Ionic Bonds

Chapter 8 Section 2

Ionization Energy

• What is “ionization energy”?Answer: the energy required to remove an

electron from a gaseous atom• This means that energy is required to form

positive ions.• Energy is released when a negative ion is

formed.

• Examples: Na & Cl1.Na + ionization energy → Na+ + e-

2.Cl + e- → Cl- + energy

3.Positive ions don’t have special names, but negative ions have their endings changed to –ide.– Oxygen ion = oxide– Nitrogen ion = ??– Chlorine ion = ???

PracticeWrite the formula for its ion formation and if energy is released or absorbed

1. Cesium2. Magnesium3. Aluminum4. Carbon5. Astatine6. Oxygen7. Bromine

Ionic Bond

• Bond in which 1 or more electrons from one atom are removed & attached to another atom.

• Results in positive & negative ions which attract each other

• Usually occurs between metals & nonmetals• Binary ionic compounds contain ____

different elements.• Two

Ionic Bond

• If an ionic bond forms between metals and the nonmetal oxygen than an oxide forms.

• Most other ionic compounds are called salts

Example: Ca + F1. Which element will GAIN electrons to form an

ion?2. How many will it gain?3. Write the formula for the ion formation?4. What is the name of the ion?5. How many will the other element lose when it

forms an ion?6. Write the formula for the ion formation.7. What is the name of the ion?

• We determined that calcium loses 2 electrons, and fluorine gains 1.

• If a fluoride ion can only take 1 of calcium’s electrons, what will calcium do with the other electron it loses?

Answer: It will look for another ion to take it.• So how many fluoride ions does each calcium

ion want to bond with?Answer: 2

Mathematically

1 Ca ion (+2) + 2 F ion (-1) = 1(+2) + 2(-1) = 0 Ca ion F ion

• Find the least common multiple of the 2 oxidation numbers – in this case, 2.

• The charges must balance so the whole compound is neutral (total charge = 0)!

• The formula will have 1 Ca and 2 F ions, so it will be CaF2.

Formula Unit

• The formula obtained is called the formula unit: the simplest ratio of the ions in an ionic compound.

• Its name will be metal + nonmetal-ide, or calcium fluoride.

Formation of an Ionic Bond

• 3 ways to show the formation of an ionic compound:1. Electron configuration2. Orbital notation3. Electron-dot structure

• 1. [Ne] 3s1 + [Ne] 3s23p5 → [Ne] + [Ar] + nrg– What happens to the [Ne] 3s1?– What happens to the [Ne] 3s23p5?– Why is there energy released?

2.Orbital notation– Write the orbital notations for both Na and Cl.– What do you think will happen to the extra

electron in the 3s orbital of Na?– What will the new orbital notations look like?

3. Electron-dot structure– Write the electron-dot structures for both Na

and Cl.– Write the electron-dot structures of the ions

formed.

Practice Problems

• Pg. 217 # 7-11

Names & Formulas for Ionic Compounds

Monatomic Ion

• A one-atom ionEx: Mg2+, N3-

• Polyatomic ion??• Ions that are made up of more than one atom• Ex: NO2

-, OH-

Polyatomic Ions

• Polyatomic ions act as a single unit (or ion), so rules for writing formulas for ionic compounds including polyatomic are the same as the rules you have followed for writing formulas for binary compounds.

Examples

1. NH4+1 + Cl-1 (ammonium + chloride)

– Are the charges balanced?– So how would you write the formula unit?– What is its name?

2. Ca+2 + PO4-3 (calcium + phosphate)

– Are the charges balanced?– Use least common multiple method to

determine the formula unit.– What is its name?

Common Polyatomic Ions• See Table 8-6, p.224, for a list of common

polyatomic ions• Write the correct formula for the ionic

compound composed of the following pairs of ions.

A.Sodium & NitrateB.Calcium & ChlorateC.Aluminum & carbonateD.Potassium & chromateE. Magnesium & carbonate

Oxyanion

• A polyatomic ion composed of an element, usually a nonmetal, bonded to one or more oxygen atoms.

• Many contain the same nonmetal & have the same charges but differ in the # of oxygen atoms.

Oxyanions

• The ion with more oxygen atoms is named using the root of the nonmetal plus the suffix –ate.

• The ion with fewer oxygen atoms is named using the root of the nonmetal plus the suffix –ite.

• For Example:• NO3

- = nitrate NO2- = nitrite

Rules for Naming Ionic Compounds

1. Name the cation first and the anion second2. Cations use the element name3. Anions add –ide to the element name4. Group 1A & Group 2A metals have only one

oxidation number; Transition metals and metals on the right side of the periodic table often have more than one oxidation #.

• The oxidation # of the cation is written as a roman numeral in parentheses after the name.

• EX: Fe2+ and O2- = FeO Iron(II) Oxide

• Fe2O3 = iron (III) oxide

Rules Continued

5. If a compound contains a polyatomic ion, name the ion.

EX: NaOH = sodium hydroxide

Review

• Pg 226 #29-33