共价键 (蓝色小球代表电子) 电子没有得失而是被共享Electrons are not transferred but shared 电负性差异小small electronegativity differences 强而有方向性Strong and directional:高熔点high melting point,.硬hard, 脆brittle,绝缘体insulator共价键  电子没有得失而是被共享Electrons are not transferred but shared  电负性差异小small electronegativity differences  强而有方向性Strong and directional: 高熔点high melting point, 硬hard, 脆brittle, 绝缘体insulator