Atom (science): Difference between revisions
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Atoms are made of a dense [[nucleus]] formed by the two [[nucleons]] (positively charged [[protons]] and zero charge [[neutrons]]) and surrounded by a much larger "cloud" of [[electrons]]. The number of protons contained in the nucleus determines the [[atomic number]] and in turn which [[element]] it is classified as. The number of neutrons further specifies the [[isotope]] number of that element. The number of electrons surrounding the nucleus is typically assumed to be equal to the number of protons in order to keep the entire atom electrically neutral. Atoms that are not neutral are called [[ions]], they are designated by their [[charge]] in units of [[elementary charge]], which is equal to the negative of the number of surplus electrons present around the atom. Thus an atom with one extra electron is charged -1, and one missing is charged +1. | Atoms are made of a dense [[nucleus]] formed by the two [[nucleons]] (positively charged [[protons]] and zero charge [[neutrons]]) and surrounded by a much larger "cloud" of [[electrons]]. The number of protons contained in the nucleus determines the [[atomic number]] and in turn which [[element]] it is classified as. The number of neutrons further specifies the [[isotope]] number of that element. The number of electrons surrounding the nucleus is typically assumed to be equal to the number of protons in order to keep the entire atom electrically neutral. Atoms that are not neutral are called [[ions]], they are designated by their [[charge]] in units of [[elementary charge]], which is equal to the negative of the number of surplus electrons present around the atom. Thus an atom with one extra electron is charged -1, and one missing is charged +1. | ||
=== Forces in the atom === | |||
The nucleus of the atom contains a high concentration of positively charged particles with no counter balancing negatively charged particles to keep it stable. In order to explain the existence of the nucleus scientists introduced the two [[nuclear forces]], the [[strong force]] and the [[weak force]]. We now understand that the nucleus is held together by the [[residual strong force]] despite its significant positive charge. The electrons which surround the atom are [[electromagnetism|electro-statically]] attracted to the nucleus due to their negative charge. | The nucleus of the atom contains a high concentration of positively charged particles with no counter balancing negatively charged particles to keep it stable. In order to explain the existence of the nucleus scientists introduced the two [[nuclear forces]], the [[strong force]] and the [[weak force]]. We now understand that the nucleus is held together by the [[residual strong force]] despite its significant positive charge. The electrons which surround the atom are [[electromagnetism|electro-statically]] attracted to the nucleus due to their negative charge. | ||
=== Electron Quantum States === | |||
=== Nuclei Quantum States === | |||
=== Decay === | |||
Most combinations of nucleons are inherently unstable and undergo a number of [[radioactive decays|radiation]] in order to form more stable nuclei. In all of the common decays a particle is emitted from the nucleus in order to compensate for some instability in the atom. | Most combinations of nucleons are inherently unstable and undergo a number of [[radioactive decays|radiation]] in order to form more stable nuclei. In all of the common decays a particle is emitted from the nucleus in order to compensate for some instability in the atom. | ||
* [[Alpha decay]] most frequently occurs in atoms which are simply too big, atoms are limited in size because the [[residual strong force]] which holds them together only acts over very small distances so that the rate of electrostatic repulsion grows faster than the rate of strong attraction as the nucleus grows. Alpha decay emits an [Alpha particle]] which is denoted with the [[Greek]] letter α. | * [[Alpha decay]] most frequently occurs in atoms which are simply too big, atoms are limited in size because the [[residual strong force]] which holds them together only acts over very small distances so that the rate of electrostatic repulsion grows faster than the rate of strong attraction as the nucleus grows. Alpha decay emits an [[Alpha particle]] which is denoted with the [[Greek]] letter α. | ||
* [[Beta+ decay]] | * [[Beta+ decay]] | ||
* [[Beta- decay]] | * [[Beta- decay]] | ||
* [[Gamma decay]] | * [[Gamma decay]] | ||
== History of the Atom == | == History of the Atom == | ||
=== J.J. | === J.J. Thomson "Plum Pudding" Model === | ||
The first widely accepted model of the atom was J.J | The first widely accepted model of the atom was J.J Thomson's Model of a positively charged cloud with electrons interspersed throughout. | ||
=== Rutherford Model === | === Rutherford Model === | ||
Ernest Rutherford, one of Thomson's students, disproved his theory by showing that there was a small positively charged core in each atom, disproving Thomson's model. Rutherford posited that the structure of an atom more closely resembled a solar system with the nucleus at the center and electrons orbiting around it. | |||
=== Today's view === | |||
For most practical purposes Rutherford's model has proven an acceptable approximation, however the quantum mechanical interpretation is that the | |||
== See Also == | == See Also == | ||
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== External links == | == External links == | ||
[http://www.aip.org/history/electron/jjelectr.htm] | |||
[[Category:CZ Live]] | [[Category:CZ Live]] | ||
[[Category:Physics Workgroup]] | [[Category:Physics Workgroup]] | ||
Revision as of 12:31, 31 October 2007
An atom (from the Greek atomos, indivisible) is the smallest physical unit that can retain its chemical properties. While atoms were once thought to be the smallest instances of mass in the universe, we now know that they are made up of smaller subatomic-particles.
Structure of the Atom
Atoms are made of a dense nucleus formed by the two nucleons (positively charged protons and zero charge neutrons) and surrounded by a much larger "cloud" of electrons. The number of protons contained in the nucleus determines the atomic number and in turn which element it is classified as. The number of neutrons further specifies the isotope number of that element. The number of electrons surrounding the nucleus is typically assumed to be equal to the number of protons in order to keep the entire atom electrically neutral. Atoms that are not neutral are called ions, they are designated by their charge in units of elementary charge, which is equal to the negative of the number of surplus electrons present around the atom. Thus an atom with one extra electron is charged -1, and one missing is charged +1.
Forces in the atom
The nucleus of the atom contains a high concentration of positively charged particles with no counter balancing negatively charged particles to keep it stable. In order to explain the existence of the nucleus scientists introduced the two nuclear forces, the strong force and the weak force. We now understand that the nucleus is held together by the residual strong force despite its significant positive charge. The electrons which surround the atom are electro-statically attracted to the nucleus due to their negative charge.
Electron Quantum States
Nuclei Quantum States
Decay
Most combinations of nucleons are inherently unstable and undergo a number of radiation in order to form more stable nuclei. In all of the common decays a particle is emitted from the nucleus in order to compensate for some instability in the atom.
- Alpha decay most frequently occurs in atoms which are simply too big, atoms are limited in size because the residual strong force which holds them together only acts over very small distances so that the rate of electrostatic repulsion grows faster than the rate of strong attraction as the nucleus grows. Alpha decay emits an Alpha particle which is denoted with the Greek letter α.
- Beta+ decay
- Beta- decay
- Gamma decay
History of the Atom
J.J. Thomson "Plum Pudding" Model
The first widely accepted model of the atom was J.J Thomson's Model of a positively charged cloud with electrons interspersed throughout.
Rutherford Model
Ernest Rutherford, one of Thomson's students, disproved his theory by showing that there was a small positively charged core in each atom, disproving Thomson's model. Rutherford posited that the structure of an atom more closely resembled a solar system with the nucleus at the center and electrons orbiting around it.
Today's view
For most practical purposes Rutherford's model has proven an acceptable approximation, however the quantum mechanical interpretation is that the