November 12, 2015 What are 3 things you know about covalent bonds? What does it mean if a covalent bond is polar? Identify the type of bond present in each of the following: CuZn Mg3P2 NO2

Agenda Bell Work-Hand In Quiz Check Homework Notes Announcements- Unit Test Wednesday and CA on Thursday next week.

What does a chemical formula tell us? Types of atoms present The ratio of atoms of each type present

These Notes should just be a reminder but an important one before we start balancing Chemical Equations on Monday.

How are chemical formulas written? Recall: each symbol begins with a CAPITAL letter, any others must be lowercase. EX. Oxygen is O, Magnesium is Mg

How are chemical formulas written? A superscript (ex. the 2+ in Ca2+) is used to tell us the charge of an atom A subscript (ex. the 2 in H2O) is used to tell us the number of atoms present. If there is only one atom, you do not have to use a subscript of 1 EX. In H2O, we know there is 1 atom of O, even though it’s not written.

Rules for Formulas Metals are always written before nonmetals. Carbon (if present) is written first Hydrogen (if present) is written first

How are chemical formulas determined? (ionic compounds) Based on the charges of the ions used All chemical compounds want to be NEUTRAL.

Example Calcium bonds with Chlorine Ca +2 and Cl-1 You need 2 atoms of chlorine for every one atom of calcium + 2 + -1 + -1 = 0 CaCl2

Example Boron bonds with sulfur B+3 and S-2 (+3) + (+3) + (-2) + (-2) + (-2) = 0 B2S3

Easy way to do this…. On the board….

Now it’s your turn…. Magnesium and Fluoride 1. Charges of the ions 2. Cross the charges 3. Charges become subscripts of the opposite atom 4. Formula

Now it’s your turn…. Rubidium and Phosphorous 1. Charges of the ions 2. Cross charges 3. Charges become subscripts 4. Formula

EX. Aluminum and phosphorous Be Aware… Subscripts should be the smallest possible number EX. Aluminum and phosphorous Al3+ and P3- Al3P3 is the same as AlP 3Al : 3 P is the same as 1 Al : 1 P