chemistry

The word chemistry comes from a modification of the word alchemy [炼金术], which referred to an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism and medicine. Alchemy is often seen as linked to the quest to turn lead [铅] or other base metals [贱金属] into gold, though alchemists were also interested in many of the questions of modern chemistry.

The modern word alchemy in turn is derived from the Arabic word al-kīmīā (الكیمیاء). This may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Kemet, which is the ancient name of Egypt in the Egyptian language. Alternately, al-kīmīā may derive from χημεία, meaning "cast together" [铸造在一起]. 化：性质或形态改变。

Chemistry is the scientific discipline [学科] involved with elements and compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.

In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant chemistry (botany), the formation of igneous [火成的] rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the properties of the soil on the moon (cosmochemistry, 宇宙化学), how medications work (pharmacology, 药理学; 药物学), and how to collect DNA evidence at a crime scene (forensics).

A chemical reaction is a transformation of some substances into one or more different substances. The basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds [化学键] between atoms. It can be symbolically depicted through a chemical equation, which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal. (When the number of atoms on either side is unequal, the transformation is referred to as a nuclear reaction or radioactive decay [衰变].) The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.

The current model of atomic structure is the quantum mechanical [量子力学] model. Traditional chemistry starts with the study of elementary particles, atoms, molecules,] substances, metals, crystals and other aggregates of matter. Matter can be studied in solid, liquid, gas and plasma states, in isolation or in combination. The interactions, reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together. Such behaviors are studied in a chemistry laboratory.

Chemistry addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. 化学键(chemical bond)是纯净物分子内或晶体内相邻两个或多个原子或离子间强烈的相互作用力的统称。There are two types of chemical bonds:

1. primary chemical bonds e.g covalent bonds, in which atoms share one or more electron(s); ionic bonds, in which an atom donates one or more electrons to another atom to produce ions (cations and anions); metallic bonds
2. secondary chemical bonds e.g. hydrogen bonds; Van der Waals force bonds, ion-ion interaction, ion-dipole [偶极子] interaction etc. A dipole is a molecule in which the centre of positive charge does not coincide with the centre of negative charge.

An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. Plasma is composed of gaseous matter that has been completely ionized, usually through high temperature.

A substance can often be classified as an acid or a base. There are several {三种} different theories which explain acid-base behavior.

Difference Between Alkali and Base

Bases react with acids to form a salt and/or H₂O. Alkalis are like a subset of bases; they are water soluble bases. The term alkali is mainly used for the hydroxides [氢氧化物] of alkali metals [锂、钠、钾等] or alkaline earth metals. The alkaline earth metals are the elements that correspond to group 2 of the modern periodic table. This group of elements includes beryllium [鈹 pí], magnesium, calcium, strontium [锶 sī], barium [钡], and radium. [link]

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来源： https://www.cnblogs.com/funwithwords/p/16293760.html