Writing Formulas Chemistry Mrs Stoops

Finding the charge (General only) Na has a Dot diagram of: Na So to become more stable, and form an ion it will LOSE 1 electron Na+1 Mg has a Dot diagram of: Mg So to become more stable, and form an ion it will LOSE 2 electrons Mg+2

SO, Cl Cl-1 S S-2 Cl has a Dot diagram of: (General only) Cl has a Dot diagram of: Cl So to become more stable, and form an ion it will GAIN 1 electron Cl-1 S S has a Dot diagram of: So to become more stable, and form an ion it will GAIN 2 electrons S-2 SO,

There is a PREDICATBLE pattern +1 You need to memorize this +2 +3 +/-4 -3 -2 -1 +1 +2

POLYATOMIC IONS Groups of atoms with a charge NEED to memorize name, symbol, and charge they have There are 12 Acetate = C2H3O2 -1 Chlorate = ClO3-1 Cyanide = CN-1 Hydroxide = OH-1 Nitrate = NO3-1 Nitrite = NO2-1 Carbonate = CO3-2 Chromate = CrO4-2 Sulfate = SO4-2 Sulfite = SO3-2 Phosphate = PO4-3 Ammonium = NH4+1

Rules for Writing Formulas Formulas always have a positive and negative part Formulas always have the positive part first Chemists don’t write the number 1 Formulas use whole numbers only Formulas are simplified and reduced when possible Add parentheses when we need more than one polyatomic ion (When a polyatomic has an extra subscript) Formulas will have NO OVERALL charge.

How to write formulas “Criss Cross” method Steps: 1. Write the positive part first with the charge and the negative part second (w/ charge) 2. Cross charge number only – Take the charge number from the “attic” and put it in the “basement” of the OTHER element. 3. Erase the original charges 4. Simplify.

Example Ca & Cl “what are the charges?” Ca +2 Cl-1 “cross the charge number” Ca +2 Cl-1 Ca +2 1 Cl-1 2 “erase charges” Ca 1 Cl 2 “reduce simplify” CaCl2

Example “cross the charges” “reduce simplify” Al OH “what are the charges?” Al+3 OH-1 “cross the charges” Al OH3 What is wrong with this? “reduce simplify” Al(OH)3

#2 Sn+4 O-2 Sn2O4 SnO2

#3 Mg PO4 Mg3(PO4)2

#4 NH4 CO3 (NH4)2CO3