[Chemistry Class Notes] Modern Periodic Table Trend Pdf for Exam

In the modern periodic table, all the elements are arranged systematically. They are assigned positions in the groups and periods according to the atomic number and the similarities in the physical and Chemical properties. The modern periodic table was formed after the introduction of the modern periodic law. This law was given by Henry Moseley. According to this law, the atomic number decides the properties of the elements. In simple words, the properties of the elements repeat themselves after regular intervals if the elements are arranged in the increasing order of their atomic number.

All the elements are arranged in groups and periods in the periodic table. Groups are vertical columns and these are 18 in number. The horizontal rows are the periods and these are 7 in number.

Elements of the Modern Periodic Table

There are different types of elements present in the modern periodic table. These elements are listed below:

• Elements of Main Group – In the modern periodic table, the Group 1 and 2 elements on the left-hand side and the elements of the Group 13 to 17 on the right-hand side are known as the main group elements. These are also called representative elements.

• Noble Gases – The elements of the Group 18 are called noble gases. These are not reactive as the outermost shell of these elements is completely filled. 

• Transition Elements – The elements belonging to Groups 3 to 12 are known as transition elements. They are present in the middle block of the periodic table. The two outermost shells of these elements are not completely filled.

• Inner Transition Elements – There are two rows of inner transition elements and each row comprises 14 elements. The first row is called the lanthanide series (elements from atomic number 58 to 71). The second row is known as the actinide series (elements from atomic number 90 to 103).

• Metals – Metals are placed on the left-hand side of the modern periodic table. Elements of Group 1 and 2 are metals. Group 1 elements are called alkali metals and Group 2 elements are called alkali earth metals.

• Non-Metals – The space on the right-hand side of the modern periodic table is occupied by the non-metals.

• Metalloids – Metalloids are placed diagonally starting from boron (Group 13) to polonium (Group 16). These elements possess the properties of both metals and non-metals.

Periodic Trends in the Modern Periodic Table

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. ‘

Number of Shells

The number of shells increases with the increase in atomic number. The 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 the same if we move left to right across a period. 

The number of electrons present in the outermost shell is 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 increase.

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.

Valence Electrons and Valency

The valency of an element refers to the number of electrons that are lost or gained by it to have a stable configuration. The valencies of elements belonging to the s and p block are calculated as 8-number of valence electrons. 

The valencies of elements belonging to the d and f block are determined by the d and f orbital electrons. The general valency of the d and f block elements is 2 and 3 respectively. 

Atomic Size (Atomic Radius Periodic Table)

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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Metallic & Non – Metallic Character

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 the 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 for hydrogen.’

Melting Point

The melting of an element is defined as the amount of energy required to change the solid phase of the element into the liquid phase. The change of the phase takes place due to the cleavage of the bonds between the atoms. If the bond will be stronger then more energy will be required to break that bond. The energy required is directly proportional to the temperature. High bond dissociation energy means high temperature. The melting point varies across the periodic table, therefore, it is not considered as the distinguishable trend. But following conclusions can be derived from the periodic table using the trend of melting point.

• Generally, all the metals have high melting points.

• Mostly, all the non-metals have low melting points.

• There is an exception in the case of non-metals. The carbon atom has a high melting point. Also, boron, which is a semi-metal, has a high melting point.

Ionization Enthalpy/ Ionization Energy

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

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

Electronegativity is a property that 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.