Which caraistic is used to group artworks into periods or styles

Artworks are grouped into periods or styles based on similarities that they share, for example a similar time of creation (for example, Medieval), a similar use of technique (for example, pointillism) or similar subject of depiction (for example, portraits).

your word would be isle.

isle is an island or peninsula especially a small one.

if you add the letter "a" you get aisle, which is a passage between 2 rows of something like chairs, shelves, or something else.

a chromatic scale uses the twelve tones of the octave, while a regular scale only uses eight, or seven different notes (as the first note is played twice)