Periodic table trends are systematic patterns in the properties of elements of the periodic table. Periodic trends depend upon the electronic configuration of elements. They arise from the changes in the atomic structure of elements with their respective periods(horizontal rows) and groups(vertical columns) in the periodic table. Periodic trends are based on the periodic law, which states that if the chemical elements are listed in order of increasing atomic number(from left to right), then the physical and chemical properties of elements will be a periodic function of their atomic numbers. We will discuss some trends of fundamental properties of elements here.
The number of shells increases with the increase in atomic number. Period number indicates the number of shells of the related element, so if we move from top to bottom in a group, the number of shells increases by 1 and remains same if we move left to right across a period.
The number of electrons present in the outermost shell are called valence electrons. If we move from top to bottom in a group, the number of valence electrons remains the same. While moving across a period, the valence electrons increases.
Valency is the combining capacity of elements or the number of electrons donated, accepted or shared during compound formation by the elements. As valence electrons remain the same on moving top to bottom, so the valency also remains the same on going down the group. While we move across a period, valency first increases and then decreases. In order to become chemically stable, the octet rule must be followed with the least energy loss. Due to energy loss, elements accept or donate a minimum number of electrons.
Atomic size refers to the distance from the atomic nucleus to the outermost electron orbit. Atomic size usually increases on going down in a group as the number of shells also increases. But, it decreases on moving left to right across the period due to the shrinking of the atom because of increasing nuclear force.
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Metals have a tendency to lose electrons. Metals are the best donors while non-metals are acceptors. There are trends in metallic character as we move across the period, the metallic character decreases from left to right as valency of elements decreases. Atoms more readily accept electrons to fill valence shells than lose them to remove the unfilled shell.
Metallic character increases on going down to the group because of the lesser nucleus force, the electrons become easier to lose as atomic radius increases. Metals are on the left-hand side of the periodic table except hydrogen.
It is the minimum amount of energy required to remove the outermost electron or the most loosely bound electron. On moving left to right in a period, atomic size decreases so the nucleus force increases. Due to this, across a period in the periodic table, ionization energy usually increases.
When moving down the group, the number of shells increases. Due to this, the effective nuclear charge reduces. Atoms lose electrons easily, so less energy is required to donate electrons.
Thus, ionization energy decreases on moving top to bottom.
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Electron affinity is the energy released by an atom when an electron is added to it. Electron affinity generally decreases on going down a group of elements because each atom is larger than the atom above it. With the larger distance between the nucleus and the outermost electron, the nucleus force decreases. On moving left to right across a period, the nuclear force increases, so electron affinity also increases, caused by the decrease in atomic radius.
Electronegativity is a property which describes an atom's ability to attract and bind with electrons. If the valence shell of an atom is less than half full, It requires less energy to lose an electron than to gain one. While if the valence shell is more than half full, it is easier to pull an electron into the valence shell than to donate it. Sorry, electronegativity increases on moving left to right across the period.
Atomic number increases down the group so atomic size also increases. Thus, electronegativity decreases on moving top to bottom in a group.
1. Which Element has the Highest Ionization Energy?
Fluorine(F), Nitrogen(N) and Helium(He)
Among the elements listed above, all of them and nonmetals. We already know that the ionization energy of non-metals is quite high due to their inability to lose electrons. Fluorine is a halogen, which means it needs just one more electron to stabilize itself. Nitrogen is short of three electrons to complete its octet. But, helium is a noble gas and has two electrons in its duplet. This implies that its K shell is already filled. Hence, helium is chemically inert.
So, Helium (He) has the highest ionization energy because helium is stable and does not readily lose or gain electrons.
2. Why is the Electronegativity Value of Most Noble Gases is Zero?
Since most of the elements of the periodic table cannot independently exist in the form of atoms due to their incomplete orbits, they are always trying to achieve the nearest inert gas configuration by donating, accepting and sharing electrons. Contrarily, the noble gases present in the periodic table do not tend to enter into chemical bonds to form compounds because their valence shells are already fully occupied. This stabilizes them and makes them chemically inert.
Most noble gases have full valence shells, so the noble gases are extremely stable and do not readily lose or gain electrons. Hence, the electronegativity of most noble gases is zero.