Video Transcript
The picture shows a model of sodium
chloride. Which of the following statements
best describes the structure of this ionic compound? (A) Part of a giant lattice of
alternating atoms. (B) Part of a giant lattice of
oppositely charged ions. (C) A giant molecule of 27
atoms. (D) A giant molecule of 27
oppositely charged ions. (E) Part of a giant lattice of
alternating sodium atoms and chloride ions.
For now, let’s clear away the
answer choices to work on this question. First of all, an ionic compound
forms when a metal element reacts with a nonmetal element. Sodium chloride forms when sodium
metal reacts with the nonmetal element chlorine. In the name of an ionic compound,
the ending of the nonmetal element is changed to “ide.”
When an ionic compound forms, metal
atoms tend to lose electrons and form positive ions. Nonmetal atoms tend to gain
electrons and form negative ions. When sodium chloride forms, each
sodium atom loses one electron from its outer energy level and forms a positively
charged sodium ion. Each chlorine atom gains one
electron in its outer energy level and forms a negatively charged chloride ion.
The oppositely charged sodium and
chloride ions are attracted to each other and form an ionic bond. The oppositely charged ions combine
to form a neutral compound. In this problem, the compound is
sodium chloride, or NaCl. So we can define an ionic compound
as a neutral compound composed of positively and negatively charged ions. Unlike covalent compounds, ionic
compounds are not made of molecules. In an ionic compound, the positive
and negative ions are arranged in a symmetrical repeating structure called a
lattice.
Now, let’s bring the answers back
up on screen to determine the correct answer. Answer choice (A) cannot be correct
because a lattice structure is composed of ions, not atoms. Choice (E) is also incorrect
because the lattice of sodium chloride contains sodium ions, not atoms, as well as
chloride ions. Both choices (C) and (D) state that
sodium chloride is a giant molecule. But we know that the structure of
an ionic compound is a lattice made of ions, not a giant molecule. So these choices are both
incorrect.
So the correct answer must be
choice (B). The statement that best describes
the structure of sodium chloride is choice (B), part of a giant lattice of
oppositely charged ions.
