General chemistry: how do u know if a molecule is ionic or not ionic just by looking at it?

Question

C6H12O6 non ionic.

NaCl, HNO3,CaCl2 all ionic. how do you know?

Answer 1

Ionic compounds form lattices. C6H12O6 is an organic compound, so it won't. The others are inorganic, NaCl and CaCl2 are salts and will definitely form crystal packing structures. No idea about HNO3, but it's inorganic and highly acidic. In water it will deprotonate to form NO3-, which has a nonzero electrical charge and hence is ionic.

Answer 2

you need to memorize your simple and polyatomic ions first, then you will be able to recognize when a molecule is made up of ions. the only way to do it is memorize them.

Answer 3

Compounds made up of only nonmetals are usually covalent. The most prevalent exceptions are the ammonium salts, such as ammonium nitrate, NH4NO3, which contains nitrogen, hydrogen, and oxygen and yet is ionic. Note that C6H12O6 contains only nonmetals and is covalent, and the same can be said about HNO3. (Yes, HNO3 is a covalent compound. H+ is not an ion found in ionic compounds. HNO3 does however behave like an ionic compound when it dissolves in water; it dissociates to give ions.)

A compound containing a metal and an electronegative nonmetal (e.g. NaCl, CaCl2, CaO, etc.) is usually ionic. However, if the metal is a transition metal, and it is in a high oxidation state (e.g. OsO4 has osmium in the +8 oxidation state) then the compound will be ionic. Generally, ionic compounds do not have oxidations states above +3. UF4 may be considered ionic with U in the +4 oxidation state; this would be possible only because U is such a large atom.

There are borderline compounds such as aluminium carbide, Al4C3. The truth is, there is no such thing as a completely ionic compound. Whenever two different atoms are bonded, there is a degree of ionic character. When the ionic character is low we call it polar covalent; when it is high we say ionic. There is no clear distinction and it would be pointless to attempt to define one.

By the way, you could have searched "how to tell if a compound is covalent or ionic" on Y! A and saved yourself 5 points. I got 54 search hits, surely one of them would have the explanation you need?