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 chemical reactivity is often determined by the electrons in the outermost shell of an atom, known as valence electrons.
2. Recognize that elements with similar numbers of outer-shell electrons tend to exhibit similar chemical properties because they form similar types of bonds.
3. Consider the periodic table, where elements in the same group (vertical column) typically have the same number of valence electrons, leading to similar chemical behaviors.
4. Identify that sodium and lithium are both in Group 1 of the periodic table, meaning they each have one valence electron, which explains their similar reactivity.
5. Similarly, chlorine and iodine are in Group 17, each having seven valence electrons, which accounts for their similar chemical properties.