Answer is: the two electrons in the fourth shell.
Atomic number of calcium is 20, it means that it has 20 protons and 20 electrons, so atom of calcium is neutral.
Electron configuration of calcium atom: ₂₀Ca 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²; calcium has two valence electrons (4s²).
In reactions it lose those two electrons ang form cation with positive charge 2+.
Atomic number is the number of protons, which is characteristic of a chemical element.
Beryllium, magnesium,calcium and strontium are alkaline earth metals. The elements have very similar properties.
Alkaline earth metals have in common an outer s- electron shell (two electrons).
Valence electrons have the greatest effect on the chemical properties of calcium
Electrons can move the shell up or down by releasing energy or absorbing energy
Excited electrons show higher electron transfer to the shell by absorbing energy
So it can be concluded that there are 2 conditions:
Ground state is the state of electrons filling skins with the lowest energy levels.
Excited state is the state of electrons which occupies a higher energy level
The state of excited electrons can be seen from the presence of electrons which do not fill the skin completely but fill the skin afterwards
Ca has atomic number 20 so the electron configuration is:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
This configuration can be said in Ground state conditions
Elemental properties can be determined by its valence electrons (electrons which fill electrons in the outer shell)
The valence electrons of an element indicate in what group and period the element is located in the periodic system so that its properties can be determined
The period of an element is determined from the valence shell (the biggest main quantum number (n) )
Groups of chemical elements are divided into two, namely:
Group A, occupying sub shell s and p
Group B, occupying sub shell d
If we look at valence electrons from Ca atoms then:
So that the Ca Atom is located in the alkaline earth group, together with beryllium (Be), magnesium (Mg), strontium (Sr), barium (Ba), and radium (Ra)
So the chemical properties of calcium :
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