OB: molecular compounds, naming and formulas, and determining how for form molecular compounds using selected oxidation states. Periodic tables mandatory now, smile, this is easier than the rest of the compounds we’ve looked at Ionic compounds form when positive cations combine in proper ratio with negative anions, attracting each other because of opposite charge. The compounds must have a cation combining with anions (+ except for that weird ammonium) all cations are metals. With molecular compounds, the easy way to spot them is that there are NO METALS. Molecular compounds form when 2 or more nonmetals bond together,in proper ratios. There are NO ions, no ionic bonds either. They combine by sharing electrons which we’ll learn about later on in the year. They have their own naming system, which is easy if you can count to ten in Latin. If you can’t, I will teach you in a few slides. CO2 NH3 CO CH4 HCl H2O There are NO METALS ever in molecular compounds. C8H18 When two or more non metals bond together they form a molecule. A molecule is the smallest part of a molecular compound. The bonds that hold these atoms together is called a covalent bond. When 2 or more ions bond, they make ionic bonds, and they form into FORMULA UNITS. NaCl does not come in molecules, since it does not exist as a single particle. It’s in crystals, or dissolved in water. NAMING RULES FOR MOLECULAR COMPOUNDS If you can remember what CO, CO2, and H2O are, the naming rules are easy carbon monoxide, carbon dioxide + dihydrogen monoxide First name rule: a single atom? Say just the atom name a multiple atom? Say a prefix first Second name rule: always use a prefix 1 MONO 6 HEXA 2 DI 7 HEPTA 3 TRI 8 OCTO 4 TETRA 9 NON 5 PENTA 10 DECA Using the 2 rules, and the Latin Prefixes, let’s name these 10 example molecules. You will have to name any molecular compound with up to 10 atoms of any kind. HF CS2 SO3 CCl4 PF5 SF6 Cl2O8 I4O9 N2F10 Hopefully you got these all correct… HF Hydrogen monofluoride CS2 Carbon disulfide SO3 Sulfur trioxide CCl4 Carbon tetrachloride PF5 Phosphorous pentafluoride SF6 Sulfur hexafluoride Cl2O8 Dichlorine octoxide I4O9 Tetraiodine nonoxide N2F10 Dinitrogen decafluoride First name rule for single atom is say that atom name. Multiple atoms in first name gets a prefix. Second name rule says always use a prefix. We will practice names to formulas first… Write the formulas for each named molecule: Phosphorous tribromide ____________ Diphosphorous trioxide ____________ Oxygen difluoride _____________ Dihydrogen monoxide ______________ Nitrogen monoxide ______________ We will practice names to formulas first… Write the formulas for each named molecule: Phosphorous tribromide PBr3 Diphosphorous trioxide P2O3 Oxygen difluoride OF2 Dihydrogen monoxide H2O Nitrogen monoxide NO Now in reverse, name these formulas with prefixes… NO2 _________________________ CI4 _________________________ N20 _________________________ SO3 _________________________ N2O5 _________________________ HCl _________________________ Now in reverse, name these formulas with prefixes… NO2 nitrogen dioxide CI4 carbon tetraiodide N20 dinitrogen monoxide SO3 sulfur trioxide N2O5 dinitrogen pentoxide HCl hydrogen monochloride Look right now at tables K and L These are the acids and bases. We will spend about two weeks on what acid and base chemistry is all about, but today we will look at their names, see that their names and formulas are on your reference tables, say the names together, and that’s that. Also, there are 7 elements that exist NOT as atoms in their natural state. Rather they exist as pairs of atoms, diatomic elements. Mr. Smith taught this to me in the 8th grade at Junior High School 202 in Ozone Park in Queens. I am happy to share his wisdom now. To remember these seven diatomic elements, we will call them the HONClBrIF twins H2 O2 N2 Cl2 Br2 I2 F2 How do we decide what ratios of nonmetal atoms fit together to make compounds? Why is water H2O and NO OTHER hydrogen-oxygen compounds exist in any other ratio? Thinking hats on now. Periodic Tables, Selected Oxidation States These numbers tell us (with some thinking) what ratios are possible, and what ratios cannot create molecules. Make this chart in your notes: H O Write in all of the possible oxidation states from the Periodic Table of the Elements H +1 -1 O -2 2:1 ratio possible X: two negatives ≠ 0 The only possible combo for H and O to bond is 2:1, which spells in chemistry: H2O Let’s determine all of the possible carbon + oxygen compounds that could form with the selected oxidation states. Remember: they must sum to zero, but the ARE NOT IONS. These atoms share electrons only. C O Let’s determine all of the possible carbon + oxygen compounds that could form with the selected oxidation states. Remember: they must sum to zero, but the ARE NOT IONS. These atoms share electrons only. C -4 +2 +4 O -2 Let’s determine all of the possible carbon + oxygen compounds that could form with the selected oxidation states. Remember: they must sum to zero, but the ARE NOT IONS. These atoms share electrons only. There is NO WAY -4 plus -2 can ever sum to zero, this selected oxidation state for carbon is not used in any carbon – oxygen compounds. C -4 +2 +4 O -2 1:1 is possible 1:2 is also CO + CO2 are possible, nothing else is according to our periodic table. Let’s do the big one: All Nitrogen + Oxygen Compounds (there are 5) N O Let’s do the big one: Nitrogen and Oxygen N -3 -2 -1 +1 +2 +3 +4 +5 O -2 Let’s do the big one: Nitrogen and Oxygen N -3 -2 -1 +1 +2 +3 +4 +5 O 5 Possible Compounds 2:1 or N2O -2 1:1 or NO 2:3 or N2O3 1:2 or NO3 2:5 or N2O5 This week… THURSDAY we will have a major review, then a celebration on naming compounds and formulas on FRIDAY Friday we start moles, bring a calculator, you’ll need it. This man is on Double Secret Probation. do you know who this is?
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