Chapter 2, Problem 2.72QP

Which of the following are elements, which are molecules but not compounds, which are compounds but not molecules, and which are both compounds and molecules? (a) SO₂, (b) S₈, (c) Cs, (d) N₂O₅, (e) O, (f) O₂, (g) O₃, (h) CH₄, (i) KBr, (j) S, (k) P₄, (l) LiF

Interpretation Introduction

Interpretation:

$S{O}_2$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Answer to Problem 2.72QP

$S{O}_2$ is both a molecule and compound.

Explanation of Solution

$S{O}_2$ is a heteronuclear diatomic molecule made up of Sulfur and Oxygen atoms.  Many such $S{O}_2$ molecules combine and exist as compound.

Interpretation Introduction

Interpretation:

$S_8$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Answer to Problem 2.72QP

$S_8$ is both element and a molecule.

Explanation of Solution

$S_8$ is an homonuclear polyatomic molecule made of Sulfur atoms.  In pure elemental form Sulfur atoms exist as polyatomic molecule.

Interpretation Introduction

Interpretation:

$Cs$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Answer to Problem 2.72QP

Cs is an element.

Explanation of Solution

Cs is merely an element.  It is not a molecule or compound as in elemental form it does not combine with other Cs atoms.

Interpretation Introduction

Interpretation:

$N_2{O}_5$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Answer to Problem 2.72QP

$N_2{O}_5$ is both a molecule and compound.

Explanation of Solution

$N_2{O}_5$ is a heteronuclear polyatomic molecule made of Nitrogen and Oxygen atoms.  Many such $N_2{O}_5$ molecules combine and exist as compound.

Interpretation Introduction

Interpretation:

$O$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Explanation of Solution

O is an element.

Interpretation Introduction

Interpretation:

$O_2$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Explanation of Solution

$O_2$ is a molecule but not compound.  $O_2$ is diatomic homonuclear molecule made of same elemental O atoms.

Interpretation Introduction

Interpretation:

$O_3$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Explanation of Solution

$O_3$ is a molecule but not compound.  $O_3$ is triatomic homonuclear molecule made of same O atoms.

Interpretation Introduction

Interpretation:

$C{H}_4$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Answer to Problem 2.72QP

$C{H}_4$ is both a molecule and compound.

Explanation of Solution

$C{H}_4$ is a heteronuclear polyatomic molecule made of Carbon and Hydrogen atoms.  Many such $C{H}_4$ molecules combine and exist as compound.

Interpretation Introduction

Interpretation:

$KBr$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Answer to Problem 2.72QP

$KBr$ is a compound.

Explanation of Solution

$KBr$ is an ionic compound formed from K and Br atoms.

Interpretation Introduction

Interpretation:

$S$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Explanation of Solution

S is an element.

Interpretation Introduction

Interpretation:

$P_4$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Answer to Problem 2.72QP

$P_4$ is both element and a molecule.

Explanation of Solution

$P_4$ is an homonuclear polyatomic molecule made of Phosphorus atoms.  In pure elemental form Phosphorus atoms exist as polyatomic molecule.

Interpretation Introduction

Interpretation:

$LiF$ is whether molecule or compound or element have to be identified.

Concept Introduction:

Element is a free state of an atom and it is the simplest form of an atom.

Molecule is made of two or more atoms of same element or different elements.  If atoms of same element combine to form a molecule then the molecule is called homonuclear molecule.  If atoms of different element combine to form a molecule then the molecule is called heteronuclear molecule.

Compound is a stable chemical substance made of many such identical entities of heteronuclear molecules.

Answer to Problem 2.72QP

$LiF$ is a compound.

Explanation of Solution

$LiF$ is an ionic compound formed from Li and F atoms.