「每日一练」ALevel化学例题解析及练习

每日一练ALevel Chemistry

今日知识点：Ionisation energy and valence electrons

例题

The table gives the successive ionisation energies for an element X.

What could be the formula of the chloride of X

A?? XCl

B?? XCl2

C?? XCl3

D?? XCl4

解析

Answer: C

Definition of Ionisation Energy

A? →? A+ + e-

The energy required for the above reaction, or removing an electron. (挪走一个电子需要的能量)

Based on the table, there is a “jump” from the 5th to the 6th ionization energies, so there are 5 valence electrons.

5th 和6th 之间的数字变化比较大, 说明挪走第6个电子的需要很高能量，很困难，即挪走5个电子后达到8电子稳定结构，所以最外层有5个电子。

If X has 5 valence electrons, it needs to get an additional 3 electrons to form an Octect. Since each chlorine can provide 1 electron to form a bonding pair, 3 Cl is needed, forming XCl3.

氯化物中心的X需要形成8电子稳定结构，所以还需要额外和Cl共用3个电子，每个Cl只能共用1个电子，所以需要3个Cl.

下面我们为大家准备了一道同类型的题目，请大家一起来试试解答。

Your turn

Three successive elements in the Periodic Table have first ionization energies which have the pattern shown in the diagram.

What could be the first element of the sequence?

A?? C

B?? N

C?? F

D?? Na

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Correct Answer：C