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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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