I don't understand what valence electrons and core electrons are.
Ex: Se = 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
What makes 4s2 and 4p4 valence electrons and the rest core
Valence electrons are those in the outside shell, usually, and sometimes the last two shells.
Na is 1s2 2s2 2p6 3s1 and the 3s1 is the valence electron. YOu know that to be true since Na has a valence of +1 (always).
Mg is 1s2 2s2 2p6 3s2 Mg has a valence of +2 (always) and that is because it can lose the last two electrons in the 4s orbital.
Valence electrons are the electrons located in the outermost energy level of an atom. These electrons are involved in the chemical reactions and bonding of atoms. Core electrons, on the other hand, are the electrons that are located in the inner energy levels or shells of an atom. They are not involved in chemical reactions or bonding.
In the example you provided (Se = 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4), the electron configuration shows the distribution of electrons within the energy levels or shells of a selenium (Se) atom.
The valence electrons in this case are the electrons in the outermost energy level, which are the 4s2 and 4p4 electrons. Therefore, selenium has a total of 6 valence electrons (2 from the 4s sublevel and 4 from the 4p sublevel). These valence electrons are the ones involved in chemical reactions and bonding with other atoms.
The remaining electrons (1s2, 2s2, 2p6, 3s2, 3p6, 3d10) are the core electrons. They are located in the inner energy levels and are not involved in chemical reactions or bonding; they mainly contribute to the stability of the atom.
Valence electrons are the electrons located in the outermost energy level (shell) of an atom. They are the electrons involved in chemical reactions and determine the chemical behavior of an element. Core electrons, on the other hand, are the electrons located in the inner energy levels (shells) of an atom.
In the example you provided (Se = 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4), we can identify the valence electrons and core electrons by looking at the electron configuration.
The electron configuration shows how the electrons are distributed in each energy level and sublevel of an atom. In the case of Selenium (Se), the electron configuration is:
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
In this configuration, we can see that the outermost energy level is the fourth energy level (n=4), which contains the sublevels 4s, 3d, and 4p.
The electrons in the 4s and 4p sublevels are considered valence electrons because they are located in the outermost energy level. In this case, there are 2 electrons in the 4s sublevel (4s2) and 4 electrons in the 4p sublevel (4p4), making a total of 6 valence electrons.
The electrons in the 1s, 2s, 2p, 3s, 3p, and 3d sublevels are considered core electrons because they are located in the inner energy levels. In this example, there are a total of 28 core electrons.
So, in summary, the 4s2 and 4p4 electrons in the electron configuration of Selenium are the valence electrons because they are located in the outermost energy level (n=4), while the rest (1s2, 2s2, 2p6, 3s2, 3p6, and 3d10) are the core electrons.