Each shell represents a distinct state of electron energy.
Each shell represents a different energy level, and a different distance from the nucleus.
Because they have only one electron in their valency shell. The second oxidation state would require the atom to lose an electron from its penultimate shell which is full.
The electron configuration for a ground-state potassium atom is 1s22s22p63s23p64s1. The noble gas shorthand configuration is [Ar]4s1.
One electron is "borrowed" from the 4s shell to completely fill up the 3d shell. This is as the nearness of the energy between the two shells results in blurring of the order of electron selection. The same thing happens in chromium.
All electron shells represent an energy level - it doesn't matter if its the outermost shell or not. In order for there to be a release of energy the electron has to be coming from a higher energy state. The only energy state higher than the outer-most electron shell would be a free electron. The only way an electron becomes a free electron is that sufficient was provided to lift it from what-ever electron shell (energy level) it was previously in to escape velocity. The energy that it then releases in returning is then this exact same amount of energy.
Outer most shell of Mn contain 2 electron in 4s orbital and 5 unpaired electron in 3d orbital hence in exiting state it has 7 unpaired electron. Thus It shown number of oxidation state................... 0, +2, +3, +4, +6, +7 etc.
The key to "happiness" for an atom is a full outer electron shell. (The outer electron shell is called the valence shell.) There are two conditions that cause a shell not to be full. Either it has only an electron or two (or three) in the outer electron shell or it's short an electron or two in that outer shell. The direct answer to the question is that if an element is chemically active, its outer electron shell is incomplete or is not full.
It represents an Energy State
The groundstate for Sodium (11-Na) is: 1S2 , 2S2, 2P6, 3S1 If you count the ^powers you notice it'll sum to 11, when Sodium is excited the outermost electron (3S1) will be excited from the 3S shell to the next shell up which is the 3P shell. The "core" electron configuration doesn't change so the first excited state is simply: 1S2 , 2S2, 2P6, 3P1 For the next excited state the electron that is now in the 3P shell will transition to the 4S shell before the 3D shell
An electron in the third shell has more energy than an electron in the second shell.
Because they have only one electron in their valency shell. The second oxidation state would require the atom to lose an electron from its penultimate shell which is full.
2-2-1
To fill their electron shells - this represents a lower energy state.
Gallium, or Ga has an electron configuration that begins with the base state of [Ar]. The outer shell is then 4s2 3d10 4p1
The inner, or K shell, of the electron cloud has the least energy.
This electron configuration represents Sr or Strontium. 2-8-18-7-3 represents Sr in the excited state; 2-8-18-8-2 represents Sr in the ground state.
Sodium is an alkali metal. All alkali metals have 1 electron in the valence shell. This means that the "desired state" is to have a full valence shell configuration. So, in order for sodium and other alkali metals to reach this state, it has to LOSE one electron, making it a positive ion (cation).
The electron configuration for a ground-state potassium atom is 1s22s22p63s23p64s1. The noble gas shorthand configuration is [Ar]4s1.