Formulas and Names of Compounds Unit 3 Formulas and Names of Compounds

Oxidation Number A positive or negative number Assigned to an element Shows its ability to combine in a compound.

What do I need to know about Oxidation Numbers? Written as a superscript.

What do I need to know about Oxidation Numbers? Tells how many electrons are unbalanced.

What do I need to know about Oxidation Numbers? Tells the charge on the ion.

What do I need to know about Oxidation Numbers? If no number is given; just a + or -, the number one (1) is assumed.

Oxidation numbers are a periodic property of elements. * there is a pattern to them * elements in the same family have the same oxidation number

Commonality in Oxidation Numbers * Family 1 = + or 1+ * Family 17 = - or 1- * Family 2 = 2+ * Family 16 = 2- * Family 13 = 3+ * Family 15 = 3- * Family 18 = 0 * Family 14 = 4+ or 4-

Noble Gases Oxidation number for this Family (group) equals 0. They have NO combining ability

METALS are always givers of electrons. (+) NON-METALS are usually takers of electrons. (-)

Binary Compound A compound that is composed of ONLY two elements. * BI means “two” * for the compound to be STABLE the total oxidation number must equal zero

You can figure out chemical formulas with the help of the oxidation numbers.

Example of Binary Compounds (soul mates) Na+ + Cℓ- = NaCℓ Be2+ + O2- = BeO Aℓ3+ + N3- = AℓN

Rules for writing formulas for Binary Compounds. 1.) Write the symbol for the element with the positive O.#. 2.) Write the symbol for the element with the negative O.#. 3.) Add subscripts so the O.#. for the compound equals zero. (use the Least Common Multiple)

Practice Formulas using LCM Bromine + Magnesium = 1- 2+ = 1+ Br1- Br1- Mg2+ = 0 MgBr2

Practice Formulas using LCM Nitrogen + Lithium = Strontium + Phosphorus =

Practice Formulas using LCM Nitrogen + Lithium = 3- 1+ = 2- N3- Li1+ Li1+ = 1- N3- Li1+ Li1+ Li1+ = 0 Li3N

Practice Formulas using LCM Strontium + Phosphorus = 2+ 3- = 1- Sr2+ Sr2+ P3- = 1+ Sr2+ Sr2+ P3- P3- = 2- Sr2+ Sr2+ Sr2+ P3- P3- = 0 Sr3P2

Crisscross Method for Writing Formulas The number value of the ionic charge is crossed over and becomes the subscript for the other ion. Ca2+ Br1- = CaBr2 Aℓ2S3 Aℓ3+ S2- = Rb4C1 C1Rb4 C4- Rb1+ =

When writing formulas, the oxidation numbers are used; but NEVER, EVER WRITTEN in the formula.

Some elements have more than one oxidation number. *found in families 3 – 12 along with LEAD & TIN * Roman Numerals are used to show the oxidation number needed

Example of elements with multiple oxidation numbers. Copper(I) or (II)…{Cu1+ or Cu2+ } Iron(II) or (III)…{Fe2+ or Fe3+ } Chromium(II) or (III)...{Cr2+ or Cr3+ } Lead(II) or (IV)…{Pb2+ or Pb4+ }

Rules for naming Binary Compounds. 1.) Write the name of the first element. 2.) Write the name of the second element. 3.) Add the ending “ide” to the second name. * if it sounds weird; it might need some adjustment.

Aℓ2S3 aluminum sulfuride (wrong) aluminum sulfuide ? Practice Names Aℓ2S3 aluminum sulfuride (wrong) aluminum sulfuide ? aluminum sulfide ? aluminum sulide ? aluminum sulfide

CaCℓ2 * calcium chlorineide (wrong) calcium chlorinide ? Practice Names CaCℓ2 * calcium chlorineide (wrong) calcium chlorinide ? calcium chloriide ? calcium chloride ? calcium chloide ? calcium chloride

Notice that subscripts are NEVER, EVER WRITTEN in the name of a binary compound!

* Lead(IV) chloride * Copper(I) nitride Roman Numerals are ALWAYS written in the name for elements that have more than one oxidation number. (but never in formulas) * Iron(II) sulfide * Lead(IV) chloride * Copper(I) nitride

* you count more than 2 capital letters in the formula How can I tell if I am dealing with a compound that is not a Binary Compound? * you count more than 2 capital letters in the formula * the name ends with “ite” or “ate” (these compounds contain a polyatomic ion) (refer to page 366)

Polyatomic Ion A positively or negatively charged, covalently bonded, group of atoms. * poly means “many”

AuSO3 gold(?) sulfur oxygen (wrong) gold(?) sulfite Naming a Non-Binary Compound AuSO3 gold(?) sulfur oxygen (wrong) gold(?) sulfite (to figure out what roman numeral to use, look at the charge on sulfite and how many Au atoms balanced it out) gold(II) sulfite

When writing formulas for compounds containing a polyatomic ion, follow the same rules for binary compounds. * add parentheses around the polyatomic ion when more than one is needed

calcium nitrate = Ca(NO3)2 Ca 2++ ( ) NO3 1- ( NO3 1- )

barium phosphate = Ba3(PO4)2 ( ) Ba 2+ + PO4 3-

The End