Chemistry in the ninth grade must memorize knowledge points, and chemistry in the ninth grade must m

The knowledge points that must be memorized in Jiushang Chemistry are as follows:Uses of common gases: (1) Oxygen: for breathing (such as diving, medical emergency). Support combustion (e.g. fuel combustion, steelmaking, gas welding).

2) Nitrogen: protective gas (chemically inactive), important raw materials (nitric acid, chemical fertilizer), liquid nitrogen freezing.

3) Rare gases (He, Ne, Ar, Kr, XE, etc.): shielding gas, electric light source (light of different colors when energized), laser technology.

Valency, aWriting and meaning: mgcl2:

The valency of magnesium in magnesium chloride is +2. b.The meaning of several numbers Fe2+ each ferrous ion has two units of positive charge.

3Fe2+: 3 ferrous ions. c.

The algebraic sum of the positive and negative valencies of each element in a compound is zero, and the valency of an element in a single element is zero.

The knowledge points that must be memorized in Jiushang Chemistry are as follows:

1. Classification of substances.

1) Mixtures and purities.

Mixture: There are two or more substances in the composition. Common concoctions are: air, seawater, tap water, soil, coal, oil, natural gas, detonation gas, and various solutions.

Pure: There is only one substance in the composition.

Macroscopically there is one ingredient and microscopic there is only one molecule.

Pure substances have a fixed composition and unique chemical properties, which can be expressed by chemical formulas.

Pure substances can be composed of one element (elemental) or multiple elemental elements (compounds).

2) Elemental substances and compounds.

Elemental: A pure substance composed of only one element. It can be divided into metal element, non-metallic element and rare gas.

Compound: A pure substance composed of two or more elements.

3) Oxides, acids, bases and salts.

Oxide: A compound composed of two elements, one of which is the element oxygen. Oxides can be divided into metal oxides and non-metal oxides; It can also be divided into acidic oxides, basic oxides and amphoteric oxides.

Acid: A positive compound in which all cations ionized in solution are hydrogen ions. Acids can be divided into strong acids and weak acids; monobasic and polyacids; Oxygenated acids and anaerobic acids, etc.

Base: The cations ionized in solution are all compounds of hydroxide ions. Bases can be divided into soluble and insoluble bases.

Salt: A compound that ionizes metal cations and acid anions during ionization. Salts can be divided into normal salts, acid salts, and basic salts.

2. Chemical terminology.

1) Relative atomic mass and relative molecular mass, molecular-atomic motion theory, and extranuclear electron arrangement.

2) The meaning of the element symbol.

An element.

One atom of this element.

If a substance is directly constituted by atoms, the elements that make up the substance can also represent this elemental substance, such as: S, P, etc.

3) Valency: The number of atoms of an element that are combined with each other determines the valency of this element. The valency is closely related to the number of electrons in the outermost shell of the atom; In a compound, the algebraic sum of the positive and negative valency of the elements is zero; The valence of the elements in the element is specified as zero price.

4) Chemical formula: The formula that uses element symbols to represent the composition of matter.

5) Chemical equation: The chemical formula is used to represent the formula of a chemical reaction. Pay attention to the principles of writing, steps, trim, reaction conditions, correct use of arrows.