集中 and 密集: focused attention and close grouping
Compare attention directed toward reading or work with closely grouped houses or people, preserving the difference between failed concentration and completed work.
Identify the activity receiving attention in 集中
Here, 集中 (しゅうちゅう) is used for directing attention toward reading or work. “周りの音が気になって、読書に集中できなかった。” says that surrounding sounds prevented the speaker from concentrating on reading.
In “午前中は仕事に集中して終わらせ、午後は庭の手入れをした。”, the speaker concentrated on the work and finished it in the morning, then tended the garden in the afternoon. Read both the focus of attention and the stated completion.
Identify what is closely grouped in 密集
密集 (みっしゅう) foregrounds people or buildings gathered closely together. “古い住宅が密集する地域では、狭い道が多い。” describes many narrow roads in an area of closely grouped old houses.
“人が密集しないよう、係員が入場を調整した。” describes staff adjusting admission to prevent people from crowding together. It states that purpose without giving numerical spacing or density.
Distinguish an activity from objects occupying space
The reading sentence concerns attention toward an activity; the housing sentence concerns buildings occupying space. Neither sentence should be turned into a judgment of learning ability or a calculation of population.
集中 can also refer to things gathering in one place, so it is not limited to mental activity. The scope here is focused attention versus the close spatial grouping of people or houses.
Does “午前中は仕事に集中して終わらせ、午後は庭の手入れをした。” state only an intention to concentrate?
Show the answer and why
No. It states that the speaker concentrated on the work, finished it in the morning, and tended the garden in the afternoon. Keep this separate from the negative statement about being unable to concentrate on reading.