The first 20 elements of the periodic table, which have atomic numbers 1-20, are listed below.
Each element consists of distinct properties owing to their atomic number, atomic mass, electronic configuration, electronegativity, electron gain enthalpy, etc.
Importance of The Atomic Number of An Element in A Periodic Table
The atomic number of an element in the periodic table provides us with the following information:
In other words, we can say that the atomic number is equal to the charge on the nucleus. Hence, it is also similar to the number of protons in the nucleus. It is numerically equal to the number of electrons in a neutral atom.
Let's try to understand it further with the example of Oxygen. Oxygen has an atomic number of 8. This implies that in the neutral state, the number of protons in the nucleus is 8. The number of electrons is 8. Similarly, in sodium, which has an atomic number of 11, the sodium atom's nucleus consists of 11 protons. It has 11 electrons surrounding the nucleus. As we know that the atomic number is equal to the number of electrons, we can easily predict the atom's electronic configuration by merely knowing its atomic number.
The atomic number tells us how many protons are there in the nucleus.
Protons - It is a subatomic (occurring within an atom) particle. It has a positive charge. It resides in the nucleus of an atom of the element.
Neutrons - It is also a subatomic particle. Neutrons have a neutral charge. A neutron weighs a little bit higher than a proton. Neutrons, along with the protons, add up to form the nucleus of the atom.
Electrons - Electrons are also subatomic. Electrons tend to orbit around the nucleus. The electrons are negatively charged. The size of the electrons is smaller than that of the nucleus. Electrons have an equal charge as the proton, but with a negative sign. The mass of an electron is almost 1/1836 times the mass of a proton.
How Does The Periodic Table Help?
The periodic table of the elements in Chemistry is the organized arrangements of all known elements in the order of their increasing atomic number represented by the number of protons of an atom.
Elements situated in the same column consist of similar properties and are denoted as groups. Elements located in the same row are called periods and consist of the equal highest unexcited electron energy levels. The periodic table can also provide us with information on an element's atomic weight and the usual charge. All this data, and much more, compiled into one universal, comprehensive reference table makes the periodic table important.
It is denoted by A.
When we add up the number of protons and the number of neutrons of the atom, it gives us the element's mass number. Neutrons and protons are collectively called nucleons because they are present in the nucleus itself. Now, let us look at a few examples. Oxygen has 8 protons, while the number of neutrons it has is also 8. This implies that the mass number of Oxygen is 8+8, that is 16.
Since the mass of an electron is approximately negligible, the element's atomic mass is almost equal to its mass number. Atomic mass is measured in terms of atomic mass unit. It is also called Dalton, denoted by D.
Noble Gases in the First 20 Elements of the Periodic Table
First, we need to know what noble gases are.
Noble gases are also called inert gases. Noble gases are situated in the 18th group of the periodic table. These are known to be the least reactive or extremely non-reactive. The noble gases were characterized later than other elements.
So, in the first 20 elements, there are three noble gases, namely, Helium (He), Neon (Ne), and Argon (Ar). Helium has an atomic number 2, Neon has an atomic number of 10, while Argon has an atomic number of 18.