Question

How do you get the subscript for an ionic bond just from looking at the periodic table? I don't understand this at all! T~T

Answer 1

do you mean the subscripts for atoms that form an ionic bond?

you have to know the oxidation state of the species reacting, this can be generalized for some elements. For example, halogens (group 7) always have a -1 oxidation state, and alkali metals (group 1) always have +1 oxidation state.

The reason for the observed oxidation states is their position on the periodic table (which is correlated to their electronic configuration) and how many electrons they have to gain/lose to achieve a stable electronic configuration, which is often that of a noble gas (an octet).

so, if you have a halogen, say Cl (which is -1) and you have Na (which is +1) you only need one of each to achieve an electrically neutral formula, because \(\sf\color{red}{the\;charges\;cancel\;out}\)

so to continue: \(\underbrace{Na^+} + \underbrace{Cl^-} \rightarrow \underbrace{NaCl}\)
+1 -1 0

Similarly, Alkaline earth metals (group 2) always forms a 2+ ion, like Magnesium

\(\underbrace{Mg^{2+}} + \underbrace{Cl^-} \rightarrow \underbrace{MgCl_2}\)
+2 -1 0

notice that you need 2 \(Cl^-\) to counter the 2+ charge on \(Mg^{2+}\).

The point is to make the unit uncharged/neutral.

btw, oxidation state refers to the amount of electrons a neutral atom has gained/lost. The term "Ion" is just the general term for something that is charged it can be positive or negative. It can be further categorized:

If it gained an electron it becomes more negative (\( Cl +e^{-}\rightarrow Cl^-\)) and it's called an "anion".

If it loses electrons it becomes positive (\(K\rightarrow K^++e^-\)) it's called a "cation".

Answer 2

Okay, and how exactly do you create a formula between two compounds?

Answer 3

what do you mean?

Answer 4

Like Nitrogen & potassium what would the chemical compound be??

Answer 5

you have to identify the type of ion they become, then balance the charges as i posted above.