Atom

Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Atom shopping experience:

1. Compare - without doubt the biggest advantage that the Atom offers shoppers today is the ability to compare thousands of Atom at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

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3. Testimonials - don't know anybody that has bought a Atom? Wrong! If the Atom is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Atom then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Atom? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Atom and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Atom wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Atom then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Atom site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Atom, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Atom, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

{| border="1" cellspacing="0" align="right" cellpadding="2" style="margin-left:1em" width=300|-! bgcolor=gray | Atom|-| align="center" | |-| align=center | A depiction of the atomic structure of the atom of helium. The darkness of the electron electron cloud corresponds to the line-of-sight integral over the probability function of the 1s Atomic orbital. The atomic nucleus is schematic, showing protons in pink and neutrons in purple. In reality, the nucleus (and the wavefunction of each of the nucleons) is also spherically symmetric. (For more complicated nuclei this is not the case.)]|}|-! bgcolor=gray | Properties|-|{| align="center"|-| atomic mass : || ≈ 1.67 × 10 to 4.52 × 10 kg

] : || zero(if the number of electrons equal the number of protons in an atom)|-| Diameter : (Atomic radii of the elements (data page))| 50 Picometre(H) to 520 pm(Cs)|-| Number of atoms in the observable universe: ] and physics, an atom (Greek language ἄτομος or átomos meaning "indivisible") is the smallest particle still characterizing a chemical element.

An atom consists of a dense atomic nucleus of positively-charged protons and electrically-neutral neutrons, surrounded by a much larger electron cloud consisting of negatively-charged electrons. An atom is electrically neutral if it has the same number of protons as electrons. The number of protons in an atom defines the chemical element to which it belongs, while the number of neutrons determines the isotope of the element.

History The idea that matter is composed of discrete units and can not be divided into any arbitrarily tiny or small quantities has been around for thousands of years.The earliest references to the concept of atoms date back to History of India in the 6th century BCE. Gangopadhyaya, Mrinalkanti. Indian Atomism: History and Sources. Atlantic Highlands, New Jersey: Humanities Press, 1981. ISBN 0-391-02177-X The Nyaya and Vaisheshika schools developed elaborate theories of how atoms combined into more complex objects (first in pairs, then trios of pairs). http://dbhs.wvusd.k12.ca.us/webdocs/AtomicStructure/Atom-Theory-in-India.htmlThe references to atoms in West, emerge a century later by Leucippus whose student, Democritus, systemized his views. In around 450 BCE, Democritus coined the term atomos, which meant "uncuttable". Though both the Indian and Greek concepts of the atom were based purely on philosophy, modern science has retained the name coined by Democritus.

A New System of Chemical Philosophy (1808).In 1803, John Dalton used the concept of atoms to explain why elements always reacted in Law of multiple proportions, and why certain gases dissolved better in water than others. He proposed that each element consists of atoms of a single, unique type, and that these atoms could join to each other, to form compound chemicals.

In 1827 a British botanist Robert Brown (botanist) used a microscope to look at dust grains floating in water. He called their erratic motion "Brownian motion". Albert Einstein would later demonstrate that this motion was due to the water molecules bombarding the grains.

In 1897, JJ Thomson, through his work on cathode rays, discovered the electron and its subatomic nature, which destroyed the concept of atoms as being indivisible units. Later, Thomson also discovered the existence of isotopes through his work on ionized gases.

Thomson believed that the electrons were distributed evenly throughout the atom, balanced by the presence of a uniform sea of positive charge. However, in 1909, the gold foil experiment was interpreted by Ernest Rutherford as suggesting that the positive charge of an atom and most of its mass was concentrated in a nucleus at the center of the atom (Rutherford model), with the electrons orbiting it like planets around a sun. In 1913, Niels Bohr added quantum mechanics into this model, which now stated that the electrons were locked or confined into clearly defined orbits, and could jump between these, but could not freely spiral inward or outward in intermediate states.

In 1926, Erwin Schrodinger, using Louis DeBroglie's 1924 proposal that all particles behave to an extent like waves, developed a mathematical model of the atom that described the electrons as three-dimensional waveforms, rather than point particles. A consequence of using waveforms to describe electrons, pointed out by Werner Heisenberg a year later, is that it is mathematically impossible to obtain precise values for both the position and momentum of a particle at any point in time; this became known as the uncertainty principle. In this concept, for any given value of position one could only obtain a range of probable values for momentum, and vice versa. Although this model was difficult to visually conceptualize, it was able to explain many observations of atomic behavior that previous models could not, such as certain structural and spectral patterns of atoms bigger than hydrogen. Thus, the planetary model of the atom was discarded in favor of one that described orbital zones around the nucleus where a given electron is most likely to exist.

Subatomic particles Though the word atom originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the "atom" is composed of various subatomic particles including:

electrons, which have a negative electric charge, a size which is so small as to be currently unmeasurable, and which are the least heavy (i.e., massive) of the three types of basic particles, with an mass of 9.11x10-31kg.
protons, which have a positive charge, with a free mass about 1836 times more than electrons (mass of 1.67x10-27kg though binding energy changes can reduce this).
neutrons, which have no charge, have a free mass about 1839 times the mass of electrons, and about the same physical size as protons (which is on the order of 2.5x10-15 m in diameter, although the "surface" of a proton or neutron is not very sharply defined).

Protons and neutrons make up a dense, massive atomic nucleus, and are collectively called nucleons. The electrons form the much larger electron cloud surrounding the nucleus. Both protons and neutrons are themselves now thought to be composed of even more elementary particles, quarks.

Atoms of the same chemical element have the same number of protons (called the atomic number). Within a single element, the number of neutrons may vary, determining the isotope of that element. The number of electrons associated with an atom is most easily changed, due to the lower energy of binding of electrons. The number of protons (and neutrons) in the atomic nucleus may also change, via nuclear fusion, nuclear fission, bombardment by high energy subatomic particles or photons, or certain (but not all) types of radioactive decay. In such processes which change the number of protons in a nucleus, the atom becomes an atom of a different chemical element.

Atoms are electric charge neutral if they have an equal number of protons and electrons. Atoms which have either a deficit or a surplus of electrons are called ions. Electrons that are furthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism atoms are able to chemical bond into molecules and other types of chemical compounds like ionic and covalent network crystals.

Atoms and molecules image clearly shows the individual atoms that make up this sheet of Gold(Miller index) surface. Surface reconstruction causes the surface atoms to deviate from the bulk crystal structure and arrange in columns several atoms wide with pits between them.

For gases and certain molecular liquids and solids (such as water and sugar), molecules are the smallest division of matter which retains chemical properties; however, there are also many solids and liquids which are made of atoms, but do not contain discrete molecules (such as salt (chemistry), Rock (geology)s, and liquid and solid metals). Thus, while molecules are common on Earth (making up all of the atmosphere and most of the oceans), most of the mass of the Earth (much of the crust, and all of the mantle and core) is not made of identifiable molecules, but rather represents atomic matter in other networked arrangements, all of which lack the particular type of small-scale interrupted order (i.e., small, strongly-bound collections of atoms held to other collections of atoms by much weaker forces) that is associated with molecular matter.

Most molecules are made up of multiple atoms; for example, a molecule of water is a combination of two hydrogen atoms and one oxygen atom. The term "molecule" in gases has been used as a synonym for the fundamental particles of the gas, whatever their structure. This definition results in a few types of gases (for example inert elements that do not form compounds, such as neon), which has "molecules" consisting of only a single atom.

Origin of atoms The first nuclei, including most of the helium and all of the deuterium in the universe, were theoretically created during big bang nucleosynthesis, about 3 minutes after the big bang. The first atoms were theoretically created 380,000 years after the big bang, an epoch called Timeline of the Big Bang#Recombination: 380.2C000 years, when the universe cooled enough to allow electrons to become attached to nuclei. Since then, atoms have been combined in stars through the process of nuclear fusion to generate atoms up to Iron. Some atoms such as 6Li are generated in space through Cosmic ray spallation. Elements heavier than Iron were generated in supernovae through the r-process and in Asymptotic giant branch through the s-process. Some elements, such as lead, formed largely through the radioactive decay of heavier elements.

Most of the atoms that currently make up the earth and all its inhabitants were present in their current form in the nebula that formed the solar system. The rest are the result of radioactive decay, and their relative proportion can be used to determine the age of the earth through radiometric dating. Most of the helium on earth is a product of alpha-decay.

There are a few trace atoms on Earth that were not present at the beginning, nor are results of radioactive decay. Carbon-14 is continuously generated by cosmic rays in the atmosphere. Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors or explosions, including all the plutonium and technetium on the earth.

Size comparisons Various analogies have been used to demonstrate the minuteness of the atom:

A human hair is about 1 million carbon atoms wide.
A single drop of water contains about 2 sextillion atoms of oxygen (2 followed by 21 zeros, 2×1021) and twice as many hydrogen atoms.

{{cite book| author = | authorlink = | coauthors = | year = 2002 | title = Prentice Hall Science Explorer | publisher = Prentice-Hall, Inc. | location = Upper Saddle River, New Jersey USA | id = ISBN 0-13-054091-9 --> Science textbook, Page 32: "There are 2,000,000,000,000,000,000,000 (that's 2 sextillion) atoms of oxygen in one drop of water—and twice as many atoms of hydrogen."

A HIV virion is the width of 800 carbon atoms and contains about 100 million atoms total. An E. coli bacterium contains perhaps 100 billion atoms, and a typical human cell roughly 100 trillion atoms.
A speck of dust might contain 3x10 (3 trillion) atoms.