perodic table(元素周期表)

Please look at question 2 first, or else you can not understand the answer, THANKS

Question 1: It is because both groups A and B have the same number of valence electron in the outer-most shell. But the valence electrons are in different orbitals.

Group A - States the outer most electrons are in S,P oribitals

Example : Group V A = the elements have 5 valence electrons in its P orbital (N,P,As).

Group B- States the outer most electrons in D obitals

Example: Group V B = the elements have 5 valence electrons in its D orbital (V,Nb,Ta).

The reason behind calling them Group A and B is because it would cause confusion when when we just say group V, you can never distingish one are they talking about, is is V or N ?? the transition metal? or the gas?

You can try this on Groups I a+b

Question 2: Transition metal have a very special propertise, as you know the electron configuration of them is normally [Ar] 4s2 3dX (X can be any number according to their atomic number.) You can see the electrons go into 4S-orbitals first, instead of 3d orbitals, that is becasuse 4s orbial has a lower energy level than the 3d orbitals. After the 3d orbitals are filled the electrons goes back to 4p orbials

Therefore in order to give a correct interpretation of how electrons are placed in the outer shells, the d block elements MUST be place between s and p block, because electrons goes into orbitals in the order:

1.4s (2)
2.3d (10)
3.4p (6)
then higher energy levels

2007-12-13 09:53:19 補充：
You may question about the how can it have 5 electrons on the outer-most shell, while there is only 3 electrons in the outermost shell?The answer that since 4s orbitals are so close to 3d orbitals electrons can travel between them.

2007-12-13 09:53:34 補充：
There is a good animation for you to look at. http://www.webelements.com/webelements/elements/text/Sm/econ.htmlMake you atomic number increase from 18 to 36 then you will know about it.

2007-12-13 09:53:45 補充：
There is a good animation for you to look at. http://www.webelements.com/webelements/elements/text/Sm/econ.htmlMake your atomic number increase from 18 to 36 then you will know about it.

Q1)

There is considerable confusion surrounding the two old systems in use (old IUPAC and CAS) that combined the use of Roman numerals with letters. In the old IUPAC system the letters A and B were designated to the left (A) and right (B) part of the table, while in the CAS system the letters A and B were designated to main group elements (A) and transition elements (B). The former system was frequently used in Europe while the latter was most common in America. The new IUPAC scheme was developed to replace both systems as they confusingly used the same names to mean different things.

The periodic table groups are as follows (in the brackets are shown the old systems: European and American):

Group 1 (IA,IA): the alkali metals or hydrogen family/lithium family
Group 2 (IIA,IIA): the alkaline earth metals or beryllium family
Group 3 (IIIA,IIIB): the scandium family
Group 4 (IVA,IVB): the titanium family
Group 5 (VA,VB): the vanadium family
Group 6 (VIA,VIB): the chromium family
Group 7 (VIIA,VIIB): the manganese family
Group 8 (VIII, VIIIB): the iron family
Group 9 (VIII, VIIIB): the cobalt family
Group 10 (VIII, VIIIB): the nickel family
Group 11 (IB,IB): the coinage metals (not an IUPAC-recommended name) or copper family
Group 12 (IIB,IIB): the zinc family
Group 13 (IIIB,IIIA): the boron family
Group 14 (IVB,IVA): the carbon family
Group 15 (VB,VA): the pnictogens (not an IUPAC-recommended name) or nitrogen family
Group 16 (VIB,VIA): the chalcogens or oxygen family
Group 17 (VIIB,VIIA): the halogens or fluorine family
Group 18 (Group 0): the noble gases or helium family/neon family

2)

With the development of modern quantum mechanical theories of electron configuration within atoms, it became apparent that each horizontal row ("period") in the table corresponded to the filling of a quantum shell of electrons. In Mendeleev's original table, each period was the same length. Modern tables have progressively longer periods further down the table, and group the elements into s-, p-, d- and f-blocks to reflect our understanding of their electron configuration.

The total number of electron shells an atom has determines the period to which it belongs. Each shell is divided into different subshells, which as atomic number increases are filled in roughly this order (the Aufbau principle). Hence the structure of the table.

For example in row 4, 3d orbital is filled before 4p orbital, hence d block is placed between s and p block.