Which element does x represent in the following expression: 2512x?

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

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

the answer would be c