Some groups of chemical elements react similarly to one another. For example, the chemistries of sodium and of lithium are similar, as are the chemistries of chlorine and of iodine. These similarities in chemistry result when different elements have similar __________.

• A. atomic size
• B. total numbers of electrons
• C. energy per electron
• D. numbers of outer-shell electrons

Answer: (D)

Verified step by step guidance

1. Understand that elements in the same group of the periodic table often exhibit similar chemical properties.
2. Recognize that these similarities are due to having the same number of valence electrons, which are the electrons in the outermost shell.
3. Recall that valence electrons determine how an element reacts chemically with other elements.
4. Consider that elements like sodium and lithium, or chlorine and iodine, belong to the same group and thus have similar numbers of outer-shell electrons.
5. Conclude that the similarities in chemistry among these elements are due to their similar numbers of outer-shell electrons, not atomic size, total numbers of electrons, or energy per electron.