Question Video: Identifying Which Chemical Entity Is a Compound Chemistry

Which of the following chemical entities is a compound? [A] H₂ [B] N₂ [C] NaCl [D] O₃ [E] Cu

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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.

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