1. Chapter 19
Chemical Bonds

2. Chemical Compounds
Chemical compounds are formed when two or more atoms combine chemically to form a new product with a new identity

3. Chemical Formula
Chemical formula = used to tell what elements a compound contains and the exact number of atoms of each element
It’s like a recipe for the compound
Ex: CaF2 1 Ca atom to 2 F atoms

4. Atoms are joined by CHEMICAL BONDS
A CHEMICAL BOND is a FORCE that joins atoms together to form a compound or molecule
Forms when atoms gain, lose, or share electrons
Follows the octet rule
8 electrons in valence shell = stability

5. Electron dot diagrams are represented using a symbol and dots to show valence electrons (bonding electrons)

6. There are 2 exceptions to the octet rule:
Hydrogen and Helium are stable with 2 electrons in their valence shell

7. Group 1A: +1 Group 2A: +2 Group 3A: +3 Group 4A: +/- 4 Group 5A: -3
Each group is assigned an oxidation number based on the number of electrons in the valence shell
Group 1A: +1
Group 2A: +2
Group 3A: +3
Group 4A: +/- 4
Group 5A: -3
Group 6A: -2
Group 7A: -1

8. Types of Chemical Bonds
There are 3 types of chemical bonds
Metallic Bonds
Ionic Bonds
Covalent Bonds
Polar
Nonpolar

9. METALLIC BONDS
Formed when metallic ions (charged atoms) are held together by their attraction to a common pool of electrons

10. Metallic (continued)
Electron pool makes metals malleable, ductile, and lustrous in conjunction with being highly conductive.
Mixture of metals formed from metallic bonds are called ALLOYS
Sterling silver: (Ag and Cu)
Brass: (Zn and Cu)
Filling in teeth: (Ag, Cu, Sn, Hg)
Stainless Steel: (Fe, Cr, Ni, C)

11. IONIC BONDS Occur between a metal and a nonmetal Na+ and Cl- form NaCl
Cation and anion pulled together by electrostatic attraction
Creates an Ionic Compound
Generally have a high melting point
Solids are usually crystalline
Salts conduct electricity when in solution
Separate into ions when in solution

12. Ionic Bond

13. Forming Binary Compounds
Atoms combine to form binary compounds using valence shell electrons:
There must be a + and – charged ion
An ION is a charged atom that has gained or lost electrons
+ is cation, - is anion
The ions must appear in the order +, -
The total + and – must add to equal zero
Numbers of ions used are represented using subscripts

14. Naming Binary Compounds
When naming binary compounds start with the cation name (ex. Sodium)
Write the name of the anion and change the ending of the word to
–IDE (ex. Chloride)
If a transition metal is used, use roman numerals to indicate the correct oxidation number
When using polyatomic ions, do not change the name of the polyatomic ion
Naming covalent molecules involves using prefixes to indicate numbers of atoms involved.

15. COVALENT BONDS
Form as a result of electrons being shared between atoms of nonmetals
Form molecules
Do not separate in solution
Do not conduct electricity
May be multiple bonds
Each pair of electrons represents a bond
1 pair = single bond
2 pairs= double bond
3 pairs = triple bonds

16. Some compounds have water
A hydrate is a compound with water chemically attached
Hydrate = water
We represent the presence of water as follows: Mg3(PO4)2 . 4H20
This is read, Magnesium phosphate tetrahydrate
Compounds without water are called anhydrous

17. The water molecule

18. Special nonmetals bond to themselves
Certain nonmetals cannot be alone and therefore bond to themselves when alone
Called DIATOMICS
Br2 H2 O2 N2 Cl2 I2 F2
Bonding to themselves satisfies the octet rule and keeps them stable

19. Polar and Nonpolar Covalent Bonds
Electrons are shared equally by atoms

20. Polar and Nonpolar Covalent Bonds
Electrons are unequally shared between atoms

21. Naming binary covalent compounds
Greek prefixes are used to indicate how many atoms of each element are in a binary covalent compound
1 = mono-
2 = di-
3 = tri-
4 = tetra-
5 = penta-
6 = hexa-
7 = hepta-
8 = octa-
Prefixes are also used to name hydrates

22. Polyatomic Ions
Polyatomic Ions (radicals) = positively or negatively charged, covalently bonded group of atoms
special group of atoms that behave like one atom with one oxidation number

23. Mass of a formula may be calculated
In order to calculate the mass of a formula, several steps are taken
List the elements in the compound
Calculate the number of atoms of each element in the compound
Multiply the number of atoms by the atomic mass of each element
Add the atomic masses and label the sum amu