问题 填空题

用化学符号表示:

(1)2个氢原子______;(2)4个银离子______;

(3)3个过氧化氢分子______;(4)标出氧化铁中铁元素的化合价______.

答案

(1)表示粒子个数的数字写在符号前面,因此2个氢原子表示为2H.

(2)表示粒子个数的数字写在符号前面;写离子符号时要在元素符号或原子团的右上角标上离子所带电荷数,是“1”时省略,且数值在前,正、负号在后;1个银离子含有1个银原子且带有1个单位的正电荷.因此4个银离子表示为4Ag+

(3)表示粒子个数的数字写在符号前面;写化学式或原子团时要在元素符号右下角标上原子个数,是“1”时省略;1个过氧化氢分子含有2个氢原子和2个氧原子.因此3个过氧化氢分子表示为3H2O2

(4)标注元素或原子团的化合价时,要写在元素符号或原子团的正上方,是“1”时不能省略,且正、负号在前,数值在后,氧化铁中铁元素的化合价为+3.因此氧化铁中铁元素的化合价标记为

+3
Fe2
O3

故答案为:(1)2H;(2)4Ag+;(3)3H2O2;(4)

+3
Fe2
O3

阅读理解

阅读理解。

     A habit is any action that we have performed so often that it becomes something that we do almost without thinking.  Some of them are  thought to be bad habits.  People spend countless  hours and  dollars each year trying to get rid of these bad habits but often fail. Why?  Change is hard work and there is no shortcut to achieve it. However, there is still some advice for you to follow.

     First, look at why  you do it.  In other words,  what's the result  of doing this thing?  If your bad habit is

shouting at  people when you are unhappy or under pressure,  what do you get from it?  It may  make you

feel a little better for the moment. Or maybe you have a bad habit  of leaving your homework undone.  The result could be that you get more time to spend on the Internet!

     Next, take  a look  on the other hand.  What are you  losing  because of  your habit?  Shouting at other

people is a bad habit because it makes people around you feel bad and unhappy. Leaving your homework undone is a bad  habit because you  may be  punished by your teacher.  Having more  Internet time means

that you are losing  the chance to  learn the things  that you need to learn.  When you think that way,  you'll

find that it's not wise to keep your bad habit! Now it is time to make a decision. What will you choose? I'm sure you will choose to do what you think is more important.

1. From the first paragraph we know that __________.

A. a habit is a terrible thing that we can never change

B. people take countless hours and dollars to get rid of habits

C. none of the people who try to break bad habits are successful

D. though it is difficult, we can still do something about our bad habits

2. The underlined sentence "there is no shortcut to achieve it" means that ________.

A. it is not easy to get rid of bad habits  

B. there is a long way and a short way

C. something dangerous may happen  

D. we must cut it in a short time.

3. According to the reading, if you want to get rid of your habits, you have to _____.

A. talk to others when you are in low spirits

B. know why you do what you do

C. finish your homework first  

D. spend less time on the Internet

4. Which of the following does NOT happen because of a bad habit according to the reading?

A. You are punished later.  

B. Making people around you feel unhappy.

C. You feel a little better after shouting at others.

D. You leave your homework at home by accident.

5. The main purpose of this passage is to __________.

A. introduce and describe  

B. complain and disagree  

C. explain and advise      

D. discuss and argue

问答题 简答题