Arthritis & Rheumatism

Researchers develop ultra-thin 'computer on the bone'

A team of University of Arizona researchers has developed an ultra-thin wireless device that grows to the surface of bone and could someday help physicians monitor bone health and healing over long periods. The devices, called ...

Medical research

Scientists are deciphering the details of immune cell activation

Chemokine receptors, located at the surface of many immune cells, play an important role in cell function. Chemokines are small proteins that bind to these receptors and control the movement and behavior of white blood cells.

Vaccination

Providing new technologies for vaccine development

Vaccines, which help the body recognize infectious microorganisms and stage a stronger and faster response, are made up of proteins that are specific to each type of microorganism. In the case of a virus, viral proteins—or ...

Diseases, Conditions, Syndromes

New drug target found for COVID-19

A new potential drug target has been identified in SARS CoV-2—the virus that causes COVID-19—by scientists at the Center of Structural Genomics of Infectious Diseases, or CSGID, who say multiple drugs will be needed to ...

Medical research

Skeletal imitation reveals how bones grow atom-by-atom

Researchers from Chalmers University of Technology, Sweden, have discovered how our bones grow at an atomic level, showing how an unstructured mass orders itself into a perfectly arranged bone structure. The discovery offers ...

Immunology

The therapeutic antibody eculizumab caught in action

In collaboration with Alexion Pharmaceuticals, Inc., scientists from Aarhus University have used X-rays to understand how the therapeutic antibody eculizumab prevents our immune system from destroying red blood cells and ...

page 1 from 3

Atom

The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutron). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determine the isotope of the element.

The name atom comes from the Greek ἄτομος/átomos, α-τεμνω, 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 divisible. The principles of quantum mechanics were used to successfully model the atom.

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, 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. Electrons that are bound to atoms 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.

This text uses material from Wikipedia, licensed under CC BY-SA