Answer
(a) $Be^{2+}$ has 4 protons and 2 electrons.
(b) $Rb^+$ 37 protons and 36 electrons.
(c) $Se^{2-} $ 34 protons and 36 electrons.
(d) $Au^{3+}$ 79 protons and 76 electrons,
Work Step by Step
The number of protons is equal to the atomic number (Z), which can be found in a periodic table, next to the symbol of the element.
To calculate the number of electrons, since each one represents a negative charge, and each proton a postive charge, we can use this formula:
$(charge) = Z - n^{\circ}e^-$
$n^{\circ}e^- = Z - (charge)$
(a) Atomic number for $Be$: $4$
$n^{\circ}e^- = 4 - (2+) = 4 - 2 = 2e^-$
(b) Atomic number for $Rb$: $37$
$n^{\circ}e^- = 37 - (1+) = 37 - 1 = 36e^-$
(c) Atomic number for $Se$: $34$
$n^{\circ}e^- = 34 - (-2) = 34 + 2 = 36e^-$
(d) Atomic number for $Au$: $79$
$n^{\circ}e^- = 79 - (3+) = 79 - 3 = 76e^-$
