Atomic structure and the Periodic Table
The Atomic Structure:
It was discovered that an atom is made up of three types of sub-atomic particles; these are protons, neutrons and electrons.
It was also discovered that in the center of an atom, there is a Nucleus which is made up of protons and neutrons.
Around the nucleus there are energy shells in which electrons are. Electrons are always orbiting the nucleus in the energy shells.
It was discovered that an atom is made up of three types of sub-atomic particles; these are protons, neutrons and electrons.
It was also discovered that in the center of an atom, there is a Nucleus which is made up of protons and neutrons.
Around the nucleus there are energy shells in which electrons are. Electrons are always orbiting the nucleus in the energy shells.
Protons and Neutrons are said to be Nucleons because together they make the nucleus. Each type of these sub- atomic particles has its own physical properties which are explained in this table:
These physical properties tell us several factors:
There are two numbers given to each type of atoms:
Atomic/Proton Number: it is the number of protons in an atom. And since an atom has an equal number of
protons and electrons, it is the number of electrons in the atom too.
Mass/Nucleon Number: it is the number of protons + number of nucleons in the nucleus of an atom. It is called mass number because its value is also mass of the atom.
If the atomic number is the number of protons, and the mass number is the number of protons and neutrons, then subtracting the proton number from the mass number will give you the number of neutrons in the atom.
When we represent the atom of an element, we give it a symbol of one or two letters where the first letter is always in capitals and the second one is in lowercase. The mass number goes above the symbol and the atomic number goes below the symbol.
- The mass of the atom is concentrated in the nucleus; this is because the mass of an electron is negligible,
- A neutron has no charge, it is neutral,
- An atom is also neutral; this is because it always contains as much positive protons as negative electrons.
There are two numbers given to each type of atoms:
Atomic/Proton Number: it is the number of protons in an atom. And since an atom has an equal number of
protons and electrons, it is the number of electrons in the atom too.
Mass/Nucleon Number: it is the number of protons + number of nucleons in the nucleus of an atom. It is called mass number because its value is also mass of the atom.
If the atomic number is the number of protons, and the mass number is the number of protons and neutrons, then subtracting the proton number from the mass number will give you the number of neutrons in the atom.
When we represent the atom of an element, we give it a symbol of one or two letters where the first letter is always in capitals and the second one is in lowercase. The mass number goes above the symbol and the atomic number goes below the symbol.
The Electronic Configuration of Atoms:
Electrons are arranged in energy shells or energy levels. But each energy shell can hold up to a certain amount of electrons.
If an atom has its 3rd energy shell holding 8e, if it receives 2 more they go to the 4th energy shell. If further 10e are received, they go to the 3rd energy shell making it saturated with 18e.
Valency electrons are the electrons in the outer most energy shell.
Electronic arrangments in some elements:
Electrons are arranged in energy shells or energy levels. But each energy shell can hold up to a certain amount of electrons.
- 1st energy shell holds up to 2e,
- 2nd energy shell holds up to 8e,
- 3rd energy shell holds up to 18e, but stable with only 8e.
If an atom has its 3rd energy shell holding 8e, if it receives 2 more they go to the 4th energy shell. If further 10e are received, they go to the 3rd energy shell making it saturated with 18e.
Valency electrons are the electrons in the outer most energy shell.
Electronic arrangments in some elements:
isotopes
Some elements have different versions of their atoms. These versions are called isotopes. Isotopes of the same
element are similar, only that they have a different number of neutrons. Chlorine for example has two isotopes, Chlorine-35 and Chlorine-37. Isotopes of the same elements do not differ in Behavior or anything, only their masses differ, as a result of having a different number of neutrons.
There are two kinds of isotopes, stable ones and unstable ones. Unstable ones have a lot of neutrons, and they are radioactive. They are called radioisotopes.
Radioactive-Isotopes are used in the medical and the industrial field. Medical uses of radioactive isotopes:
element are similar, only that they have a different number of neutrons. Chlorine for example has two isotopes, Chlorine-35 and Chlorine-37. Isotopes of the same elements do not differ in Behavior or anything, only their masses differ, as a result of having a different number of neutrons.
There are two kinds of isotopes, stable ones and unstable ones. Unstable ones have a lot of neutrons, and they are radioactive. They are called radioisotopes.
Radioactive-Isotopes are used in the medical and the industrial field. Medical uses of radioactive isotopes:
- treatment of cancer
- radiotherapy
- treatment of thyroid gland
- X-rays
- tracer
- studies in body
- sterilising equipment
- locating tumours
- detection of leaks
- thickness of paper etc.
- nuclear fuel for generating electricity
- nuclear weapons
- radiographs of welds
- measuring wear
- sterilising food
The rule of calculating the Ar of an element is:
The relative atomic mass of an element is the average mass of all its isotopes compared to one-twelfth the mass of an atom of Carbon-12.
The relative atomic mass of an element is the average mass of all its isotopes compared to one-twelfth the mass of an atom of Carbon-12.
M is the mass number
If we have two isotopes of Chlorine; Chlorine-35 and Chlorine 37. The percentage of abundance of these two isotopes in the world is 75% and 25% respectively. We could calculate the Ar by:
If we have two isotopes of Chlorine; Chlorine-35 and Chlorine 37. The percentage of abundance of these two isotopes in the world is 75% and 25% respectively. We could calculate the Ar by: