Classification of Elements and Periodicity in Properties

• The Periodic Table is crucial in chemistry, providing support for students, suggesting research avenues for professionals, and organizing the whole of chemistry
• It demonstrates that chemical elements are not random but display trends and group together in families
• An awareness of the Periodic Table is essential for understanding the fundamental building blocks of chemistry, the chemical elements
• After studying the Classification of Elements and Periodicity in Properties unit, students will be able to:

  • Appreciate how grouping elements according to their properties led to the development of the Periodic Table
  • Understand the Periodic Law
  • Understand the significance of atomic number and electronic configuration for periodic classification
  • Name elements with Z > 100 according to IUPAC nomenclature
  • Classify elements into s, p, d, f blocks and learn their main characteristics
  • Recognize periodic trends in physical and chemical properties of elements
  • Compare the reactivity of elements and correlate it with their occurrence in nature
  • Explain the relationship between ionization enthalpy and metallic character
  • Use scientific vocabulary appropriately to communicate ideas related to important properties of atoms like atomic/ionic radii, ionization enthalpy, electron gain enthalpy, electronegativity, and valence
• Efforts to classify elements arose due to the difficulty of individually studying a large number of elements and their compounds, leading to the search for a systematic way to organize knowledge about elements
• The genesis of Periodic Classification:

  • Johann Dobereiner noted trends among properties of elements in triads in the early 1800s
  • John Alexander Newlands proposed the Law of Octaves in 1865, arranging elements by atomic weights and noting similarities every eighth element
  • Dmitri Mendeleev and Lothar Meyer developed the Periodic Law, arranging elements by increasing atomic weights, leading to the Modern Periodic Table
• Mendeleev's Periodic Law states that the properties of elements are a periodic function of their atomic weights
• Mendeleev arranged elements in rows and columns based on increasing atomic weights, ensuring elements with similar properties were in the same vertical column or group
• Mendeleev's system of classifying elements was more elaborate than Meyer's, using a broader range of physical and chemical properties to classify elements
• Mendeleev made bold quantitative predictions about undiscovered elements, leaving gaps in the table for them, such as Eka-aluminium and Eka-silicon, which were later discovered
• Mendeleev's Periodic Table was developed without knowledge of the internal structure of the atom
• In the early 20th century, Henry Moseley observed regularities in the characteristic X-ray spectra of elements
• Moseley's observations led to the modification of Mendeleev's Periodic Law
• The modern Periodic Law states that the physical and chemical properties of elements are periodic functions of their atomic numbers
• The Periodic Law is essentially the consequence of the periodic variation in electronic configurations, which determine the physical and chemical properties of elements and their compounds
• The modern version of the Periodic Table is the "long form," with periods (horizontal rows) and groups (vertical columns)
• Elements with similar outer electronic configurations are arranged in vertical columns, known as groups or families
• The seventh period is incomplete and, like the sixth period, would theoretically have a maximum of 32 elements based on quantum numbers
• The IUPAC recommends numbering groups from 1 to 18 in the modern Periodic Table
• New elements with atomic numbers above 100 are named using numerical roots and "ium" at the end
• The naming of new elements with atomic numbers above 100 follows a systematic nomenclature until their discovery is proved and their name is officially recognized
• The IUPAC names for elements with atomic numbers above 100 are shown in Table 3.5
• The permanent name and symbol for a new element are given by a vote of IUPAC representatives from each country
• As of now, elements with atomic numbers up to 118 have been discovered, and their official names have been announced by IUPAC
• The electronic configuration of an element reflects the quantum numbers of the last orbital filled
• The period in the Periodic Table indicates the value of n for the outermost or valence shell
• The number of elements in each period is twice the number of atomic orbitals available in the energy level being filled
• The first period (n = 1) starts with the filling of the lowest level (1s), containing hydrogen (1s1) and helium (1s2) when the first shell (K) is completed
• The second period (n = 2) starts with lithium, and the third electron enters the 2s orbital. Beryllium has the electronic configuration 1s22s2
• Starting from boron, the 2p orbitals are filled with electrons when the L shell is completed at neon (2s22p6), resulting in 8 elements in the second period
• The third period (n = 3) begins at sodium, with the added electron entering a 3s orbital. Successive filling of 3s and 3p orbitals gives rise to the third period of 8 elements from sodium to argon
• The fourth period (n = 4) starts at potassium, with the added electrons filling up the 4s orbital. Before the 4p orbital is filled, filling up of 3d orbitals becomes energetically favorable, leading to the 3d transition series of elements starting from scandium (Z = 21) with the electronic configuration 3d14s2
• The fourth period ends at krypton with the filling up of the 4p orbitals, totaling 18 elements in this period
• The fifth period (n = 5) begins with rubidium and contains the 4d transition series starting at yttrium (Z = 39). This period ends at xenon with the filling up of the 5p orbitals
• The sixth period (n = 6) contains 32 elements, with successive electrons entering 6s, 4f, 5d, and 6p orbitals. The filling up of the 4f orbitals begins with cerium (Z = 58) and ends at lutetium (Z = 71) to give the lanthanoid series
• The seventh period (n = 7) is similar to the sixth period, with the successive filling up of the 7s, 5f, 6d, and 7p orbitals, including most man-made radioactive elements
• The presence of 18 elements in the 5th period of the Periodic Table is justified by the energy order of the available orbitals (4d, 5s, and 5p) and the total number of orbitals available (9), accommodating a maximum of 18 electrons
• Elements in the same vertical column or group have similar valence shell electronic configurations, the same number of electrons in the outer orbitals, and similar properties
• The elements in a vertical column of the Periodic Table constitute a group or family and exhibit similar chemical behavior due to having the same number and distribution of electrons in their outermost orbitals
• Elements are classified into s-block, p-block, d-block, and f-block based on the type of atomic orbitals being filled with electrons