Formulas and Nomenclature

Charge of Ions called OXIDATION NUMBER Related to the number of electrons that are lost or gained when an atom becomes an ion Listen to this Group2 Group 1 Group 13 Group 14 Group 15 Group 16 Group 17 Group

Oxidation numbers Same for all elements in a group or family (+) means that the atom loses electrons when forming a cation; formed by metals (-) means that the atom gains electrons when forming an anion ; formed by nonmetals The Noble Gases have oxidation number of zero because they are nonreactive and do not lose or gain electrons.

Transition Metals and Charge Some transition metals form ions that have multiple charges. (MULTIVALENT) Ex. Fe 2+ or Fe 3+ Ex. Mn 2+ or Mn 5+ or Mn 7+ These metals DO NOT form ions with more than one charge. (MONOVALENT) Ag 1+, Zn 2+, Cd 2+, Al 3+ (Remember AZCA, they also make a stair step)

Classifying metals: Type 1 metal (MONOVALENT): Group 1,2 and Al, Zn, Cd, Ag These metals only have 1 charge Al is +3 Zn and Cd are +2 Ag is +1 Type 2 metal (MULTIVALENT): all metals that are not type 1 metals Can have 2 or more charges

POLYATOMIC IONPOLYATOMIC ION (PAI) Two or more nonmetal atoms bonded together Act as a single unit with a net charge LISTED ON YOUR STAAR CHART Chlorate, ClO 3 -1 is the same as (ClO 3 ) -1 which means that 1 chlorine atom is bonded to 3 oxygen atoms and as a group it has a charge of -1

Chemical Formula A symbolic representation of a chemical compound.

Formula Anatomy of an Ionic Compound 2MgCl 2 Elements Coefficient- tells the number of formula units Subscript- tells the ratio of atoms 1Mg : 2 Cl Chemistry definition of formula unit- the empirical formula of any ionic compound used as an independent entity for stoichiometric calculations. Formula Unit – The smallest “piece” of an ionic compound. Ratios- we use ratios because the charge (cation to anion) must be neutral.

Added Info Binary Compound- compounds made of two TYPES of elements. Ex. Al 2 S 3 Non ex. AlPO 4 Ternary Compound – compounds made of more than two types of elements Ex. AlPO 4 Contains Polyatomic Ion Does not contain Polyatomic Ion

WRITING FORMULAS FOR IONIC COMPOUNDS WRITING FORMULAS FOR IONIC COMPOUNDS : 1.Write the symbol for each ion. Positive ion goes first. 2.Write the oxidation number for each ion above the symbol. For type 2 metals, the Roman numeral after the metal tells you the oxidation number 3.Criss-cross the oxidation numbers (not the + or -). These numbers become the subscripts. 4.If a subscript is needed for the PAI, you must enclose it in parentheses first, then write the subscript outside of the parentheses. 5.Watch ThisWatch This

When writing formulas the more metallic element goes first, then the nonmetal

Example: Write the formula for the compound that contains aluminum and sulfur.

Example: Write the formula for the compound that forms when sodium and oxygen combine.

Example: Write the formula for the iron (II) chloride.

Example: Write the formula for the compound that contains calcium and phosphate.

16 WRITING NAMES FOR IONIC COMPOUNDS 1.Write the name of the metal first. 2.IF THE METAL IS A TYPE 2 METAL, write the oxidation number of the metal in parentheses. (You will have to work backwards from the subscripts to determine the oxidation number.) 3. Write the name of the nonmetal, changing the ending to “ide.” 4.IF EITHER PART OF THE COMPOUND IS A POLYATOMIC ION, write the name of the polyatomic nonmetal from the chart. DO NOT CHANGE THE ENDING OF THE PAI. 5.Watch ThisWatch This

Example: Write the name for the compound that contains lithium and nitrogen.

Example: Name this: NiF 2

Example: Name this: Ca(C 2 H 3 O 2 ) 2

Example: Write the name for the compound that contains lithium and nitrogen.

Example: Name this compound: NiF 2

Example: Name this compound: Ca(C 2 H 3 O 2 ) 2

Percent composition Watch This

Percent CompositionPercent Composition write all Percent Composition Percent Composition (% mass): the percentage by mass of each element in a compound Watch This

% Composition Practice What is the percent of Li and O in Li 2 O?

What is the percent of each element in Na 2 SO 3 ?

How much sodium is in 25 grams of Na 2 SO 3 ?

Covalent Molecules What are the common names for these molecules: Dihydrogen monoxide H 2 O Water Carbon tetrahydride CH 4 methane Nitrogen Trihydride NH 3 Ammonia

Naming Covalent Binary Molecules 1.Write the name of the first element. The less electronegative element goes first. 2.Change the nonmetal’s ending to –ide. 3.Use prefixes to indicate the number of each type of atom. *Exception-the first element will never have the prefix mono 1-mono 2-di 3-tri 4-tetra 5-penta 6-hexa 7-hepta 8-octa 9-nona 10-deca 30

Practice Write the name for the following molecules: 31

Writing formulas for molecules The prefixes tell you the subscript for each atom. 32

Practice Write the formulas for the following molecules: 33

Empirical formula Empirical - To be derived from observation, experiment, or data. Empirical formula - the simplest whole number ratio between two (or more) elements 34 Watch This Watch this first

Steps to determine the empirical formula of a compound: 1.Determine the mass of each element in the sample. 2.Divide the mass of each element by the molar mass (from the PT) to determine the number of moles of each element. Round to the thousandths (._ _ _ )! 3.Divide the # of moles of each element by the smallest # of moles. This is the mole ratio for each element in the compound. 4.If your answers to step 3 are whole numbers, these are written as the subscripts. 5.If your answers to step 3 are NOT whole numbers, multiply by 2, 3, or 5 to obtain a whole number if increments of 0.5, 0.3 or 0.2 are given, respectively. 35

36 example What is the empirical formula for a sulfur oxide compound containing 50% sulfur and 50% oxygen? Step 1: Since % means “parts per hundred”, assume we are working with a 100 g sample. That means we have 50 g of sulfur and 50 g of oxygen.

Step 2: Use dimensional analysis to convert grams to moles 50 g S __1 mol_ = moles S 32.1 g 50 g O _1 mol_ = moles O 16.0 g 37 Label Properly!! Round to thousandths (._ _ _)

Step 3: Divide by the smallest number of moles to obtain a mole ratio moles S = 1 S Label Properly!! moles O moles S = 2 O So, we have 1 S for every 2 O. These numbers become the subscripts and the formula is SO 2 In our example, we did not need the 4 th step since the ratio came out to a whole number. 38

A compound contains 54.1 g of Mg and 45.9 g of P. Determine the compound’s empirical formula. Note: This time, we already have the number of grams so we can skip to step 2. Another example 39

Step 2: Use Dimensional Analysis to convert grams to moles g Mg___1 mol_ = moles Mg 24.3 g 45.9 g P __1 mol_ = moles P 31.0 g 40 Label Properly!! Round to thousandths place (._ _ _ )

Step 3: Divide by the smallest number of moles to obtain a mole ratio moles P = 1 P Label Properly!! moles Mg moles P = 1.5 Mg Notice, the bottom answer did not come out to a whole number this time. 41

Skip to step 5 since answers are not whole numbers. Step 5: Multiply answers from step 3 so that you get whole numbers. We had 1.5 Mg and 1 P 0.5 = ½ flip it and you have your scale factor, x 2 = 3 Mg and 1 x 2 = 2 P. The ratio did not change, it is just a whole number ratio now. So, we have 3 Mg for every 2 P or the formula Mg 3 P 2 42

Now that you know the steps, here is a jingle to make them easier to remember: Percent to mass step 1 Mass to mole step 2 Divide by small step 3 Multiply ‘til whole steps 4 and 5 Note: You may not need all of the steps. 43

Molecular formula  A formula that is reducible.  It is a multiple of an empirical formula. Ex. Can C 8 H 12 be reduced?  Of course, it’s divisible by 4. So, dividing by 4 reduces the formula to C 2 H 3.  C 8 H 12 is the molecular formula.  C 2 H 3 is the empirical formula. 44

Empirical formula Mass of empirical formula molecular formula Mass of molecular formula This template can help you organize your information and find what you are missing. 45

Ex. The molar mass of a molecular formula is g/mole and it’s empirical formula is P 2 O 5. Determine the molecular formula.  Draw your chart and fill in the info from the problem. 46 P2O5P2O g/mol ? g/mole Now, divide the molar mass of the MF by the molar mass of the EF. ( g/mole)/( g/mole) = 2. Scale factor is 2. Multiply the subscripts in the EF by 2 and the MF is… P 4 O 10 from word problem use PT to calculate

practice A compound is made from 2.00 g carbon, g hydrogen, and 2.66 g oxygen. Its molar mass is 90.0 g/mole. Determine the molecular formula. 47