How can I differentiate between Ionic compounds, molecular compounds, and acids given only the formula?

Question

I need to be able to find the difference between an Ionic compound, a molecular (or covalent) compound, and an acid given only the chemical formula (no charges or roman numerals)?

Answer 1

Ionic compounds involve ions, so they are typically the combination of a metal and a nonmetal, such as NaCl, CaBr2, AlCl3, etc. Some ions that are made completely of nonmetal can form ionic compounds. The main example is the ammonium ion, NH4+, so when you find anything with NH4X, where X = Cl, Br, I, NO3, etc, they are also ionic compounds. The NH4+ is sometimes called a pseudo alkali metal ion, since it behaves as an alkali metal ion, hence, its name, ammonium, same ending as for alkali metals, lithium, sodium, potassium, etc.

Molecular compounds always involve two nonmetals, CO, CO2, NH3, N2O4, etc. That is how you can identify them easily, the bonding does not involve ions at all, so they are nonconductors of electricity under any circumstance, unlike ionic compounds that conduct electricity when dissolved in water or when molten. All hydrocarbons are molecular compounds for the most part, alkanes CnH2n+2 (CH4, C2H6, C3H8) and their derivatives, CH3Cl, C2H5Cl, and so on.

For acids, they must have at least one hydrogen atom covalently bonded to a rather electronegative elements, such as F, Cl, Br, or O. HF, HCl, HBr, HI, are binary acids. Other types of acids are the oxyacids, they contain oxygen and the hydrogen is bonded to the oxygen atoms in the molecule. The oxygen atoms are bonded to the nonmetal in the compound. Examples, HClO4 (perchloric acid), HNO3 (nitric acid), H2SO4, (sulfuric acid) and so on. To indicate the number of acidic protons in those acids, they are written first, so HClO4 (one acidic proton), H2SO4 (two acidic protons), H3PO4 (phosphoric acid, three acidic protons). When the compound has more than one type of hydrogen atoms (acidic vs. nonacidic), they are separated, so acetic acid becomes HC2H3O2 (the single proton is acidic, is bonded to the oxygen atom, the other three are nonacidic, they are bonded to one of the carbon atoms). This can be indicated in the following form as well: CH3COOH, from this formula you see the two different type of hydrogen atoms in this molecule.

Answer 2

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RE:
How can I differentiate between Ionic compounds, molecular compounds, and acids given only the formula?
I need to be able to find the difference between an Ionic compound, a molecular (or covalent) compound, and an acid given only the chemical formula (no charges or roman numerals)?

Answer 3

Its a nice question and many of my students get confused in it, first to know if its a covalent compound ( molecular ) think about non-metals, it must be formed by two non-metals or you can say its formed by a semi-metal + non-metal so you will have a covalent compound like: CO3, SiPO4...
Now to know if its an ionic compoud think about cation ( ions with negative charge ) + anion ( ions with negative charge ) but note that the ionic compound never starts with a negative charge!! Always start with the cation, another way to know is to see if it starts with a metal then non-metals so if you noticed its always ions, now to know the formula of the compound, you have to do the criss cross method, which means you only circle the number of the charge and put it next to the other ion to know how many atoms are there for this compound. Examples: Mg2+ H- it will be MgH2
Thats all the important stuff about ionic and molecular compounds for more information ask me on yahoo and tag

Answer 4

Molecular Compound

Answer 5

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1. Ionic compunds are between a metal and a nonmetal, so look for a metal (ex: Li, Ca, Al, K, Pb, Fe, Mg, Mn, Na etc) when you're trying to figure out what kind of compound it is. ex:) CaCl2 2. Covalent compounds are between two nonmetals, like H, C, O, N, S, P, Cl, F, I, etc. ex:) CH4 3. There are many different definitions of acids. So I'm guessing you just have to recognize the most common ones like HCl, HSO4, HCO3 etc.

Answer 6

This is a difficult question. First of all, acids invariably contain hydrogen atoms, and the hydrogen atom will be bound to an electronegative atom. For example: HF, HCl, HBr, HI. 99% of the time it will either be bound to a halogen or to an oxygen atom. Hydrogen bound to other atoms usually shows negligible acidity.

As for differentiating between ionic and molecular compounds, this turns out to be difficult. In general, there is no sharp dividing line: for example, aluminium chloride is on the borderline between covalent and ionic. Generally, the compound's ionic character will be increased if the cation is large, the anion small, and the charges on the cation and anion are small. The charge on a cation does not exceed +3 in ionic compounds, with the possible exception that some metals of high atomic number may form +4 ions. For example, OsO4 is obviously covalent, since Os8+ cannot exist. UF4 may be ionic since uranium is such a heavy metal (I don't mean density-wise), or it may be borderline.

Alkali metals form almost exclusively ionic compounds, except for organometallics. Beryllium forms no compounds which are unequivocally ionic - BeF2 and BeO, which we would expect to be the most ionic of beryllium compounds, are on the borderline. Magnesium forms mostly ionic compounds, with the major exceptions of the hydride and organometallics. The heavier alkaline earths form mostly ionic compounds, again with the possible exception of the organometallics. Transition metal compounds are usually considered ionic if the oxidation state of the metal is +3 or less, covalent otherwise. Nonmetals cannot form positive ions, with the exception of polyatomic ions - compounds of NH4+ are usually ionic; other polyatomic cations are rare. The atoms C, N, O, F, P, S, Cl, Se, Br, Te, and I are known to form anions with electropositive metals. The metalloids form mostly covalent compounds - the fluorides and oxides are usually borderline (with the exception of boron, which forms almost no ionic compounds - Na3B may be ionic.) The post-transition metals often form borderline compounds as well, although the fluorides and oxides in low oxidation states are usually considered ionic.

Answer 7

ionic compounds usually contain a metal and a non metal while a molecular compound contains two non metals. and an acid usually contains hydrogen bonded to a radical e.g NO3-,SO42-

Answer 8

ionic compounds=(metal)+(non-metal)
eg.nacl
molecular compound=(non-metal)+(non-metal)
eg.co2