"Chemical Formula and Valence" Water in Nature PPT Courseware 3

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"Chemical Formula and Valence" Water in Nature PPT Courseware 3

2. Compound price

The ratio of the number of atoms of the elements that make up some substances

Conclusion: There is a certain ratio between the atoms of each element in the compound

In chemistry, "valency" is used to represent the number of mutual combinations between atoms.

1. How to express chemical valence

Write a + or - sign above the element, followed by the value. Note that 1 cannot be omitted.

Question: What determines the valency of an element?

The number of electrons in the outermost shell of the element's atom

When determining the valency of an element, you need to pay attention to the following points:

1. When metal elements and non-metal elements combine, the metal elements show positive valence and the non-metal elements show negative valence;

2. Some elements can show different valencies in different substances;

3. The valence of an element is a property displayed by the atoms of an element when forming a compound. Therefore, in a simple substance, the valence of an element is 0. The algebraic sum of positive and negative valencies in a compound is 0

The formula for the valence of some common elements. The valence of some common atomic groups.

Monovalent Potassium Hydrochloride Sodium Silver Divalent Oxygen Magnesium Barium Calcium Zinc

Copper one two, iron two three, three aluminum four silicon five nitrogen phosphorus,

For carbon dioxide, sulfur and carbon dioxide, the positive and negative prices must be recorded clearly.

The price is different depending on the conditions. The single substance is zero and never changes.

Example: It is known that in a certain phosphorus oxide, phosphorus has a valence of +5 and oxygen has a valence of -2. Write the chemical formula of this phosphorus oxide.

Solution: 1. Write the symbols of the elements that make up the compound: positive valence comes first, negative valence comes last,

2. Find the least common multiple of the absolute values ​​of positive and negative valencies → 5×2=10

3. Find the number of atoms of each element: least common multiple/positive valence (or negative valence) = number of atoms

4. Write the atomic number at the bottom right of each element symbol: →P2O5

5. Check for correctness: sum of positive and negative valence algebras = 0 → +5×2+(-2)×5=0

Answer: The chemical formula of this phosphorus oxide is P2O5

How to read chemical formulas

1. A substance composed of two elements is read as: "something changes into something" (read from back to front)

2. The oxides are read as: "Oxidation of certain, sub-oxidation of certain, several oxidation of several certain"

3. The substance composed of hydrogen element and atomic group is read as: "a certain acid"

4. The substance composed of metallic elements and hydroxide is read as: "hydrogen oxide"

5. Substances composed of metal elements and atomic groups (except hydroxide and ammonium radicals) are read as "a certain acid"

6. "NH4+" is regarded as a metallic element when named.

7.Fe +2 +3 is read as "iron or copper" when the price is high.

Cu +1 +2 is read as "ferrous iron or copper" at low prices.

Note: When it contains "Fe" or "Cu", be sure to mark the valence before naming to determine whether to add "sub".

Write the text expressions of the following reactions, and write the chemical formula of the substance below the corresponding substance, whether it is a decomposition reaction or a combination reaction, and indicate the type of reaction.

1. Use potassium permanganate to produce oxygen

2. Use potassium chlorate and manganese dioxide to produce oxygen

3. Use hydrogen peroxide to produce oxygen

4. Electrolyzed water

5. Hydrogen burns in air and explodes

6. Red phosphorus burns in air

7. Sulfur burns in the air

8. Iron wire burns in oxygen

9. Magnesium strips burn in air

10. Heated Patina

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Update Time: 2024-06-29

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