Trends in the Modern Periodic Table: Trends in Elements

Ans. In the Modern Periodic table, elements are placed on following basis:

• Increasing atomic numbers of the Elements
• Elements that have the same number of valence electrons are positioned in the same group.
• For instance, elements having 1 valence electron are in the 1st group. 
• Similarly, elements that share an equal number of shells are placed in the same period (row).

Ans. Electro-positivity is a phenomenon in which an atom donates electrons and form positively charged ions. Alkali and Alkaline earth metals primarily exhibit this tendency. For example, Sodium is one such kind of electro-positive element that readily releases an electron.

Ans. The phenomenon of an electron gaining entrance in a new shell increases the distance between the nucleus and the outermost electron. This causes the atomic size to increase down a group. However, along a period, the distance between the nucleus and the outermost shell remains equal as no new shell is formed. The distance between the nucleus and the electron decreases due to attraction, resulting in the decrease of atomic size along a period.

Ans. The five trends of the Periodic Table are as follows:

1. Atomic Number: The elements in the periodic table are arranged in order of increasing atomic number, which is the number of protons in the element's nucleus. This arrangement helps to predict the properties and behaviour of elements based on their atomic number.
2. Periodicity: This grouping of elements helps to predict the chemical and physical properties of elements based on their position in the table.
3. Valence Electron: Elements in the same group, or column, of the periodic table have the same number of valence electrons, which are the electrons in the outermost energy level of an atom. This similarity in valence electrons helps to predict the chemical reactivity of elements based on their group.
4. Electron Affinity: The electron affinity trend of the periodic table refers to the energy change that occurs when an atom gains an electron. This trend helps to predict how easily an element will gain or lose electrons in chemical reactions.
5. Melting and Boiling Points: The melting and boiling points of elements vary greatly across the periodic table, and these trends help predict the stability of elements and their suitability for certain uses. 

Ans. Owing to the fact that the number of electrons in the outermost shell of all elements in a group is the same, they carry the same electronic configuration. This results in them having similar chemical and physical properties.

Ans. While moving along a period from left to right, the valency increases primarily till 4 and starts declining later.

Ans. The trend of the variation of the valency in the modern periodic table while going down in the group are as follows:

• Increasing Valency: As one goes down a group in the modern periodic table, the valency of the elements increases. 
• Similar Electron Configurations: Elements in the same group have similar electron configurations in their valence shell. 
• Group Number as Valency: The group number of an element is also its valency. For example, elements in group 1 have a valency of 1, elements in group 2 have a valency of 2, and so on.
• Stability: As one goes down a group, the valency increases and the elements become more stable due to the increased shielding effect from the inner electrons.
• Reactivity: Due to the increase in valency, elements in the lower groups are more reactive than those in the higher groups of the periodic table. 

Ans. The difference in the approach between the Mendeleev’s and the Modern Periodic Law are as follows:

• Mendeleev's periodic law is based on the idea that elements with similar chemical properties should be arranged in the same vertical column, or group, in the periodic table. On the other hand, Modern periodic law is based on the arrangement of elements in increasing atomic numbers.
• Mendeleev's table was based on the relative atomic masses of the elements, while the modern periodic table is based on the atomic number of the elements.
• Mendeleev's table also left gaps for elements that had not yet been discovered, while the modern periodic table is complete with all the known elements.
• Mendeleev's table was based on the relative atomic masses of the elements, while the modern periodic table is based on the atomic number of the elements.
• Mendeleev's table also left gaps for elements that had not yet been discovered, while the modern periodic table is complete with all the known elements.

Ans. Electron affinity is the energy change that occurs when an atom gains an electron to form a negative ion. It is a measure of the atom's ability to attract electrons.

• Trend Across the Table: The electron affinity trend in the modern periodic table shows that electron affinity generally increases as one moves from left to right across a period and decreases as one moves down a group.
• Group 1 and 2 Elements: Elements in group 1 and 2 generally have low electron affinity values as they have only one or two valence electrons and are already in a stable electronic configuration, making it difficult for them to gain more electrons.
• Group 17 and 18 Elements: Elements in group 17 and 18 generally have high electron affinity values as they have only one or two valence electrons and are already in a stable electronic configuration, making it easy for them to gain more electrons.
• Between Groups: Electron affinity decreases as you go down a group because the atomic radius increases, making it harder for the outermost electrons to be attracted to the nucleus.
• Significance: Understanding the electron affinity trends in the periodic table helps predict the chemical reactivity of elements and the stability of their compounds.

Ans. Two criteria that are used in the development of the Modern Periodic Table are as follows:

Atomic Number

• One of the main criteria used in the development of the modern periodic table is the atomic number of elements. 
• The elements are arranged in the table in order of increasing atomic number, which is the number of protons in the element's nucleus. 
• This arrangement helps to predict the properties and behaviour of elements based on their atomic number.

Electron Configuration

• The second criteria used in the development of the modern periodic table is the electron configuration of elements. 
• Elements in the periodic table are grouped into periods, or rows, based on their electron configuration. 
• This arrangement also helps to understand the trends of electron affinity, valency, reactivity and other properties which are based on the electron configuration of an element.

Ans.  The oxidation state of an element is a measure of its ability to gain or lose electrons. An element with a positive oxidation state has lost electrons, and is therefore an oxidising agent. An element with a negative oxidation state has gained electrons, and is therefore a reducing agent.

• Standard Reduction Potential: The standard reduction potential of an element can also indicate its oxidising or reducing character. Elements with a more positive reduction potential are more likely to act as oxidising agents, while elements with a more negative reduction potential are more likely to act as reducing agents.
• Reactivity: The oxidising character of an element can also be determined by its reactivity, elements that are highly reactive are more likely to act as oxidising agents.
• Experimentally: Oxidising character of an element can also be determined experimentally by using the oxidation-reduction reactions. 
• Comparison: The oxidising character of an element can also be determined by comparing with known oxidising agents like oxygen and chlorine.