1. Compounds
Kelley Kuhn
CCA

2. Compounds!
Why do atoms form compounds? To become more stable! The only atoms that are truly stable just alone are the noble gases. There are two main categories of compounds that atoms form: ionic compounds and covalent compounds.

3. IONIC COMPOUNDS
electrons are transferred from one atom to another creating ions.These ions then form compounds based on electromagnetic attraction between atoms of opposing charges. These compounds are composed of a metal cation (+ ion) and a nonmetal anion (-ion).

4. COVALENT COMPOUNDS
electrons are shared in a bond which holds two nonmetal atoms together. Covalent compounds may be either nonpolar if the electrons are shared equally in the bond between the atoms or polar if the electrons in the bond shift toward one atom disproportionately.

5. How do I determine the type of compound I have?
If the compound begins with hydrogen (H), it is an acid. (HCl, H2SO4, H3PO4) Two exceptions to this rule: H2O and H2O2.
If the compound begins with a carbon and only contains carbon and hydrogen, it is a hydrocarbon. (C3H8, C6H12)
If the compound begins with a metal or NH4, it is an ionic compound. (NaCl, KNO3)
If the compound begins with a nonmetal, it is a covalent compound. (H2O, P2O5, H2O2)

6. Ionic Compounds
In an ionic compound, we find both monatomic ions and polyatomic ions.
Monatomic ions: ions of a single atom, i.e., Fe 2+ Fe 3+ Cl- O2-
For monatomic cations, the names are derived by taking the name of the metal and adding the word “ion”
For monatomic anions, the names are derived by taking the name of the nonmetal and changing the ending to “ide”

7. Ionic Compounds
Polyatomic ions: ions composed of two or more atoms covalently bonded together, i.e.,
PO (1 P and 4 O with a charge of negative three)
OH- (1 O and 1 H with a charge of negative one)
NH4+ (1 N and 4 H with a charge of positive one)

8. Ionic versus Covalent Ionic Covalent
Extremely high melting and boiling points
Low to medium melting and boiling points
All solids at room temp
May be gases, liquids or solids at room temp
Electrons are transferred
Electrons are shared
Form a crystal lattice
Form compounds that can be complex in shape and size
NaCl, KOH, CaCO3, NaHCO3
H2O, CO2, C12H22O11
SiO2, C2H5OH

9. Ionic versus Covalent Cont.
May be insoluble, soluble,or partially soluble in water
If they are soluble in water, they are polar.
Soluble ionic compounds dissolve in water into their component ions to generate strongly electrolytic solutions
If they are insoluble in water, they are nonpolar.
Partially soluble ionic compounds only dissolve in minute quantities and generate weak electrolytic solutions
Those polar substances that do dissolve remain as whole molecules and do not form electrolytic solutions.

10. Bonding
When two atoms bond in a covalent compound, the difference between the individual electronegativities of the atoms will determine if the bond is ionic, polar, or nonpolar.
The electronegativity scale is relative in that all atoms are given values based on how they compare to fluorine, F, the most electronegative atom of all! Fluorine is assigned the value of 4.0 (the highest) with the range bottoming at 0.7 (Cs). The larger the difference in electronegativity values, the greater the polarity of the bond will be.

11. Are these bonds polar?
Determine the difference in electronegativities of the following pairs of atoms:
C-H
Na-O
S-H
O-F
F-H
N-O
These bonds are polar if the difference in electronegativities is greater than .4

12. Are the bonds polar, cont.
Now, put the following pairs in order from least polar (smallest electronegativity difference) to most polar (greatest electronegativity difference).
All of the bonds in a molecule are evaluated when determining if a molecule is polar or nonpolar. Even if a molecule contains several polar bonds, the arrangement of these bonds may cancel each other out, resulting in a nonpolar molecule.