Lecture 18: Ionic Bonding

Question 1

What are chemical bonds?

Answer 1

The attractive forces that hold atoms or ions together in a unit (molecule or ionic compound)

Question 2

Why do chemical bonds form?

Answer 2

The system strives to achieve the lowest possible energy

Question 3

What are the types of bonds?

Answer 3

Covalent
Ionic
Polar-covalent

Question 4

How do chemical bonds arise?

Answer 4

They arise from the interactions of the valence electrons of the combining atoms

Question 5

Ionic Bonding

Answer 5

The result of electrostatic attraction between closely packed, oppositely charged ions

Occurs between metallics and non-metallics combine to form neutral compounds

Question 6

How are electrons transferred in an ionic bond?

Answer 6

From metallic to non-metallic

Due to large differences in electronegativity

Question 7

Why do metal cations and non-metallic anions generally adopt a noble gas configuration?

Answer 7

To achieve maximum stability

Question 8

Elements on the left side of the periodic table ______ electrons to form ______ and achieve ________ _____ ___________________

Answer 8

Lose

Cations

Noble gas configuration

Question 9

Elements on the right side of the periodic table _____ electrons to form _______ and achieve _______ ______ _____________________

Answer 9

Gain

Anions

Noble gas configuration

Question 10

What is Coulomb’s law used for?

Answer 10

To calculate the energy of electrostatic interaction between a pair of ions

Question 11

What do these variables mean in Coulomb’s law?
(2.31 x 10^-19 Jxnm)(Q1Q2/r)
V
r
Q1 and Q2
(backwards fancy E) superscript O

Answer 11

V: Energy of attraction in Joules
r: Distance between the ion centers
Q1 and Q2: Ion charges (+1, +2, etc)
Last one: The permittivity of a vacuum

Question 12

In what structure are ionic compounds typically packed?

Answer 12

Lattice structure

Infinite array of cations and anions and grows infinitely in 3 directions

Question 13

What are the physical properties of ionic compounds?

Answer 13

1) High melting point
2) Conduct electricity in molten/aqueous form
3) Brittle when you start moving the material

Question 14

Why are solid binary ionic compounds so stable?

Answer 14

Strong attractive forces between postive and negative ions

Question 15

What does this variable represent?ΔH(subscript)int​

Answer 15

Energy of attraction

Question 16

What is the equation for energy of attraction?

Answer 16

ΔH(subscript)int​=ΔH(sub)attractive +ΔH(sub)repulsive

Question 17

What does ΔH(sub)attractive represent?

Answer 17

Dominated by attraction between oppositely charged ions

Question 18

What does ΔH(sub)repulsive
represent?

Answer 18

p+/p+ and e-/e- repulsion

Question 19

What is another phrase that means the same thing as internuclear distance?

Answer 19

Bond length

Question 20

The packing of a lattice occurs in a certain way to…

Answer 20

Limit cation-cation interactions and anion-anion interactions

Question 21

Lattice Energy (enthalpy)

Answer 21

Change in enthalpy that occurs when separated gaseous ions are packed together to form one mole of an ionic solid

Question 22

The more ________ (exothermic) the lattice energy, the more ________ the solid

Answer 22

Negative

Stable

Question 23

What does Hess’s Law explain?

Answer 23

It doesn’t matter what path we take, just where we start and end

Question 24

ΔH(sub)LE cannot be measured directly so we use…

Answer 24

Hess’s Law

Question 25

Born-Haber Cycle for the formation of NaCl(s)

Answer 25

Design a cycle of reactions for which the enthalpy changes are known for all the steps but one (ΔH(sub)LE) Since we can measure the standard enthalpy of formation ΔH(sub)f (equation) Since delta H is a state function we can use Hess' Law to break this reaction into a number of steps

Question 26

What does ΔH(sub)f refer to?

Answer 26

The enthalpy change involved in the formation of 1 mole of a substance from its elements in their standard states

Question 27

What are the steps for the Born-Haber cycle for formation of NaCl?

Answer 27

1) Sublimation and Dissociation -Sublimation of 1 mole of solid sodium metal; dissociation of 0.5 moles of chlorine molecules into gaseous chlorine atoms 2) Make gaseous ions Ionization of gaseous sodium (makes cations and anions); formation of gaseous Cl- ions from gaseous chlorine atoms 3) Formation of solid sodium chloride from gaseous ions (lattice energy) 4) Find delta H f

Question 28

What is the equation for lattice energy?

Answer 28

ΔH(sub)LE = kQ1Q2 --------------- r LE= Lattice energy k=constant Q1Q2= numerical charges on ions r=shortest distance between ion centres

Question 29

The magnitude of lattice energy depends on:

Answer 29

1) The value of k: depends on the geometry of crystal lattice (orientation and number of nearest ions) 2) Size of ions: dictates how close together they can get See slide 20 for diagram of interaction between ions and how that affects lattice energy

Question 30

As the size of the anion increases (move down a group), the lattice energy _________

Answer 30

Lowers (becomes more positive) because the radius is increased LiF: -1036 LiCl:-853 LiBr: -807 LiI: -757

Question 31

As the size of the cation increases (move down a group), the lattice energy _________

Answer 31

Lowers (becomes more positive) because the nucleus is gaining more strength and drawing electrons in more closely

Question 32

What are the factors to consider for the relative size of (isoelectronic) ions?

Answer 32

Number of electrons Number of protons

Question 33

For isoelectronic cations, the ________ ____ ________ the smaller the ion

Answer 33

For isoelectronic cations, the higher the charge, the smaller the ion More positive=smaller Mg2+ < Na+ Mg has more protons so it is smaller even though they both have 10 e-

Question 34

For isoelectronic anions, the _________ ____ _______, the larger the anion

Answer 34

For isoelectronic anions, the higher the charge, the larger the anion More negative=larger O2- > F- Oxygen has a higher charge so it is the larger anion

Question 35

A series of isoelectronic ions: all have the...

Answer 35

same number of electrons but different numbers of protons therefore a different nuclear charge from one another

Question 36

In general, the effects of ion charges are ______ ________ than effects of ion sizes

Answer 36

much larger