Advanced Chemistry

Chapter 8: Basic Concepts of Chemical Bonding

Sections 8.1 – 8.5 Notes

What’s a Chemical Bond?

Whenever atoms or ions are strongly attached to one another, we say that there is a chemical bond

Three types of Chemical Bonds Metallic Ionic Covalent

Bond Types – Brief Review

Ionic Refers to the electrostatic forces that exist between

ions of opposite charge Covalent

Results from the sharing of electrons between nonmetals

Metallic Are relatively freely moving electrons found between

metals

Bond Polarity

Bond polarity is determine by differences in electronegativity

Non-Polar Covalent 0.0

Polar Covalent

0.1- 1.9

Ionic Bond

>2.0

Dipole Moments

Covalent compounds with differences in electronegativity produce dipole moments, that’s why they are polar molecules!

Dipole moment increases with charge!

u = Qr

Calculating Dipole Moments

u = QrWhere: u = dipole moment measured in debyes (D)Q = product of charges of atoms involved in bondr = separation of charge in meters (m)Convert using 1D = 3.34 x 10-30 C·m

The distance between the centers (bond length) of H and Cl atoms in the HCl molecule is 1.27 Angstrom.

A) Calculate the dipole moment using a +1 and -1 charge respectively

Ionic Bonding Attraction between ions..generally metals and nonmetals..this you

know.. But what happens to energy in ion formation?

Forming a cation (metals losing an electron) is an endothermic process..meaning energy is put in to remove an electron

Forming a anion (done by nonmetals) is an exothermic process The difference between the processes is the overall energy

change for one mole of reactant

Ionic Bonds and Lattice Formation

The ions are drawn together and a lattice of ionic structure is formed

The Lattice Energy is the measure of how much stabilization results from the arranging of oppositely charged ions in an ionic solid

It is, the energy required to completely separate a mole of a solid ionic compound into its gaseous ions

Lattice Energy Example

NaCl(s) Na+(g) + Cl- (g)

Hlattice = +788 kJ/mole

This means the forming of NaCl is highly exothermic, H = -788 kJ/mole

Lattice Energies

The large positive endothermic lattice energies makes ionic bonds strong..

The strong attractions also make the compounds hard, brittle materials with high melting points

E = kQ1Q2

r2

Potential energy of twointeracting charged particlesrelates by this equation

Practice Problem

Which substance would you expect to have the greatest lattice energy? AgCl, CuO, or CrN

The greatest lattice energy results from the largestproduct of the ionic charges…thusCrN has (+3)(-3) = 9

Electron Configuration of Ions

Ions like loose or gain electrons to form noble-gas electron formations

This results in the most energy-favorable and stable formation

Even though an increase in ionic states would result in a higher lattice energy, it is not enough to remove an electron from a completed energy level or add to an unfavorable higher energy level

e- configuration of Transition Metals

Transition metals (d block) cannot reach the noble gas configuration due to their location on the table

So…they achieve stability by loosing electrons from the highest n shell..

So, they loose valence electrons first, then as many d

electrons as are required to reach the charge on the ion

Example

Fe [Ar] 4s2 3d6

In forming the Fe3+ ion, 2e- are lost from the 4s subshell and 1 from 3d so…

Fe3+ [Ar] 3d5

Practice Problem

Write the electron configuration for Cr3+

[Ar] 3d3

Sizes of ions

Ionic size plays a crucial role in determining the structure and stability of ionic solids

It determines both the lattice energy of the solid and the way in which the ions pack in a solid

Ionic size also determines the properties of ions in solutions

Ion Size

Ion size depends on nuclear charge, the number of electrons it possesses, and the orbitals in which the outer electrons exist

Cations are smaller than their parent atoms Anions are larger than their parent atoms For Ions with the same charge, size increases

as we go down a group in the PT

The term isoelectronic means that the ions possess the same number of electrons Ex: O2-, F-, Na+, Mg2+ and Al3+

All have the configuration of Neon The nuclear charge increases while # of e remain the same…so Radius decreases due to larger attractive force between nucleus

and electrons

Ion Size and isoelectronic series

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