Chemistry Unit 3: Periodic Classification of Elements
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Questions and Answers

What is the basis of arranging elements in Dobernier's Triads?

  • Chemical reactivity
  • Atomic volume
  • Electronegativity
  • Atomic mass (correct)

    • In the Triad of Li, Na, and K, what is the atomic mass of sodium?

  • 21 u
  • 23 u (correct)
  • 24 u
  • 22 u

    • Which element did Newlands claim showed similar properties in his Law of Octaves?

  • Every 6th element
  • Every 10th element
  • Every 8th element (correct)
  • Every 7th element

    • What was a major limitation of Newlands' classification system?

    <p>It mixed elements with different properties.</p> Signup and view all the answers

    In which year did Newlands propose his Law of Octaves?

    <p>1865</p> Signup and view all the answers

    How did Dobernier define the atomic mass of the middle element in a Triad?

    <p>It is the average of the extreme elements' atomic masses.</p> Signup and view all the answers

    Which elements were incorrectly placed together in Newlands' system despite differing properties?

    <p>Cobalt and nickel</p> Signup and view all the answers

    What was a critical flaw in Newlands' ability to account for newly discovered elements?

    <p>He prepared his table for only 56 elements.</p> Signup and view all the answers

    What was a limitation of Newland's law of octaves regarding the arrangement of elements?

    <p>It did not account for any noble gases in the arrangement.</p> Signup and view all the answers

    How did Newland classify the elements in his law of octaves?

    <p>In the order of increasing atomic masses.</p> Signup and view all the answers

    Which of the following statements is true about the limitations of Newland's classification?

    <p>It placed elements with different properties in the same group.</p> Signup and view all the answers

    What was the main issue Newland faced regarding the number of elements he classified?

    <p>He did not leave spaces for elements that could be discovered later.</p> Signup and view all the answers

    What is a key feature observed in Newland's law of octaves?

    <p>Every 8th element exhibited similar properties to the first element in the group.</p> Signup and view all the answers

    What does periodicity in the classification of elements imply?

    <p>Repetition in properties of elements after a fixed interval.</p> Signup and view all the answers

    Why is the classification of elements necessary?

    <p>To enhance the understanding of elements with similar characteristics.</p> Signup and view all the answers

    How many elements are currently known, according to the classification discussed?

    <p>118 elements</p> Signup and view all the answers

    What characterizes the arrangement of elements in the periodic table?

    <p>Elements with similar properties are grouped together systematically.</p> Signup and view all the answers

    Which of the following best describes the primary goal of classifying elements?

    <p>To provide a systematic and logical way to study elements.</p> Signup and view all the answers

    Which of the following statements about Mendeleev's classification of elements is true?

    <p>He left gaps in his table for undiscovered elements.</p> Signup and view all the answers

    What does the term 'Eka' signify in Mendeleev's periodic table?

    <p>It means 'next' in Sanskrit, suggesting the following element in a series.</p> Signup and view all the answers

    Which element's atomic mass did Mendeleev correct, resulting in a significant adjustment?

    <p>Beryllium</p> Signup and view all the answers

    How many groups did Mendeleev's periodic table contain?

    <p>9</p> Signup and view all the answers

    What was one of the primary achievements of Mendeleev's periodic table?

    <p>It enabled a systematic study and memorization of element properties.</p> Signup and view all the answers

    What is the position of Hydrogen in the periodic table?

    <p>Between alkali metals and halogens</p> Signup and view all the answers

    Why is Cobalt placed before Nickel in Mendeleev's periodic table despite having a higher atomic mass?

    <p>To maintain periodic trends</p> Signup and view all the answers

    How does Mendeleev's periodic table treat the isotopes of Hydrogen?

    <p>Each isotope is placed in separate locations</p> Signup and view all the answers

    What differentiates the placement of Lanthanoids and Actinoids from other elements in the periodic table?

    <p>They are placed at the bottom of the periodic table</p> Signup and view all the answers

    What is a unique characteristic of isotopes in the context of Mendeleev's periodic table?

    <p>They have the same atomic number</p> Signup and view all the answers

    What is the systematic name for the element with atomic number 120?

    <p>unbinilium</p> Signup and view all the answers

    Which electronic configuration corresponds to element 86 in the periodic table?

    <p>1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s1 5p1</p> Signup and view all the answers

    Which of the following is the correct nomenclature for element 115?

    <p>ununpentium</p> Signup and view all the answers

    Identify the correct electronic configuration for the element directly following element 43.

    <p>1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s1</p> Signup and view all the answers

    Which block of the periodic table does element 115 belong to?

    <p>D-Block</p> Signup and view all the answers

    What fundamental property of elements did Moseley determine is related to x-ray spectra?

    <p>Atomic number</p> Signup and view all the answers

    How did Moseley generate x-rays for his experiments?

    <p>By focusing high-energy electrons on a target element</p> Signup and view all the answers

    What was the relationship Moseley observed regarding x-ray frequencies?

    <p>Frequency proportional to atomic number</p> Signup and view all the answers

    In what year did Moseley discover the link between x-ray spectra and atomic number?

    <p>1913</p> Signup and view all the answers

    Which property did Moseley determine was NOT fundamental for the classification of elements?

    <p>Atomic weight</p> Signup and view all the answers

    What is the general electronic configuration of S-block elements?

    <p>ns1-2</p> Signup and view all the answers

    Which of the following groups are included in the P-block elements?

    <p>Groups 13 to 18</p> Signup and view all the answers

    Which property is characteristic of S-block elements when heated?

    <p>They emit unique flame colors.</p> Signup and view all the answers

    Which statement about P-block elements is true?

    <p>They contain both metals and non-metals.</p> Signup and view all the answers

    What is the combined term for S and P-block elements?

    <p>Representable elements</p> Signup and view all the answers

    Which characteristic is unique to d-block elements compared to f-block elements?

    <p>They can form alloys.</p> Signup and view all the answers

    Which of the following statements about f-block elements is false?

    <p>Their compounds are typically colorless.</p> Signup and view all the answers

    What is a common property of both d-block and f-block elements?

    <p>They have complex colored compounds.</p> Signup and view all the answers

    Which of the following features is primarily associated with d-block elements?

    <p>They contain a significant number of unpaired electrons.</p> Signup and view all the answers

    Which statement accurately describes the d-block elements?

    <p>They can exhibit multiple oxidation states.</p> Signup and view all the answers

    Why does the atomic radius increase when moving down a group in the periodic table?

    <p>The number of electron shells increases.</p> Signup and view all the answers

    What happens to the atomic radius when moving from left to right across a period?

    <p>The atomic radius decreases because electrons are added to the same shell.</p> Signup and view all the answers

    What is the covalent radius if the internuclear distance of covalently bonded atoms is 100 pm?

    <p>50 pm</p> Signup and view all the answers

    How does the formation of a cation affect the atomic radius?

    <p>The radius decreases due to loss of electrons and reduced electron-electron repulsion.</p> Signup and view all the answers

    What is the effect on atomic radius when an atom gains electrons to form an anion?

    <p>The atomic radius increases due to increased electron-electron repulsion.</p> Signup and view all the answers

    Study Notes

    Introduction to Periodic Classification

    • Periodicity refers to the recurring properties of elements at fixed intervals.
    • Elements with similar characteristics are grouped, forming the foundation of the periodic table.

    Importance of Classifying Elements

    • Currently, there are 118 known elements, with ongoing discoveries necessitating organization.
    • Classification groups elements with similar properties, facilitating study and understanding.

    History of Classification

    • Early classification focused on groups, such as Dobernier's Triads, where elements with similar properties were categorized in threes based on atomic mass.
    • Examples:
      • Lithium (Li), Sodium (Na), Potassium (K): Na = 23 u derived from the average of Li and K.
      • Calcium (Ca), Strontium (Sr), Barium (Ba): Sr = 88.5 u derived from the average of Ca and Ba.
      • Chlorine (Cl), Bromine (Br), Iodine (I): Br = 81.2 u derived from the average of Cl and I.

    Newlands' Law of Octaves

    • Proposed by John Newlands in 1865, this law suggested that every eighth element shares properties when arranged by increasing atomic weight.
    • Limitations:
      • Incorrect placements of elements like Calcium and Potassium.
      • Failed to account for new elements; only 56 elements were included, with no prediction of future discoveries.
      • Inflexibility in classifying newly discovered noble gases.

    Mendeleev's Periodic Table

    • Developed by Dmitri Mendeleev, it grouped 63 elements based on periodic properties related to atomic mass.
    • Organized into groups (vertical) and periods (horizontal), with a total of 9 groups and 7 periods.
    • Successfully predicted the existence and properties of undiscovered elements like Gallium and Germanium, referred to as Eka aluminium and Eka silicon.

    Achievements of Mendeleev's Table

    • Enhanced systematic study and memorization of elements.
    • Corrected atomic masses, notably of Beryllium.
    • Predicted properties of new elements; left gaps for undiscovered ones.

    Challenges with Mendeleev's Table

    • Misplaced hydrogen, which shares properties with both alkali metals and halogens.
    • Incorrect ordering of Cobalt (Co) and Nickel (Ni).
    • Isotopes wrongly placed in different locations despite having the same atomic number.
    • Lanthanoids and actinoids were positioned outside the main table.

    Modern Periodic Law

    • Mosley's discovery in 1913 linked atomic number to x-ray spectra.
    • Established atomic number as the fundamental property over atomic mass, leading to a more accurate periodic arrangement.

    Nomenclature of Elements with Atomic Numbers >100

    • Unique prefixes denote quantities from 0 to 9.
    • Example: Ununpentium (Uup) for atomic number 115.

    Long Form of the Periodic Table

    Atomic No. S-Block Alkaline Earth Metals D-Block Transition Elements
    Alkali Metal
    F-Block
    Lanthanoids
    Actinoids

    S-Block Elements

    • Comprised of groups 1 and 2, consisting of highly reactive elements.
    • General electronic configuration: ns1-2; good conductors of heat and electricity.

    P-Block Elements

    • Contains elements whose last electron enters the p-subshell (ns2np1-6).
    • Includes groups 13 to 18:
      • Pnictogens (Group 15)
      • Chalcogens (Group 16)
      • Halogens (Group 17)
      • Noble gases (Group 18)

    D-Block and F-Block Elements

    • D-Block: Last electron enters d-subshell, characterized by high melting points, variable oxidation states, and often paramagnetic properties.
    • F-Block: Contains lanthanides and actinides, generally heavy metals, with high boiling points and often radioactive qualities.

    Periodicity in Properties

    Atomic Radius

    • Defined as the distance from the nucleus to the outer electron shell.
    • Increases down a group due to additional electron shells.
    • Decreases across a period due to increasing nuclear charge pulling electrons closer.

    Types of Atomic Radii

    • Covalent Radius: Half the internuclear distance in covalent bonds (example: 37 pm).

    Changes in Atomic Radius with Charge

    • Cations: Formation reduces electron count, decreasing atomic size.
    • Anions: Formation increases electron count, leading to greater size due to increased repulsion.

    These key points summarize the periodic classification of elements and the trends in their properties, providing a foundational understanding for further studies in chemistry.

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    Explore the periodic classification of elements in Chemistry Unit 3. This quiz covers the significance of classifying elements and the properties that repeat systematically. By understanding these concepts, you will appreciate the formation of the periodic table and its importance in chemistry.

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