问题 填空题

B元素与最活泼的非金属元素F形成化合物BF3,检测发现BF3分子中三根B­—F键的键长相等且键角也相等,可以判断出BF3分子为__________分子(选填“极性”或“非极性”); BF3晶体的熔点比SiO2晶体________(选填“高”、“低”)。

答案

非极性, 低

题目分析:BF3分子中三根B­—F键的键长相等且键角也相等,由此可以判断出BF3分子为平面正三角形结构,属于非极性分子;由于二氧化硅形成的晶体是原子晶体,则BF3晶体的熔点比SiO2晶体低。

点评:该题是常识性知识的考查,也是高考中的常见考点。试题基础性强,有利于调动学生的学习兴趣和学习积极性,提高学生的应试能力和学习效率。

阅读理解

There are fifty states in the United States. The largest in population is California,the largest in area is Alaska. Alaska is the smallest in population and Rhode Island is the smallest in size. The oldest states are the ones along the Atlantic coast. The newest states are Alaska and Hawaii. Alaska is also the coldest state. California and Florida are the warmer. Henry and his family live in Seattle, a big city, on the Pacific coast. But Los Angeles and San Francisco, also on the Pacific coast, are larger than Seattle. Henry's cousin, Susan, lives in New York. It is the largest city in the United States. Thousands of people visit New York each year. The most important city in the United States is Washington D. C. It is the capital, but it is much smaller than New York.

小题1:How many states are there in the U. S. A ?

A.Five

B.Forty- Five.

C.Fifty

D.Fifteen.小题2:Which state is the largest in population?

A.California.

B.Rhode-Island.

C.Alaska

D.Los Angeles.小题3:Which state is the smallest in population?

A.Rhode Island.

B.Seattle.

C.San Francisco.

D.Alaska.小题4:Which of the following is true?

A.The oldest states are the ones along the Pacific coast.

B.Washington is the most important and the largest city.

C.New York is the largest city in the United States.

D.Henry's cousin lives in the Seattle.小题5:Why is Washington D. C. the most important American city?

Because _________.

A. it is the largest city                   B. it is the largest in population

C. it is the most beautiful city       D. it is the capital of the United States

单项选择题