (Mg(Mg2+2+)) aid in aid in digestive digestive processes.processes.

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Cations of Group 1A Cations of Group 1A elements always have a elements always have a charge of 1+.charge of 1+.

Cations of group 2A Cations of group 2A elements always have a elements always have a charge of 2+.charge of 2+.

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Formation of CationsFormation of Cations A copper atom can ionize to form a 1+ cation (CuA copper atom can ionize to form a 1+ cation (Cu++). By ). By

losing its lone 4losing its lone 4ss electron, copper attains a pseudo electron, copper attains a pseudo noble-gas electron configuration.noble-gas electron configuration.

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Formation of AnionsFormation of Anions


How are anions formed?How are anions formed?

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The gain of negatively charged electrons by a The gain of negatively charged electrons by a neutral atom produces an anion.neutral atom produces an anion.

An anion is an atom or a group of An anion is an atom or a group of atoms with a negative charge.atoms with a negative charge.

The name of an anion typically The name of an anion typically ends in -ends in -ideide..

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The figure shows The figure shows the symbols of the symbols of anions formed by anions formed by some elements in some elements in Groups 5A, 6A, Groups 5A, 6A, and 7A.and 7A.

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A A gain of one electrongain of one electron gives chlorine an octet gives chlorine an octet and converts a and converts a chlorine atomchlorine atom into a into a chloride chloride ionion. It has the same electron configuration as the . It has the same electron configuration as the noble gas argon. noble gas argon.

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Formation of AnionsFormation of Anions Both a chloride ion and the argon atom have an Both a chloride ion and the argon atom have an

octet of electrons in their highest occupied octet of electrons in their highest occupied energy levels.energy levels.

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In this equation, each dot in the electron dot In this equation, each dot in the electron dot structure represents an electron in the structure represents an electron in the valence shell in the electron configuration valence shell in the electron configuration diagramdiagram..

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The negatively The negatively charged ions in charged ions in seawater—seawater—thethe anionsanions—are mostly —are mostly chloride ions.chloride ions.

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The ions that are produced when The ions that are produced when atoms of chlorine and other halogens atoms of chlorine and other halogens gain electrons are called gain electrons are called halide ionshalide ions..

All halogen atoms have All halogen atoms have sevenseven valence electrons. valence electrons. All halogen atoms need to All halogen atoms need to gain onlygain only one electronone electron to to

achieve the electron configuration of a noble gas.achieve the electron configuration of a noble gas.

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Formation of AnionsFormation of Anions Oxygen is in Group 6A.Oxygen is in Group 6A.

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Formation of AnionsFormation of Anions7.1

Conceptual Problem 7.1Conceptual Problem 7.17.1

Conceptual Problem 7.1Conceptual Problem 7.1

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Conceptual Problem 7.1Conceptual Problem 7.17.1

7.1 Section Quiz.7.1 Section Quiz.

1. How many valence electrons are there in 1. How many valence electrons are there in an atom of oxygen?an atom of oxygen? 22 44 66 88

7.1 Section Quiz.7.1 Section Quiz. 2. Atoms that tend to gain a noble gas 2. Atoms that tend to gain a noble gas

configuration by losing valence electrons areconfiguration by losing valence electrons are metals.metals. nonmetals.nonmetals. noble gases.noble gases. representative elements.representative elements.

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


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


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Chemistry 7.1