CBSE Class 10 Science Revision Notes Chapter 5

CBSE Class 10 Science Chapter 5 Periodic Classification of Elements Notes

Class 10 Science contains a vast and comprehensive curriculum. Chapter 5 Periodic Classification of Elements is one of the important chapters which needs thorough revision and practice. Moreover, preparing as per the CBSE Syllabus is essential to learning a particular topic efficiently and securing good marks in examinations. Hence, Extramarks has provided Class 10 Science Chapter 5 Notes which can be readily accessed by students from the official website. 

Apart from this, students can specifically refer to Class 10 Science Chapter 5 Periodic Classification of Elements Notes which have been prepared to adhere to the latest CBSE guidelines and NCERT books. This will help students learn and revise these fundamental concepts and formulas from the very beginning. 

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Introduction:

The periodic categorization of elements refers to classifying and grouping chemical elements based on their properties. To build a good foundation in Chemistry, you must memorise the periodic table, as you will need it in subsequent sections. However, before studying the periodic table, you must first grasp how it is formed. To that end, Extramarks has compiled exact and thorough Class 10 Science Chapter 5 Notes to help you prepare.

• Initially, scientists divided elements into two significant categories: metals and nonmetals. Some elements displayed features that prevented them from being classed as metals or nonmetals. Therefore they were dubbed metalloids. This categorization was insufficient for scientific investigation. Many chemists have sought to create a sensible and systematic taxonomy. It was based on each element’s physical and chemical characteristics. These findings were then collated into a table.
• A periodic table is a table that arranges known elements according to their characteristics, so that related elements are grouped in the same vertical column, and dissimilar ones are separated.

Dobereiner’s Triads:

• Johann Wolfgang Dobereiner, a German scientist, organised the elements with comparable characteristics into groups in 1817.
• He discovered several such groupings that had three components. As a result, these organizations were dubbed triads.
• The elements in a triad were grouped in ascending order of their atomic masses. 
• The arithmetic mean of the atomic masses of the first and third elements was almost the same as that of the second or middle element. 
• This distinguishing trait may be used to determine if elements form a trio.

Newlands’ Law of Octaves:

• Many of the then-known elements were sorted in ascending order of their atomic weights by an English chemist named John Newlands in 1866. 
• So he began with the element with the lowest atomic mass (hydrogen) and concluded with Thorium, the 56th element. 
• He noted that the qualities of the eighth element were identical to those of the first element.
• It was determined that there is a systematic link between the order of atomic masses and the recurrence of fundamental characteristics. 
• When written in tabular form, this connection revealed a periodic repeating of the features of the components. As a result, the word periodicity was coined.
• The Law of Octaves was discovered to be relevant only up to Calcium since, beyond Calcium, no eighth element has qualities equivalent to the first. 
• John Newlands thought that there were only 56 elements in nature and that no additional elements would be discovered in the future. 
• However, numerous additional elements were found later on whose characteristics contradicted the Law of Octaves. So this was also insufficient.

Mendeleev’s Periodic Table:

• Dmitri Ivanovich Mendeleev, a Russian scientist, categorised the then-known 63 elements in the form of a table in 1869 based on their physical and chemical characteristics in ascending order of atomic masses.
• He had discovered that when the elements were grouped in increasing atomic mass order, their characteristics recurred cyclically. 
• This discovery concluded that the elements’ physical and chemical characteristics are periodic functions of their atomic masses. 
• This became known as the chemical periodicity law.
• A periodic table is a tabular representation of all known elements based on this rule. 
• It has eight vertical columns labelled “groups” and seven horizontal rows labelled “periods.”
• The eight groups are divided into two sub-groups, A and B. The qualities of elements in a sub-group resemble each other more than the attributes of elements in the two sub-groups.

Achievements of Mendeleev’s Periodic Table:

• Systematic Study of Elements 

The table organized elements with comparable qualities into categories. This was beneficial in methodically understanding and retaining the characteristics of a vast number of components.

• Prediction of New Elements

Mendeleev predicted additional elements and left three gaps for these unknown elements. He was able to forecast their qualities with some accuracy. He gave them the names eka-boron, eka-aluminum, and eka-silicon.

• Correction of Atomic Masses 

Mendeleev adjusted the atomic masses of elements based on their placements in the periodic table. Beryllium’s atomic mass was reduced from 13.5 to 9.0.

Limitations of Mendeleev’s Classification:

• Hydrogen has the same electrical configuration as alkali metals. It mixes with halogens, oxygen, and sulphur to produce compounds such as HCL, H2O, and H2S while also existing as a diatomic molecule like halogens. As a result, Mendeleev was unable to assign a correct place to hydrogen.
• The features of the isotopes are similar, but their atomic weights differ. Mendeleev’s classification would have separated them into various groups based on their atomic masses. However, isotopes were not separated since their characteristics were identical.
• Mendeleev did not follow the rising atomic masses but instead categorised some elements based on similarities in their characteristics. Argon, having an atomic mass of 39.9, was positioned ahead of potassium, with an atomic value of 39.1.

The Modern Periodic Table:

• In 1913, an English scientist called Henry Mosely discovered that an element’s atomic number, indicated by the letter ‘Z,’ was a more fundamental attribute to categorise them than their atomic masses. 
• As a result, Mendeleev’s periodic table was revised. 
• The elements were now classified according to their rising atomic number.
• This became known as the Modern Periodic Law, which holds that “element attributes are a periodic function of their atomic number.” 
• As a result, a new classification of elements based on this was created, dubbed the “Modern Periodic Table.”
• It was simple to forecast the characteristics of the elements when they were placed in increasing atomic number order using this grouping approach. 
• It should be mentioned that element periodicity is determined by the electrical configuration or the number of protons in the nucleus.

Salient Features of the Modern Periodic Table:

The table is divided into 18 vertical columns called groups and seven horizontal rows called periods.

1. Periods: This table contains seven periods. The elements in the periods share the same valence shell or energy shell. Moving from left to right inside a period raises the number of electrons in the energy shells by one. The formula 2n2, where n is the number of shells from the nucleus, may be used to calculate the number of elements present in a period.
2. Groups: The periodic table is divided into 18 categories. The group comprises elements with the same number of electrons in the valence shell or the atom’s outermost shell.
3. Blocks: The periodic table is split into four blocks based on the valence electron subshell. They are as follows: s-Block, p-Block, d-block, and f-block elements. 

Position of Elements in The Periodic Table:

The positions of the individual elements are determined by their valence shells and the number of electrons present in those shells. Sodium (Z – 11, 2,8,1) has three shells. Therefore, it is in period three and has one valence electron in the outermost shell, so it is in group 1. The chemical nature of an element is determined by its position in the periodic table.

• Noble gases

This is a collection of elements in group 18 that are tasteless and odourless monatomic gases with minimal chemical reactivity. Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon are six such gases (Rn).

• Normal elements

This includes all components in groups 1 through 7.

• Alkali metals

The elements in Group 1, namely Lithium (Li) – Francium (Fr), except Hydrogen (H), are referred to as alkali metals because they create hydroxide with water, which is a strong alkali.

• Alkaline earth metals

These elements in Group 2 range from Beryllium (Be) to Radium (Ra). They are less reactive than alkali metals present in compounds.

• Transition elements 

Elements from groups 3 to 11 make up the transition elements. These are so named because their characteristics change from left to right, including increased atomic size, ionisation energy, and electronegativity.

• Inner transition elements

These are elements with comparable characteristics that have been placed at the end of group 3 in periods 7 and 8.

• Halogens

They are a group of elements in Group 17. These are nonmetals that can exist as solids, liquids, or gases.

Properties of the Periodic Table:

• Valency

The number of electrons acquired or lost by an atom to complete its outermost shell and have a stable electronic configuration is called valency. The number of electrons in the valence shell is represented by this valency. It is worth noting that the valency increases from left to right in a period before decreasing. The valency in the group remains constant as it moves lower.

• Atomic Size

The atomic radius of the atom, defined as the distance between the atom’s nucleus and its outermost shell, determines its atomic size.

• Ionization Energy

It is the energy necessary to eliminate the electrons existing in the atom’s outermost shell.

• Electron Affinity

It is defined as the amount of energy change caused by the addition of an electron to the atom or an electron’s capacity to take electrons.

Metallic and non-metallic properties:

The non-metals like sulphur and chlorine are located on the right side of the periodic table, while metals like Na and Mg are located on the left side. Since silicon exhibits some characteristics of both metals and non-metals, it is categorised as a semi-metal or metalloid. Silicon is in the middle of the group. Metals and non-metals are divided by a zigzag line in the Modern Periodic Table. The borderline elements, also known as metalloids or semi-metals, include boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. These elements have intermediate qualities.

• Metals are elements that have a propensity to shed electrons and gain a positive charge.
• Due to their metallic character, elements are electropositive and have low ionisation energy. This metallic character fades with time.
• Elements’ non-metallic nature suggests that they can receive electrons and acquire a negative charge. 
• As a result of their non-metallic origin, they are electronegative and have considerable ionisation energies.
• As a result, the nonmetallic nature grows with time. As a result, as one moves through a period from left to right, the metallic character reduces, the non-metallic character grows, and a semi-metallic nature exists in between.
• As atomic size decreases, so does the metallic character, and they have a more significant potential to lose electrons.
  

Class 10 Science Chapter 5 Notes PDF Download

Class 10 Chemistry Chapter 5 Notes Summary

• Elements are classed based on their property similarity.
• Döbereiner classified the elements into triads, whereas Newlands proposed the Law of Octaves.
• Mendeléev organised the elements in ascending order of their atomic weights and chemical characteristics.
• Mendeléev even anticipated the presence of several elements that had yet to be found based on gaps in his periodic table.
• Anomalies in the organisation of atoms based on rising atomic mass might be addressed by arranging the elements in increasing atomic number order, a fundamental feature of the element found by Moseley.
• The Modern Periodic Table organises elements into 18 vertical columns called groups and seven horizontal rows called periods.
• Elements organised in this manner exhibit periodicity of attributes such as atomic size, valency or combining capability, and metallic and non-metallic character.

Lothar Meyer’s Curves

This is another method of depicting the periodic arrangement of elements plotted in a graph by a German scientist.