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MANUAL TITLE GOES HERE

of all the different isotopes in a sample, with each isotope's contribution to the average

determined by how big a fraction of the sample it makes up.

Electrons configuration

Each element in periodic table has different number of electrons. The electron
configuration is the standard notation used to describe the electronic structure of an atom
and to understand the shape and energy of its electrons. The electron configuration of an
atom also representation of the arrangement of electrons distributed among the orbital shells

and subshells. Commonly, the electron configuration is used to describe the orbitals of an
atom in its ground state, but it can also be used to represent an atom that has ionized into a
cation or anion by compensating with the loss of or gain of electrons in their subsequent
orbitals. Many of the physical and chemical properties of elements can be correlated to their

unique electron configurations. The valence electrons, electrons in the outermost shell, are
the determining factor for the unique chemistry of the element.

The arrangement of electrons in an atom can be determined by using simple formula as below:

2
e-max = 2n ; n = number of shell
Example 1. Lithium with atomic number is 3.

n = 1 ---------> 2(1) = 2 --------> 1 . shell carries 2 electrons.
2
st
Because the number of electrons is equal to the atomic number, which in Lithium is 3, the
remain 1 electron carried in 2 shell or the outer shell. Figure 2.3: shows electrons configured
nd
in Lithium. The number of electrons in the last orbit or outer shell is called electron valency.

Figure 2.3: Number of electrons in every shell Lithium atom

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