Chemical Formulas & Equations December 03, 2012

Bell-Ringer Heat from the hot plate provides the energy, which causes atoms in the sugar molecule to vibrate and eventually break apart. The sugar is then chemically changed when these free atoms rearrange themselves and come back together to create new substances. Burnt sugar has a black charcoal appearance, bitter taste, and distinct smell. These characteristics indicate that white sugar lost its original properties when heated. Burnt sugar released water vapor and formed a new substance called carbon.

Introduction Chemical symbols are put together to make chemical formulas that describe substances. Chemical formulas can be put together to describe chemical reactions.

Chemical Formulas A chemical formula is a shorthand way to use chemical symbols and numbers to represent a substance. A chemical formula shows how many atoms of each kind are present in a molecule. A subscript is a number written below and to the right of a chemical symbol in a formula. H2OH2O O2O2 C 6 H 12 O 6

Writing Formulas for Covalent Compounds Covalent compounds are usually composed of two nonmetals. Use prefixes. (See pg. 393) – Ex: mono=1, di=2, tri=3, tetra=4 The prefixes tell you how many atoms of each element are in a formula.

Covalent Compounds CO 2 ? N 2 O?

Writing Formulas for Ionic Compounds Ionic compounds are composed of a metal and nonmetal. Make sure the charge is 0. – “Formula must have subscripts that cause the charges of the ions to cancel out.” Change the name of the nonmetal ending to “-ide”

Remember Octet Rule

Ionic Compounds NaCl – A sodium ion has a 1+ charge. – A chloride ion has 1- charge. – One sodium ion and one chloride ion have an overall charge of (1+) + (1-) = 0. MgCl 2 – A magnesium ion has 2+ charge. – A chloride ion has 1- charge. – One magnesium ion and two chloride ions have an overall charge of (2+) + 2(1-) = 0.

Practice 10/(6)ionic.htm 10/(6)ionic.htm Go to 2 nd QTR Week 6 and click on practice links.

Homework Write the chemical names given below on the board. Have students identify each compound as ionic or covalent. Use the table of prefixes on pg. 393 and a periodic table to write the formula for each compound. – Sulfur trioxide – Calcium fluoride – Phosphorus pentachloride – Dinitrogen trioxide – Lithium oxide