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Periodic trends in Chemical Properties

  • Last Updated : 02 Dec, 2021

The modern periodic table is based on the law that an element’s properties are a periodic function of its atomic number. These properties are related to the elements’ electronic configuration. As we move across a period from left to right or down the group, we notice a common trend in properties. This property trend is referred to as periodic properties. Atomic size, metallic character, non-metallic character, ionisation potential, electron affinity, and electronegativity are all important periodic properties.

What is the Periodic Law?

Periodic trends are founded on periodic law. The chemical elements are enumerated in order of increasing atomic number, and main properties undergo cyclic changes, according to the periodic law. At regular intervals, elements with comparable chemical characteristics reappear. 

Dmitri Mendeleev established this principle. He also asserted that the periodic chart was based on different physical and chemical properties of elements, not merely atomic weights. The recurrence of features was later discovered to be attributable to the recurrence of comparable electronic configurations in the outer shells of atoms.

Periodic Table Trends

The periodic trends are based on the Periodic Law, which states that if the chemical elements are listed in increasing atomic number order, many of their properties undergo cyclical changes, with elements with similar properties recurring at regular intervals. Many of the physical and chemical properties of lithium, such as its vigorous reactivity with water, recur in sodium, potassium, and caesium after arranging elements in increasing atomic numbers.

Mendeleev discovered this principle in 1871, following a number of investigations throughout the nineteenth century. Mendeleev also proposed an elemental periodic system based not only on atomic weights but also on the chemical and physical properties of the elements and their compounds. Henry Moseley discovered in 1913 that periodicity is determined by the atomic number rather than the atomic weight. Lothar Meyer presented his table following Mendeleev, but he disagreed with Mendeleev’s Periodic law. Initially, there was no theoretical explanation for the Periodic Law, and it was only used as an empirical principle; however, with the development of quantum mechanics, it became possible to understand the theoretical basis for the Periodic Law.

When elements are listed in increasing atomic number order, the periodic recurrence of elements with similar physical and chemical properties results directly from the periodic recurrence of similar electronic configurations in respective atoms’ outer shells. One of the most significant events in the history of chemical science was the discovery of the Periodic Law. Almost every chemist employs and continues to employ the Periodic Law. The Periodic Law also resulted in the creation of the periodic table, which is now widely used in a variety of fields.

Atomic size

The atomic radius is the distance between the nucleus’s centre and the atom’s outermost shell. As we progress from one period to the next, the atomic size of a group grows due to the addition of shells. Over time, the atomic size decreases while the number of shells remains constant and the nuclear charge increases. This causes electrons to be drawn from the outermost shell towards the nucleus, reducing its size.

Metallic character

Metals are the elements that lose electrons to form cations. The metallic character increases as we move down the group because atomic size increases, resulting in easy electron loss. It, on the other hand, decreases over time as we move from left to right. This occurs because the nuclear charge increases, making it more difficult for an atom to lose electrons.

Non-metallic character

Non-metals are elements that have a proclivity to gain electrons. Moving across a period increases the tendency to gain electrons due to an increase in nuclear charge and a decrease in atomic size. As a result, the nonmetallic character increases over time. The non-metallic character decreases as we move down the group due to the increase in atomic size.

Ionization potential

The ionisation potential is defined as the amount of energy required to remove an electron from the outermost shell of a gaseous atom and convert it into a positively charged gaseous ion. The periodic properties of ionisation potential increase as the atomic size decreases over time due to an increase in nuclear charge. The ionisation potential decreases as we move down the group due to the increase in atomic size. Factors That Affect the Ionization Energy Levels  

  1. Nuclear Charge: The force of attraction between the nucleus and valence electrons decreases as the nuclear charge decreases, resulting in decreased ionisation energy.
  2. Shielding Effect: Shielding effect increases as nuclear charge grows, hence as the shielding effect increases, so does ionisation energy.
  3. Atomic Radius: The force of attraction between the nucleus and valence electrons reduces as the atomic radius grows. As a result, as the atomic radius increases, the ionisation reduces.
  4. Half-Filled Valence Shells: Ionization energy is high in pseudo-filled or half-filled valence shells.

The periodic trend does not apply to any of the elements in the oxygen and boron families. They take a little less energy than the standard trend.

Electron affinity

A certain amount of energy is released when electrons are added to a neutral gaseous atom. This is referred to as electron affinity. Electron affinity causes the formation of a negative ion or anion. On the periodic table, it increases from left to right and decreases from top to bottom. Electron affinity decreases as atomic size increases, and vice versa. The electron affinity is also affected by the screening effect and the reactivity of non-metals.

Melting Point

The melting point of an element is the amount of energy required to change the state of an element from solid to liquid. Which essentially means severing a few ties. As a result, the melting point rises as the strength of the bond between the atoms increases.

Boiling Point

The boiling point is determined by the amount of heat required to convert a liquid to a gaseous state, just as the melting point is determined by the strength of the bonds between atoms.

Electronegativity

The ability of an atom to attract a pair of electrons is referred to as electronegativity. The electronegativity of elements is affected by the size of an atom and its nuclear charge. It increases as we move from left to right across the periodic table and decreases as we move from top to bottom. Fluorine has a higher electronegative value, while caesium has a lower electronegative value. 

It also differs between metals and non-metals. Nonmetals have a higher electronegative potential than metals. It also aids in the identification of the types of bonds formed between the elements. The group 13 elements are an exception, and electronegativity rises from aluminium to thallium as a result. In addition, tin has a stronger electronegativity than lead in group 14.

Metallic character

Metallic character is defined as the characteristics associated with the metals found on the periodic table. Metallic lustre, hardness, malleability, thermal conductivity, and other properties are examples of these characteristics. The elements on the left side of the periodic table have a more metallic character. It decreases from left to right due to electron addition and increases from top to bottom due to electron removal. When the atomic number increases, so do the ability to lose electrons.

Non-metallic character

The periodic table shows that the nonmetallic character of elements increases from left to right and decreases from top to bottom. The elements with this property do not have metallic properties.

Shielding Effect

It can be characterized as the inner electrons resisting an outer electron. It can also be used to describe how many nuclei are capable of controlling electrons in the outer shell. Because of the increasing shielding effect, the effective nuclear charge drops along with the group. The effective nuclear charge rises over time as the nuclear charge rises.

Sample Questions

Question 1: What is the modern periodic table based on?

Answer:

The modern periodic table is based on the law that an element’s properties are a periodic function of its atomic number. These properties are related to the elements’ electronic configuration.

Question 2: What is the effect on metallic character as we move in a periodic table?

Answer:

The metallic character increases as we move down the group because atomic size increases, resulting in easy electron loss. It, on the other hand, decreases over time as we move from left to right.

Question 3: Define electron affinity.

Answer:

A certain amount of energy is released when electrons are added to a neutral gaseous atom. This is referred to as electron affinity.

Question 4: What is the effect on electronegativity as we move in a periodic table?

Answer:

The electronegativity of elements is affected by the size of an atom and its nuclear charge. It increases as we move from left to right across the periodic table and decreases as we move from top to bottom.

Question 5: What are some metallic characteristics?

Answer:

Metallic character is defined as the characteristics associated with the metals found on the periodic table. Metallic lustre, hardness, malleability, thermal conductivity, and other properties are examples of these characteristics.


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