3.1: Two Types of Bonding

1. Define the octet rule.

2. Describe how ionic bonds are formed.

?Chemists have concluded that atoms are especially stable if they have eight electrons in their outermost shell. This useful rule of thumb is called the octet rule, and it is a key to understanding why compounds form.

These elements—helium, neon, argon, krypton, xenon, and radon—do not form compounds very easily, which suggests that they are especially stable as lone atoms. (the noble gas elements) (Of the noble gases, only krypton, xenon, and radon have been found to make compounds.) (Despite our focus on the octet rule, we must remember that for small atoms, such as hydrogen, helium, and lithium, the first shell is, or becomes, the outermost shell and hold only two electrons. Therefore, these atoms satisfy a “duet rule” rather than the octet rule.)

There are two ways for an atom that does not have an octet of valence electrons to obtain an octet in its outer shell:

1. One way is the transfer of electrons between two atoms until all atoms have octets. (ionic bond?離子鍵)?The attraction of oppositely charged ions is what makes ionic bonds.

2. The second way for an atom to obtain an octet of electrons is by sharing electrons with another atom. ?(covalent bond 共價鍵)

3.2: Ions

1. Define the two types of ions.

2. Use Lewis diagrams to illustrate ion formation.

Electron Transfer, ET?電子轉(zhuǎn)移

electron configurations?電子排布?

The term isoelectronic refers to an atom and an ion of a different atom (or two different ions) that have the same electron configuration. The sodium ion is isoelectronic with the neon atom.

1A 1+

2A 2+

3A 3+

5A 3-

6A 2-

7A 1-

Lewis Diagrams?

Chemists use simple diagrams to show an atom’s valence electrons and how they transfer. These diagrams have two advantages over the electron shell diagrams. First, they show only valence electrons. Second, instead of having a circle around the chemical symbol to represent the electron shell, they have up to eight dots around the symbol; each dot represents a valence electron. These dots are arranged to the right and left and above and below the symbol, with no more than two dots on a side.

Ions can be positively charged or negatively charged.

A Lewis diagram is used to show how electrons are transferred to make ions and ionic compounds.

charge balance?電荷平衡

3.3: Formulas for Ionic Compounds

1. Write the chemical formula for a simple ionic compound.

2. Recognize polyatomic ions in chemical formulas.

Ionic compounds exist as alternating positive and negative ions in regular, three-dimensional arrays called crystals.

ex. NaCl?

There are no individual? NaCl “particles” in the array; instead, there is a continuous lattice of alternating sodium and chloride ions.

However, we can use the ratio of sodium ions to chloride ions, expressed in the lowest possible whole numbers, as a way of describing the compound. In the case of sodium chloride, the ratio of sodium ions to chloride ions, expressed in lowest whole numbers, is 1:1, Thus,? NaCl is the chemical formula for sodium chloride, which is a concise way of describing the relative number of different ions in the compound. A macroscopic sample is composed of myriads of NaCl pairs; each individual pair called a formula unit.?

The formula for an ionic compound follows several conventions:

1. The cation is written before the anion.?(Because most metals form cations and most nonmetals form anions, formulas typically list the metal first and then the nonmetal.)

2. Charges are not written in a formula. (Remember that in an ionic compound, the component species are ions, not neutral atoms, even though the formula does not contain charges.)

3. The proper formula for an ionic compound always has a net zero charge, meaning the total positive charge must equal the total negative charge. (To determine the proper formula of any combination of ions, determine how many of each ion is needed to balance the total positive and negative charges in the compound.)

There are two ways to recognize ionic compounds:?

An ionic compound can be identified by its chemical formula: metal + nonmetal or polyatomic ions.

1. Compounds between metal and nonmetal elements are usually ionic.

2. If you recognize the formula of a polyatomic ion in a compound, the compound is ionic. (Groups of atoms with an overall charge, called polyatomic ions, also exist.)

3.4: Ionic Nomenclature

To use the rules for naming ionic compounds

Naming Ions:

1. The name of a monatomic cation is simply the name of the element followed by the word "ion"

(Ions with more than one possible charge:)

ex. Fe^(2+), Fe^(3+)

2.??"Stock system"?用于形成一種以上常見正離子的元素。離子的正電荷由元素名稱后括號中的羅馬數(shù)字表示：iron(II) ion,?iron(III) ion

3.??"Common system"?This system recognizes that many metals have two common cations. -ic表示兩個陽離子電荷中較大的一個，-ous表示較小的一個:?ferrous ion,?ferric ion

4. monatomic anion?的名稱由元素名稱的詞干、后綴 -ide和單詞"ion"組成:?

F^? fluoride ion

Cl^? chloride ion

Naming Compounds:

將陽離子的名稱放在首位，然后是陰離子的名稱，并從兩部分中刪除"ion"一詞

Ba^(2+) barium ion + NO3^(-) nitrate ion: barium nitrate

3.5: Formula Mass

3.6: Characteristics of Ionic Compounds

To describe the physical properties of ionic compounds.

1. Melting Points:?Ionic compounds have high melting points.

Because of the many simultaneous attractions between cations and anions that occur, ionic crystal lattices are very strong.?Because of the many simultaneous attractions between cations and anions that occur, ionic crystal lattices are very strong.?

2.?Shattering:?Ionic compounds are hard and brittle.

3.?Conductivity:?Ionic compounds dissociate into ions when dissolved in water. Solutions of ionic compounds and melted ionic compounds conduct electricity, but solid materials do not.