Criss-cross notes

Criss-Cross Method Criss-cross is a _________ to help you find chemical __________ when you _________ atoms. shortcut formulas combine **Formulas contain both the ________ in a compound and the _______ of that element. elements amount

How Many? NaCl = 1 sodium 1 chlorine MgCl 2 = 1 magnesium 2 chlorines This number is called a ________subscript It tells you the _______ of the atom ________ in front of it! amount directly

First – you need to determine the _________ number for each atom. oxidation To get started… You can find them in the ______- ______ corner on the Periodic Table. upper right

Oxidation Oxidation numbers are the _____ that will form when atoms _________ their _________ shells. ions completevalence Cl Cl -1 Oxidation number

More than one? Many atoms have more than one oxidation state! We will use the ______ one listed! first (This is the one most _________ formed in nature!) commonly

Find the correct formula for a compound!! Use the oxidation #’s Put the _______ one first H +1 + O -2  H 2 O positive

What just happened? By switching the numbers, the _________ number of one atom becomes the _________ for the other! oxidation subscript This also makes sure that we end up with a _______ compound – all the ________ of the ions add up to ______. neutral charges zero

Stuff to remember… ‘Ones’ are ________. (Think Math!) invisible If both of your ions have the _____ oxidation number -- ______ to the ______ common number! same reducelowest It will make more sense after examples…

Ca + Br  CaBr Mg + Cl  MgCl Sr + O  Sr 2 O  SrO

Don’t forget the rules for naming: 1. ______ always goes first! Metal 2. ________ goes second – and ends in _____! Nonmetal “-ide”