1.Tom had gone out when his mother got home.

1.第一句无错.
when引导的时间状语从句和主句的动作可以先后发生,所以后面用一般过去时got home,而前面用过去完成时had gone out,表明go out发生在get home之前.
2.第二句稍微有点问题.
1）此句最好要用在间接引语即宾语从句中时才可以.
如：She said that Tom would go out as soon as his mother got home.
否则如果是单独的句子的话,从句动作get home已经发生了,而主句却是用了过去将来时,不妥啊.
2）如果是单独出现这句的话,只能理解成虚拟语气,但是as soon as引导的从句是不会使用虚拟语气的.
3）所以,此句有错,不如改成：
Tom went out as soon as his mother got home.

1。当TOM的妈妈回家时，TOM已经出去了
2。当TOM的妈妈回家时，TOM会尽可能快地出去