recall the stability associated with one atom that has actually a completely-filled valence shell Construct an atom follow to the Bohr model

Key Terms

Octet rule: A dominance stating that atoms lose, gain, or share electron in order to have a full valence covering of 8 electrons. (Hydrogen is excluded since it can hold a maximum of 2 electron in its valence shell. ) Electron shell: The collective states of every electrons in an atom having the same principal quantum number (visualized together an orbit in i beg your pardon the electrons move).

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Electron Shells

Niels Bohr proposed very early model the the atom as a central nucleus comprise protons and neutrons gift orbited by electrons in shells. As previously discussed, there is a connection in between the number of protons in an element, the atomic number that distinguishes one element from another, and the number of electrons it has. In every electrically-neutral atoms, the variety of electrons is the exact same as the variety of protons. Every element, as soon as electrically neutral, has a variety of electrons same to its atomic number.

An at an early stage model the the atom was developed in 1913 by Danish scientist Niels Bohr (1885–1962). The Bohr version shows the atom as a central nucleus containing protons and neutrons v the electron in one orbitals at details distances indigenous the nucleus (Figure \(\PageIndex1\)). These orbits type electron shells or energy levels, which are a means of visualizing the variety of electrons in the assorted shells. These power levels room designated by a number and also the symbol "n." because that example, the 1n shell represents the an initial energy level located closest come the nucleus.

api/deki/files/53809/MuortGpmSwmsC0elWBWY.jpg?revision=1" />Figure \(\PageIndex2\): Bohr diagrams for neutral lithium, fluorine and aluminum atoms.

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Lithium has three electrons: two go to K shell and the continuing to be one goes come the l shell. Its electronic configuration is K(2), L(1) Fluorine has nine electrons: 2 go come K shell and the staying seven go to the l shell. Its digital configuration is K(2), L(7). Note that L deserve to have 8 electrons. Aluminum has thirteen electrons: 2 go come the K shell, eight go to the together shell, and remaining 3 go come the M shell. Its electronic configuration is K(2), L(8), M(3). Keep in mind that the M shell deserve to have 18 electrons.

Orbitals in the Bohr model

Electrons to fill orbit shells in a regular order. Under conventional conditions, atoms fill the inner shells (closer come the nucleus) first, often resulting in a variable number of electrons in the outermost shell. The innermost shell has actually a preferably of 2 electrons, but the following two electron shells deserve to each have a preferably of eight electrons. This is well-known as the octet dominance which claims that, with the exemption of the innermost shell, atoms are much more stable energetically once they have eight electron in your valence shell, the outermost electron shell. Examples of some neutral atoms and also their electron construction are presented in figure \(\PageIndex3\). As shown, helium has a complete outer electron shell, v two electrons pour it until it is full its very first and just shell. Similarly, neon has a complete outer 2n shell containing eight electrons. In contrast, chlorine and sodium have seven and also one electron in their outer shells, respectively. Theoretically, they would certainly be more energetically secure if they adhered to the octet rule and also had eight.