This alkali metal is Rubidium Rb, having atomic no 37
The d suborbitals begin at period 4, but the d-sublevel is actually 3d. The first element is scandium, which has the atomic number of 21.
Electrons occupy orbitals in a definite sequence, filling orbitals with lower energies first. Generally, orbitals in a lower energy level have lower energies than those in a higher energy level. But, in the third level the energy ranges of the principal energy levels begin to overlap. As a result, the 4s sublevel is lower in energy than the 3d sublevel, so it fills first.
In the ground state of a chromium atom (atomic number 24), the electron configuration is [Ar] 3d^5 4s^1, with 5 electrons in the 3d sublevel and 1 electron in the 4s sublevel. This configuration is due to the stability achieved by half-filling the 3d sublevel before completely filling the 4s sublevel.
5
CARBON
The element that completes the 7s sublevel is radium, with the electron configuration 7s2.
The 2p sublevel is completed with six electrons and is found in elements from carbon (C) onwards. The seventh element, nitrogen (N), is the element that completes the 2p sublevel.
The 3p sublevel is completed by the noble gas element Argon (Ar) which has 18 electrons in total.
B. 1s22s22p63s23p64s23d5----Chromium: [Ar]1s22s22p63s23p63d54s1Manganese: [Ar]1s22s22p63s23p63d54s2
1s2 2s2 2p6 3s2 3p6 4s2 3d5
The 5p sublevel is completed with 6 electrons with the addition of the element radon (Rn).
The correct electron configuration would be 3d5 as each orbital in the 3d sublevel can hold up to 2 electrons, and we have 5 electrons to place in this sublevel.
The 3d sublevel is not filled until after the 4s sublevel, because the 3d sublevel has more energy than the 4s sublevel, and less energy than the 4p sublevel.
The 2s sublevel can hold a maximum of 2 electrons.
Chromium
The d suborbitals begin at period 4, but the d-sublevel is actually 3d. The first element is scandium, which has the atomic number of 21.
Calcium is the element that has 2 electrons in the 4s sublevel.