Introductory Chemistry (5th Edition)

a) $-2$ b) $+3$ c) $+4$ d) $-1$
When an element possess more electrons than protons, then the element is an anion (has a negative charge). When an element possess fewer electrons than protons, then that element is a cation (has a positive charge). a) Oxygen has an atomic number of 8. But in this case, it is possessing 10 electrons. Since number of electrons $\gt$ No. of protons. Therefore it has a charge of $-(10-8)$ $= -2$ b) Aluminium has an atomic number of 13. But in this case, it is possessing 13 electrons. Number of electrons $\lt$ number of protons, so it has a charge of $+(13-10)$ $= +3$ c) Titanium has an atomic number of 22. But, in this case, it is possessing 18 electrons. Number of electrons $\lt$ number of protons. Therefore, so it has a charge of $+(22-18)$ $= +4$ d) Iodine has an atomic number of 53. But in this case, it is possessing 54 electrons. Number of electrons $\gt$ number of. Therefore it has a charge of $-(54-53)$ $= -1$