Unit 5 Chemical Formulas and Bonding Once upon a time, there were two elements. Not wasting any time, they ran to the justice of the periodic table. He said “Will you sodium, donate An electron to chlorine?” They fell in love at first sight!! There names were Sodium (Na for short) and Chlorine (Cl for short)

“You may now…..form an ionic compound” Na said …. “I Will” “I Will” Then the Justice of the Periodic Table said “Will you chlorine accept an electron from sodium?” Cl said …. “I Will” “I Will” “Well then” said the Justice of the Periodic Table, “I now Pronounce you Sodium Chloride! Let me be the first to introduce you to NaCl!

Distinguish between the common and systematic names of chemical substances. 6.1 Common and Systematic Names Discuss the formation, charge, and naming of simple ions. 6.2 Elements and Ions Write the chemical formula for an ionic compound from the name of the compound. 6.3 Writing Formulas from Names of Ionic Compounds Learning Objectives

Name binary ionic and molecular compounds. 6.4 Naming Binary Compounds Use the rules to name an acid from its formula and to write the formula of an acid from its name. 6.5 Acids Learning Objectives

Example sodium (Na) The formula for most elements is the symbol of the element. Exception: certain elements exist as polyatomic (multiatom) molecules under standard conditions Example 7 elements exist as diatomic molecules (contain two atom units) H 2, O 2, N 2, F 2, Cl 2, Br 2, and I 2 Gases LiquidSolid Two other elements exist in polyatomic arrangements Sulfur - S 8 Phosphorus - P 4 Elements and Ions

Lewis Dot Diagram The Lewis Dot diagram shows us how each element satisfies the octet rule The Octet Rules states all elements (Except H, He, Li and B) try achieving Nobel Gas status by getting 8 valence electrons in their outer most energy level. The “s and p” electrons are represented around the element symbol. -This only works for the representative elements - The order electrons enter: s 1 - s 2 - p 1 - p 2 - p 3 - p 4 - p 5 - p 6 s 1 s 2 P1P1 P3P3 p 5 p4p4 P2P2 p6p6

Barium = BaSelenium = Se Iodine = I :: Monatomic ions …all ions formed from a single element *********************************************** Cations … positively charged ions  Naming monatomic cations: the atom and cation have the same name.  Metals form cations - Column IA = +1 - Column IIA = +2 - Column IIIA = +3 - Column IVA = +4 for metals and –4 for nonmetals. *Lead (Pb) and Tin (Sn) can also be +2 - Transitions elements: Use the electron configuration to determine the oxidations states “or” they will be give in the oxidation state as Roman numerals in the element name. Ex…iron (III) chloride; Fe +3

Anions … negatively charged ions *Nonmetals form anions - Column IVA nonmetals = -4 - Column VA nonmetals = -3 - Column VIA nonmetals = -2 - Column VIIA = -1 *Naming monatomic Anions: all single anions have the suffix “ide” added to the end of the first part of the atoms name. Ex…. Atom name  ion name Oxygen Chlorine Phosphorus oxide chloride phosphide

Polyatomic Ions : Two or more elements covalently bonded to produce an overall + or - charge.  The names of polyatomic ions always have a suffix. o Most Common suffixes…”ate”, “ite” o Ions ending in “ate” have one more oxygen than ions ending in “ite” Sulfate Sulfite Nitrate Nitrite SO 4 -2 SO 3 -2 NO 3 -1 NO 2 -1

The prefix “per” can be used with any polyatomic ion that ends with “ate” ° “per” indicates there is one more oxygen than there are in the regular “ate “ form. Ex… Chlorateperchlorate ClO 3 -1 ClO 4 -1 The prefix “hypo” can be used with any polyatomic ion that ends with “ite” ° “hypo” indicates there is one less oxygen than there are in the regular “ite “ form. Ex… Chloritehypochlorite ClO -1 ClO 2 -1

Each subscript describes the number of atoms for the preceding element. There are 2 hydrogen. We only need to use subscripts if there are two or more atoms of any given element. Chemical Formulas When writing formulas: Write the symbol for the more metallic element or polyatomic ion first. Recall: the elements furthest to the left on the periodic table are more metallic. Finish the formula with the most nonmetallic element or polyatomic ion. Each capital letter indicates a new element. H2OH2O

 An electrostatic attraction between cations and anions.  Ionic bonds occur between a metal and a nonmetal or two oppositely charged ions. EX..CaO or NH 4 NO 3  The cation donates electrons to the anion.  The cation’s oxidation number ( not charge) becomes the anion’s subscript and the anion’s oxidation number ( not charge) becomes the cation’s subscript if the oxidation states do not add up to zero.  If the oxidation states are equal in charge but opposite in sign (+ or -) then they form a compound with a 1:1 ratio.  An ionic formula is always written with the cation followed by the anion. Na +1 + Cl -1  NaClK +1 + SiO 3 -2  K 2 SiO 3 NH CO 3 -2  (NH 4 ) 2 CO 3 Ionic bonding / formula’s

1. Assign an oxidation number to each ion. Ca S Recall how do write an Ionic formula? 2. If the oxidation numbers add up to zero, the formula is represented just as the symbols… remember to start with the cation. Ca +2 S -2  CaS If the oxidation numbers do not add up to zero we will use a “crisscross” method. Similar to cross multiplication. Ca Cl Now write the new formula without the oxidation numbers, but with the new subscripts. CaCl 2 The two from calcium’s oxidation state becomes chloride’s subscript. You only need write a subscript if the oxidation state is greater than |1|.

6. Now write the new formula without the oxidation numbers, but with the new subscripts. 5. One addition, if you are using a polyatomic ion and the oxidation numbers do not add up, l use the “crisscross” method but always put parentheses around the polyatomic ion if its subscript is greater than 1. Al +3 SO 4 -2 ( ) Notice, just the oxidation numbers are used to determine the subscripts. Any subscript brought in by a polyatomic ion, is never changed! Al 2 (SO 4 ) 3

Covalent Compounds (Molecules) Inter-molecular forces between elements hold covalent compounds together. A sharing of electrons between elements creates the covalent bond. Sharing is used to satisfy the octet rule. Binary covalent compounds occur between two nonmetals Again, the most metallic element is listed first. If the two elements are in the same row, the element farthest to the left is written first. If the two elements are in the same column, the element farthest down the column is listed first. The number of atoms per element is indicated using a Greek prefix. (Mono, di, tri, tetra, penta, hexa, hepta, oct) In covalent bonding, the valence electrons are rearranged so they can achieve the octet rule for both elements involved in the bond.

Covalent bonds can form single, double and triple bonds to help achieve the octet rule. Single bonds  1 pair (2 electrons) indicated with a single line. Structural Formulas (molecular models) specify how and which atoms are bonded to each other in a molecule. H 2 OCOCO 2 O H H Try the other two…. Double bonds  2 pair (4 electrons) indicated with a double line. Triple bonds  3 pair (6 electrons) indicated with a triple line.

COCO 2

: F – S – F : : F : : F : Exceptions to the Octet Rule (Don’t ya hate exceptions!!) Exceptions occur most frequently in covalently bonded compounds. Atoms with more than an octet Some atoms beyond the second row (notably sulfur and phosphorus) form bonds that give them more than an octet of electrons. The additional electrons fill the 3d orbitals of these atoms. Example: SF 4

Atoms with less than an octet Many compounds of boron do not follow the octet rule. Example: BF 3 : F : B : F : : F : Molecules with an odd number of electrons: A molecule with an odd number of electrons cannot follow the octet rule. Nitrogen is the most notable problem atom! These make compounds, they are just less stable. Example: NO N : : O

Naming Covalent Compounds 1. A prefix is used to describe the number of atoms per element in the compound. i.Exception: If there is only 1 of the first element, no prefix is needed. 2. Prefixes: 1 = mono, 2 = di, 3 = tri, 4 = tetra, 5 = penta, 6 = hexa, 7 = hepta, 8 = octa 3.All binary ionic and covalent compounds end in “ide”. 4.There are no polyatomic ions used since covalent compounds are not balanced based on their oxidation states. N2O5N2O5 Dinitrogen pentoxide SO 2 Sulfur dioxide

Binary Compounds Binary compounds have only two elements. Binary ionic compounds are always written as empirical formulas.  Empirical formulas have the lowest whole number ratio of ions in the compound. Covalent compounds are written as molecular formulas  Molecular formulas indicate exactly how many atoms are present in the formula of the molecule.  These formulas are NOT reduced to the lowest whole number ratio of ions in the compound. C 8 H 18, C 4 H 10

Is the bond Ionic or Covalent Recall:  If the compound starts with a metal, it is almost always ionic.  If the compound starts with a nonmetal, it is almost always covalent. Determine whether you have an ionic or a covalent bond by finding the difference in electronegativities. Recall: Electronegativity: The desire to hold the electrons more closely to it during the chemical bond. Non-metals have a higher electronegativity, therefore, the electrons are drawn closer to the nonmetal while in a bond.

Bond type by electronegativy Electronegativity differenceBond Type < 0.4 nonpolar covalent between 0.4 and (1.7)2.0 polar covalent > (1.7) 2.0 ionic NO Using your periodic table, the electronegativity is the number written in green. For nitrogen E = 3.0, for Oxygen E=3.5 Subtract: always set up to get a positive number: 3.5 – 3.0 = 0.5 Therefore, the compound NO is polar covalent What does Polar mean? It means the one element has more unshared electrons on it than the other element. O.5 is very close to the 0.4, so it is weakly polar covalent.

Binary Acids: Contain only two types of elements Naming Inorganic Acids … Ex..HCl, HBr, HF Prefix…hydro…represents the hydrogen Followed by the anions 1 st syllable Suffix… end with “ic” Follow with the word “acid” HCl…hydro…chlo…ic acid HBr…hydro…brom…ic acid HF….

Naming acids that contain polyatomic anions. Ex…HNO 3, H 2 SO 3, H 3 PO 4 Name this type of acid after the polyatomic anion. If the anion has the ending “ate” then replace the “ate” with the new suffix of “ic” If the anion has the ending “ite” then replace the “ite” with the new suffix of “ous” Follow with the word acid. HNO 3 …recognize the polyatomic anion as “nitrate” Nitrate  Nitric acid H 2 SO 3… recognize the polyatomic anion as “sulfite” Sulfite  Sulfurous H 3 PO 4 … Phosphoric Acid

Hydrates vs Anhydrous Hydrates are compounds that have water molecules which cling to the ionic portion of the compound. There is no actual bond that exists. Naming hydrates: CuCl 2 5H 2 O 1)Name the ionic compound first: 2)Indicate the number of waters attached using the prefixes Mono, di, tri, tetra, penta, hexa, hepta, oct 3)End with the word “hydrate Copper (II) Chloride pentahydrate Anhydrous simply refers to the ionic compound without the water. In the above example the anhydrous compound would be Copper (II) Chloride.