Dinitrogen Pentaoxide. * Notice that the prefix mono is omitted in the first element

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1 Naming Binary Covalent Molecules Binary molecules come from the combination of two nonmetals (-or- a nonmetal and a metalloid acting as a nonmetal). MOLECULES DO NOT INVOLVE IONS. Ionic bonding create compounds called salts; Covalent bonding creates molecular compounds, often called molecules. As a result, they have a slightly different naming system. Chemists use prefixes to indicate the number of atoms in each molecule. The prefixes are listed in the table below: # of Atoms Prefix # of Atoms Prefix 1 Mono 6 Hexa 2 Di 7 Hepta 3 Tri 8 Octa 4 Tetra 9 Nona 5 Penta 10 Deca When naming molecules, the first element name is given, followed by the second element with an ~ide ending. The first element gets a prefix when there is more than one atom in the molecule.* The second element ALWAYS gets a prefix. Here are some examples: Molecule Name NO* Nitrogen Monoxide N 2 O Dinitrogen Monoxide NO 2 * Nitrogen Dioxide N 2 O 3 Dinitrogen Trioxide N 2 O 4 Dinitrogen Tetraoxide N 2 O 5 Dinitrogen Pentaoxide * Notice that the prefix mono is omitted in the first element Prefixes are necessary when naming molecules because the atoms can combine in any whole number ratio. N 2 O, for example, cannot simply be called nitrogen oxide, because there are several other molecules that contain nitrogen and oxygen (see above chart). We must specify that there are two nitrogen atoms bonded to a single oxygen atom. When dealing with ionic compounds, there is only one way for a cation and anion to combine and balance their charges to form a neutral compound. As a result, there is no need to use prefixes. This is why CaCl 2 is called calcium chloride, rather than calcium dichloride, because it will always take (1) Ca +2 to cancel out (2) Cl -1.

2 Lewis Dot Structure Instructions CCl 2 O O C Cl Cl O = 6 C = 4 Cl = 7 Cl = N/A on this atom but here s O O: 6-1= 5 example: C: 4 3 =1 C Cl: 7 1 =6 Cl Cl Cl: 7 1 =6 Note the valence dots around central atom O and C only have 7 electrons 1. Arrange atoms as symmetrically as possible. The odd (i.e. different) atom with the most open spots for bonding usually goes in the middle. Usually, the arrangement most symmetrical is correct. Note: C is almost always the center atom whereas H is never the central atom!!!!!!! 2. Count the total number of valence electrons on for all atoms in the molecule. 3. Draw single bonds between the central atom and each surrounding atom. Each single bond represents a shared pair of electrons; each atom originally donates one electron to each pair. Subtract this amount from the valence count. Period 1 & 2 elements obey the Octet Rule; Elements BELOW Period 2 can break the Octet Rule. 4. Place electron pairs around peripheral atoms. Remove electrons used from total valence count. 5. If any valence electrons are left, place those electrons around the central atom until octet is reached. Remove the electrons used in this step from the total valence electron count. 6. Check for octet with each atom. Note: H will never reach octet!!!!! If octet is satisfied for all atoms, then you are done. If not. 7. If octet is still not reached, then multiple bonds must be used. Take a pair of electrons from each peripheral atom to form multiple bonds and octet is satisfied for all atoms. Check again for octet.

3 I. Complete the Chart for the prefixes of # of atoms: # of Atoms Prefix # of Atoms Prefix II. Complete Chart: Name of Molecule Formula of Molecule Lewis Dot Structure carbon dioxide phosphorus triiodide sulfur dichloride nitrogen trifluoride dioxygen difluoride phosphorous pentabromide arsenic tribromide dihydrogen monoxide N2F4

4 SCl4 CF3l SiO2 P4O10 SbCl5 SnI4 CSe2 III. Determine whether compounds are covalent or ionic and give them their proper names. Chemical Formula Covalent / Ionic Proper Name Ba(NO 3 ) 2 CO PCl 3 KI CF 4 MgO Cu 2 S SO 2 NCl 3 XeF 6

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