Some atoms of the same element have different nucleon number. Do you know what are these elements called? In this lesson we will learn about;
What are Isotopes?
Uses of Isotopes
Arrangement of electrons in atoms
What are Isotopes?
Isotopes are atoms of the same element with the same number of protons and electrons but different number of neutrons. Hence, isotopes of same element have different nucleon number. Most elements occur naturally as a mixture of isotopes. Chlorine consists of two isotopes: chlorine-35 and chlorine-37.
Chlorine-35 has 17 electrons and protons, but 18 neutrons.
Chlorine-37 has 17 electrons and protons, but 20 neutrons.
Isotopes have same chemical properties because chemical reactions involves electrons not neutrons, therefore isotopes have similar chemical properties because they have same number of electrons. They have different physical properties because physical properties are affected by mass. Isotopes have different masses hence they have different physical properties. Chlorine-35 and Chlorine-37 both react with sodium to produce sodium chloride.
But chlorine-37 will be denser than chlorine-35.
Uses of Isotopes:
Isotopes that emit high-energy radiation are called radioisotopes. They are radio active substances. There uses are listed below:
Field of Application: | Isotopes: | Uses of Radioisotopes: |
Medical | technetium-99 | Detection of tumors |
Medical | iodine-131 | treatment of thyroid disorder |
Safety and Security | californium-252 | Detection of explosives |
Safety and Security | americium-241 | Used in smoke detectors |
Archaeology | carbon-14 | Estimating the age of things that contain carbon |
Geology | uranium-238 | Estimating the age of rocks |
Arrangement of Electrons
The arrangement of the electrons determine the chemical properties of the atom. Electrons move around the nucleus in regions called electron shells.
Each electron shells corresponds to a specific energy level and can only hold a certain number of electrons. The shells closest to the nucleus corresponds to the lowest energy level and the shells furthest away from the nucleus corresponds to the highest energy level. The arrangement of electrons in an atom can be represented as electronic structure or electronic configuration.
What are Valence Electrons?
The valence shell or outer shell, refers to the shell furthest away from the nucleus. The electrons present in the outer most shell of an atom are called outer electrons or valence electrons.
In the Periodic Table, there are 7 ( horizontal ) rows of elements called periods and 8 ( vertical ) columns of elements called groups.
Groups determine the number of valence electrons of an atom of an element.
Periods determine the number of shells of an atom of an element.
For example, magnesium is in group number 2 and in period number 3. It has 3 shells and 2 valence electrons in each of its atom.
Electronic configuration of Magnesium is: 2, 8, 2
Electronic structure of Magnesium is:
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