# How Many Electrons are in Each Shell?

The number of electrons an atom can hold depends on the number of protons in the nucleus, influencing how many electrons can fit in each orbit or shell around the nucleus. But just how many electrons are there in each shell? We'll look at the shapes of the atomic orbitals and what determines their size to help you understand where this number comes from!

### The Basics:

The electrons in an atom orbit the nucleus in shells. The first shell can hold up to two electrons, the second shell can hold up to eight electrons, the third shell can hold up to 18 electrons, and so on. These atoms with their respective number of electrons are called neutral atoms. If a tepid atom gains or loses an electron, it becomes either positively charged or negatively charged. An atom that has lost an electron is called an ion. An ion that has gained one or more electrons is called a cation. An ion that has lost one or more electrons is called an anion. An anion that has gained one or more electrons is called a cation.

A positive ion (cation) can be composed of excess protons and electrons; likewise, a negative ion (anion) can be composed of excess electrons and protons. The ionization energy for an atom is the amount of energy required to remove all of its electrons from their orbits around the nucleus. As you might have guessed, it’s usually pretty hard to do this! But if we did manage to somehow strip all of those electrons away from our hydrogen atom, what would happen? That’s right: we would have a bare proton left behind—a hydrogen ion!

### The S Orbitals (H, He, Li, Be, B):

The S orbitals have a maximum of 2 electrons. The first shell, which is closest to the nucleus, can hold a maximum of 2 electrons. The second shell can hold 8 electrons (2+6). The third shell can hold 18 electrons (2+6+10), and so on. It turns out that there are four different levels of energy for each electron because they're all moving at different speeds. If an electron moves too fast or too slow, it falls to the wrong level and takes on an entirely new set of properties. That's why you never see any other type of electron besides these four: They're made up entirely from these levels!

### The P Orbitals (F, Ne, Na, Mg, Al):

The P orbitals can each hold a maximum of six electrons. The first shell can hold a maximum of two electrons, the second shell can hold a maximum of eight electrons, the third shell can hold a maximum of 18 electrons, and so on. In total, there are seven orbitals in which electrons can reside: 1s, 2s, 2p, 3s, 3p, 4s, and 4p. The energies of these orbitals correspond to their increasing number as follows: K=1/2, L=1/3, M=1/4. N=1/5, O=1/6, P=1/7. For example, a magnesium atom has 12 electrons (a single electron occupies one energy level at a time). Six of those electrons occupy the 2s orbital; three occupy the 2p orbital; one occupies the 3s orbital, and one occupies the 3p orbital.

### The D Orbitals (C, N, O):

The d orbitals have five electrons. The first two electrons go into the 1s orbital, and the next two go into the 2s orbital. The last electron goes into the 2p orbital. The p Orbitals (F, Na):: The p orbitals also have four spaces for electrons. The first two electrons go into the 1s orbital and the next two go into the 2s orbital. The third electron has a choice of going into either the 2s or 2p orbital but once it is in one of these it cannot move to another without changing its state. The fourth electron can only be placed in the 3s or 3p orbitals because there are no other slots available.

### The F Orbitals (Si, P):

The F orbitals of Si and P elements can accommodate a maximum of 14 electrons. The configuration of these orbitals is 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p4. The G Orbitals (Ge, As):: The G orbitals of Ge and As elements can accommodate a maximum of 18 electrons.

The H Orbitals (He, Ne):: All the s, p, d, f subshells fill up first with He followed by Ne for the 1st orbital. Subsequent atoms follow the sequence p then d then f with He as the exception to this order since all his subshells have filled up. For example, Li has 1s2 2s1 electron whereas Na has 1s2 2s22p6 3s1 electron. Notice that there are two additional electron shells than what is listed above.

Read: Biology Tricks For NEET Exam 2023

### Final thought

As you probably know, electrons orbit the nucleus of an atom in shells. But did you know that the number of electrons in each shell corresponds to the period number of the element on the periodic table? For example, hydrogen has one electron in its first shell, while helium has two electrons in its first shell.

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