PCl5 is a binary, molecular compound. Binary: two elements (P and Cl) QUESTION: Which of the following is the correct name for PCl5? A. phosphorus chloride, B. phosphorus chlorine C. phosphorus pentachlorine D. phosphorus pentachloride PCl5 is a binary, molecular compound. Binary: two elements (P and Cl) Molecular: both elements are nonmetals Rule: name first element, then second element, but… Change ending of second element to ide Add Greek prefix corresponding to subscript: di=2, tri=3, tetra=4, penta=5, hexa=6, hepta=7 octa=8, nona=9, deca=10 SCRIPT: Which of the following is the correct name for PCl5? A. phosphorus chloride, B. phosphorus chlorine C. phosphorus pentachlorine D. phosphorus pentachloride PAUSE To name a compound given its formula, we need to first classify the compound, then apply the rule for that type of compound. CLICK PCl5 is a binary, molecular compound. By binary, we mean that it is made up of only two elements…. In this case, phosphorus and chlorine CLICK It’s a molecular compound because both elements are nonmetals. If the first element were a metal, the compound would be classified as ionic. The rule for naming binary molecular molecular compound is this. Name the first element, then second element, but… Change ending of second element to ide… This means that choices B and C are wrong. CROSS OUT “ine” in chlorine And… We must add Greek prefix to each element’s name. The prefix should correspond to the subscript. If the subscript is 2, the prefix is di… If the subscript is 3, the prefix is tri… If the subscript is 4, the prefix is penta…which is the case here for chlorine… HIGHLIGHT 5 in PCl5 and penta in choice D. Therefore, choice A is wrong… it’s missing the penta prefix. CALLOUT “Need penta prefix” before chloride No prefix is added if the subscript is one, which is the case here for phosphorus. CALLOUT “Implied subscript=1” pointing to P in PCl5. If there is no subscript next to the symbol for an element, it is implied to be one. Other greek prefixes you should memorize are Hexa for 6, hepta for 7, octa for 8, nona for 9, and deca for 10. CLICK PAUSE END RECORDING

Video ID: 1-26-1 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08