Junior High School Chemistry Unit 4 Topic 4 Lesson 2 Five-character Teaching Design
Teaching Objectives] 1It is known that the valency of the elements in the element is 0;
2.According to the algebraic sum of positive and negative valency algebra in the compound is 0, the valency of some unknown elements (or atomic clusters) can be calculated;
3.It can deduce the chemical formula of the actual compound according to the valency of the constituent elements;
4.By using the valency of known elements (or atomic clusters) to deduce the valency of unknown elements (atomic clusters) in compounds, and using the valencies of constituent elements (or atomic clusters) to deduce the chemical formulas of compounds that actually exist, the laws of chemistry learning are preliminarily explored, rote memorization is reduced, and the positive emotions of chemistry learning are enhanced.
Teaching Focus] Teaching Objectives.
Teaching Difficulties] Teaching Objective 3
Teaching process] set up questions, create situations 1].
1.Suspense is introduced, stimulating interest:
1) Please retell a common elemental valence rhyme or song that you have compiled?
2) Please indicate the valency of atomic clusters such as OH, CO3, NO3, SO4 and NH4.
3) For some elements with variable valency, how do we determine its valency in a compound? Is it possible to deduce the valency of an element that we have no memory or have forgotten based on the known elemental valence? We will be able to solve the problem by learning the following.
2.Ask questions and guide learning:
1) According to memory, please mark the valency of each element of the following compounds (if it is the atomic group, the valency of the atomic group): H2O, Cao, Al2O3, Ba(OH)2, ZnSO4
Please calculate the algebraic sum of the valency algebra of each element of the above compounds?
What are the commonalities of the valency algebra of the above element compounds? What patterns can you deduce?
According to the above law, can you determine the valency of chlorine in Kclo3 and CaCl2?
2) Valency is a property exhibited by the atoms of an element when forming a compound.
Reading and Thinking, **Communication 1].
1.Students then read the following contents in "Table 4-2" of textbook p85; Think independently about the above questions;
2.Students communicate in groups**;
3.Individual guidance on teacher tours;
Distinguish and analyze the dial, guide **1].
Calculation method of the algebraic sum of the valency of each element of a compound: the sum of the product of the valency of each element and its number of atoms.
For example, valency algebra sum: (+2) 1+(-1) 2=2-2=0
Write the conclusion and jointly identify 1] (summary board book, continue to the previous lesson).
Second, valence.
5.What characteristics of valency must be noted?
1) There are positive and negative valences
Oxygen is usually -2 valence;
Hydrogen is usually +1 valence;
When metallic elements and non-metallic elements are combined, metallic elements show positive valence, and non-metallic elements show negative valence.
Some elements can exhibit different valences in different elements;
2) In the compound, the algebraic sum of positive and negative valency is 0; From this, the valency of some unremembered elements or clusters of atoms in a compound can be determined;
3) The valency of the elements in the element is 0;
Classroom Exercise, Evaluation Reflection 1] Knowing that h is +1 valence and o is -2 valence, please determine the valency of chlorine in the following substances: Cl2, HCl, HCl, HCO3, HClO4
Set up questions and create scenarios 2] 1. Introduce suspense and stimulate interest: As we have already seen in the previous section, we can deduce the chemical formulas of some compounds that actually exist according to the valence, which greatly reduces our task of memorizing chemical formulas. So how do you deduce the chemical formula that actually exists from the valency?
2.Ask a question and lead the learning: Knowing that phosphorus is +5 valence and oxygen is -2 valence, write the chemical formula of the compounds they form?
1) What do you need to know to write a chemical formula for a compound?
2) What is the general order in which the positive and negative valence elements (or clusters) are left and right when writing the chemical formula of a compound?
3) How to determine the number of atoms of an element based on valency?
4) How to check that the chemical formula you have written is correct?
Reading and Thinking, **Communication 2].
1.Students then read the relevant content of textbook p86; Think independently about the above questions;
2.Students communicate in groups**;
3.Individual guidance on teacher tours;
Distinguish and analyze the dial, guide **2].
Write the conclusion and jointly identify 2] (board conclusion).
Second, valence.
6.The chemical formula of the compound that actually exists can be deduced by applying valency:
1) The order of the elements (or roots): generally positive right, negative left;
2) Determine the number of atoms (or roots) of the element
3) Write the atomic number in the lower right corner of the element symbol, if it is a root, use parentheses to enclose the root, and write it in the lower right corner of the parentheses;
4) the test, when the algebraic sum of valency is zero, is correct;
Classroom exercises, evaluation and reflection 2].
1. Classroom assessment (the assessment questions are presented by projection, and the students write the answers in the exercise book).
2. Evaluation and reflection.
1.Students exchange papers;
2.student self-reflection and evaluation;
3.Teachers respond to the feedback from the assessment and make up for the gaps;
Assignment] 1. Classwork: Question P89 of the textbook; 2. Extracurricular homework: (1) Question (4) of Question P89 of textbook; (2) continue to memorize the valency of common elements;
Designer: Zhen'an County Education and Teaching Research Office Ding Jinian).