Advanced Chemistry

1
Advanced Chemistry

• Chapter 8 Basic Concepts of Chemical Bonding
• Sections 8.1 8.5 Notes

2
Whats 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

3
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

4
Bond Polarity

• Bond polarity is determine by differences in
  electronegativity

Non-Polar Covalent 0.0 Polar Covalent 0.1-
1.9 Ionic Bond gt2.0
5
Dipole Moments

• Covalent compounds with differences in
  electronegativity produce dipole moments, thats
  why they are polar molecules!
• Dipole moment increases with charge!

u Qr
6
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 Cm

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
7
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

8
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

9
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
10
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
11
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 chargesthus CrN has
(3)(-3) 9
12
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

13
e- configuration of Transition Metals

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

14
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

15
Practice Problem

• Write the electron configuration for Cr3

Ar 3d3
16
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

17
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

18
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 sameso
• Radius decreases due to larger attractive force
  between nucleus and electrons

end