1. CHEMICAL BONDS

2. Chemical Bond
Mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.
Ionic Bond
Bonding that results from the electrical attraction between large numbers of cations and anions
A large difference in electronegativity between two atoms in a bond will result in ionic bonding

3. Covalent (Molecular) Bond
Sharing electrons pairs between two atoms
A small difference in electronegativity between two atoms in a bond will result in covalent bonding.
Electronegativity
A measure of the ability of an atom in a chemical compound to attract electrons.

4. Valence Electrons
Electrons in the highest occupied energy level of an elements’ atom
Determines the chemical properties of an element
Examples:

5. The Octet Rule
Atoms tend to gain, lose, or share enough electrons to become surrounded by eight valence electrons
Metallic elements lose electrons
Non-metallic elements gain electrons or share them

6. Electron Dot Notation
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 element’s symbol
Example:

7. Learning Check A. X would be the electron dot formula for
A. X would be the electron dot formula for
1) Na 2) K 3) Al
 
B  X  would be the electron dot formula
1) B ) N 3) P

8. Dot notation can be used to represent molecules
Example: (H : H) represents a shared electron pair
An unshared pair or lone pair is a pair of electrons that is not involved in bonding and belongs exclusively to one atom
Example: Lone Pair

9. Lewis Structures
Electron distribution is depicted with Lewis electron dot structures
Electrons are distributed as shared or Bond Pairs or unshared or Lone Pairs

10. Steps: Write electron dot notation for each atom in molecule.
Determine total number of valence electrons.
Arrange atoms to form skeleton structure for molecule.
If Carbon is present it will go in the center. Otherwise least electronegative atoms will be in the center. Hydrogen never is in the center

11. Steps Continued Connect atoms by electron-pair bonds
Add unshared pairs of electrons so each nonmetal is surrounded by 8 electrons
Count the electrons to see it matches the number of valence electrons
If too many electrons create double or triple bonds.

12. Lewis Structure Bond Formula
Electrons are shared and represented by a dash
lone electrons are represented by dots.
To determine how many bonds exist in a molecule, use the following formula:
N-A = # of Bonds 2

13. N-A = # of Bonds 2 Where: N = # of needed electrons,
( 8 for all elements but H, which is 2.)
A = # of available electrons (the number of valence electrons.)

14. The least electronegative element is the central atom.

15. Example:
Write the Lewis structure of NH3
The total number of valence electrons is:
The number of electrons needed is:
A = 8
1 x 8 = 8
N = 14
3 x 2 = 6

16. The Skeleton structure is:
N – A 2
14 – 8 2
= 3 Bonds

17. Connect the atoms with electron pairs
Connect the atoms with electron pairs. Remember 8 electrons are needed to obey the octet rule
Finish the structure by using the remaining electrons as lone pairs
Check that the final Lewis structure has the correct number of valence electrons (8) except Hydrogen (2)

18. Write the Lewis structure of H2CO
Needed (N)
Available (A)
2 (H)
2 x 1
= 2
2 (H)
2 x 2
= 4
1 (C)
1 x 8
= 8
1 (C)
1 x 4
= 4
1 (O)
1 x 6
= 6
1 (O)
1 x 8
= 8
A = 12
N = 20

19. Write the Lewis structure of H2CO cont.
H | C= O | H
N – A 2
20 – 12 2
= 4 Bonds

20. This is the chlorine molecule,Cl Cl
This is the chlorine molecule,
Cl2 or
Single Covalent Bond
Covalent bond produced by the sharing of one pair of electrons between two atoms

21. Multiple Covalent Bonds
Double Bond
Covalent bond produced by the sharing of two pairs of electrons between two atoms
Shown by either two side-by-side pairs of dots or by two parallel dashes

22. O O =
For convenience, the double bond
can be shown as two dashes.

23. Triple Bond
Covalent Bond produced by sharing of three pairs of electrons between two atoms
Carbon forms a number of compounds containing triple bonds
Lewis structures for molecules that contain carbon, oxygen or nitrogen, remember that multiple bonds between pairs are possible

24. If too many electrons have been used, subtract one or more pairs until the total number of valence electrons is correct. Then move one or more lone electron pairs to existing bonds between non-hydrogen atoms until the outer shells of all atoms are completely filled.

25. Ionic Bonding & Ionic Compounds
Composed of positive (cations) and negative (anions) ions that are combined so that the numbers of positive and negative charges are equal.

26. Most ionic compounds exist as crystalline solids.
A crystal of any ionic compound is a 3-D network of positive and negative ions mutually attracted to each other.
Formation of an ionic bond can be viewed as a transfer of electrons

28. Ionic Bonds: One Big Greedy Thief Dog!

29. Crystal Lattice
In an ionic compound, the ions minimize their potential energy by combining in an orderly arrangement.
The distance between ions and their arrangement in a crystal represents a balance among all forces.

30. Properties of Ionic Compounds
High melting points
Solids at room temperature
Soluble in polar solvents, insoluble in Nonpolar solvents
Molten compounds & aqueous solutions conduct electricity

31. Metallic Bonding
Chemical bonding is different in metals than it is in ionic, molecular or covalent network compounds

32. Metallic Bonding
Chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons
An attraction of the free-floating valence electrons for the positively charged metal ions.

33. Metallic Properties Good conductors of electricity and heat
Malleability
Ability of a substance to be hammered or beaten into thin sheets
Ductility
Ability of a substance to be drawn, pulled, or extruded through a small opening to produce a wire.