1. Ch. 6 – Part 1: Covalent Bonding
Chemical Bonding
Ch. 6 – Part 1: Covalent Bonding

2. What is a chemical bond?
mutual electrical attraction between the nuclei and valence electrons of different atoms that bind the atoms together
Why don’t noble gases do this?
Already have filled s and p orbitals
stable octet: 8 valence e- (or 2 if, you’re helium)
Atoms that don’t have a stable octet are more reactive

3. Key Point #1: By forming bonds with each other, most atoms reduce their potential energy, becoming more stable.
Because forming bonds involves the rearrangement of atoms to recreate new substances, this is considered a chemical change. All chemical changes involve energy changes.

4. Types of Bonds What type of bonds can be formed? Ionic bond
Covalent bond
Nonpolar covalent
Polar covalent
Ionic bonding: bonds that result from electrical attractions between cations and anions
1 atom losses electrons
1 atom gains electrons
Covalent bonding: sharing of electrons between 2 or more atoms

5. Key Point 2: Rarely is bonding between atoms purely ionic or purely covalent.
Instead, it usually falls somewhere between the two extremes. Why?
Key Point 3: The extent of ionic or covalent bonding between two atoms can be estimated by calculating the difference in each elements’ electronegativity.

6. Covalent Bonding
Large difference in E.N.: bond has more ionic character
Small difference in E.N: bond has more covalent character
Types of Covalent Bonds
Non-polar covalent bonding: both electrons equally shared between atoms
Polar covalent bonding: unequal attraction for the shared electrons

7. 6.1 Practice Worksheet Part 1
The property of electronegativity, which is the measure of an atom’s ability to attract electrons, can be used to predict the degree to which the bonding between atoms of two elements is ionic or covalent.
The greater the electronegativity difference, the more ionic the bonding is.

8. If the calculated electronegative difference is…
> 1.7 : ionic bond is formed
> 0.3 , < 1.7 : polar-covalent bond
0 – 0.3 : non-polar covalent bond
Increasing difference in electronegativity
Nonpolar
Covalent
share e-
Polar Covalent
partial transfer of e-
Ionic
transfer e-

9. Electronegativity Difference
Elements
Electronegativity
Electronegativity Difference
Bond Type
Element 1
Element 2
Mg to Cl
H to O
C to Cl
N to H
C to S
K to F
Na to Cl
H to H
3.0
1.8
Ionic
1.2
2.1
3.5
1.4
Polar covalent
2.5
3.0 .5
Polar covalent
3.0
2.1 .9
Polar covalent
2.5
2.5
Non-polar covalent .8
4.0
3.2
Ionic .9
3.0
2.1
Ionic
2.1
2.1
Non-polar covalent

10. Polyatomic Ions
It is also possible if a compound contains polyatomic ions, for both types of bonding to be present.
Monatomic Ions: Fe2+ , Na+, Cl-
Polyatomic Ions: PO43-, NH4+ , NO-1
Groups of atoms are bonded covalent together, but because of few or more than expected valence electrons they have an overall charge (so they can also bond ionically with other ions)
Ex: Ca2+ and SO42-  CaSO4 (metal & diff. nonmetals)

11. Classify the following as ionic, covalent, or both
1. CaCl2 = __________
5. BaSO4 = ___________
(metal & nonmetal)
(metal & diff. nonmetals)
2. CO2 = __________
6. H2O = ____________
(nonmetal & nonmetal)
3. MgO = __________
7. SO3 = ___________
4. HCl = ___________
8. AlPO4 = ___________
Covalent
Covalent
Ionic
Covalent
Covalent
Both

12. Section 6.2
Covalent Bonding

13. What is a molecule?
Neutral group of atoms that are held together by covalent bonds.
Chemical formula: indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts.

14. Formation of Covalent Bonds
The electrons of one atom and protons of the other atom attract each another.
The two nuclei and two electrons repel each other.
These two forces cancel out to
form a covalent bond at a length
where the potential energy is
at a minimum.

16. Bond Length vs. Bond Energy
Bond length (pm): distance between two bonded atoms at their minimum potential energy
Bond energy (KJ/mol): energy required to break a chemical bond and form neutral isolated atoms.
Breaking bonds: absorbs (requires) energy
Forming bonds: releases energy
A few general principles –
Bond length increases with atomic size
Bond length and bond energy are inverses
As you increase the number of bonds (between 2 atoms), bond energy increases while bond length decreases

17. Bond Energies & Bond Lengths

18. Octet Rule Hydrogen forms bonds surrounded by only two electrons.
Octet Rule: chemical compounds tend to form so that each atom has an octet of e-’s in its highest occupied energy level
Exceptions to the octet rule:
Atoms that cannot fit eight electrons
Atoms that can fit more than eight electrons
Hydrogen forms bonds surrounded by only two electrons.
Boron has just three valence electrons, so it tends to form bonds in which it is surrounded by six electrons.
Phosphorus, Sulfur, & Xenon can form bonds with expanded valence, involving more than eight electrons.

19. Writing Lewis Structures
Lewis Structures: formulas in which atomic symbols represent nuclei and inner shells, dot-pairs/dashes represent shared electron pairs, and dots adjacent to only one atomic symbol represent unshared pairs of electrons.
Structural formulas: represent kind, number, arrangement, and bonds in a molecule but not does not include unshared pairs of electrons.