Answer:
when the forward and reverse reactions occur at equal rates.
chemical reaction is in equilibrium when the concentrations of reactants and products are constant - their ratio does not vary.
Thus BeF2 is of most covalent character.
Anyways, covalent/ionic character is a bit tricky to figure out; we measure the difference in electronegativity of two elements bonding together and we use the following rule of thumb: if the charge is 0 (or a little more), the bond is non-polar covalent; if the charge is > 0 but < 2.0 (some references say 1.7), the bond is polar covalent; if the charge is > 2.0 then the bond is ionic. Covalent character refers to smaller electronegativity difference while ionic character refers to greater electronegativity difference.
Now, notice all of our bonds are with F, fluorine, which has the highest electronegativity of 3.98. This means that to determine character we need to consider the electronegativities of the other elements -- whichever has the greatest electronegativity has the least difference and most covalent character.
Na, sodium, has electronegativity of 0.93, so our difference is ~3 -- meaning our bond is ionic. Ca, calcium, has 1.00, leaving our difference to again be ~3 and therefore the bond is ionic. Be, beryllium, has 1.57 yielding a difference of ~2.5, meaning we're still dealing with ionic bond. Cs, cesium, has 0.79, meaning our difference is again ~3 and therefore again our compound is of ionic bond. Lastly, we have Sr, strontium, with an electronegativity of 0.95 and therefore again a difference of roughly 3 and an ionic bond.
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The compound NaCI is an example of a salt. Salt is formed from a neutralization action of an acid and a base. From the type of reaction itself, we can say that the pH should be neutral or at pH 7.0. No matter what type of acid or base is used.
So, water reacts with hydrochloric acid in the following formula
H2O + HCl —-> H3O+ + Cl-
We can visualize that when the two react, the hydrogen ions is taken on by the water molecule. This satisfies one of the definitions for a base
Bronsted acids = anything that donates a proton (H+ ion)
Bronsted bases = anything that accepts a proton (H+ ion)
So, as we can see, that is exactly what is happening. The Cl- and H+ detach and then the water takes on that extra H+.
H3O+ is what we call a hydronium ion
