Unit: Chemical Bonding

I. Compound Pure substances - has 2 or more elements chemically combined –Water (H 2 O) –Salt (NaCl) –Oxygen (O 2 ) –Sugar Sucrose (C 12 H 22 O 11 )

A. Different Combinations of elements produce different substances H 2 O  Water H 2 O 2  Peroxide O 2  Oxygen O 3  Ozone

B. Compound has new set of properties The individual elements that make up the compound lose their own properties H 2  gas, combustible O 2  gas, supports combustion H 2 O  liquid, clear, extinguishes a flame

B. Compound has new set of properties Na  Reactive, solid metal Cl 2  poisonous green gas NaCl  table salt

C. Atoms form compounds when the compound is Noble gases  Chemically stable –8 valence e-’s Elements w/out 8 valence electrons more stable in compounds Atoms can lose, gain, or share electrons to become stable A chemical bond is the force that hold atoms together in a compound  more stable than the separate atoms.

III. Chemical Formulas Shorthand way to represent chemical compounds use chemical symbols combined to make compound ex. H2OH2O Subscript

Subscripts The # represents the number of atoms of the previous element that are in one molecule of the compound If there is NO subscript after the element, then “ 1 ” is understood to be there – “1” is never written!!!!

How many atoms of each element are in these ? 1. C 6 H 12 O 6 2. CaCl 2 3. Mg(OH) 2 4. Ca(H 2 PO 4 ) 2

IV. Electron Dot Diagrams (Lewis Dot diagrams) Use element’s Valence electrons  electrons in outer shell Write elements chemical symbol Use a dot to represent valence e - ’s Place valence e - ’s around symbol **Hint: Like you would sit at the dinner table

Electron Dot Diagrams Sulfur NeonChlorine

V. Octet Rule Atoms are very stable with 8 valence electrons –( 4 pairs) atoms wants to have a full octet by either gaining, losing, or sharing electrons during chemical combinations

VII. Oxidation Numbers Stands for  The # of electrons an atom gains, loses, or shares to become stable –(also is its ion’s charge) “ + ” #  means lose that # of electrons “ - ” #  means will gain/share that # of electrons

VII. Oxidation Numbers Ex. SodiumChlorine Na +1 Cl -1

VIII. Writing Chemical Formulas Use oxidation numbers Use Criss-Cross Method When writing formulas, remember compounds are Neutral ***Positive Oxidation number written first (metal)

VIII. Writing Chemical Formulas Compound of Sulfur and Calcium?

Writing Chemical Formulas Compound of Sodium and Oxygen?

Writing Chemical Formulas Compound w/ Lithium and Carbonate ion  CO 3 -2

Use Criss-Cross Method to write chemical formula: 1. Mg and O 2. O and Al 3. I and K 4. Mg and OH Ca and CO 3 -2 Answers: MgO Al 2 O 3 KI Mg(OH) 2 CaCO 3

VIII. Type of Bonds A. Ionic Bonding: –Electrons are transferred – 1 atom loses and other atom gains electrons –Ion – charged atom, no longer neutral Can be positive (+) or negative (-)

Na combining with Chlorine The sum of the charges on the ions is zero!!

Lithium Fluoride

Ionic Bonds occur: Nonmetal  Sumo wrestler Metal  Child Between Metals bonding with Nonmetals

Ionic Compounds Two ions have opposite electrical charges therefore attracted to each other –Holds Ionic Bonds together Weak bond between elements

Ionic compounds form Crystal Lattice structure –regular repeating arrangement due to “+” tend to be near “-“

Ionic Bond  weaker bonds between elements than covalent bonds –Are easier to break into ions But strong bonds b/w molecules –Substances tend to be solids at Room Temp –Have high melting points

B. Covalent Bonding “Co” – to share “Valance” – electrons electrons are shared, not transferred

Covalent Bonding Happens when both atoms attract electrons Nonmetal with Nonmetal Also Hydrogen with Nonmetal

Covalent Bonding Attraction b/w nucleus and shared electrons hold the atom together

Covalent Bonding Ex. Hydrogen with Carbon

Covalent Bonding - Covalent bonds often occur b/w atoms of same element  Diatomic molecules Ex. O 2, F 2, Br 2, I 2, N 2, H 2 - When these are found in nature, always 2 atoms covalently bonded

Covalent Bonding F 2 Cl 2

Covalent Bonding More than 2 electrons can be shared b/w atoms Ex. Carbon and Oxygen

Covalent Bonding If 3 pairs of electrons are shared called a triple bond Ex. N 2

Covalent Bonds  Strong bonds between elements But Weak bonds b/w molecules –Triple bonds are strongest, then double, then single Substances Tend to be liquids or gases at room temp. Have Low boiling points

Covalent Bonding Molecule - smallest part of a bonded substance, compound, that has properties of that substance - Are neutral, no overall charge - Can be Polar or Nonpolar

1. Polar Covalent molecules one end is slightly negative and one end is slightly positive, the overall molecule is still neutral Ex. Water

2. Nonpolar Molecules – Electrons are shared equally –Ex. Oil, fuels, fats

IX. Polyatomic Ions Group of covalently bonded atoms that act as a single atom when bonding with other atoms As a group have a charge Form ionic bonds with other elements Ex. Sodium and Hydroxide Ion Calcium and Carbonate Ion

X. Predicting Types of Bonds Compound b/w Metal & Nonmetal – Form Ionic Bond Compound b/w Nonmetal & Nonmetals –Form Covalent Bond –Like a Tug of war b/w 2 sumo wrestlers Compound b/w polyatomic ion & element –Form ionic bond

Predicting Types of Bonds Ex. F + Mg ? –Ionic O + Cl ? –Covalent Na + OH -1 ? –Ionic

XI. Naming compounds **Binary compounds – compounds containing only two elements See Handout

A. Binary Ionic 1. Write Positively Charged ion first - usually the METAL 2. Then add Name of Negative ion with end changed to “-ide” - Usually the NONMETAL  NaCl  Li 2 O  CaO Write formula for Magnesium Oxide. - Make sure that oxidation #’s add to zero!!

B. Naming Compounds with Transition Metals - remember transition metals may have more than one Oxidation Number - form positive ions Ex. Copper  Iron 

1. Write name of Transition Metal first 2. In Parenthesis ( ) write a Roman Numeral to indicate the ox # of the Transition metal in this compound 3. Write name of nonmetal and Change end to “-ide” Ex. Cu +1 and Cl Cu +2 and Cl

Write the name for the following: 1. PbO 2. TiCl 4 3. HgCl 4 Write the Chemical formula: 1. Tin (IV) Flouride 2. Lead (I) Sulfide 3. Cobalt (III) Chloride

C. Naming Binary Molecular (covalently bonded) Compounds 1. Write element that is Least Electronegative first a. Use your table for this

2. On the most electronegative element give a prefix for # of atoms of that element in the compound Prefix# of atoms mono1 di2 tri3 tetra4 penta5 hexa6 hepta7 octa8 3. Change end of 2 nd element to “-ide” Ex. CCl 4 Ex. CO

Name the following: 1. SO 2 2. SiO 2 3. SF 6

X. Molar Mass of a Compound A. Mole – the unit of measurement used to count numbers of atoms, molecules or formula units - Abbreviated “mol” - The number of things in one mole is 6.02 X Avogadro’s number 1 mole = 6.02 X 10 23

B. Using this we can count the number of atoms in one mole of a substance Ex. 1 mole of Carbon is 6.02 X at atoms of Carbon 1 mole of Na is 6.02 X atoms of sodium

Molar Mass – the mass of one mole of a substance Ex. The mass of one Carbon-12 atom is exactly 12 amu  The mass of one mole of C-12 is 12 grams

** Molar mass is the mass in grams of the average atomic mass of the substance** ex. Molar mass of Iron? grams

Try these! Find the molar mass of each substance. 1. Oxygen 2. Uranium 3. Copper

C.Finding the molar Mass of a Compound: -find the molar mass of each element in the compound -multiple it times the number atoms of that element in the compound - the Sum of the molar masses = the Molecular Mass (or gram formula weight) of the compound ex. Ethanol – C 2 H 6 O

Try These: 1. Ca Cl 2 2. C 6 H 5 Br 3. (NH 4 ) 3 PO 4

Which Has the largest Mass? 3 Mol of Magnesium or 1 mol of sucrose or 10 mol of helium