Element X is an element of Mg which is located in group 2A and period 3
with 12 = atomic number and 25 = mass number
The Atomic Number (Z) indicates the number of protons in an atom of an element. If the atom is neutral then the number of protons will be equal to the number of electrons. So the atomic number can also indicate the number of electrons.
So atomic number = number of protons = number of electrons
Mass Number (A) is the sum of protons and neutrons
Mass Number (A) = Number of protons + Number of Neutrons
So that the relationship between atomic numbers and mass numbers can be formulated as follows:
Atomic Number (Z) = Mass Number (A) - Number of Neutrons
In the following element notation,
Information
X = symbol of elemental atom
A = mass number
= number of protons + number of neutrons
Z = atomic number
= number of protons = number of electrons, on neutral elements
In an atom, there are levels of energy in the skin and sub skin.
This energy level is expressed in the form of electron configurations.
Charging electrons in the sub skin uses the following sequence:
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p⁶, 6s², etc.
The location of the element group in the periodic system is determined by the number of valence electrons that fill the last sub-skin
The element period is determined from the valence shell (the largest main quantum number (n))
The chemical element group is divided into two, namely:
Group A, occupies sub skins s and p
Group B, occupies sub skin d
In the most probable question, the notation is meant
So that shows:
12 = atomic number
25 = mass number
To determine the X element, we must know where the element is in the modern periodic system
Determining the location of the group and its period is sought by writing down the electron configuration
Because atomic number = 12, the number of electrons is also = 12, so the electron configuration is:
1s² 2s² sp⁶ 3s²
The last valence electron is in the 3s² orbitals so that:
Period: main quantum number (n) = 3
Group: because it ends at s orbitals with 2 electrons, the group is 2A (electrons occupying s and p orbitals are group A)
So element X is located in period 3 and group 3A. Elements that fulfill these 2 conditions are: Mg
the electron configuration for barium (Ba) in noble-gas notation link
the formation of a bond.
link
quantum number
link
Keywords: the electron configuration, orbitals, period, group , the modern periodic system
