1. Molecular Compounds

2. Types of Compounds Ionic Metal (or NH 4 + ) with a non-metal Transfer of electrons from metal  non-metal Have ionic bonds Molecular Non-metals only Sharing of electrons between non-metals Have covalent bonds

3. Properties Ionic Solid (s) High melting points When dissolved in water, aqueous (aq), ionic compounds are electrolytes (good conductors of electricity) Electrolytes when melted. Molecular Solid (s), liquid (l) or gas(g) Lower melting points When dissolved in water, (aq) or melted they are not electolytes

4. A molecular compound A molecular compound, is a pure substance that is formed from covalent bonds between nonmetals. Examples include: Water H 2 O (l) Carbon Dioxide CO 2 (g) Oxygen O 2(g)

5. Covalent Bonding sharingA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. This sharing allows the atoms to form a stable electron arrangement. For H 2 (g) that stable arrangement has 2 e-’s For other molecular compounds an octet is required by sharing.

6. Diatomic Molecules A diatomic molecule is a molecule consisting of only two atoms, of either the same or different chemical elements. http://www.dnatube.com/vid eo/1290/Covalent-bondhttp://www.dnatube.com/vid eo/1290/Covalent-bond O 2 Oxygen N 2 Nitrogen gas

7. Diatomic Molecules Here are some examples of diatomic molecules (same element): hydrogen (H 2 ) nitrogen (N 2 ) oxygen (O 2 ) fluorine (F 2 ) chlorine (Cl 2 ) bromine (Br 2 ) iodine (I 2 ) Here are some examples of diatomic molecules (different elements): CO – Carbon Monoxide NO – Nitrogen Monoxide HF – Hydrogen Fluoride HCl – Hydrogen Chloride HBr – Hydrogen Bromide N 2 O- dinitrogen monoxide SO 3 - sulfur trioxide

8. Diatomic Elements I Bring Clay For Our New Home *to help you remember the molecular diatomic elements.

9. Diatomic Compounds Since many combinations of some atoms are possible, the number of atoms in the molecule is often stated using Latin prefixes. –Carbon monoxide is CO while carbon dioxide is CO 2. –Memorize the prefixes!

10. Common Prefixes onemono sixhexa twodi sevenhepta threetri eightocta fourtetra ninenona fivepenta tendeca NBr 3 = Nitrogen tribromide Dihydrogen dioxide = H 2 O 2

11. Rules Use the Greek prefixes to indicate how many of each element are present in the formula. Mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca,… Drop mono for the first element. Drop all prefixes if the first element is hydrogen. Drop the second o in mono prior to a vowel. Drop the a in prefixes ending in a prior to a vowel.

12. Examples: N 2 S N 2 O 3 CO 2 (g) HCl CO(g) N 2 O 4 Dinitrogen monosulfide dinitrogen trioxide carbon dioxide hydrogen chloride carbon monoxide dinitrogen tetroxide

13. Naming Molecular Compounds Can be more complicated than ionic compounds. There are also “common” names that will need to be memorized, such as: Water (H 2 O) Methane (CH 4 ) Hydrogen peroxide (H 2 0 2 ) Sucrose C 12 H 22 O 11

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15. Writing Formulas for Molecular Compounds Method is similar to the one used for ionic compounds. The combining capacity of a nonmetal tells you how many covalent bonds are needed to form a stable molecule. To figure out an atoms combining capacity you need to see where it falls on the periodic table or know how many valence electrons it has. Methane CH 4

16. Writing Molecular Compounds Step by Step Carbon & Sulfur Step 1: –Write the symbols and combining capacities

17. Step 2: –Use the crisscross rule & the combining capacities to get the proper subscripts. Writing Molecular Compounds Step by Step Carbon & Sulfur This formula becomes C 2 S 4 reduced to CS 2.