Energy & Green Tech

Pivotal battery discovery could impact transportation and the grid

Battery-powered vehicles have made a significant dent in the transportation market. But that market still needs lower cost batteries that can power vehicles for greater ranges. Also desirable are low-cost batteries able to ...

Energy & Green Tech

New insight could lead to better silicon solar panels

Researchers at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) and Colorado School of Mines are applying a new technique to identify defects in silicon solar cells that cause a drop in efficiency. ...

Engineering

Bringing order to hydrogen energy devices

Researchers at Kyoto University's Institute for Cell-Material Sciences (iCeMS) have developed a new approach to speed up hydrogen atoms moving through a crystal lattice structure at lower temperatures. They reported their ...

Energy & Green Tech

Weakness is strength for this low-temperature battery

Nanoengineers at the University of California San Diego have discovered new fundamental insights for developing lithium metal batteries that perform well at ultra-low temperatures; mainly, that the weaker the electrolyte ...

Electronics & Semiconductors

Layered solar cell technology boosts efficiency, affordability

The future's getting brighter for solar power. Researchers from CU Boulder have created a low-cost solar cell with one of the highest power-conversion efficiencies to date, by layering cells and using a unique combination ...

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