设R的化合价为x,x为奇数时化学式：R2Ox、RClx.M=2R+16x,2N=2R+71x,x＝（2N-M)/(71-16).x为偶数时化学式：ROx、RCl2x.M=R+16x,N=R+71x,x=(N-M)/(71-16).