Chemistry is the scientific discipline involved with compounds composed of atoms, i. In the scope of its stepwise drawing of a penguin for kids, 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. The history of chemistry spans a period from very old times to the present. Since several millennia BC, civilizations were using technologies that would eventually form the basis of the various branches of chemistry. The word chemistry comes from alchemy, which referred to an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism and medicine. In origin, the term is borrowed from the Greek χημία or χημεία. Laboratory, Institute of Biochemistry, University of Cologne in Germany.
The current model of atomic structure is the quantum mechanical model. The chemistry laboratory stereotypically uses various forms of laboratory glassware. 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 between atoms. Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure, phase, as well as their chemical compositions. The atom is the basic unit of chemistry.
It consists of a dense core called the atomic nucleus surrounded by a space hosting an electron cloud. Standard form of the periodic table of chemical elements. A chemical element is a pure substance which is composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z. The mass number is the sum of the number of protons and neutrons in a nucleus. The standard presentation of the chemical elements is in the periodic table, which orders elements by atomic number. The periodic table is arranged in groups, or columns, and periods, or rows.
A compound is a pure chemical substance composed of more than one element. The properties of a compound bear little similarity to those of its elements. A molecule is the smallest indivisible portion of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the “molecule” a charge, the result is sometimes named a molecular ion or a polyatomic ion. However, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the Earth are chemical compounds without molecules.