化合价》教案

化合价》教案

教学目标：通过实例了解化合价的含义，掌握元素化合价与化学式的关系。

教学方法：启发讲解，讲练结合。

教学过程：

1.复提问：请写出氯化钠、氯化氢的化学式，并解释为什么它们是由一个钠原子和一个氯原子以及一个氢原子和一个氯原子结合的。（根据原子结构回答）

2.让学生画出原子结构示意图，分析电子得失情况。引导学生用它们的原子结构示意图，根据原子最外层要成为稳定结构，形成稳定化合物的道理。

3.比较NaCl、HCl、H2O几个化学式，可知元素相互化合时，其原子个数比有一定的数值。这是元素形成化合物时的一种性质。这种性质就是元素的化合价。

4.定义化合价：一种元素一定数目的原子跟其他元素一定数目的原子化合的性质，叫做这种元素的化合价。

5.确定化合价：请学生画一些原子结构示意图，分析得失电子情况。并指出化合价有正价和负价及零价之分。

6.化合价的规律：

在化合物里，氧通常显-2价，氢通常显+1价，金属元素通常显正价，非金属元素通常显负价。但在氧化物里，氧显负价，其他元素显正价。

在化合物里，正负化合价的代数和为零。公式：化合价×原子个数。这是化合价计算的重要法则。

在单质中元素的化合价为零。

通过实例和规律的讲解，学生可以更好地理解化合价的含义和元素化合价与化学式的关系。

Some XXX。For example。in FeCl2 and FeCl3.the valences

of iron are +2 and +3.respectively。In H2S and SO2.the valences of sulfur are -2 and +4.respectively。The reason for the variability

is that the atoms of these XXX different ns。and the number of

XXX.

Let students look at the XXX.

XXX。in zinc sulfate。zinc has a valence of +2.and sulfate

has a valence of -2.In calcium hydroxide。calcium has a valence

of +2.and hydroxide has a valence of -1.(Brief n: The valence of an

atomic group is the algebraic sum of the positive and negative

valences of the elements that make up the group。For example。the valence of hydroxide is (-2) + (+1) = -1.)

Blackboard] IV。Writing and significance of valences

Student Practice] XXX: H2.H2O。NaOH.

Lecture] Note: The way to indicate the valence of an element

is different from the way to write XXX。+2.-1.-2.etc。written

above the element symbol。while the charge carried by ions is indicated by 1+。1-。2+。2-。etc。written in the upper right

corner of the element symbol。For example: Na+。Cl-。Zn2+。etc.

Summary] Guide students to summarize the writing of XXX.

Valences: On top of the head。number before the symbol.

Ions: Carried on the shoulders。number before the symbol。XXX.

Practice] Practice the meaning of valences。such as:

2 +2

Mg MgO

Let students try to come up with a XXX:

Valence mnemonic: One-valent hydrogen。gold。potassium。sodium。and silver。Two-valent calcium。magnesium。barium。and zinc。Copper。mercury。iron。and aluminum have one or

two valences。Silicon has four valences。and carbon has two or

four XXX form have a valence of zero and many elements have

variable valences。The algebraic sum of positive and negative

valences is zero。and the XXX.

Blackboard] V。XXX formulas

From the ns and examples above。it can be seen that the

nship een them is very close.

1.XXX of an unknown element from a chemical formula

n rule: The algebraic sum of positive and negative valences is

zero.

XXX: What is the XXX?

n: First write out the chemical formula: KClO3.Look up the

valences in the table and find that K has a valence of +1 and O has a valence of -2.Let x be the valence of Cl。According to the rule

that the algebraic sum of positive and negative valences is zero。we have 1 + x + (-2)×3 = 0.so x = 6 - 1 = 5.

Answer: In potassium chlorate。the valence of chlorine is +5.

Emphasis] The positive sign cannot be omitted。and +1

cannot be written as +。and 1 cannot be omitted.

Student Practice] Find the valences of the elements marked in

KMnO4.K2MnO4.H2O2.ClO2.and NH4NO3.

Blackboard] 2.Writing chemical formulas using valences

XXX: There are two oxides of phosphorus with valences of

+3 and +5.respectively。Write the chemical formulas of these two

oxides.

n: (1) Write the chemical formula of the oxide with +3

valence of phosphorus.

Method 1: LCM method +3 -2

①Write down the XXX: P O

求两种元素化合价绝对值的最小公倍数为6.

接着，我们可以求出各元素的原子个数。由于化合价绝对值的最小公倍数为6，因此氧的原子个数为6÷3=2，磷的原子个数为6÷2=3.因此，化学式为P2O3.

另外，我们可以使用十字相交法来写出化学式。具体来说，我们可以将化合价的绝对值交叉，然后进行最简约分。

作为练，让学生写出+5价磷的氧化物的化学式。

总的来说，本节课研究了如何求两种元素化合价绝对值的最小公倍数，以及如何使用十字相交法来写出化学式。