Video Transcript
Which of the following chemical
entities is a compound? (A) H2, (B) N2, (C) NaCl, (D) O3,
or (E) Cu.
A compound is a species composed of
atoms of two or more different elements that are chemically combined. An element is a substance that
consists of only one type of atom and cannot be broken down into anything simpler
through a chemical reaction. There are 118 known elements that
have been organized into the periodic table of elements. Each element has its own unique
name and chemical symbol, which is either a capital letter or a capital letter
followed by a lowercase letter.
For example, answer choice (E),
capital C lowercase u is the chemical symbol of the element copper. As answer choice (E) is an element
and we are trying to determine which chemical entity is a compound, we can eliminate
answer choice (E).
Three of the answer choices have a
single chemical symbol that is followed by a numerical subscript. The subscript indicates the number
of atoms of the preceding element that are in one unit of the entity. So answer choice (A) H2 is an
entity that contains two atoms of the element hydrogen. Although this entity contains two
atoms, the two atoms are the same. Therefore, H2 is also an element
and cannot be the answer to this question.
Answer choice (B) N2 consists of
two atoms of the element nitrogen. As the entity only contains one
type of atom, N2 is an element and cannot be the answer to this question.
Answer choice (D), O3 consists of
three atoms of the element oxygen. Once again, all of the atoms in the
entity are the same. So O3 is an element and cannot be
the answer to this question.
The chemical formula shown in
answer choice (C) contains two capital letters, indicating that there are two
different chemical symbols. Na is the chemical symbol of
sodium, and Cl is the chemical symbol of chlorine. So the entity NaCl contains two or
more different elements and is a compound.
So the correct answer to the
question “Which of the following chemical entities is a compound?” is answer choice
(C), NaCl.
