Non-metal elements are those in the periodic table excluding metals and metalloids, with lower melting points, boiling points, and electrical conductivity, and are mostly gaseous or solid. They play an important role in life and industry, such as oxygen for breathing, hydrogen for energy, and carbon for manufacturing graphite and diamonds.

This mind map elaborately explains two geometric concepts: "definition of similarity, properties of similar triangles". The "definition of similarity" section clarifies the definition and criteria for similarity; "properties of similar triangles" delves into the properties and applications of similar triangles. These are very important for mastering geometric knowledge.