<p>Is it acceptable to write compounds slightly differently, for example</p>
<p>H3P + BCl3 --> PH3BCl3</p>
<p>rather than</p>
<p>PH3 + BCl3 → H3PBCl3</p>
<p>?</p>
<p>derKommissar, i think that is fine, but why?</p>
<p>Thanks... I was just wondering if I need to worry about it.</p>
<p>For instance, why is PH3 written with the P first, but H3PBCl3 written with the H first? Just to hint at the structure?</p>
<p>well i think its fine but usually, H's always come first... like in HCl or H2SO4, cus its an acid... like why OH is usually last</p>
<p>it really doesn't matter. you can even right H2O as HOH, and it would be fine.</p>
<p>are you sure it's fine? my teacher says it's in the order of electronegativity or something... not really sure if that's right but i know that there is a systematic way for naming compounds with many different elements.</p>
<p>I didn't have time to read this page, but it could be helpful.</p>
<p>I think it matters a little. You never see H2O written as OH2. This is just a guess (I'm not sure about this at all) but I think that if there are multiple atoms of an element, that element has priority over its bonded element(s).</p>
<p>The answer is - sometimes the order of elements matters and sometimes it doesn't. :-)
When writing ionic compounds, it absolutely matters - the positive element or polyatomic ion precedes the negative element or polyatomic ion. (This is the electronegativity rule Spiffystars refers to.) NaCl is never written ClNa, and it would be considered wrong to do so. When writing covalent compounds, there is more leeway. For example, methanol can be written as CH4O (the molecular formula), but is more commonly written as CH3OH in order to convey structural information. In question 4 (reaction writing), writing NaCl backwords as ClNa would likely lose points, but an organic chemical can be written in any order as long as all of the elements are present with the correct subscripts. In fact sometimes organic compounds are written with a combination of purely molecular formula and some structural information. Organic acids (ex: acetic acid written as HC2H3O2) are often written with the acidic proton (the most positive element) first so you can see which hydrogens are acidic hydrogens. (Note the C2H3O2 conveys no structural information.) It would be just as acceptable, though, to write acetic acid as CH3COOH. Note the most positive (acidic) proton is now last.</p>
<p>Looking at the first example (PH3 + BCl3 = H3PBCl3) I would point out several things. First, when compounds comprising metals or metalloids with nonmetals are written (like BCl3) the "most positive first" convention is typically followed even if the the combination has too much covalent character to be considered ionic. This is also the reason why hydrogen halides (HCl, HBr, etc) are written with H first, but metal hydrides (ex: LiH) are written with H last. (Oxidation number of H is +1 in HCl, but -1 in LiH.) For PH3, however, the convention being followed is more along the lines of a structural formula. (The oxidation number of H in PH3 is +1, while P is -3 - clearly not the "positive first" rule.) You can think of Nitrogen and Phosphorus compounds (ex: NH3, PH3, PCl3) as following the organic tradition of conveying structure through the element order. (Compare to CH3CH2CH3.) When PH3 and BCl3 react, however, the coordinate covalent bond that is formed when the lone pair of the phosphorus fills the "empty orbital space" in the incomplete octet of Boron is a classic example of a lewis acid/lewis base reaction. For traditional reasons, the product is written as H3P-BCl3 (often with the bond line drawn between the two halves) to emphasize the reaction that has taken place. There is no concrete rule that says you can't write it as PH3-BCl3, but I would at least put the line in to clearly indicate you understand the reaction that has taken place.</p>
<p>Oh wow! Thanks for taking the time to do that... it helps :)</p>
<p>Don't turn around, thecomisar is here!</p>
<p>You joined in 2006 and have almost 1600 posts but I've never seen you post before. Man that is a fun song.</p>
<p>Anyway since gfaith wrote that nice explanation I've got nothing constructive to say.</p>
<p>hahaha... 2006 was my SAT-crazy year, so I posted a lot on the SAT I prep board. And now I post on Summer Programs, mostly... but I'll probably be spending more time on here.</p>
<p>I like that song too :)</p>