问题 问答题

图为周期表的一小部分,A、B、C、D的位置关系如图所示.且它们均为短周期元素,其中C元素的最外层电子数是电子层数的2倍,回答下列问题:

(1)写出B、C、D最高价氧化物对应水化物的化学式:______、______、______其中酸性最强的是______

(2)写出A、B、C、所形成氢化物的化学式:______、______、______其中最稳定的是______.

(3)写D的单质与C的氢化物反应的化学方程式______.

答案

A、B、C、D均为短周期元素,根据元素在周期表中的位置知,A位于第二周期,B、C、D位于第三周期,C元素的最外层电子数是电子层数的2倍,其电子层数是3,则其最外层电子数是6,所以C是S元素,则B是P元素、A是O元素、D是Cl元素,

(1)非金属元素的最高价氧化物的水化物是酸,其最高价氧化物的水化物的化学式分别是H3PO4、H2SO4、HClO4,非金属的非金属性越强,其最高价氧化物的水化物酸性越强,B、C、D三种元素的非金属性P<S<Cl,所以酸性最强的是HClO4,故答案为:H3PO4;H2SO4;HClO4;HClO4

(2)A、B、C、所形成氢化物的化学式分别是:H2O、PH3、H2S,非金属的非金属性越强,其氢化物的稳定性越强,这几种元素的非金属性P<S<O,所以最稳定的氢化物是,故答案为:H2O;PH3;H2S;H2O;

(3)氯气具有强氧化性,硫化氢具有还原性,二者能发生氧化会反应而生成硫和氯化氢,反应方程式为:H2S+Cl2=2HCl+S↓,故答案为:H2S+Cl2=2HCl+S↓.

多项选择题
问答题

When workers become more efficient, it’s normally a good thing. But lately, it has acted as a powerful brake on job creation. And the question of whether the recent surge in productivity has run its course is the key to whether job growth is finally poised to take off.

One of the great surprises of the economic downturn that began 27 months ago is this.. Businesses are producing only 3 percent fewer goods and services than they were at the end of 2007, yet Americans are working nearly 10 percent fewer hours because of a mix of layoffs and cutbacks in the workweek.

(46) That means high-level gains in productivity--which in the long run is the key to a higher standard of living but in the short run contributes to sky-high unemployment. So long as employers can squeeze dramatically higher output from every worker, they won’t need to hire again despite the growing economy.

(47) On Friday, the Labor Department will release a closely watched March employment report expected to show the pest job growth in three years, driven by stabilization in the economy and a rebound from February snowstorms.

A p March job-growth number-at a time when the economy is growing at only a middling pace--would suggest that the productivity boom has largely run its course. (48) Regardless, the question of what caused the burst in workers’ efficiency is one of the great unanswered questions of the expansion and has huge stakes for the economy over the coming year.

"It is an episode that we’re going to--we, economists in general--are going to want to understand better and look at for a long time," Federal Reserve Chairman Ben S. Bernanke said at a hearing last week in which he described the productivity gains as "extraordinary" and acknowledged he had not foreseen them.

(49) Businesses have certainly not been investing in new equipment that might enable workers to be more efficient-capital expenditures plummeted during the recession and are rebounding slowly. (50) And the structural shifts occurring in the economy are so profound that one would expect productivity to be lower, rather than higher, as people need new training to work in parts of the economy that are growing, such as exports and the clean-energy sector.

So what’s happening As best as anyone can guess, the crisis that began in 2007 and deepened in 2008 caused both businesses and workers to panic.

(46) That means high-level gains in productivity--which in the long run is the key to a higher standard of living but in the short run contributes to sky-high unemployment.