问题 问答题

下表是元素周期表的一部分,表中的每个字母表示一种短周期元素,回答下列问题:

(1)画出C的原子结构示意图______.

(2)E在元素周期表中的位置是第3周期______族.

(3)B、C、D、F四种元素所形成的气态氢化物最稳定的是______(填化学式).

(4)E、F、G元素的最高价氧化物对应水化物的酸性最强的是______(填化学式).

(5)A、B、G三元素形成的化合物的电子式是______,其中所含的化学键有哪些类型______.

答案

(1)C为O元素,原子序数为8,原子核外有两个电子层,最外层电子数为6,则原子结构示意图为

故答案为:

(2)E为P元素,原子序数为15,核外有3个电子层,最外层电子数为5,则位于周期表第三周期ⅤA族,

故答案为:第ⅤA;

(3)B、C、D、F四种元素中非金属性最强的是F元素,对应的氢化物的稳定性最强,故答案为:HF;

(4)同周期元素从左到右元素的非金属性逐渐增强,对应的最高价氧化物的水化物的酸性逐渐增强,故答案为:HClO4

(5)A、B、G三元素形成的化合物为NH4Cl,为离子化合物,含有离子键和共价键,

电子式为

故答案为:

;离子键和共价键.

问答题 简答题
单项选择题

Weak dollar or no, $ 46,000-the price for a single year of undergraduate instruction amid the red brick of Harvard Yard-is (1) But nowadays cost is (2) barrier to entry at many of America’s best universities. Formidable financial-assistance policies have (3) fees or slashed them deeply for needy students. And last month Harvard announced a new plan designed to (4) the sticker-shock for undergraduates from middle and even upper-income families too.

Since then, other rich American universities have unveiled (5) initiatives. Yale, Harvard’s bitterest (6) , revealed its plans on January 14th. Students whose families make (7) than $60,000 a year will pay nothing at all. Families earning up to $ 200,000 a year will have to pay an average of 10% of their incomes. The university will (8) its financial- assistance budget by 43%, to over $ 80m.

Harvard will have a similar arrangement for families making up to $180,000. That makes the price of going to Harvard or Yale (9) to attending a state-run university for middle-and upper-income students. The universities will also not require any student to take out (10) to pay for their (11) , a policy introduced by Princeton in 2001 and by the University of Pennsylvania just after Harvard’s (12) . No applicant who gains admission, officials say, should feel (13) to go elsewhere because he or she can’t afford the fees.

None of that is quite as altruistic as it sounds. Harvard and Yale are, after all, now likely to lure more students away from previously (14) options, particularly state-run universities, (15) their already impressive admissions figures and reputations.

The schemes also provide a (16) for structuring university fees in which high prices for rich students help offset modest prices for poorer ones and families are less (17) on federal grants and government-backed loans.

Less wealthy private colleges whose fees are high will not be able to (18) Harvard or Yale easily. But America’s state-run universities, which have traditionally kept their fees low and stable, might well try a differentiated (19) scheme as they raise cash to compete academically with their private (20) . Indeed, the University of California system has already started to implement a sliding-fee scale.

5()

A.different

B.same

C.similar

D.encouraging