Chemistry is one of the very important branches of physical science that studies the arrangement, configuration attributes and change of matter. Chemistry is mainly associated with atoms and molecules and their interactions and changes such as the properties of the chemical bonds formed between atoms to generate chemical compounds.Therefore, chemistry studies the involvement of electrons and various forms of energy in photochemical, oxidation-reduction reactions, changes in phases of matter, and separation of mixtures. Preparation and properties of complex substances, such as alloys, polymers, biological molecules, and pharmaceutical agents are considered in specialized fields of chemistry. The periodic table of elements is arranged in groups, or columns, and periods, or rows. The periodic table is useful in identifying periodic trends.
Chemistry is sometimes called the central science because it bridges other natural sciences like physics, geology and biology. Chemistry is a branch of physical science but distinct from physics. The origin of the word chemistry has been widely uncertain The history of chemistry can be traced to certain practices, known as alchemy, which had been practiced for several thousands of year in different parts of the world. In chemistry, the matter is defined as anything that has rest mass and volume (it takes up space) and is made up of particles. The particles that makeup matter have rest mass as well – not all particles have rest mass, such as the photon. Matter can be a pure chemical substance or a mixture of substances.
The atom is the smallest unit of chemistry. It consists of a solid core called the nucleus which is surrounded by a space known as the electron cloud. The nucleus is made up of completely charged protons and uncharged neutrons (together called nucleons), while the electron cloud consists of negatively-charged electrons which influence the nucleus. In a neutral atom, the negatively-charged electrons balance out the positive charge of the protons. The nucleus is solid; the mass of a nucleon is 1,836 times that of an electron, yet the radius of an atom is about 10,000 times that of its nucleus.
The atom is also the smallest unit that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state(s), coordination number, and preferred types of bonds to form (e.g., metallic, ionic, covalent).Although all the nuclei of all atoms belonging to one element will have the same atomic number, they may not necessarily have the same mass number; atoms of an element which have different mass numbers are known as isotopes. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, but atoms of carbon may have mass numbers of 12 or 13.