Question Video: Understanding Melting Point Trends for Transition Metals versus Main-Group Elements Chemistry • 7th Grade

Shown in the graph are the melting points of the first 56 elements of the periodic table and the groups in which they occur. The transition metals are positioned between groups 3 and 11. Which of the following is the most accurate comparison of the melting points shown in the graph? [A] The transition metals and main-group elements display a similar range of melting points. [B] The transition metals have lower melting points than almost all of the main-group elements. [C] The transition metals have lower melting points than all of the main-group elements. [D] The transition metals have higher melting points than almost all of the main-group elements. [E] The transition metals have higher melting points than all of the main-group elements.

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Video Transcript

Shown in the graph are the melting points of the first 56 elements of the periodic table and the groups in which they occur. The transition metals are positioned between groups three and 11. Which of the following is the most accurate comparison of the melting points shown in the graph? (A) The transition metals and main-group elements display a similar range of melting points. (B) The transition metals have lower melting points than almost all of the main-group elements. (C) The transition metals have lower melting points than all of the main-group elements. (D) The transition metals have higher melting points than almost all of the main-group elements. Or (E) the transition metals have higher melting points than all of the main-group elements.

First of all, let’s clear some space by removing the answer choices. Then, let’s increase the size of the graph. The question tells us that the graph shows the melting points of the first 56 elements. The first 56 elements of the periodic table range from hydrogen with an atomic number of one to barium with an atomic number of 56. These elements span the groups from one to 18 and are part of the s, p, and d blocks. The d-block elements are sometimes loosely referred to as the transition metals; however, not all d-block elements are transition metals according to IUPAC. A transition metal is an element whose atoms have an incomplete d subshell or that can give rise to cations with an incomplete d subshell.

The elements in group 12 have complete d subshells and so are not generally considered transition metals. This is why the question tells us that the transition metals are positioned between groups three and 11. If we look at the point on the graph between groups three and 11, we can see that the lowest melting point belongs to an atom in group 11. Although this is the lowest melting point of the transition metal elements, if we compare it to the rest of the plot it is still higher than all of the other elements bar four. So, the graph shows us that the transition metals have a higher melting point than almost all of the main-group elements.

Now that we’ve come to this conclusion, let’s look through the answer choices in turn. Option (A) is “The transition metals and main-group elements display a similar range of melting points.” We can see from the graph that the transition metals generally have a higher melting point than the main-group elements. So, we can determine that this option is incorrect.

Option (B) is “The transition metals have lower melting points than almost all of the main-group elements.” This is not true, as the transition metals have higher melting points than almost all of the main-group elements. So, we can determine that option (B) is also incorrect.

Option (C) is “The transition metals have lower melting points than all of the main-group elements.” Again, the transition metals tend to have higher melting points than the main-group elements. Thus, option (C) is also incorrect.

Option (D) is “The transition metals have higher melting points than almost all of the main-group elements.” This is a correct statement and is most likely to be the answer to this question. But to confirm, let’s look at option (E).

Option (E) is “The transition metals have higher melting points than all of the main-group elements.” We can see from the graph that some of the main-group elements have higher melting points than some of the transition metals. So, option (E) is not correct and is not the answer to this question.

So, we can be sure that the answer to the question “Which of the following is the most accurate comparison of the melting points shown in the graph?” is (D). The transition metals have higher melting points than almost all of the main-group elements.

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