Chemical Bonding I: Chemical Bonding I: Ions & Ionic BondsIons & Ionic Bonds

Glencoe: Chapter EightGlencoe: Chapter Eight

8.1: Forming Chemical Bonds8.1: Forming Chemical Bonds

Chemical bondsChemical bonds are the attractive forces are the attractive forces that hold two or more atoms together. that hold two or more atoms together.

Valence electrons are used to arrange Valence electrons are used to arrange elements into groups. They are also elements into groups. They are also involved in the formation of chemical involved in the formation of chemical bonds.bonds.

Why lose electrons?Why lose electrons?Sodium has one valence electron, Sodium has one valence electron,

represented by represented by 1s1s22 2s 2s22 2p 2p66 3s3s11

When sodium loses its valence electron, it When sodium loses its valence electron, it

looks like: looks like: 1s1s22 2s 2s22 2p 2p66

What element is this???What element is this???The octet rule states that atoms gain, lose The octet rule states that atoms gain, lose

or share electrons in order to acquire a full or share electrons in order to acquire a full set of 8 valence electrons (or completely set of 8 valence electrons (or completely filled s and p orbitals) filled s and p orbitals) to get an unusually to get an unusually stable configuration.stable configuration.

Formation of Positive IonsFormation of Positive Ions

Positive ions form when electrons are lost.Positive ions form when electrons are lost.Metals typically form cations.Metals typically form cations.Reactivity of metals is based on the ease Reactivity of metals is based on the ease

at which electrons are lost.at which electrons are lost.Positive ions are called Positive ions are called cationscations..

Transition MetalsTransition Metals

Transition metals have an outer energy Transition metals have an outer energy level of nslevel of ns22. Going from left to right, inner . Going from left to right, inner d sublevels are being filled.d sublevels are being filled.

Transition metals commonly form +2 Transition metals commonly form +2 cations because they lose those two cations because they lose those two valence electrons. However, d orbital valence electrons. However, d orbital electrons may also be lost.electrons may also be lost.

Formation of Negative IonsFormation of Negative Ions

Nonmetals form negative ions, called Nonmetals form negative ions, called anionsanions. Nonmetals have high electron . Nonmetals have high electron affinities.affinities.

Anions are formed through the addition of Anions are formed through the addition of one or more electrons in the outer energy one or more electrons in the outer energy level.level.

Anions are designated with the –Anions are designated with the –ideide ending. Ex: nitrogen becomes nitride.ending. Ex: nitrogen becomes nitride.

Ionic RadiusIonic Radius

Atoms can gain or lose electrons to form Atoms can gain or lose electrons to form ions. Because electrons are negatively ions. Because electrons are negatively charged, atoms that gain or lose electrons charged, atoms that gain or lose electrons acquire a net charge.acquire a net charge.

An ion is a atom or a bonded group of An ion is a atom or a bonded group of atoms with a +/- charge.atoms with a +/- charge.

When atoms lose electrons and form When atoms lose electrons and form cations, they cations, they always always become smaller.become smaller.

The reason for the size decrease is The reason for the size decrease is because the electron lost is always a because the electron lost is always a valence electron. valence electron.

The loss of a valence electron may leave a The loss of a valence electron may leave a completely empty outer orbital, which completely empty outer orbital, which results in a smaller radius.results in a smaller radius.

The resulting electrostatic repulsion The resulting electrostatic repulsion between the remaining electrons causes between the remaining electrons causes them to be pulled closer to the nucleus.them to be pulled closer to the nucleus.

When atoms gain electrons, they form When atoms gain electrons, they form negatively charged ions called negatively charged ions called anions.anions. They always become larger as a result.They always become larger as a result.

The addition of an electron to an atom The addition of an electron to an atom increases the electrostatic repulsion increases the electrostatic repulsion between the valence electrons, forcing between the valence electrons, forcing them apart. them apart.

The increased distance results in a larger The increased distance results in a larger radius.radius.

Trends within periodsTrends within periods

As you move across a period, cations get As you move across a period, cations get smaller. Then when you get to group 15, smaller. Then when you get to group 15, the much larger anions also get smaller. the much larger anions also get smaller. So, for ionic radii, the general trend within So, for ionic radii, the general trend within a period is for it to decrease from left to a period is for it to decrease from left to right.right.

Trends within groupsTrends within groups

As you move down a group, an ionAs you move down a group, an ion’’s s valence electrons are in higher principal valence electrons are in higher principal energy levels, resulting in a gradual energy levels, resulting in a gradual increase in ionic size.increase in ionic size.

Thus, the ionic radii for both cations and Thus, the ionic radii for both cations and anions increase as you move down anions increase as you move down groups.groups.

Introduction of the Introduction of the Green SheetGreen Sheet

Ionic Compounds- Give and TakeIonic Compounds- Give and Take

Attraction between + ions and - ionsAttraction between + ions and - ions Electrons go from metals to nonmetalsElectrons go from metals to nonmetals

electron transferelectron transfer

metal metal nonmetal nonmetal ion ion++ ion ion––

Electrons Electrons lostlost = Electrons = Electrons gaingain

Formulas of Ionic CompoundsFormulas of Ionic Compounds

Formulas of ionic compounds are determined Formulas of ionic compounds are determined from the charges on the ionsfrom the charges on the ions

atomsatoms ions ions

––

Na Na + + F : F : Na Na+ + : F : : F : NaF NaF

sodium fluorine sodium fluoride formulasodium fluorine sodium fluoride formula

Charge balance: Charge balance: 1+1+ 1-1- = = 0 0

Writing a FormulaWriting a Formula

Write the formula for the ionic compound that will Write the formula for the ionic compound that will form between Baform between Ba2+2+ and Cl and Cl..

Solution:Solution:

1. Balance charge with + and – ions 1. Balance charge with + and – ions

2. Write the positive ion of metal first, and then 2. Write the positive ion of metal first, and then thethe

negative ion negative ion BaBa2+2+ ClCl ClCl3. Write the number of ions needed as subscripts3. Write the number of ions needed as subscripts

BaClBaCl22

Learning Check Learning Check

Write the correct formula for the Write the correct formula for the compounds containing the following ions:compounds containing the following ions:A. A. NaNa++, , SS2-2-

1) NaS1) NaS 2) Na 2) Na22SS 3) NaS3) NaS22

B. AlB. Al3+3+, Cl, Cl--

1) AlCl1) AlCl33 2) AlCl 2) AlCl 3) Al3) Al33ClCl

C. MgC. Mg2+2+, N, N3-3-

1) MgN1) MgN 2) Mg 2) Mg22NN33 3) Mg3) Mg33NN22

Naming Binary Ionic CompoundsNaming Binary Ionic Compounds

Contain 2 different elementsContain 2 different elementsName the metal first, then the nonmetal as Name the metal first, then the nonmetal as --

ideide..Use name of a metal with a fixed chargeUse name of a metal with a fixed charge

Groups 1A, 2A, 3AGroups 1A, 2A, 3A

and and Ag, Zn, and Cd Ag, Zn, and Cd

Examples:Examples:

NaClNaCl sodium chloridesodium chloride

ZnIZnI22 zinc iodidezinc iodide

AlAl22OO33 aluminum oxidealuminum oxide

Learning Check Learning Check

Complete the names of the following binary Complete the names of the following binary compounds:compounds:

NaNa33NN sodium sodium ________________________________

KBrKBr potassiumpotassium ________________________________

AlAl22OO33 aluminum aluminum ________________________________

MgSMgS __________________________________________________

Transition MetalsTransition Metals

Many form 2 or more positive ions Many form 2 or more positive ions

1+1+ 2+ 1+ or 2+ 2+ or 3+ 2+ 1+ or 2+ 2+ or 3+

AgAg++ Cd Cd2+2+ CuCu++,, CuCu2+2+ Fe Fe2+2+, Fe, Fe3+3+

silver cadmium copper(I) ion silver cadmium copper(I) ion iron(II) iron(II) ion ion

ion ionion ion copper (II) ion iron(III) copper (II) ion iron(III) ionion

ZnZn2+2+

zinc ionzinc ion

Names of Variable IonsNames of Variable Ions

Use a roman number after the name of a Use a roman number after the name of a metal that forms two or more ionsmetal that forms two or more ions

Transition metals and Transition metals and the metals in groups 4A and 5A the metals in groups 4A and 5A

FeClFeCl33 (Fe(Fe3+3+)) iron (III) chlorideiron (III) chloride

CuClCuCl (Cu(Cu++ ) ) copper (I) chloridecopper (I) chloride

SnFSnF44 (Sn(Sn4+4+)) tin (IV) fluoridetin (IV) fluoride

PbClPbCl22 (Pb(Pb2+2+)) lead (II) chloridelead (II) chloride

FeFe22SS33 (Fe(Fe3+3+)) iron (III) sulfideiron (III) sulfide

Learning Check Learning Check

Complete the names of the following binary Complete the names of the following binary

compounds with variable metal ions:compounds with variable metal ions:

FeBrFeBr22 iron (_____) bromideiron (_____) bromide

CuCu22OO copper (_____) oxidecopper (_____) oxide

SnClSnCl44 ___(_____ ) _________________(_____ ) ______________

FeFe22OO33 ________________________________________________

CuSCuS ________________________________________________

Complete p. 236, #47 – 56 Complete p. 236, #47 – 56 & #60 - 78 even. This will & #60 - 78 even. This will help you better understand help you better understand ionic bond formation.ionic bond formation.