离子半径Ionic radius

阳离子比相应原子小，因为失去了最外层电子，剩余电子受到更强的核吸引，如 Na 原子 186 pm，Na⁺ 102 pm。阴离子比相应原子大，因为增加的电子之间相互排斥，如 Cl⁻ 181 pm。同族离子从上到下半径增大。

Cations are smaller than their atoms because the outer shell is lost and the remaining electrons are held more tightly: Na 186 pm, Na⁺ 102 pm. Anions are larger than their atoms because the extra electrons repel each other: Cl⁻ 181 pm. Down a group ionic radii increase.

电子数相同的离子，核电荷越大，半径越小：O²⁻（140 pm）> F⁻（133 pm）> Na⁺（102 pm）> Mg²⁺（72 pm）> Al³⁺（54 pm），它们都有 10 个电子。

For ions with the same number of electrons, the larger the nuclear charge the smaller the ion: O²⁻ (140 pm) > F⁻ (133 pm) > Na⁺ (102 pm) > Mg²⁺ (72 pm) > Al³⁺ (54 pm), all with ten electrons.

离子越小、电荷越高，晶格能越大，离子化合物熔点越高；小而高电荷的阳离子极化能力强，使相邻阴离子电子云变形，化合物带有共价性，并影响水合离子的酸性和碳酸盐的热稳定性。

Smaller, more highly charged ions give larger lattice energies and higher melting points; small, highly charged cations are strongly polarising, distorting neighbouring anions and giving compounds covalent character, which also affects the acidity of hydrated ions and the thermal stability of carbonates.