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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.

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Advanced chemistry

Advanced Chemistry

Chapter 8: Basic Concepts of Chemical Bonding

Sections 8.1 – 8.5 Notes


What s a chemical bond

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

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

  • 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

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

Calculating Dipole Moments

u = Qr

Where:

u = dipole moment measured in debyes (D)

Q = product of charges of atoms involved in bond

r = 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

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

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

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

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

Potential energy of two

interacting charged particles

relates by this equation

Q1Q2

E = k

r2


Practice problem

Practice Problem

  • Which substance would you expect to have the greatest lattice energy?

    • AgCl, CuO, or CrN

The greatest lattice energy results from the largest

product of the ionic charges…thus

CrN has (+3)(-3) = 9


Electron configuration of ions

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

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 nshell..

  • So, they loose valence electrons first, then as many d electrons as are required to reach the charge on the ion


Example

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 problem1

Practice Problem

  • Write the electron configuration for Cr3+

[Ar] 3d3


Sizes of ions

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

  • 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


Ion size and isoelectronic series

Ion Size and isoelectronic series

  • 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

end


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