What determines the lenght of each period in the periodic table?

Answer 1

The number of elements in each period is the sum of (1) the maximum number of electrons permitted in the quantum state characterized by the same number as the number of the period and (2) the maximum number of electrons permitted in a quantum state characterized by a lower quantum than the number of the period but with an energy level for the electron that is less than the energy state of the next electron that can be added to the highest numbered quantum level of the atom with an atomic number lower by one than the atomic number of the atom concerned.

A somewhat oversimplified explanation of this rather complicated rule follows:

Item (2) of the rule occurs only in periods 4 and higher, because the third quantum number is the lowest one that can contain d electrons. In argon, with atomic number 18, the first three quantum levels contain all the s and p electrons that are allowed. Another electron is required to form potassium, which contains 19 protons, and it happens that a 4s electron has a lower energy than a 3d electron, so that the two allowed s electrons with quantum number 4 are added to form potassium and calcium successively. However a 4p electron has more energy than a 3d electron; therefore, the ten 3d electrons are added successively to form the elements with atomic numbers from 21 to 30, the first transition metals, before a 4d electron is added to form gallium, with atomic number 31.

A similar situation arises in period 6 to form the inner transition elements. Although the fourth period is allowed to contain f electrons, their energy level is higher than that of 5s, 5p, 5d, and 6s electrons, so that no f electrons are present in atoms of the first five periods in their ground states. However, at atomic number 56, all of the s, p, and d quantum states of the first five quantum numbers have been occupied, and it happens that the energy of the first 4felectron is lower than that of the first 6p electron. Therefore, the 4f quantum level is filled with all of its electrons, from atomic numbers 57 through 71, and only then is n 6p electron added to form an atom with atomic number 72.

A corresponding phenomenon occurs again in the 7th period, since the 5f orbitals have lower energies than the 7porbitals.

The above explanation is oversimplified because not all f orbitals with the same quantum number have exactly the same energy, so that there can be instances in the transition and inner transition elements in which the "next" f electron has higher energy than the "next" p electron with a quantum number higher by two. Therefore, a few of the transition elements contain one or more p electrons of their highest orbital number instead of one or more of the f electrons that would be expected from the discussion above.

Answer 2

The length of each period is determined by the energy levels that are filling with electrons. For example, H and He are the only elements in Period 1. That's because only the 1s orbital is being filled, and it can have a maximum of two electrons. In the 2nd period, the 1s, 2s, and 2p energy levels are filling with electrons as you move from left to right across the period. Neon, the noble gas at the end of the 2nd period, has the maximum number of electrons allowed for that level. It's electron configuration is 1s22s22p6 with a total of 8 electrons in the 2nd energy level, and there are 8 elements in that period. As subsequent periods are added to the Periodic Table, they get longer because the numbers of energy levels that are being filled increase. If you do a search for periodic tables with electron configurations, you can find several that you may like to print out.

Answer 3

The number of electrons determines the number on the periodic table

Answer 4

The length of each period is determined by the number of electrons that can occupy the sublevels being filled in that period.

Answer 5

The length of each period is determined by the number of electrons that can occupy the sublevels being filled in that period.

Answer 6

By the number of (valence electrons) the element contains.