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Chapter 5 Notes
The number of electrons allowed in each shell changes as the shell
number goes up.
Shell number Number of electrons
Shells are energy levels and the energy increases. The energy level
number is called the principal quantum number, n.
Maximum number of electrons in a shell=2n².
Shells are made up of atomic orbitals which is a region around the
nucleus that can hold up to two electrons with opposite spins .
There are s , p, d and f orbitals and each has a different shape .
Sorbitals the electron cloud is in the shape of a sphere, and can hold
two electrons. The greater the shell number, the greater the radius of
the sorbital. Each shell from n=1 only has one sorbital .
Porbitals the electron cloud is in the shape of a dumbbell. Each
shell from n=2 contains 3 porbitals . The greater the shell number, the
further the porbital is from the nucleus.
Dorbitals each shell from n=3 contains five dorbitals .
Forbitals each shell from n=4 contains seven forbitals .
Shell Number of Subshells Number of Number of
orbitals present electrons electrons
s p d f in in shell
1 1 1s 2 2
2 1 3 2s+2p 2+6 8
3 1 3 5 3s+3p+3d 2+6+10 18
4 1 3 5 7 4s+4p+4d+4f 2+6+10+14 32
Each shell gains a new type of orbital.
The diagram shows the order in which the shells fill up.
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Electrons in an orbital must have opposite spins as it helps to
counteract the repulsion between the negative charges of the two
One electron occupies each orbital before pairing begins .
Electronic configurations should be shown in shell order rather than
order of filling.
The highest energy subshell determines which block an element is
categorised into sblock , pblock or dblock .
The 4s electrons are filled first but also empty before the 3d subshell.…read more