ICSE/Chemistry

Periodic Table, Periodic Properties and Variation of Properties

Elements

Elements are pure substances made up of only one type of atom. When studying periodic table, we study about these elements and their place in the periodic table.

Introduction to Periodic Table

The periodic table is a tabular display of the chemical elements, which are in order of increasing atomic number, as well as an illustration showing how they chemically behave. It consists of seven horizontal rows known as periods and eighteen columns’ knowns as groups.

Approaches to Periodic Classification of Elements

1. Dobereiner’s triads

Dobereiner states that when elements are organised in triads with the first and third elements having increasing atomic masses, the arithmetic mean of their atomic masses is roughly equal to the second elements atomic mass. Additionally, he suggested that this law applied to other properties of components as well. Density was one of these qualities.

2. Newlands Law of Octaves

According to the law of octaves, every eighth element possesses characteristics that are similar when the elements are ordered in ascending order of atomic mass.

3. Lother Mayer’s Law

In 1869, Lother Mayer stated that atomic volume is the periodic function of the atomic mass.

4. Mendeleev’s Periodic Law

According to Mendeleevs 1869 periodic law, properties of elements arranged in increasing atomic mass order would reoccur at regular intervals or periods.

To make sure that items with related qualities were arranged in the same vertical column, Mendeleev left a number of gaps in his table. At the time that the gaps in the periodic table were still unfilled, Mendeleev gave the undiscovered elements the names eka-boron, eka-aluminum, and eka-silicon. When these elements were later identified, eka-boron was renamed scandium, eka-aluminum was dubbed gallium, and eka-silicon was renamed germanium.

Anomalies of Mendeleev’s Periodic Law:

· Position of Hydrogen

· Position of Noble Gases

· Position of Rare Earth Metals

· Cause of Periodicity

· Anomalous Pair of Elements

· Position of Isotopes

Question: What elements are included in law of triads and law of octaves?

Answer: The elements that were discovered at that time were included in the above-mentioned laws. To study more about the laws and elements present, visithttps://youtube.com/channel/UCoqI7C9rI2UbFPITF2bPgnQ.

5. Modern Periodic Law

The physical and chemical characteristics of elements are periodic functions of their atomic numbers. The number of protons or electrons in a neutral atom is equal to the atomic number. In Modern Periodic Table elements are arranged in the form of periods and groups. The modern periodic contains 118 elements including natural elements such as metals, non-metals, metalloids and noble gases.

Groups

There are 18 groups in periodic table. These include:

· Group 1- These group elements are called alkali metals. They form strong alkali with water.

· Group 2- Alkaline Earth Metals, they form weaker alkalic when compared to group 1.

· Group 3, 4, 5, 6, 7, 8, 9, 10, 11, 12- They are known as transition metals. Their last two outermost shells are incomplete.

· Group 13- Boron family, boron is the first member of the group.

· Group 14- Carbon family

· Group 15- Nitrogen Family

· Group 16- Oxygen family also known as chalcogens because they form ores.

· Group 17- Halogen family, they form salt with water.

· Group 18- Noble or Inert Gases

Periods

There are 7 periods in periodic table. Period is determined by the number of shells in an atom. For example, period one has one shell and period two has two shells. Lanthanides and Actinides of group 3 have similar properties and since they are in a greater number, they are represented outside the periodic table.

Question: What are the elements present in each of the groups?

Answer: There are 118 elements which are present in each of the groups according to their property. You can study the properties of these elements athttps://youtube.com/channel/UCoqI7C9rI2UbFPITF2bPgnQ.

Periodicity

Periodicity describes patterns or recurrent changes in an elements properties as its atomic number rises. Periodicity is brought on by predictable and recurring changes in the atomic structure of elements. Periodicity can occur along the period or along the group, i.e., either from left to right or from top to bottom. The given below properties are shown with the help of periodicity:

· Ionization Energy: The ionization energy of an element is the total energy required to strip off an electron from the outermost shell of an atom. Ionization energy increases from left to right across the chart and declines from top to bottom.

· Electronegativity: The electronegativity of an element is a measure of its ability to attract electrons. Electronegativity increases from left to right across the chart and declines from top to bottom.

· Atomic Radius: This is half the distance between the centers of two atoms that are just touching. The atomic radius decreases from left to right across a period and increase from top to bottom down a group.

· Electron Affinity: The electron affinity is the total energy released when an electron is added to a neutral atom in the gas phase. Electron affinity increases from left to right across a period and decreases from top to bottom down a group.

· Valency: It represents the combining capacity of the element. It can also be said as the number of electrons an atom can donate or share. Valency first decreases from left to right, then reaches 4 and starts decreasing. Down the group valency remains same.

· Metallic Character: Elements which have the capacity to lose their valence electrons are considered as metals. After losing an electron they form positive ion. Metallic character increases when going down the group and decreases from left to right.

· Non-Metallic Character: Elements which have the capacity to accept electrons in their valance shell and then negative ion is formed, these elements are referred to as non-metals. Non-Metallic character decreases down the group and increases from left to right. Group 14 to group 18 elements are nonmetals.