- (a) Modern periodic law
- (b) Hund’s rule
- (c) Law of octaves
- (d) Pauli’s exclusion principle
Answer:
(c) Law of Octaves
- (a) atomic numbers
- (b) atomic masses
- (c) similarities
- (d) anomalies
Answer:
(a) atomic numbers
- (a) 7 groups and 18 periods
- (b) 18 groups and 7 periods
- (c) 17 groups and 8 periods
- (d) 8 groups and 17 periods
Answer:
(b) 18 groups and 7 periods
Answer: first and third elements
Answer: Group 18
Answer: atomic mass
Answer: mercury
| List I | List II |
|---|---|
| Triads | Dobereiner |
| Alkali metal | Sodium |
| Law of octaves | Newlands |
| Alkaline earth metal | Calcium |
| Modern periodic law | Henry Moseley |
If false, correct the statement.
This statement is true. Newlands' law of octaves was based on the atomic masses of elements, where he arranged elements in order of increasing atomic mass and observed that every eighth element had similar properties. However, this arrangement had limitations and did not work well for heavier elements. The modern periodic table, developed by Mendeleev and later refined, is based on atomic numbers rather than atomic masses. Atomic number represents the number of protons in an atom and is a more fundamental property than atomic mass. This change from atomic mass to atomic number as the organizing principle resolved many inconsistencies and made the periodic table more accurate and useful for predicting element properties.
This statement is false. Metals generally lose electrons rather than gain them. Metals have a tendency to lose valence electrons from their outermost shell to achieve a stable electron configuration, forming positively charged ions called cations. This is because metals have relatively low ionization energies and low electronegativity values. By losing electrons, metals achieve the electron configuration of the nearest noble gas. Non-metals, on the other hand, tend to gain electrons to complete their valence shells and form negatively charged ions called anions.
This statement is false. Alloys are mixtures of two or more elements where at least one is a metal, and they typically exhibit properties characteristic of metals. Metalloids, not alloys, are the elements that possess properties of both metals and non-metals. Metalloids such as silicon, germanium, arsenic, and antimony have intermediate properties between metals and non-metals. They can conduct electricity under certain conditions but not as effectively as metals, and they have properties that vary depending on their physical form and the conditions under which they are tested. Alloys, being primarily metallic in nature, retain metallic properties such as conductivity and malleability.
This statement is true. Lanthanides and actinides are placed separately below the main body of the periodic table because they resemble one another very closely in their chemical properties. The lanthanides are a series of 15 elements with atomic numbers 57 to 71, while the actinides are a series of 15 elements with atomic numbers 89 to 103. Within each series, the elements have very similar chemical properties because they are filling their inner f-orbitals while their outer electron configurations remain relatively constant. If these elements were inserted into the main periodic table in their proper positions, the table would become extremely wide and difficult to use. By placing them separately, the periodic table remains compact and more practical for reference and study.
This statement is true. Group 17 elements are indeed called halogens. The term halogen comes from Greek words meaning salt-former, which reflects their tendency to form salts with metals. The halogen group includes fluorine, chlorine, bromine, iodine, and astatine. These elements are highly reactive non-metals with seven valence electrons in their outermost shell, giving them a valency of minus one. Halogens readily gain one electron to achieve a stable noble gas configuration. They form diatomic molecules in their elemental state and are known for their strong oxidizing properties. Halogens are widely used in various applications including disinfection, bleaching, and the production of organic compounds. Their reactivity decreases as you move down the group, with fluorine being the most reactive and iodine being the least reactive among the common halogens.
Statement
Elements in same group generally show similar properties, whereas elements across a period show different properties.
Reason
Difference in electronic configuration causes variation in chemical properties across a period.
Answer:
(a) Statement is true and reason correctly explains the statement.
The Modern Periodic Law states that the physical and chemical properties of elements are periodic functions of their atomic numbers. This means that when elements are arranged in order of increasing atomic number, their properties repeat in a regular and predictable pattern. The atomic number, which represents the number of protons in an atom's nucleus, is the fundamental basis for organizing the periodic table. This law replaced Mendeleev's earlier law based on atomic masses, as atomic number provides a more accurate and consistent ordering of elements. The periodic nature of element properties arises from the periodic repetition of electron configurations in the outermost shells of atoms. Elements with similar outermost electron configurations, which occur at regular intervals when arranged by atomic number, exhibit similar chemical and physical properties. This periodic relationship allows scientists to predict the properties of elements and their compounds based on their position in the periodic table.
Groups
Vertical columns in periodic table are called groups.
There are:
Periods
Horizontal rows in periodic table are called periods.
There are:
(i) Dissimilar Elements in Same Group
Some elements with unlike properties were placed in the same group in order to preserve periodicity.
(ii) Position of Hydrogen Uncertain
Hydrogen resembles both:
- alkali metals
- halogens
(iii) Increasing Atomic Mass Order Not Strictly Followed
Examples:
- Cobalt and Nickel
- Tellurium and Iodine
(iv) No Position for Isotopes
Isotopes have same chemical properties but different masses.
(v) No Clear Explanation of Electronic Structure
Mendeleev’s table did not explain the arrangement of electrons, and noble gases were not included in the original table.
The Modern Periodic Table has several important features that organize elements systematically. Elements are arranged in increasing order of atomic number, which provides a logical progression through the periodic table. The horizontal rows in the periodic table are called periods, and there are 7 periods in total. All elements within the same period have the same number of electron shells or energy levels. The vertical columns in the periodic table are called groups, and there are 18 groups in the modern periodic table. Elements that belong to the same group are often grouped into families based on their similar chemical properties and behavior. This organization allows chemists to predict the properties of elements and understand their chemical behavior based on their position in the periodic table.
Elements in the same group of the periodic table show similar chemical properties because they possess the same number of valence electrons, which are the electrons in the outermost shell of an atom. The valence electrons are primarily responsible for determining how an element reacts with other elements and what types of chemical bonds it forms. Since all elements in a group have the same number of valence electrons, they tend to lose, gain, or share electrons in similar ways during chemical reactions. This similarity in electron configuration leads to predictable and comparable chemical behavior among elements within a group, making it possible to classify elements into families with similar properties.
Answer:
Across a period:
- atomic number increases
- valence electrons increase
Hence chemical properties gradually change.
Answer:
Group 1 elements are called alkali metals.
Examples:
- Lithium
- Sodium
- Potassium
Answer:
Group 17 elements are called halogens.
Examples:
- Fluorine
- Chlorine
- Bromine
They are highly reactive non-metals.
Answer:
Group 18 elements are called noble gases.
Examples:
- Helium
- Neon
- Argon
They are chemically inert because outer shell is completely filled.
Applying Newlands’ Law of Octaves
Set I:
F, Mg, C, O, B
Set II:
Al, Si, S, Cl, Ca
Similar Pairs
| Pair | Reason |
|---|---|
| F – Cl | Halogens |
| Mg – Ca | Alkaline earth metals |
| C – Si | Same group |
| O – S | Chalcogens |
| B – Al | Same group |
- Decreases across period
- Increases down group
- Decreases across period
- Increases down group
- Increases from 1 to 4
- Then decreases to 0
Reactivity of elements changes as we move down a group in the periodic table, but the direction of change differs between metals and non-metals. For metals, reactivity increases as we move down a group because the atomic size increases and the valence electrons become farther from the nucleus, making them easier to lose. This results in metals becoming more reactive and more likely to form positive ions as we descend a group. In contrast, for non-metals, reactivity decreases as we move down a group because although the atomic size increases, the ability to gain electrons decreases due to the increased distance of valence electrons from the nucleus. Non-metals become less reactive and less likely to gain electrons as we move down a group. This opposite trend in reactivity between metals and non-metals is an important characteristic of the periodic table and helps explain the chemical behavior of different elements.
Dobereiner
- Grouped elements into triads.
Newlands
- Proposed Law of Octaves.
Mendeleev
- Arranged by atomic masses.
Moseley
- Proposed modern periodic law based on atomic number.
Modern Periodic Table
- 18 groups
- 7 periods
- Based on atomic number
- Elements arranged systematically according to electronic configuration
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