About junior high school chemistry questions Elemental, common elemental and chemical formulas in ju

The point is that you're mixing multiple concepts together!

Concepts in chemistry have their own emphasis, and as long as you grasp this emphasis, you will not be confused.

For example, elemental matter, which emphasizes the composition of (an element) and is used to represent the purest substance.

Another example is metals, which mainly refer to a class of elemental substances, with some commonalities (luster, electrical conductivity, thermal conductivity, ductility, etc.), and they are divided into a class called metals for the sake of research convenience.

Speaking of gases, people began to think that they were inactive gases because they were not active, and they were called noble gases very rarely in the air, but later they found that they were not very "lazy" and changed to noble gases. It's really emphasizing the elements that are packed with each electron shell.

Valency is the situation in which electrons are gained or lost while reacting with other substances emphasized. Of course, the elemental element is 0 valence if it is not combined with other atoms, if it loses electrons, it will be + valence, and if it gains electrons, it will be - valence.

From the questions you added, it can be seen that you confuse the concepts of elemental matter and elemental. Oxygen is elemental and oxygen is an element.

1. Noble gas elements belong to non-metallic elements.

2. Elemental matter is a pure substance composed of an element, which is the definition of elementality, and this sentence is used to judge whether a substance belongs to elemental matter. First, it must be composed of the same element, and secondly, it must be pure, not a mixture. For example, diamond and graphite are both made up of the same element, but they are mixtures, so they cannot be said to be elemental.

3. Pure substances of noble gases, metals, solid non-metals, and non-metallic gases (H2, Cl2, etc., which cannot include CO2, CH4, etc.) are all elemental.

4. The valency of the element is 0, which is good. For example, the O in O2 is the 0 valence, and the O in H2O is the -2 valence, and for example, the O in N2O2 is the -1 valence. The valency must be measured in the compound.

The valency can be understood like this:

When an element forms a compound, there are two situations: (1) the outer electrons are gained and lost to form a compound, if the electrons are lost, the positive valence is displayed, the electrons are negative, and the number of electrons gained and lost is the number of valences; (2) If the electron pairs are biased towards an atom, the atom will show a negative valence, and conversely, if the electron pairs deviate from an atom, the atom will show a positive valence. For example, O2 shares electron pairs that are impartial, so 0 valence is displayed. H2O,O and 2H are combined with 2 shared electron pairs, and the electron pairs are offset towards O, so O shows -2 valence and H shows +1 valence.

Noble gases belong to the genus of non-metallic origin. The elements in the periodic table that contain gold are generally metallic elements, otherwise they are non-metallic elements.

Noble gases are also non-metallic gases. There are two conditions for elementality: one is the same element.

The second is purity. Those who meet these two points are elemental. Here's an example:

Ozone and oxygen are put in a gas cylinder, which can only be said to be a mixture, because although they are the same element, they are not pure, so they are not elemental.

The valency of any elemental substance is 0, and only the element has a valency in the compound.

You do confuse them.

First of all, the element, from the side of the name to distinguish what it is, there are metal elements next to the word gold, there are non-metallic elements next to the word stone or three points next to the water or gas prefix, but the noble gas is separate, it includes helium, neon, argon and other gases. That is, there are three types of elements: metallic elements, non-metallic elements, and noble gas elements.

Secondly, elemental matter is a pure substance composed of the same element. It is analyzed from the point of view of matter. Notice, that's where you mix and that's the key.

Elemental elements can be divided into three categories according to the type of element, metallic elemental, non-metallic elemental, and noble gas elemental.

Again, the valency of the elements in the element is 0, which refers to the valency of the oxygen element in oxygen or ozone, which is the element, where the valency of the element is 0. And oxygen is -2 valence refers to its valency in compounds, such as -2 valence for oxygen in water and -2 valence for oxygen in copper oxide.

There are also special cases, such as the -1 valence of oxygen in hydrogen peroxide H2O2.

Noble gases are non-metals. Elemental matter is the same substance composed of the same element, as long as you understand this sentence, it should be fine. O2 is elemental, so it shows zero valence, and the valency of an element is different in different compounds, and it cannot be generalized!

You should be talking about noble gas elements instead of noble gases, noble gas elements are non-metallic elements, and, usually we say that oxygen is a substance, and oxygen, which means an element, oxygen is a element.

Elemental is a pure substance composed of an element, first of all, elemental is composed of an element, if there are two or more elements, it is a mixture or compound; Then there are pure substances, some of which are composed of one element, but there are two different forms, such as oxygen and ozone, both of which are composed of oxygen elements, but mixed together are mixtures, and only when they exist alone (that is, when they are pure) they are elemental. Use these two items to judge whether it is elemental.

It is one of the rare gases, metals and solid non-metallic and non-metallic gases, and cannot be judged as elemental.

The valency of the elemental element is 0, the valency of the oxygen element in oxygen is 0, -2 is the general valency of the oxygen element in the compound (note that it is a compound), in addition, the oxygen element in the hydrogen peroxide is -1 valence.

Concepts and other things are easier to understand when comparing the differences between them.

Noble gases are, of course, non-metals.

It is right that the element includes these 123.

But the reverse should be discussed separately, noble gases are elemental, metals are elemental, solid non-metals are not all elemental, for example, graphite is elemental, but magnesium oxide is not elemental.

Non-metallic gases are not all elemental, such as oxygen, but carbon dioxide is not.

The valency of an elemental substance is 0, so the valency of O in oxygen is O, and -2 is the general valency of O in the compound.

Elements can be divided into metallic elements and non-metallic noble gas elements.

An elemental substance is a pure substance made up of an element.

Elemental matter is divided into 1, rare gas elemental 2, metal elemental 3, and non-metallic element.

The valency of oxygen in oxygen is zero, and in all elemental elements, the valency of the element is zero.

Oxygen is usually -2 valent in compounds. The valencies of common elements are the valencies that are usually expressed in compounds.

Elemental: A pure substance composed of the same elements.

Commonly used elements are: oxygen O2, hydrogen H2, nitrogen N2, carbon C, sulfur S, phosphorus P, copper Cu, iron Fe, zinc Zn, etc.

An elementary substance is a pure substance made up of the same element. The presence of an element in a elemental substance is called the free state of the element. Introduction: An elementary substance is a pure substance composed of the same element.

1. Metallic elements:

Metal aluminum (Al), metal iron (Fe), metal calcium (Ca), metal potassium (K), metal mercury (Hg).

2. Non-metallic:

Oxygen (O), Sulfur (S), Silicon (Si), Phosphorus (P), Iodine (I), Hydrogen (H), Nitrogen (N).

3. Noble gases:

Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (XE), Radon (RN).

Valency mnemonics.

Monovalent potassium hydrofluoride, sodium silver, divalent barium oxygen, calcium, magnesium, zinc.

3. Aluminum, 4 silicon, pentavalent phosphorus, 246 sulfur, 24 carbon.

12 copper, mercury, 23 iron, 157 chlorine should be recorded.

N-1 copper, potassium, potassium, sodium, silver, n-2, copper, magnesium, calcium, barium, zinc.

3. Aluminum, 4 silicon, 46 sulfur, 245 nitrogen, 35 phosphorus.

157 chlorodiferric 2467 manganese is positive.

Carbon has positive four and positive two, and then keep the negative price in mind.

Negative iodine bromo, chlorofluorocarbon, negative dioxysulfur, triazonium phosphorus.

n-monohydro, silver and potassium, sodium, n-dicalcium, magnesium, barium, zinc, mercury and copper.

Aluminum positive three, silicon positive four, ferrous positive two-iron positive three.

Chlorine is at the end minus monovalent and sulfur oxide is minus bivalent at the end.

Don't forget that the quality price of the unit is zero.

For example, in the mixture of red phosphorus and white phosphorus, the chemical elements are all phosphorus, but they are mixtures, not elemental substances.

Metals: Aluminum (Al), Iron (Fe), Calcium (Ca), Potassium (K), Mercury (Hg) Non-metals: Oxygen (O), Sulfur (S), Silicon (Si), Phosphorus (P), Iodine (I), Hydrogen (H), Nitrogen (N) Noble Gases:

Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (XE), Radon (RN).

All metals. Noble gas. And what oxygen and so on.

Do you want to take the test? Hydrogen, oxygen, carbon, and nitrogen are often examined.

Are you referring to the textbook? Seems like a lot, right?

Elemental substances are pure substances composed of the same elements. Elemental matter is the specific form in which the elements exist in a free state. The same element can form several different elements.

Elemental substances are pure substances composed of the same elements. The presence of an element in a elemental substance is called the free state of the element. In general, the properties of elemental matter are closely related to the properties of its elements.

For example, many metals have obvious metallicity, so their elemental reducibility is very strong. The differences in the properties of different types of elements are most prominently reflected in the structure.

Metals: Aluminum (Al), Iron (Fe), Calcium (Ca), Potassium (K), Mercury (Hg).

Non-metals: oxygen (O), sulfur (S), silicon (Si), phosphorus (P), iodine (I), hydrogen (H), nitrogen (N).

Noble gases: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (XE), radon (RN).

Definition: A substance that is formed by the mechanical mixing of two or several different elemental substances or compounds, called a mixture.

Instructions:1A mixture, unlike a compound, has no fixed composition. The components in the mixture still retain their original properties.

2.The components of a mixture can be uniformly dispersed (e.g., solution) or non-uniformly (e.g., turbid liquid or solid mixture), but do not react chemically with each other. As the different components attract or repel each other, the overall properties of the mixture may be affected.

3.The mixture can be separated by physical methods (such as crystallization, sublimation, distillation, extraction, etc.) according to the different physical properties of the components it contains (such as solubility, boiling point, density, magnetism, etc.).

Definition: A substance composed of only one element or one compound is called a pure substance.

Instructions:1Pure substances have a fixed composition, and abrasion resistance can be expressed by a certain chemical formula. Pure matter cannot be separated by physical methods, but only by chemical methods.

2.In fact, there is no such thing as a completely pure substance. A substance that contains impurities in quantities that do not cause harmful effects in production and scientific research can be regarded as pure.

3.The purity of the reagent selected in the experiment is too high, which will cause unnecessary waste due to too high **; The purity grade of the selected reagent is too low, which will cause the experiment to fail due to the interference of impurities in the reagent. Reagents or raw materials of comparable purity should be selected according to the application.

Definition: A pure substance composed of different elements is called a compound.

Instructions:1Compounds generally have a fixed composition. The composition of a compound can generally be expressed by a chemical formula.

2.Compounds have definite physical and chemical properties that differ from the properties of their constituent elements.

3.The elements in a compound cannot be separated by simple mechanical or physical methods, but must be separated by chemical methods.

Copper sulfate crystal is a blue crystal composed mainly of copper sulfate pentahydrate, that is, the hydrate of copper sulfate. It can be used for electroplating or dyeing, and is also known as blue alum, bile alum.

When a small amount of water is added, it is the following reaction.

Anhydrous copper sulphate + water = copper sulphate pentahydrate to obtain copper sulphate crystals.

Water is added to dissolve the crystals to obtain a copper sulfate solution.

The amount of water added to obtain copper sulphate crystals can be calculated using the above reaction. Above this amount, some copper sulphate crystals will dissolve to form a solution.

This case involves the concept of saturation. To put it simply, at the beginning, there is more copper sulfate, less water, copper sulfate is insoluble, and it is still crystalline; When too much water is added, the copper sulfate in the solution does not reach saturation and can exist in liquid form. The amount of water added to form the crystals and the solution depends on the saturation (or solubility) of the copper sulphate at the temperature at which it is placed.

The solubility values of substances are listed in the appendix of high school chemistry textbooks.

Anhydrous copper sulfate will react with water (and the solubility of copper sulfate is not very high), and with the increase of water volume, take one, three, five crystal water in order (from the phenomenon is that the color gradually turns blue), the amount of crystal water can be used by colorimetric meter or high temperature calcination with desiccant to absorb water (such as: magnesium perchlorate, anhydrous calcium chloride, soda asbestos, soda lime, etc.).

Option A: Because the calcium carbonate is solid, it will disappear when it reacts with hydrochloric acid, and it can be judged that the reaction has been made, and option B is the same as copper hydroxide, which is a white solid that reacts with sulfuric acid to form copper sulfate, and the copper sulfate solution is blue.

Option D is the same as iron oxide is a solid reaction with hydrochloric acid to produce iron chloride solution is reddish-brown, it can be judged that this C option, sodium hydroxide is colorless when dissolved in water, nitric acid is also colorless, the essence of the reaction between the two liquids is neutralization, generating water and sodium nitrate, sodium nitrate is also colorless when dissolved in water, so acid-base indicators should be added dropwise, such as purple litmus solution, red when acid, blue when alkalin, nitric acid and purple litmus solution can be observed that the solution is red, Then add sodium hydroxide to the mixed solution, and the red color of the solution can be seen with the naked eye, and slowly fade.