What is Atoms: Definition and 876 Discussions

An atom is the smallest unit of ordinary matter that forms a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small, typically around 100 picometers across. They are so small that accurately predicting their behavior using classical physics—as if they were tennis balls, for example—is not possible due to quantum effects.
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. More than 99.94% of an atom's mass is in the nucleus. The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge. If the number of protons and electrons are equal, then the atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively – such atoms are called ions.
The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force. The protons and neutrons in the nucleus are attracted to each other by the nuclear force. This force is usually stronger than the electromagnetic force that repels the positively charged protons from one another. Under certain circumstances, the repelling electromagnetic force becomes stronger than the nuclear force. In this case, the nucleus splits and leaves behind different elements. This is a form of nuclear decay.
The number of protons in the nucleus is the atomic number and it defines to which chemical element the atom belongs. For example, any atom that contains 29 protons is copper. The number of neutrons defines the isotope of the element. Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules or crystals. The ability of atoms to associate and dissociate is responsible for most of the physical changes observed in nature. Chemistry is the discipline that studies these changes.

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  1. C

    Atoms Everywhere: Unseeing Them Again?

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  2. F

    What causes the random decay of atoms in different interpretations?

    What causes the "random" decay of atoms in different interpretations? I'd like proponents of each interpretation to explain what their interpretation says about this issue? What happens/causes radio active decay? I know that atleast dBB and MWI needs to have a deterministic answer to this...
  3. B

    Age of Atoms: How Old Am I Really?

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  4. S

    Did Gravity Exist Before the Big Bang?

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  5. baywax

    Antimatter atoms trapped for 16 minutes

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  6. G

    Atoms and the law of perpetual motion

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  7. R

    Closed Orbit of Hydrogen Atoms. How to find the classical turning point

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  8. H

    Entangled Atoms and propagation.

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  9. R

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  10. S

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  11. N

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  12. N

    RMS speed of Hydrogen Atoms in space

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  13. N

    Rms speed of Hydrogen atoms in space

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  14. S

    What gives atoms the properties of a chemichal?

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  15. M

    How to get parameters of interaction between atoms of H2 and C6H6?

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  16. P

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  17. I

    Atoms decay via alpha emission have a half-life of 150 min

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  18. Ƒ

    Molecules, atoms, quarks, and so on

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  19. S

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  20. A

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  21. P

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  22. N

    Preparing Atoms in Hyperfine State F=2: Optically Pumping?

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  23. N

    The potential energy of two atoms-

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  24. G

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  25. T

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  26. QuarkCharmer

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  27. C

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  28. B

    Exploring Light and Atoms: A Scientific Inquiry

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  29. N

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  30. J

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  31. N

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  32. W

    Do Atoms Get Destroyed When Metal Melts?

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  33. D

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  34. C

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  35. B

    Fermi Energy of Non-Interacting Identical Li Atoms in a 3D Harmonic Potential Well

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  36. C

    Atoms contained in a human body

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  37. B

    Why Do Atoms Bond? Understanding Molecular Bonds

    Can someone post a picture of 2 bonded atoms... But not those googled ones. I am trying to understand how does that look at molecular level. Why would 2 atoms bond to form a molecule. eg. hydrogen, covalent bond. I know now 2 atoms of hydrogen have full shell, but that electron doesn't...
  38. A

    Why do the PE of atoms decrease when they form bonds

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  39. B

    Lennard-Jones potential for 3 atoms

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  40. S

    How is the Energy of a Star's Atoms Calculated and Related to its Temperature?

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  41. C

    Hydrocarbons have different structures but the same atoms

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  42. W

    Physics - Thermodynamics - Pressure caused by Nitrogen atoms hitting a surface

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  43. B

    Historical qustion-models of atoms

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  44. K

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  45. N

    If you don't believe in atoms

    Hello, Someone I know doesn't believe in atoms. I know it sounds strange: the person acknowledges that the model that is used is useful for calculations, but apparently the idea of an atom sounds "too perfect". And apparently the structure of an atom lattice is also too perfect. But aren't...
  46. A

    Why Carbon Atoms Don't Form Square or Triangular Rings

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  47. S

    Do Atoms Exist in All Vacuums?

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  48. E

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  49. S

    What is the optimal basis set for a full CI calculation of low Z elements?

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  50. L

    Does nuclear decay apply to atoms of matter consumed by black holes?

    I can offer no further insight.
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