1. Chapter 20
Chemical Bonds

2. Sec. 1: Stability in Bonding
Atoms from different elements can combine to form compounds.
When atoms combine, the compound has different properties than the elements.
Ex. Sodium Chloride (table salt) is made of sodium & chlorine.
Sodium is a soft metal that reacts violently with water.
Chlorine is a poisonous greenish-yellow gas.

3. Formulas
Chemical Formula—tells what elements a compound contains and the exact number of the atoms of each element.
Ex. NaCl has 1 atom of sodium & 1 atom of chlorine
Ex. H2O has 2 atoms of hydrogen and 1 atom of oxygen.
A subscript (small # written below) is written after a symbol to tell how many atoms of that element are in the compound.

4. Atomic Stability
Atoms combine to form a compound that is more stable than the separate atoms.
Noble gases are already stable and do not form compounds.
Their outer energy level is full of electrons.
Atoms can gain, lose, or share electrons to get a full valence electron shell.
Chemical Bond—the force that holds atoms together in a compound.

5. Sodium & Chlorine http://science360
Sodium has 1 valence electron.
Chlorine has 7, so it needs 1 more electron to be stable.
If sodium give its 1 valence e- to chlorine, they are both stable with 8 valence e-.

6. Water Molecule http://science360
In water, each hydrogen atom needs 1 e- to fill its outer shell.
Oxygen needs 2 e- to fill its outer shell.
To be stable, the atoms share electrons.

7. Island of Stability- Teacher Domain

8. Types of Bonds Ionic Bonds Covalent Bonds
Contain a metal & a nonmetal (at least 1 of each)
Electrons are gained or lost
Ex. Salt, NaCl
Covalent Bonds
Contain 2 or more nonmetals or hydrogen
Electrons are shared
Ex. Water, H2O

9. Ions
When atoms gain or lose electrons in an ionic bond, they form ions.
Ion—an atom with a positive or negative charge.
You can tell the charge of the ion that an element will form based on its position on the periodic table.
Polyatomic Ions—ions made of more than one atom.

10. Write the charges on you periodic table!!!1+ 2+ 3+ 3- 2- 1-

11. Oxidation number—the charge of an ion1+ 2+ 3+ 3- 2- 1-

12. Types of Ions Cations—ions that have a positive charge
There are 2 types of ions: cations & anions.
Cations—ions that have a positive charge
They form by atoms losing electrons
Metals form cations
Anions—ions that have a negative charge
They form by atoms gaining electrons
Nonmetals form anions

13. Ionic Bonding
In an ionic bond, one atoms gives electrons to another atom.
When atoms combine in an ionic bond, it is called a formula unit.
Ex. NaCl is a formula unit
The charge of a formula unit is always 0.
The positive and negative charges must always balance each other.

14. Multiple Oxidation Numbers
Some metals (other metals & transition metals) can have more than 1 oxidation number.
If an element can have more than 1 oxidation number, the charge of the ion is written as a roman numeral in parentheses.
Ex. Copper (I) ion is Cu1+
Copper (II) ion is Cu2+

15. Writing Formulas for Ionic Compounds
Write the symbol for the cation (either the metal element symbol or polyatomic ion) first
Ex. Mg2+ or NH4+
Write the symbol for the anion (either the element symbol or polyatomic ion) second
Ex. Cl- O2-
Use subscripts to balance the charges of the ions.
Ex. KCl, (NH4)2O, MgO, MgCl2

17. Balancing Chemical Formulas Practice
Write the name of the chemical formula, ions and charges, and the chemical formulas when you get them balanced for 25 problems!!!!!
Don’t forget subscripts and parenthesis!

19. Naming Ionic Compounds
Write the name of the cation first (remember cations are metals)
Ex. Ca2+ is calcium
Some elements can have more than 1 charge (see table 2 p. 616)
If it does put the charge of the ion using roman numerals and put it in parentheses.
Ex. Cu2+ Copper (II)

20. Ionic Naming Continued
Write the name of the anion second, but change the ending to –ide.
Ex. Chlorine becomes Chloride
If the anion is a polyatomic ion DO NOT CHANGE THE ENDING.
Ex. NO3- is still named Nitrate
Put the cation & anion together to get the full name.
KI is Potassium Iodide
CuSO4 is Copper (II) Sulfate

22. Making Ionic Compounds
Precipitate- cause (a substance) to be deposited in solid form from a solution.
***Gravity is your friend! Keep the droppers above puddle!

24. Covalent Bonds Covalent bonds share electrons
Composed of 2 or more nonmetals (and H)
Covalent compounds are called molecules
Molecules can be polar or nonpolar
Polar molecule—slightly positive and negative at parts—but overall neutral
e- are unevenly shared
Nonpolar molecule—electrons are shared equally—completely neutral

25. Naming Covalent Compounds
Mono—1
Di—2
Tri—3
Tetra—4
Penta—5
Hexa—6
Hepta—7
Octa—8
Nona—9
Deca—10
Use prefixes to tell how many of each element you have.
This is done because you can have different covalent compounds containing the same elements.
Change the ending of the 2nd element to -ide
Ex. N2O is dinitrogen monoxide.
You can leave off the prefix mono- on the first element.
Ex. NO2 is nitrogen dioxide
Not mononitrogen dioxide

26. Formulas for Covalent Compounds
Use the prefixes as the subscript in the formula.
Ex. Phosphorus Trichloride
PCl3
Dinitrogen Tetrafluoride
N2F4