Thread: How to tell the difference between an ionic and molecular compound?

how can three chlorine atoms and an iodine atom combine?

what is an electrolyte?

how can i tell how many valence electrons an atom has? especially for the ones in the middle of the periodic table
hydrogen occurs as a mixture of two isotopes, one of which is twice as heavy as the other.
- law of conservation of mass or the law of constant composition?

Ionic compounds generally form when the atoms have a large difference in electronegativity. If they are similar, they tend to form covalent bonds.
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Actually, it is 6 chlorine atoms that bond to two iodine atoms. The result is Iodine trichloride.

The bonds between the iodine and chlorine are all covalent bonds. The two iodine atoms share a common pair of chlorine atoms. At the ends of the molecule, each iodine atom has two unshared chlorine atoms, so in reality, each iodine atom is bonded to four chlorine atoms (2 shared and 2 unshared).
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The definition of an electrolyte (from Wikipedia) is:
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible.
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The number of valence electrons is essentially the number of electrons in the current subshell being filled beyond the last noble gas configuration. So for example, Krypton (atomic no. 36) is considered to have 0 valence electrons (it is a noble gas). Element 37, rubidium, would have 1 valence electron, element 38, strontium, would have 2, at which point the s-orbital is filled. The d-orbitals start to fill leading to element 39, Yttrium, would have 1, zirconium (element 40) would have 2 , and so on until you reach element 48 at which the d-orbitals are filled. Then starting with element 49, the p-orbitals begin filling and you have 1 valence electron; element 50 has 2, and so on until the p-orbital is filled leading to element 54, Xenon, which is the next noble gas.

There are exceptions to this rule for the transition metals (the elements in the middle of the chart). I don't know if you have gotten into orbitals, but d-orbitals really complicate how to calculate actual valence electrons. The first two elements in each period are easy, they fill up the single s-orbital. After filling the s-orbitals, the d-orbitals are filled; so for each d-orbital filled, that counts as one valence electron (the first two s-orbitals are not normally considered to be valence electrons). However, orbital hybridization can occur creating various energy sub-levels in the d-orbitals (see crystal field theory if you are interested).
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Actually, Hydrogen has three isotopes.
1H: which has one proton and one electron
2H (also known as deuterium, or heavy hydrogen); which has one proton, one electron, and one neutron

and 3H (also known as tritium); has one proton, two neutrons, and one electron. This isotope is extremely rare.
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The law of conservation of mass states that during a reaction, matter is neither created nor destroyed. However, some of the mass can be converted into energy which would result in an apparent loss in mass; but this does not violate the law of conservation of mass since the loss of mass is accounted for in the conversion to energy.

You sure asked some tough questions- had to do some research.

Please let me know if you need any of these clarified, especially the question about valence electrons. That could take several hours in a chemistry lecture to cover that material.