Chemical Formulas & Naming

What We Already Know O We have talked about pure substance being broken down into elements and compounds --more than one element combined is a compound O We have talked about how to figure out the number of valence electrons an element has O So, how do these things relate to forming a compound…why do the elements even want to hang out together?

Compounds A chemical formula tells us both the elements involved and how many of each are necessary AlBr 3 In this case, one Aluminum and 3 bromine are present If there is only one of something present then no subscript is used

How many atoms are present in these compounds? O NaHCO 3 O H 2 SO 4 O KNO 3 Here’s a tricky one… O Mg(OH) 2

Mg(OH) 2 In this case there is a hydroxide ion present (OH) and everything that is inside the parenthesis has to multiplied by what is outside the parenthesis

Let’s try another one… Mg(NO 3 ) 2 There is one Mg There are two N There are 6 O

Octet Rule O Atoms tend to want to achieve the electron configuration of a noble gas which has eight electrons in is highest occupied energy level O Atoms are willing to gain or lose an e - to achieve this O Gaining or losing an e - causes the atom to then be a charged particle.

Ions An atom with no charge has an equal number of protons and electrons So what about atoms with a charge? Its called an ion O Cation- A positively charged ion formed by an atom’s loss of a valence electron. Example Na + O Anion- A negatively charged ion produced by an atom gaining an electron. Example Cl -

Ions Continued O Monatomic ions is one element with a charge O Polyatomic ions is more than one element with a charge Example: SO 4 2-

Which Elements Will Gain and Which Will Lose Electron

Combining Elements It is the tendency to lose or to gain electrons that determine why elements combine a certain way Although ions carry a charge they have to combine in such a way that their charge cancels out. Na + Cl - Sodium wants to lose an electron and Chlorine is more than happy to accept that electron

The 5 Steps for writing an ionic compound formula: 1. Write the symbols of the two elements. 2. Write the valence of each as superscripts. 3. Drop the positive and negative signs. 4. Crisscross the superscripts so they become subscripts. 5. Reduce when possible.

Formula for boron oxide 1.Write the symbols of the two elements. B O

Formula for boron oxide 2. Write the valence for each element B 3+ O 2-

Formula for boron oxide 3. Drop the positive & negative sign. B 3 O 2

Formula for boron oxide 4. Crisscross the superscripts so they become subscripts. B 3 O 2

Formula for boron oxide 5. Reduce subscripts when possible. (not possible here) B 2 O 3

Examples of Reduction of Subscripts: Sr 2 O 2 SrO Al 3 P 3 AlP Pb 2 O 4 PbO 2 Subscripts can only be reduced if they are divisible by the same number Reduces to

Naming Ionic Compounds (Regular & Polyatomic) 1. Write the name of the cation (metal) 2. Write the name if the anion (nonmetal) -If only 2 elements, cut off the ending of the 2 nd element and add “ide” -If a polyatomic ion, use the name the class copy data sheet gives you.

Examples 1. NaCl 2. MgSO 4 3. K 3 PO 4 4. Ca(ClO 3 ) 2 5. NH 4 NO 2 O Sodium chloride O Magnesium sulfate O Potassium phosphate O Calcium chlorate O Ammonium nitrite

Naming Ionic Compounds (Variable Charge) 1. Check to see that these metal are in the d- block and have a variable charge 2. Write the name of the cation (metal) with (roman numerals which indicates charge) 3. Write the name of the anion (nonmetal or polyatomic ion) 4. The anion is named by adding –ide to the root of the element name

Examples: O Lead (IV) Oxide O Iron (II) sulfate O Cobalt (II) chloride O Copper (II) phosphate O Zinc chloride O PbO 2 O FeSO 4 O CoCl 2 O Cu 3 (PO4) 2 O ZnCl 2