What's number of valence electrons?

The number of valence electrons is the number of electrons in the outermost shell of an atom. These electrons are the ones that are involved in chemical reactions, and their number is often used to predict the reactivity of an atom and its ability to form chemical bonds. In general, atoms with a small number of valence electrons are more reactive, while atoms with a larger number of valence electrons are less reactive. The number of valence electrons can be determined by looking at the periodic table of elements, which shows the number of electrons in the outermost shell for each element.

Tell me the color of some chemical marterial?

The color of a chemical substance is determined by the wavelengths of light that it absorbs and reflects. Different chemical substances can have different colors, depending on their chemical composition and structure. For example, copper sulfate is a blue crystalline solid, sodium chloride (table salt) is a white crystalline solid, and iron oxide (rust) is a red-brown powder. Some chemicals are colorless, such as water and ethanol, while others are brightly colored, such as the dyes used in food, clothing, and cosmetics. The color of a chemical substance can also change depending on its concentration, temperature, and the presence of other chemicals.

The chemical substance introduced during middle school

There are many different chemical substances that are introduced in middle school, as students begin to learn about the basics of chemistry. Some common examples include:

• Water (H2O): Water is a colorless, tasteless, and odorless liquid that is essential for life on Earth. It is made up of two hydrogen atoms bonded to one oxygen atom.
• Oxygen (O2): Oxygen is a colorless, tasteless, and odorless gas that makes up about 21% of the Earth's atmosphere. It is essential for respiration in plants and animals, and is required for the burning of fuel.
• Carbon dioxide (CO2): Carbon dioxide is a colorless, odorless gas that is produced by the burning of fossil fuels, the respiration of plants and animals, and the fermentation of sugars. It is a greenhouse gas that contributes to global warming.
• Salt (NaCl): Salt is a white crystalline solid that is made up of sodium and chlorine atoms. It is a common food seasoning, and is also used to preserve food and make soap.
• Acids and bases: Acids are chemicals that release hydrogen ions (H+) when they are dissolved in water, while bases are chemicals that release hydroxide ions (OH-) when they are dissolved in water. Acids and bases have different chemical properties and react with each other to form neutral compounds, such as salt and water.

These are just a few examples of the many chemical substances that are introduced in middle school. As students learn more about chemistry, they will encounter a wide range of chemical substances with different properties and uses.

https://www.bilibili.com/video/BV1wb411x78e?p=15  分子和原子

What construct the substance?

Substances are made up of atoms原子, molecules分子, or ions离子.

Atoms are the basic units of matter, and are made up of protons质子, neutrons中子, and electrons电子.

Molecules分子 are formed when two or more atoms combine chemically, and can be made up of atoms of the same element (such as oxygen molecules, O2) or different elements (such as water molecules, H2O).

Ions are atoms or molecules that have gained or lost one or more electrons, giving them a net positive or negative charge. The number and arrangement of atoms, molecules, or ions in a substance determine its chemical composition and physical properties, such as its color, density, and melting and boiling points.