News tagged with atoms

Related topics: electrons , molecules , physical review letters , graphene , particles

Unhealthy attachments

Using the surface forces apparatus and an atomic force microscope, researchers at UC Santa Barbara have taken a molecular approach to myelin membrane interactions, leading to insights into demyelinating diseases, ...

Feb 25, 2014
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Researchers extend human epigenomic map

Ten years ago, scientists announced the end of the Human Genome Project, the international attempt to learn which combination of four nucleotides—adenine, thymine, cytosine, and guanine—is unique to homo sapien DNA. This ...

Aug 08, 2013
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New hope for hormone resistant breast cancer

A new finding provides fresh hope for the millions of women worldwide with oestrogen receptor positive breast cancer. Australian scientists have shown that a specific change, which occurs when tumours become resistant to ...

Jul 22, 2013
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Typhoid's lethal secret revealed

Typhoid fever is one of the oldest documented diseases known to have afflicted mankind but what makes it so lethal has remained a mystery for centuries. In a study appearing online July 10 in the journal Nature, Yale resear ...

Jul 10, 2013
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New insights into how genes turn on and off

Researchers at UC Davis and the University of British Columbia have shed new light on methylation, a critical process that helps control how genes are expressed. Working with placentas, the team discovered that 37 percent ...

Mar 27, 2013
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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.

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