How does the number of electrons relate to an element's atomic number? Why?

2 answers:

8 0

The number of protons in the nucleus of the atom is equal to the atomic number. The number of electrons in a neutral atom is equal to the number of protons. The mass number of the atom is equal to the sum of the number of protons and neutrons in the nucleus.
Hope it helped

Shalnov [3]4 years ago

4 0

The number of electrons equals the number of protons in a neutral atom (ie something that isn't an ion), and in turn the number of protons determine the atomic number (and therefore its chemical identity).

If we're talking about ions then the number of electrons does not match up with the atomic number. For example, the potassium ion $K^{+}$ has 18 electrons. It lost an electron which gives it a charge of +1, yet it's proton count is 19 and so is the atomic number.

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Phosphoric acid (h3po4) is tribasic, with pka's of 2.14, 6.86, and 12.4. The charge of the ionic form that predominates at ph 3.

Annette [7]

Correct answer is $H_2PO_4^-$ .

Phosphoric acid is a polyprotic acid having 3 acidic hyrdogen therefore it will have 3 pka values.

The equations for the release of acidic hydrogen can be written as:

$\\H_3PO_4\rightleftharpoons H_2PO_4^-+H^+\text{ pka=2.14}\\H_2PO_4^-\rightleftharpoons HPO_4^2^-+H^+\text{ pka=6.86}\\HPO_4^2^-\rightleftharpoons PO_4^3^-+H^+\text{ pka=12.4}$

From the pka values we can judge the idea of pH as using Henderson-Hasselbalch Equation, we get the relation between pH and pka.

$HA\rightarrow H^-+A^-$

Using the following equation, relation of pH and pka is

$pH=pka+log\frac{[A^-]}{HA}$

Using this equation, we can find that the equation having pka= 2. 14 is closest to the pH=3.2 so the ionic form in this equation will be dominant at the same pH.

Therefore at pH=3.2 the ionic form $H_2PO_4^-$ of $H_3PO_4$ is dominant.