Çi ye Atom?

Pargîk dihêne min herî ya zêde yên ku hewce bike bibe yê ji xwe re bibe ne hatiye an bi pargîkan din re birêvebikin da molecule.

Sala 1808-an, kemist famos îngilîsî, fizîkdar û meteorolojî John Dalton teoriya we ya pargîk wergerandin. Li dema wan, çend karanîn kimiyayî nehatiyan bi teoriya Dalton ê çab bikin. Demek, teoria wateyên teorîkî kemistiyayê bû. Postulatan teoriya atomîk a Dalton vêyên in.

• Hemî materiya ji pargîkan kêmtir û nabejiyên di nav pargîkan de derbasên din heye.

• Hemî pargîkan elementan yekem li ser propertiyên jî dibedixwe betir lê dike nav pargîkan elementan din.

• Pargîkan elementan din bi yekbir digire da compound form dikin.

• Reaksiyon kimiyayî tu niha didekirina wêne pargîkan.

• Pargîkan nehatiyan lê bidin tênekin ne hatiye an binasekîn.

Teoriya Dalton ê piçeyên çend hate, ew bû; ewro hûn dîtin ku pargîkan nehatiyan tênekin. Diwêje, pargîkan elementan yekem di ser massa (isotopes) de girindin. Teoria şeşave dike ke existence of allotropes bêtir bike.

Lê li dema moderna, mafan pargîk dike têkiliyên merivane modela Rutherford’s atomic model û Bohr’s atomic model. Hemî materiya ji pargîkan ne. Pargîkan guhurtin:

1. Nucleus

2. Electrons

Nucleus of Atom

Nucleus li navenda markazî pargîk de ye. Diametra nucleus yekê 1/10000 diametra pargîk guhur ye. Heqiqi massa pargîk li ser nucleus concentrate ye. Nucleus guhurtin ji div pargîkan:

1. Proton

2. Neutron

Proton

Protons ji pargîkan posîtif chargen. Charge li ser har proton 1.6 × 10-19 Coulomb ye. Number of protons in nucleus of an atom represents the atomic number of atom.

Neutron

Neutrons nekîn charge elektrîkî ne. Ji ber, neutrons ji pargîkan elektrîkî neutral ne. Massa har neutron bi massa proton yekê ye.
Nucleus li ser presence of positively charged protons positif charge ye. Li hemî material, weight of the atom and radioactive properties are associated with the nucleus.

Electrons

An electron is a negatively charged particle present in the atoms. Charge on each electron is – 1.6 × 10 – 19 Coulomb. These electrons surround the nucleus. Some facts about electrons in an atom are listed and explained below,

• If an atom is having the same number of protons and electrons, the atom is electrically neutral as the negative charge of electrons neutralizes the positive charge of protons.

• The electrons revolve around the nucleus in shells (also called orbits).

• A force of attraction is excreted on negatively charged electrons by positively charged nucleus. This force of attraction works as centripetal force required for electrons revolution around the nucleus.

• The electrons which are near to nucleus are tightly bound with the nucleus and it is more difficult to pull out (remove) these electrons from the atom than those which are far away from the nucleus.

• The structure of aluminum atoms is shown in figure below-

• A definite amount of energy is required to remove the electron from its orbit. The energy required to remove the electron from the first orbit is much more as compared to the energy required to remove the electron from the outer orbit. This is due to the force of attraction excreted by nucleus on electrons in the first orbit is much more as compared to the force of attraction excreted on electrons of outer orbit. Similarly, the energy required to remove the electron from the second orbit will be less as compared to the first orbit and greater than the third orbit. Hence, we can say that the electrons in the orbit are associated with a definite amount of energy. Thus the orbits or shells are also referred as energy levels.

• The energy levels are denoted by the letters K, L, M, N, etc. Where, K is the nearest orbit to the nucleus and having lowest energy level. Conversely, the outermost orbit is having highest energy level.

• The maximum number of electrons in any energy level is given by, ‘2n2’, where, n is an integer and represents the “principal quantum number”. For different energy levels the value of ‘n’ and maximum number of electrons as given in table below

• The above formula (2n2) used for determining the maximum number of electrons in any shell, has some limitations. The Number of electrons in outermost shell (highest energy level) cannot exceed beyond 8. For example let’s consider the atom of calcium, it is having 20 electrons orbiting around its nucleus. As per formula of above rule i.e. 2n2, the electrons distribution will be as 2 electrons in K level, 8 electrons in L level and there will be balance 10 electrons. But the electrons in outer most energy level cannot exceed 8. Hence, there will be 8 electrons in M level and balance 2 electrons will go to next energy level i.e. 2 electrons will go the N level. The electron configuration of Calcium atom is shown in figure below-

• The electrons in the outermost energy level are called “valence electrons”. The maximum possible number of “valence electrons” is 8. If the number of electrons in outermost orbit is 8, the atom becomes stable. The material whose atoms naturally having 8 electrons in their outermost shell (orbit), does not react with other material. Inert gases such as Helium, Neon, Argon, krypton etc. are having completely filled outer most shells and hence do not react with other materials.