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chapter : periodic classification of elements....
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Answers
Explanation:
When the elements are arranged according to increasing atomic masses, the physical and chemical properties of every eighth element are similar to that of the first.
Newlands compared these octaves to the series of eight notes of a musical scale.
Assumptions and Limitations:
1. The law was applicable for elements with atomic masses up to 40.
2. Properties of new elements discovered did not fit into the law of octaves.
3. In a few cases, Newlands placed two elements in the same slot to fit elements in the table.
4. He also grouped unlike elements under the same slot.
To know more about Dobereiner’s Triads and Newland’s Law of Octaves, visit here.
Mendeleev’s Periodic Table and Law
The physical and chemical properties of elements are periodic functions of their atomic weights.
Features of Mendeleev’s Periodic Table
● Twelve horizontal rows, which were condensed to 7, known as periods.
● Eight vertical columns known as groups.
● Groups I to VII subdivided into A and B subgroups.
● Group VIII doesn’t have any subgroups and contains three elements in each row.
● Elements in the same group exhibit similar properties.
Metals
Metals are electropositive as they form bonds by losing electrons.
In general cases, oxides of metals are basic in nature.
Nonmetals
Nonmetals are electronegative as they form bonds by gaining electrons.
In general cases, oxides of non-metals are acidic in nature.
Metalloids
The elements which show the properties of both metals and nonmetals are called metalloids or semimetals.
For example – Boron, silicon, germanium, arsenic, antimony, tellurium and polonium.
To know more about Modern Periodic Table and Its Significance, visit here.
Trends in the Modern Periodic Table
Trends in Modern Periodic Table
In a group – Elements have the same number of valence electrons.
Down the group – number of shells increases.
In a period – Elements have the same number of shells.
Along the period – valence shell electrons increase by one unit.
Variation of Valency
Valency of an element can be calculated from the electronic configuration in two ways –
Valency = number of valence electrons (if they are 1, 2, 3 or 4).
Valency = 8 – number of valence electrons (if they are 5, 6, 7 or 8).
All the elements of a group have the same number of valence electrons. Therefore, they all have the same valency.
Variation of Atomic Size
Atomic size or radii: It is defined as the distance from the centre of the nucleus to the valence shell of the atom.
Along the period – Atomic radius decreases because effective nuclear charge increases by one unit and it pulls valence electrons or the electron cloud closer to the nucleus.
Down the group – Atomic radius increases because new shells are added, hence, the distance between the nucleus and valence electrons or the electron cloud increases.
Variation of Metallic Properties
Along the period – Metallic character decreases because the tendency to lose valence electrons decreases due to increasing nuclear charge.
Down the group- As the distance between the nucleus and outermost electron increases, nuclear pull decreases. This increases the tendency of an atom to lose valence electron/s, hence metallic character increases.
Variation of Nonmetallic Properties
Along the period – Non-metallic character increases as the tendency to gain electrons in the valence shell increases due to increasing nuclear charge.
Down the group – As the distance between the nucleus and valence shell increases, nuclear pull decreases. This decreases the tendency of an atom to gain an electron its valence shell, hence non-metallic character decreases.
Variation of Electronegativity
Along the period – Electronegativity increases as the tendency to gain electrons in the valence shell increases due to increasing nuclear charge.
Down the group – As the distance between the nucleus and valence shell increases, nuclear pull decreases. This decreases the tendency of an atom to gain an electron, hence electronegativity decreases.
Explanation:
When the elements are arranged according to increasing atomic masses, the physical and chemical properties of every eighth element are similar to that of the first.
Newlands compared these octaves to the series of eight notes of a musical scale.
Assumptions and Limitations:
1. The law was applicable for elements with atomic masses up to 40.
2. Properties of new elements discovered did not fit into the law of octaves.
3. In a few cases, Newlands placed two elements in the same slot to fit elements in the table.
4. He also grouped unlike elements under the same slot.
To know more about Dobereiner’s Triads and Newland’s Law of Octaves, visit here.
Mendeleev’s Periodic Table and Law
The physical and chemical properties of elements are periodic functions of their atomic weights.
Features of Mendeleev’s Periodic Table
● Twelve horizontal rows, which were condensed to 7, known as periods.
● Eight vertical columns known as groups.
● Groups I to VII subdivided into A and B subgroups.
● Group VIII doesn’t have any subgroups and contains three elements in each row.
● Elements in the same group exhibit similar properties.
Metals
Metals are electropositive as they form bonds by losing electrons.
In general cases, oxides of metals are basic in nature.
Nonmetals
Nonmetals are electronegative as they form bonds by gaining electrons.
In general cases, oxides of non-metals are acidic in nature.
Metalloids
The elements which show the properties of both metals and nonmetals are called metalloids or semimetals.
For example – Boron, silicon, germanium, arsenic, antimony, tellurium and polonium.
To know more about Modern Periodic Table and Its Significance, visit here.
Trends in the Modern Periodic Table
Trends in Modern Periodic Table
In a group – Elements have the same number of valence electrons.
Down the group – number of shells increases.
In a period – Elements have the same number of shells.
Along the period – valence shell electrons increase by one unit.
Variation of Valency
Valency of an element can be calculated from the electronic configuration in two ways –
Valency = number of valence electrons (if they are 1, 2, 3 or 4).
Valency = 8 – number of valence electrons (if they are 5, 6, 7 or 8).
All the elements of a group have the same number of valence electrons. Therefore, they all have the same valency.
Variation of Atomic Size
Atomic size or radii: It is defined as the distance from the centre of the nucleus to the valence shell of the atom.
Along the period – Atomic radius decreases because effective nuclear charge increases by one unit and it pulls valence electrons or the electron cloud closer to the nucleus.
Down the group – Atomic radius increases because new shells are added, hence, the distance between the nucleus and valence electrons or the electron cloud increases.
Variation of Metallic Properties
Along the period – Metallic character decreases because the tendency to lose valence electrons decreases due to increasing nuclear charge.
Down the group- As the distance between the nucleus and outermost electron increases, nuclear pull decreases. This increases the tendency of an atom to lose valence electron/s, hence metallic character increases.
Variation of Nonmetallic Properties
Along the period – Non-metallic character increases as the tendency to gain electrons in the valence shell increases due to increasing nuclear charge.
Down the group – As the distance between the nucleus and valence shell increases, nuclear pull decreases. This decreases the tendency of an atom to gain an electron its valence shell, hence non-metallic character decreases.
Variation of Electronegativity
Along the period – Electronegativity increases as the tendency to gain electrons in the valence shell increases due to increasing nuclear charge.
Down the group – As the distance between the nucleus and valence shell increases, nuclear pull decreases. This decreases the tendency of an atom to gain an electron, hence electronegativity decreases.