Using drones to reduce disease-spreading mosquito populations

Vector-borne diseases are illnesses that can be transmitted to humans by blood-feeding insects, such as mosquitoes, ticks and fleas. Mosquitoes are known to contribute to the spread of a number of vector-borne diseases, including ...

Energy & Green Tech

UN agency: North Europe radiation likely linked to reactor

The U.N. nuclear agency said Friday that slightly elevated levels of radioactivity detected in northern Europe likely were related to a nuclear reactor that was either operating or undergoing maintenance, but it's still unclear ...

Energy & Green Tech

Seeing 'under the hood' in batteries

From next-gen smartphones to longer-range electric cars and an improved power grid, better batteries are driving tech innovation. And to push batteries beyond their present-day performance, researchers want to see "under ...

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 ...

Energy & Green Tech

UAE issues licence for first Arab nuclear power plant

The United Arab Emirates said Monday it has issued an operating licence for a reactor at its Barakah nuclear power plant, the first in the Arab world, hailing it as a "new chapter".

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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.

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