位置特征分析,就是通過分析命題特點(diǎn),將元素放到周期表中的準(zhǔn)確位置,然后利用類比法或利用周期律對(duì)元素性質(zhì)進(jìn)行合理的推斷,從而使問題得到解決。
[例1] 已知短周期元素的離子aA2+、bB+ 、cC3-、dD-都具有相同的電子層結(jié)構(gòu),則下列敘述中正確的是( )
A、原子半徑 A>B>C>D B、 原子序數(shù)d>c>b>a
C、離子半徑 C>D>B>A D、 非金屬性 A>B>D>C
解析:由aA2+、bB+ 、cC3-、dD-都具有相同的電子層結(jié)構(gòu),得出A、B、C、D在周期表中的位置為:
由周期表中的遞變規(guī)律可知:原子半徑:B>A>C>D ; 原子序數(shù):a>b>d>c ; 離子半徑:C>D>B>A ;非金屬性:D>C>A>B 。綜上答案為C。
一種元素的位置、性質(zhì)、結(jié)構(gòu)之間存在著必然聯(lián)系,若能將命題中涉及到的元素準(zhǔn)確定位,巧妙比較,會(huì)使問題迅速解決。
100.You ____ the book to me.You can keep it if you like.
A.can't return B.needn't have returned C.may not return D.can't have returned
鞏固練習(xí)答案:
1-5 ADBAA 6-10 A DABD 11~15 BACBC 16~20 ADAAC 21~25 ACBBB
26~30 ABBCC 31~35 DDBAB 36-40 CBCDB 41-45 DACBD 46--50 DCBBB
51-- 55 CDAAB 56--60 BBCBA 61--65 DCAAA 66--70 DDDCB 71--75 BDCDD
76--80 CABCD 81--85BCCCC 86--90BADBA 91--95 CBBBB 96--100 CBACB
99.I don't know what's the m atter.The train____here an hour ago.
A.shall arrive B.should arrive C.should have arrived D.ought have arrived
98.I can't find my umbrella.I ____it at the office.
A.could have left B.can leave C.should have left D.shall have
97.Li Ming ____ to visit his maths teacher last night.(but I am not sure)
A.must have gone B.might have gone C.might go D.may go
96.I didn't hear the phone.I ____ asleep.
A.must be B.should be C.must have been D.should have been
95. Sorry, I am late again. I ____ have taken a taxi to come here.
A. need B. should C. will D.must
94. ---Shall I tell Li Ming about it? ---No, you _____, he has known-about it already.
A. oughtn't to B. needn't C. shouldn't D. mustn't
93. ---I hear you've got a set of valuable Australian coins. ____ I have a look? ---Yes, certainly.
A. Do B. May C. Shall D. Should
92. Sir, you ____ be sitting in this seat. It is for women or childen only.
A. can't B. oughtn't to C. won't D. needn't
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