How to grasp the key points in chemistry in junior high school?

1. Correctly understand the concepts and principles of chemistry, and grasp the key "words" and "words".

2. Pay attention to chemical terms, element symbols, chemical formulas, ion symbols, valency symbols, and chemical equations must be memorized.

3. Pay attention to chemical experiments, especially experimental phenomena, and be accurate in expression. The name of a chemical instrument cannot be misplaced.

4. According to the relevant calculations of chemical formulas and chemical equations, in the relevant calculations of chemical equations, a. The chemical equations must be written correctly (the chemical formula cannot be wrong, it must be balanced); b. Good at finding relationships.

Methods of learning chemistry.

Due to the length of the article, I have to link to you. Forgiveness!

Are you familiar with the structure of chemistry textbooks? The learning of knowledge should be outlined, and after the knowledge can be formed into a network, it is natural to know where the focus is, and the content of chemistry learning is not much, but it is relatively scattered, so it is necessary to classify and summarize the learning, don't rush to take it slowly.

Help common substances and elements to liveness that the back of the table, there is the formula.

1. Common gases and their properties: H2, O2, CO, CO2, CH4

Flammability: H2, CO, CH4 Reducibility: H2, CO Toxicity: CO

Density is greater than air: O2, CO2 soluble in water: CO2 The simplest organic matter: CH4

2. Common names for common substances:

Purified substances: CO2 (dry ice), C2H5OH (alcohol), CH3COOH (acetic acid), CAO (quicklime), CA (OH)2 (hydrated lime, slaked lime), Na2CO3 (soda ash), NAOH (caustic soda, caustic soda, caustic soda), CUSO4?5H2O (cholelum, blue alum).

Mixture: Coal (C) Natural Gas, Biogas (CH4), Pig Iron, Steel (Fe), Rust, Hematite (Fe2O3).

Magnetite (Fe3O4), lime water, lime slurry [Ca(OH)2], limestone, marble (CaCO3), hydrochloric acid (HCl).

Volatile: concentrated hydrochloric acid, concentrated nitric acid, water absorption: concentrated sulfuric acid, solid sodium hydroxide (deliquescent).

Dehydration: Concentrated sulfuric acid toxicity: Nano2 (sodium nitrite), CuSO4 (copper sulfate), CH3OH (methanol).

Exothermic in water: concentrated sulfuric acid (when diluted), solid sodium hydroxide (when dissolved), cao (when reacted with water).

Purple litmus test solution and colorless phenolphthalein test solution pH value.

Acidic red colorless pH < 7

Neutral purple colorless pH = 7

Basic blue-red pH 7

Note: Salts are not necessarily neutral, for example, NaCl solution is neutral, but Na2CO3 solution is alkaline, while acidic salt (e.g., NaHSO4) solution is acidic.

Candle burning experiment (no product name can be used to describe the phenomenon).

1) Flame: Flame Center, Inner Flame (brightest), Outer Flame (Highest Temperature).

2) Compare the temperature of each flame layer: use a matchstick to put it flat into the flame. Phenomenon: Carbonization at both ends; Conclusion: The outer flame has the highest temperature.

3) Test product H2O: Cover the flame with a dry cold beaker, and there is a water mist in the beaker.

CO2: Remove the beaker, pour in clarified lime water, shake, and become turbid.

4) After extinguishing: there is white smoke (paraffin vapor), light the white smoke, and the candle rekindles.

1. In terms of equations, the displacement reaction can be pushed out by itself with the activity order table, the metathesis can be pushed out with the material solubility table, and the rest should be memorized.

2. Chemical instruments, all must be memorized in terms of name, usage, precautions, etc. 3. Experiments, each experiment in the book must be carefully remembered, especially the steps, instruments, drugs and precautions.

4. Life application, pay attention to reading, don't feel that books are wasted, books are very useful junior high school chemistry actually comes and goes, and it really won't be done more than a few times, and the final stage of review should return to the textbook, don't underestimate the textbook! Reading every word in the textbook will help you a lot. I myself got a full score in chemistry in the Guangzhou high school entrance examination last year, and chemistry is my strong subject, I hope these experiences will help you.

I wish you all the best in the high school entrance examination!

Remember, chemical equations are the basis for solving all problems ...

I don't know the textbook version you are studying, but generally speaking, the focus of the first volume is to understand chemistry, mainly the application of chemistry, the learning focus of chemistry, as well as the color, composition, and properties of some common substances, as well as some chemical reactions expressed in words, as for the specific knowledge points, then look at the textbook...

1. The three types of particles that make up matter are molecules, atoms, and ions.

2. The three reducing agents commonly used to reduce copper oxide: hydrogen, carbon monoxide and carbon.

3. Hydrogen as a fuel has three advantages: abundant resources, high calorific value, and the product after combustion is water that does not pollute the environment.

4. There are generally three kinds of particles that make up atoms: protons, neutrons, and electrons.

5. There are only three kinds of ferrous metals: iron, manganese, and chromium.

6. The elements that make up the substance can be divided into three categories, namely: (1) metallic elements, (2) non-metallic elements, and (3) rare gas elements.

7. There are three kinds of iron oxides, and their chemical formulas are (1) FeO, (2) Fe2O3, (3) Fe3O4.

8. The characteristics of the solution are three (1) homogeneity; (2) stability; (3) Mixture.

9. The chemical equation has three meanings: (1) it indicates what substances participate in the reaction and what substances are produced as a result; (2) the ratio of the number of particles of molecules or atoms of reactants and products; (3) Indicates the mass ratio between each reactant and product. There are two principles of chemical equations:

based on objective facts; Follow the law of conservation of mass.

10. Pig iron is generally divided into three types: white iron, gray iron, and ductile iron.

11. Carbon steel can be divided into three types: high-carbon steel, medium-carbon steel, and low-carbon steel.

12. There are three kinds of iron ore commonly used in ironmaking: (1) hematite (the main component is Fe2O3); (2) magnetite (Fe3O4); (3) Siderite (FeCO3).

13. There are three main types of equipment for steelmaking: converter, electric furnace and open-hearth.

14. The three reaction conditions that are often related to temperature are ignition, heating, and high temperature.

15. There are two ways to turn a saturated solution into an unsaturated solution: (1) heating up, (2) adding solvent; There are three ways to turn an unsaturated solution into a saturated solution: cooling, adding solutes, and evaporating the solvent at a constant temperature.

Note: Substances whose solubility decreases with temperature, such as: calcium hydroxide solution changes from saturated solution to unsaturated solution

Cooling, solvent addition; There are three ways to change unsaturated solution to saturated solution: heating up, adding solutes, and evaporating solvents at constant temperature).

16. There are generally three methods of gas collection: drainage method, upward emptying method, and downward emptying method.

17. There are three main causes of water pollution: (1) waste residue, waste gas and waste water in industrial production; (2) Arbitrary discharge of domestic sewage; (3) Pesticides and fertilizers used in agricultural production flow into rivers with rainwater.

18. There are three types of fire extinguishers commonly used: foam fire extinguishers; dry chemical fire extinguishers; Liquid carbon dioxide fire extinguisher.

19. The solubility of solid substances changes with temperature can be divided into three categories: (1) the solubility of most solid substances increases with the increase of temperature; (2) The solubility of a few substances is not affected by temperature very much; (3) The solubility of a very small number of substances decreases with the increase of temperature.

20. There are three reasons why CO2 can extinguish fires: it cannot burn, it cannot support combustion, and it is denser than air.

1. Basic reaction types

Chemical reaction: multi-change one.

Decomposition reaction: one becomes many.

Displacement reaction: one order for one order.

Metathesis reactions: exchange ions.

2. The valence (normality) of common elements

monovalent potassium, sodium, hydrogen and silver, bivalent calcium, magnesium, barium and zinc, trivalent metal element aluminum; 157 variable chlorine, 245 nitrogen, sulfur 46, 35 phosphorus, 24 carbon; One or two copper, two three iron, two four six or seven manganese special.

3. Steps to produce oxygen in the laboratory

Tea (check) Zhuang (loaded) fixed-point collection of profits (departure) interest (extinguished)".

Check": Check the airtightness of the device.

loaded": Hold the medicine and connect the device.

Fixed": The test tube is fixed on the iron stand.

"Point": Light an alcohol lamp for heating.

Received": Collects gases.

off": The conduit is removed from the water.

Off": Turn off the alcohol lamp and stop the heat.

1.There must be a physical change in a chemical change, and there is not necessarily a chemical change in a physical change.

2.Metals are not necessarily solid at room temperature (e.g., Hg is liquid), and non-metals are not necessarily gases or solids (e.g., br2 is liquid) Note: Metals and non-metals refer to elemental substances and cannot be confused with the constituent elements of matter.

3.The cluster of atoms must be charged ions, but the clusters are not necessarily acid radicals (e.g., NH4+, OH-);

Acid radicals are also not necessarily atomic clusters (e.g., Cl-called hydrochlorate).

4.Slow oxidation does not necessarily cause spontaneous combustion. Combustion must be a chemical change. It doesn't have to be a chemical change. (e.g. a pressure cooker** is a physical change.) )

5.Neutrons are not always present in the nucleus of an atom (e.g., H atoms have no neutrons).