Ключевые слова: abbreviation, alkaline, atom, atomic, atomic number 20, basic, black, bones, ca, calcium, cement, chemical, chemistry, contraction, earth, education, electron, element, essential, flat, icon, illustration, information, lab, laboratory, mass, material, mendeleev, metal, molecular, molecule, muscle, name, periodic, physics, proton, reactive, school, science, scientific, sign, square, structure, symbol, system, table, technology, universe, weight,