In A Lehman Explanation, What Are The Main Differences Between Molecular Weight And Formula Weight?
Tuesday, December 29th, 2009 at
5:25 pm
All I know is that one is covalent while the other is ionic, and that having hydrogen in the mix will automatically make it covalent since it will distinguish if it’s polar on non-polar. Also, I read something about certain elements and/or compounds being naturally covalent/ionic, the thing is, how do you know? Feel free to correct anything I’ve said wrong, and please, help me 
Thanks!
Tagged with: Between • Differences • Explanation • Formula • Lehman • Main • Molecular • Weight • What
Filed under: Free Baby Stuff
Like this post? Subscribe to my RSS feed and get loads more!
Formula weight can apply to any compound whose composition can be expressed by a formula. This includes ionic compounds (e.g. NaCl), covalent giant structures (e.g. SiO2) and covalent molecular structures (e.g. CO2). The formula weight is simply the sum of the atomic weights of the atoms in the formula.
Molecular weight can only be applied to compounds which exist as discrete molecules (i.e. not chemically bonded to neighbouring molecules), e.g. CO2, H2, P4O10, C2H5OH. The molecular weight is the sum of the atomic weights of each atom in one molecule. All such compounds have covalent bonds but the converse is not true – some compunds with covalent bonds do not form molecules (they form giant structures, e.g. SiO2) so they cannot be assigned a molecular weight.
‘Cleveland’ is correct about how to identify whether the bonding is ionic or covalent.
Quatum physics is a mystery
Formula weight is used to measure ionic compounds, molecular weight to measure covalent compounds. For practical puposes in chemistry they are the same.
To decide if something is ionic or covalent yoyu need to look at the electronegativeity difference >1.7 =ionic bond
A rule of thumbs is that those things that are far apart onthte periodic table are bonded ionically