"Valence" Representation of Chemical Elements and Substance Composition PPT Courseware Simple campus recruitment activity planning plan summary enterprise and institution recruitment publicity lecture PPT template is a general PPT template for business post competition provided by the manuscript PPT, simple campus recruitment activity planning plan summary enterprise and institution recruitment promotion Lecture PPT template, you can edit and modify the text and pictures in the source file by downloading the source file. If you want more exquisite business PPT templates, you can come to grid resource. Doug resource PPT, massive PPT template slide material download, we only make high-quality PPT templates!
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"Valence" Representation of Chemical Elements and Substance Composition PPT Courseware
learning target
1. Understand the meaning of valence, and memorize the valences of common elements and atomic groups.
2. Be able to use chemical formulas to express the composition of substances, and use valence to deduce chemical formulas.
Valence
Conclusion: There is a certain ratio between the atoms of each element in the compound
Note: The valence of an element is only known when it forms a compound, that is, the valence of an element is zero.
1. Relevant rules of chemical valence
(1) In any compound, the algebraic sum of positive and negative valences is zero.
(2) In compounds, hydrogen usually has a valence of +1, and oxygen usually has a valence of -2.
(3) Metallic elements usually have a positive valence, while non-metallic elements usually have a negative valence.
(4) The valence of elements in a single substance is zero.
(5) Many elements have variable valencies, and the same element can have different valencies in different compounds. For example, the valencies of iron in FeO and Fe2O3 are +2 and +3 respectively.
Compare and find patterns
Comparison of ion symbols and valences:
Ion symbols and valences are represented differently:
Ion: The number comes first, and the "+" and "-" signs follow; it is written in the upper right corner.
Valence: Numbers at the end, “+” and “-” signs at the front; write directly above.
The relationship between the valence and the charge of the ion: the same number and the same sign
Atomic group: A group of atoms that participates in the reaction as a whole (just like an atom). The atomic group is also called a root.
Notice:
① Atomic groups cannot exist alone;
②Charged atomic groups are also ions.
Roots: NaOH, Ca(OH)2, Cu(NO3)2, NH4NO3, BaSO4, CaCO3, H3PO4
ion:
OH-: hydroxide ion CO32-: carbonate ion
NH4+: ammonium ion SO42-: sulfate ion
NO3-: nitrate ion PO43-: phosphate ion
2. The relationship between chemical formula and valency
(1) Calculate the valence of an element based on its chemical formula
Principle: The algebraic sum of positive and negative valences in a compound is zero.
(2) Find the chemical formula based on the valence
Steps: (Digital Crossover Method)
① Write symbols
② Standard price
③ The absolute value of the chemical valence is placed crosswise in the lower right corner of the element symbol
④ Simplify
⑤ Check
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