Question

model 3: defining elements and compounds
the model:
fe is the elemental form of iron.
c is the elemental form of carbon.
cl₂ is the elemental form of chlorine.
fecl₃ is a compound formed from the elements iron and chlorine

1. what does the subscript 2 indicate in cl₂?
2. what is implied when there is no subscript?
3. evaluate the statement, “the formulas for elements never contain a subscript.” is this statement true?
4. from the two examples provided, would you expect the formula s₈ to represent a compound to an element?
5. using examples from the model, explain how you classified s₈.

exercising your knowledge

1. classify each formula below as an element or a compound:

a. co
b. cacl₂
c. csoh
d. br₂
e. nabr
f. sio₂
g. pf₅
h. p₄
i. of₂
j. c₆h₁₂o₆
pogil™ activities for high school biology 3

Explanation:

Step1: Interpret sub - script in $Cl_2$

The subscript 2 in $Cl_2$ indicates that there are 2 chlorine atoms bonded together to form a chlorine molecule.

Step2: Meaning of no sub - script

When there is no subscript, it implies that there is 1 atom of that element in the formula unit. For example, Fe represents 1 iron atom and C represents 1 carbon atom.

Step3: Evaluate statement about element formulas

The statement "The formulas for elements never contain a subscript" is false. Some elements exist as polyatomic molecules, like $Cl_2$, $S_8$, and $P_4$, where the subscript indicates the number of atoms in the molecule.

Step4: Classify $S_8$

Based on the examples of $Cl_2$ (elemental form of chlorine) and the fact that $S_8$ is made up of only sulfur atoms, $S_8$ represents an element. Sulfur commonly exists as an octatomic molecule in its elemental state.

Step5: Explain classification of $S_8$

In the model, $Cl_2$ is an elemental form of chlorine with multiple atoms of the same element. Similarly, $S_8$ has only sulfur atoms, so it is an element.

Step6: Classify given formulas

a. Co is an element (cobalt).
b. $CaCl_2$ is a compound (calcium chloride, made of calcium and chlorine).
c. $CsOH$ is a compound (cesium hydroxide, made of cesium, oxygen, and hydrogen).
d. $Br_2$ is an element (bromine exists as a diatomic molecule).
e. $NaBr$ is a compound (sodium bromide, made of sodium and bromine).
f. $SiO_2$ is a compound (silicon dioxide, made of silicon and oxygen).
g. $PF_5$ is a compound (phosphorus pentafluoride, made of phosphorus and fluorine).
h. $P_4$ is an element (phosphorus exists as a polyatomic molecule).
i. $OF_2$ is a compound (oxygen difluoride, made of oxygen and fluorine).
j. $C_6H_{12}O_6$ is a compound (glucose, made of carbon, hydrogen, and oxygen).

Answer:

1. It indicates 2 chlorine atoms bonded together to form a molecule.
2. It implies 1 atom of that element in the formula unit.
3. False.
4. Element.
5. Similar to $Cl_2$, $S_8$ has only one type of atom (sulfur), so it is an element.

6.
a. Element
b. Compound
c. Compound
d. Element
e. Compound
f. Compound
g. Compound
h. Element
i. Compound
j. Compound