Bonding

1
Bonding
2

• Bonding electrical attraction between atoms
  nuclei and valence e-
• Why bond?
• More stability

3
Ionic vs. Covalent Bonding

• Ionic bonds
• Between metal and nonmetal only
• e- are transferred
• Joined by electrostatic forces
• Very strong
• Another name is salt
• Most crystalline solids at room temp
• Conduct electric current in molten state or in
  solution (electrolyte)
• Movement of ions flow of electricity

4

• Covalent bonding
• Many molecules are gases and liquids
• Have weaker bonds
• e- are shared
• Occurs b/t 2 nonmetals

5
Section 3 Ionic Bonding and Ionic Compounds
Chapter 6
Ionic Compounds

• Most ionic compounds exist as crystalline solids.
  (minimize their potential energy)
• A crystal of any ionic compound is a 3-D network
  of () and (-) ions mutually attracted to each
  other.

6
NaCl and CsCl Crystal Lattices
Section 3 Ionic Bonding and Ionic Compounds
Chapter 6
7
Chapter 6
Electron-Dot Notation

• To keep track of valence electrons, it is helpful
  to use electron-dot notation.
• Electron-dot notation is an electron-configuration
  notation in which only the valence electrons of
  an atom of a particular element are shown,
  indicated by dots placed around the elements
  symbol. The inner-shell electrons are not shown.

8
Drawing Lewis Structures

• Count valence e- of all atoms in compound this
  is the number of e- you may work with
• Most atoms like 8 e- surrounding them, except H
  (only 2 e-)
• Space atoms out symmetrically with Hs on outside
• Central atom is least EN atom, except if C is
  involved and NEVER H
• Put 1 pair of e- in between each atom (shared
  pairs)
• Put remaining e- around atoms (lone or unshared
  pairs)

9

• If there are not enough e- to put around as lone
  pairs, make a lone pair another shared pair
  (double and triple bonds)
• Never make a multiple bond if you dont have to
• Polyatomic Ions
• Do same thing as before, but
• Add e- if its a negative charge
• Subtract e- if its a positive charge
• Put ion in brackets with charge on outside

10
Resonance

• Structure that occurs when it is possible to draw
  2 or more valid e- dot structures
• Double-headed arrows used to connect structures
• EX
• O3
• SO2

11
Exceptions to Octet Rule

• Cannot be satisfied in molecules whose total is
  odd
• Some molecules have more or fewer than 8 e-
• Atoms that have more than 8 e- usually bonded to
  highly EN atoms, like the halogens
• bonding involves e- in d and f orbitals
• EX
• BF3
• SF6
• PCl5

12
VSEPR

• Valence Shell Electron Pair Repulsion
• Repulsion b/t e- prs causes molecular shapes to
  adjust so that valence-electron prs stay as far
  apart as possible
• Determines geometry of molecules
• See lab for shapes to know

13
Electronegativity and Polarity

• Electronegativity (EN) how attractive an atom is
  to shared pair of e- greater difference, more
  ionic and the more polar

14
Trends in EN on Per. Table

• As you go across period left to right, atoms have
  same E levels and same shielding e-.
• Increased nuclear charge increased attraction
  of valence e- to nucleus
• Therefore, EN increases
• As you go down group, add more E levels and e-.
• Increased shielding balances increased nuclear
  charge, which means less e- attraction to nucleus
• Therefore, EN decreases
• EXCEPTIONS high values in d-block because
  d-orbitals shielded differently than s and p

15
Molecular Polarity

• Polar bonds often make molecules entirely polar
• Molecules can be nonpolar but have polar bonds
• When polar bonds cancel each other out
• Ex CO2

16
Metallic Bonding

• The unique characteristics of metallic bonding
  gives metals their characteristic properties
• electrical conductivity
• thermal conductivity
• malleability
• ductility
• shiny appearance

17

• In a metal, the vacant orbitals in the atoms
  outer energy levels overlap.
• This overlapping of orbitals allows the outer
  electrons of the atoms to roam freely throughout
  the entire metal.
• The electrons are delocalized, which means that
  they do not belong to any one atom but move
  freely about the metals network of empty atomic
  orbitals.
• These mobile electrons form a sea of electrons
  around the metal atoms, which are packed together
  in a crystal lattice.

18

• The chemical bonding that results from the
  attraction between metal atoms and the
  surrounding sea of electrons is called metallic
  bonding.