## Chemistry (7th Edition)

Published by Pearson

# Chapter 2 - Atoms, Molecules, and Ions - Section Problems - Page 74: 125

#### Answer

(a) "X" represents Strontium (Sr) (b) "X" represents Bromine (Br)

#### Work Step by Step

The charge of an ion can be calculated by: $(charge) = Z - n^{\circ}e^-$ Where: $Z$ is the atomic number (Because it represents the number of protons, and each one has a positive charge). $n^{\circ}e^-$ is the number of electrons, each one gives a negative charge to the ion/atom. Adding ($n^{\circ}e^-$) to both sides of the equation: $(charge) + n^{\circ}e^- = Z$ (a) $(2+) + 36 = 38$ Therefore, "X" has an atomic number of 38, which looking in the periodic table gives us the Strontium element. (b) $(-1) + 36 = 35$ Therefore, "X" has an atomic number of 35, which looking in the periodic table gives us the Bromine element.

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