Introduction
The periodic table may be the grand slam of science, the greatest single accomplishment of theoretical chemistry and physics. It gives an amazing amount of organized, certain information about all matter at the atomic level or larger, in spite of the fact that our knowledge of subatomic particles and interactions is
incomplete.
The periodic table of the chemical elements (also periodic table of the elements or just the periodic table) is a tabular display of the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
The periodic table is now ubiquitous within the academic discipline of chemistry, providing a useful framework to classify, systematize, and compare all of the many different forms of chemical behavior. The table has found many applications in chemistry, physics, biology, and engineering, especially chemical engineering....
[various representations of the Periodic Table are available at http://www.google.com/images?rlz=1T4ADFA_enUS364US393&q=%22periodic+table%22+of+elements&um=1&ie=UTF-8&source=univ&sa=X&ei=lFZnTd7aJcH78Aab3ej2Cw&ved=0CFEQsAQ&biw=1003&bih=539 ]
The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table. It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows.
http://en.wikipedia.org/wiki/Periodic_table
The periodic table is organized in rows and columns called Periods and Groups respectively. Each row (period) in the table corresponds to the filling of a quantum shell of electrons. The elements in a group have similar configurations of the outermost electron shells of their atoms (most chemical properties are dominated by the orbital location of the outermost electron). See http://knol.google.com/k/spiros-karos/periodic-table-of-elements/2jszrulazj6wg/88# for more details on the meaning of groups and periods.
http://wiki.answers.com/Q/How_do_elements_get_into_the_periodic_table_of_elements
atomic number – In the modern periodic table, the elements are actually arranged in order of increasing atomic number--that's the number of protons in one atom of a particular element. An undisturbed atom is electrically neutral, so the number of electrons in it is the same as its atomic number.
Atomic weight almost always increases with atomic number, so Mendeleev's sequence of elements was almost exactly the same as the one used today, though there are a couple of weird exceptions. In general, it's correct to think of atoms getting heavier as you go down a column or to the right across a row.
http://www.colorado.edu/physics/2000/periodic_table/atomic_number.html
= = = = = = = = = = = = = = = = = = = =
Atomic weight
Atomic weight includes the combined mass of the element's protons, electrons and neutrons. Most elements have isotopes – that means that some atoms have a certain number of neutrons and others have a different number of neutrons. Normally this is a discrete distribution of a specific number of neutrons (which is to say that neutrons are not randomly distributed within an element – certain isotopes prevail). Hafnium, for example, is “further down” the periodic table than zirconium, but it is “lighter” because it has a mixture of isotopes with fewer neutrons than does zirconium. This is a rare exception to the general rule that the further down or to the right an element is on the periodic table, the greater is the atomic weight.
Different celestial bodies have different mixtures of isotopes for the elements. The “atomic weight” for an element of Earth's copper, for example, is slightly but universally different than the atomic weight of copper from a meteor that originated on Mars. This would not match the atomic weight of copper from a meteor originating from Venus. Thus, through laboratory analysis, we can tell whether a rock is natural to the Earth or of non-terrestrial origin. The exception here deals with rocks from Earth and Earth's Moon. We know from the NASA Apollo missions and the rocks brought back to Earth that these have the same distribution of isotopes and the same atomic weight element by element as elements of Earth. This proves that the Earth and Moon were once a single planetary body before a collision separated them. No other explanation is reasonable.
Shell levels
Particles have “mass.” The larger the particle, the more mass they have. Particles always move in wave formation. Suppose we have a steel sphere we roll from point A to point B. It may appear to move in a straight line, but we know from physics that in moves in a wave-- both above and below a straight line rolling from A to B. The larger this sphere, the more relatively tiny is the wave action. We can ignore the wave action of particles for large items and use Euclidean geometry when talking about size and motion. But for subatomic chemistry, this common sense approach doesn't work. A tiny electron revolves around a proton. To find the electron, we would have to pump energy or radiation into it, which moves it significantly. So there is no real-time way to know exactly where the electron is. This peculiarity is called the Heisenberg uncertainty principle. For hydrogen, an element with a single proton, the electron is located at the surface of a spherical cloud forming essentially a spherical shell around the proton. For helium, there are two protons and thus two electrons, which are located on the surface of two egg-shaped clouds around the protons.
As elements get larger (because of a greater number of protons at the center), the shape of the orbital probability spheres changes from spherical to egg-shaped to tear-drop shaped around the core of the atom. There is a critical point here that cannot be underestimated in its significance: though we don't know the exact location of the electrons, we do know that they are located at the surface of the sphere or egg or teardrop and not in between. If we excite an electron orbiting in a spherical manner, it will stay where it is until the energy it is receiving allows it to jump to an egg-shaped orbital. If we excite it further it will jump to a teardrop orbital when, but only when, it has enough energy. There are names for these orbital shapes: s, p, d, and f (and, theoretically, g, h, i and k). These orbitals are discrete – electrons only move their orbital shape when the move from one shape to another. They don't dance around in between these distinct shapes. An example is a neon light. We take neon gas and pump electrons through it. Some electrons replace those already existing in the outer shell of the neon atom. With enough energy, they “bump” the orbit to a larger and different probability shape. When this happens, they are primed for returning to their normal shape, and when this happens, they reduce their energy, return to the smaller and normal orbital, and expend the spare energy by emitting a photon. This is how neon (and other fluorescent) lights work.
As noted above, we can't know exactly where an electron is, but we can know what the orbit looks like and what the size of that orbital is. Another critical advantage is that we can assume that all of the inner shells of an elemental atom are stable. The outer shell is doing all the swapping and energy transfers; so, electrically and chemically, an element is defined by this outer shell (and its tendency to shrug off or accept spare electrons – its valence). The outer shell is termed the valence shell, and this is plain from simply looking at a periodic table and noting where, by row and column, that element is located.
These ideas are presented along with some complex mathematical concepts and a probability animated diagram at Wikipedia's “atomic orbital” topic at this link: http://en.wikipedia.org/wiki/Atomic_orbital
[this concludes the section of the discussion written by the blog author, who is also responsible for the brief introduction at the beginning of this piece and the concluding footnote]
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
A block of the periodic table of elements is a set of adjacent groups. The term appears to have been first used (in French) by Charles Janet. The respective highest-energy electrons in each element in a block belong to the same atomic orbital type. Each block is named after its characteristic orbital; thus, the blocks are:
The following is the order for filling the "subshell" orbitals, according to the Aufbau principle, which also gives the linear order of the "blocks" (as atomic number increases) in the periodic table:
For discussion of the nature of why the energies of the blocks naturally appear in this order in complex atoms, see atomic orbital and electron configuration.
http://en.wikipedia.org/wiki/Periodic_table_block
= = = = = = = = = = = = = = = = = =
Footnote
Charles Janet (1849-1932) devised a periodic chart which flows easily and without breaks through the increasing shell levels. Janet also conceived of an element “zero” consisting of two neutrons (with no electrons nor protons) as well as negative matter in a negative periodic table, in other words, he correctly theorized the existence of anti-matter. Janet died in 1932, just before the discovery of the neutron, the positron [itself the first known anti-matter particle] and heavy hydrogen (which is a hydrogen elemental atom with a second neutron). See http://en.wikipedia.org/wiki/Charles_Janet – the special periodic chart at this link shows the elements in clear, increasing shell order. Janet's correct speculations, though he was neither a physicist nor a chemist, show the intuitive power and probable truth to his model of the periodic table of the elements. His correct speculation of the existence of antimatter commands high respect.
The periodic table may be the grand slam of science, the greatest single accomplishment of theoretical chemistry and physics. It gives an amazing amount of organized, certain information about all matter at the atomic level or larger, in spite of the fact that our knowledge of subatomic particles and interactions is
incomplete.
The periodic table of the chemical elements (also periodic table of the elements or just the periodic table) is a tabular display of the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
The periodic table is now ubiquitous within the academic discipline of chemistry, providing a useful framework to classify, systematize, and compare all of the many different forms of chemical behavior. The table has found many applications in chemistry, physics, biology, and engineering, especially chemical engineering....
[various representations of the Periodic Table are available at http://www.google.com/images?rlz=1T4ADFA_enUS364US393&q=%22periodic+table%22+of+elements&um=1&ie=UTF-8&source=univ&sa=X&ei=lFZnTd7aJcH78Aab3ej2Cw&ved=0CFEQsAQ&biw=1003&bih=539 ]
The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table. It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows.
http://en.wikipedia.org/wiki/Periodic_table
The periodic table is organized in rows and columns called Periods and Groups respectively. Each row (period) in the table corresponds to the filling of a quantum shell of electrons. The elements in a group have similar configurations of the outermost electron shells of their atoms (most chemical properties are dominated by the orbital location of the outermost electron). See http://knol.google.com/k/spiros-karos/periodic-table-of-elements/2jszrulazj6wg/88# for more details on the meaning of groups and periods.
http://wiki.answers.com/Q/How_do_elements_get_into_the_periodic_table_of_elements
atomic number – In the modern periodic table, the elements are actually arranged in order of increasing atomic number--that's the number of protons in one atom of a particular element. An undisturbed atom is electrically neutral, so the number of electrons in it is the same as its atomic number.
Atomic weight almost always increases with atomic number, so Mendeleev's sequence of elements was almost exactly the same as the one used today, though there are a couple of weird exceptions. In general, it's correct to think of atoms getting heavier as you go down a column or to the right across a row.
http://www.colorado.edu/physics/2000/periodic_table/atomic_number.html
= = = = = = = = = = = = = = = = = = = =
Atomic weight
Atomic weight includes the combined mass of the element's protons, electrons and neutrons. Most elements have isotopes – that means that some atoms have a certain number of neutrons and others have a different number of neutrons. Normally this is a discrete distribution of a specific number of neutrons (which is to say that neutrons are not randomly distributed within an element – certain isotopes prevail). Hafnium, for example, is “further down” the periodic table than zirconium, but it is “lighter” because it has a mixture of isotopes with fewer neutrons than does zirconium. This is a rare exception to the general rule that the further down or to the right an element is on the periodic table, the greater is the atomic weight.
Different celestial bodies have different mixtures of isotopes for the elements. The “atomic weight” for an element of Earth's copper, for example, is slightly but universally different than the atomic weight of copper from a meteor that originated on Mars. This would not match the atomic weight of copper from a meteor originating from Venus. Thus, through laboratory analysis, we can tell whether a rock is natural to the Earth or of non-terrestrial origin. The exception here deals with rocks from Earth and Earth's Moon. We know from the NASA Apollo missions and the rocks brought back to Earth that these have the same distribution of isotopes and the same atomic weight element by element as elements of Earth. This proves that the Earth and Moon were once a single planetary body before a collision separated them. No other explanation is reasonable.
Shell levels
Particles have “mass.” The larger the particle, the more mass they have. Particles always move in wave formation. Suppose we have a steel sphere we roll from point A to point B. It may appear to move in a straight line, but we know from physics that in moves in a wave-- both above and below a straight line rolling from A to B. The larger this sphere, the more relatively tiny is the wave action. We can ignore the wave action of particles for large items and use Euclidean geometry when talking about size and motion. But for subatomic chemistry, this common sense approach doesn't work. A tiny electron revolves around a proton. To find the electron, we would have to pump energy or radiation into it, which moves it significantly. So there is no real-time way to know exactly where the electron is. This peculiarity is called the Heisenberg uncertainty principle. For hydrogen, an element with a single proton, the electron is located at the surface of a spherical cloud forming essentially a spherical shell around the proton. For helium, there are two protons and thus two electrons, which are located on the surface of two egg-shaped clouds around the protons.
As elements get larger (because of a greater number of protons at the center), the shape of the orbital probability spheres changes from spherical to egg-shaped to tear-drop shaped around the core of the atom. There is a critical point here that cannot be underestimated in its significance: though we don't know the exact location of the electrons, we do know that they are located at the surface of the sphere or egg or teardrop and not in between. If we excite an electron orbiting in a spherical manner, it will stay where it is until the energy it is receiving allows it to jump to an egg-shaped orbital. If we excite it further it will jump to a teardrop orbital when, but only when, it has enough energy. There are names for these orbital shapes: s, p, d, and f (and, theoretically, g, h, i and k). These orbitals are discrete – electrons only move their orbital shape when the move from one shape to another. They don't dance around in between these distinct shapes. An example is a neon light. We take neon gas and pump electrons through it. Some electrons replace those already existing in the outer shell of the neon atom. With enough energy, they “bump” the orbit to a larger and different probability shape. When this happens, they are primed for returning to their normal shape, and when this happens, they reduce their energy, return to the smaller and normal orbital, and expend the spare energy by emitting a photon. This is how neon (and other fluorescent) lights work.
As noted above, we can't know exactly where an electron is, but we can know what the orbit looks like and what the size of that orbital is. Another critical advantage is that we can assume that all of the inner shells of an elemental atom are stable. The outer shell is doing all the swapping and energy transfers; so, electrically and chemically, an element is defined by this outer shell (and its tendency to shrug off or accept spare electrons – its valence). The outer shell is termed the valence shell, and this is plain from simply looking at a periodic table and noting where, by row and column, that element is located.
These ideas are presented along with some complex mathematical concepts and a probability animated diagram at Wikipedia's “atomic orbital” topic at this link: http://en.wikipedia.org/wiki/Atomic_orbital
“Blocks” of Shell levels
[this concludes the section of the discussion written by the blog author, who is also responsible for the brief introduction at the beginning of this piece and the concluding footnote]
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
A block of the periodic table of elements is a set of adjacent groups. The term appears to have been first used (in French) by Charles Janet. The respective highest-energy electrons in each element in a block belong to the same atomic orbital type. Each block is named after its characteristic orbital; thus, the blocks are:
- g-block (hypothetical)
The following is the order for filling the "subshell" orbitals, according to the Aufbau principle, which also gives the linear order of the "blocks" (as atomic number increases) in the periodic table:
- 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, ...
For discussion of the nature of why the energies of the blocks naturally appear in this order in complex atoms, see atomic orbital and electron configuration.
http://en.wikipedia.org/wiki/Periodic_table_block
= = = = = = = = = = = = = = = = = =
Footnote
Charles Janet (1849-1932) devised a periodic chart which flows easily and without breaks through the increasing shell levels. Janet also conceived of an element “zero” consisting of two neutrons (with no electrons nor protons) as well as negative matter in a negative periodic table, in other words, he correctly theorized the existence of anti-matter. Janet died in 1932, just before the discovery of the neutron, the positron [itself the first known anti-matter particle] and heavy hydrogen (which is a hydrogen elemental atom with a second neutron). See http://en.wikipedia.org/wiki/Charles_Janet – the special periodic chart at this link shows the elements in clear, increasing shell order. Janet's correct speculations, though he was neither a physicist nor a chemist, show the intuitive power and probable truth to his model of the periodic table of the elements. His correct speculation of the existence of antimatter commands high respect.
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