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( Atom)
The atom is the smallest unit of an element that retains the chemical properties of that element. An atom has an electron cloud consisting of negatively charged electrons surrounding a dense nucleus. The nucleus contains positively charged protons and electrically neutral neutrons. When the number of protons in the nucleus equals the number of electrons, the atom is electrically neutral; otherwise it is an ion and has a net positive or negative charge. An atom is classified according to its number of protons and neutrons the number of protons determines the chemical element and the number of neutrons determines the isotope of that element. The name atom comes from the Greek ?t?µ??/átomos, a-teµ??, which means uncuttable, something that cannot be divided further. The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the 'atom' was not indivisible. The principles of quantum mechanics were used to successfully model the atom.[1][2] Relative to everyday experience, atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.9% of an atom's mass is concentrated in the nucleus,[note 1] with protons and neutrons having roughly equal mass. Each element has at least one isotope with unstable nuclei that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus.[3] Electrons possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties. The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny quantities has been around for millennia, but these ideas were founded in abstract, philosophical reasoning rather than experimentation and empirical observation. The nature of atoms in philosophy varied considerably over time and between cultures and schools, and often had spiritual elements. Nevertheless, the basic idea of the atom was adopted by scientists thousands of years later because it elegantly explained new discoveries in the field of chemistry.[4]
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Atom Subcategories
Atom Articles
Ancient Trees and the Atom Bomb by Lucy Evans
In today`s world you will find it very difficult to come across examples of living fossils. Living fossil is a term used by scientists which means living animals and plants that are largely unaltered from the fossilised remains of their predecessors....
Body Building Anatomy by John Smi
The anatomy of body building includes knowing what muscles are located where and how they are grown most effectively. It can be confusing, so as you read this article, find a mirror and locate the muscles on your own body. When you are body buildin...
Anatomy Of A Good Moisturizer by Stephen Cauldry
Attempting to decode the ingredients on the back of a skin moisturizer product can be a little overwhelming. Luckily for those of us lacking a degree in chemistry, all moisturizers are pretty much structured in the same fashion. Moisturizers mimic th...
The Penis - Know Your (Or Your Partner's) Anatomy by sacha tarkovsky
The man’s sexual (and excretory) organ, the penis, is not as simple as it may appear. One should know all about his penis, and connected sexual organs, as it plays, in one way or another, an important part in every man’s life.
The Penis Size ...
The Pubococcygeus Muscle : An Important Anatomy Lesson by Marc Deschamps
Copyright 2006 Marc Deschamps
What most people don't know is that the pubococcygeus muscle (pyoo-bo-cocksee-gee-us) or PC muscle plays a crucial role in the functioning of the penis.
The pubococcygeus muscle is actually a group of muscles...
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