Modern Periodic Table

• Who made an early periodic table?

  Mendeleev
• How are elements arranged in the modern periodic table?

  Elements are arranged in order of atomic number in periods and groups
• What do electronic structures model?

  They model how electrons are arranged in atoms
• What are the characteristics of periods and groups in the periodic table?

  • Periods: Horizontal rows in the periodic table
  • Groups: Vertical columns containing elements with similar chemical properties
• Why is the table called the periodic table?

  Because elements with similar properties occur at regular intervals
• What is a pair reversal in the context of Mendeleev's periodic table?

  It refers to the incorrect positioning of elements due to lack of knowledge about isotopes
• What did Mendeleev not know about that affected his periodic table?

  He did not know about isotopes
• What is an isotope?

  Atoms of an element with the same number of protons and electrons but different numbers of neutrons
• Why were the positions of iodine and tellurium reversed in Mendeleev's table?

  Because iodine has one naturally occurring isotope, iodine-127, which is the most abundant
• What isotopes are associated with tellurium?

  Tellurium-128 and tellurium-130
• How does the relative abundance of tellurium isotopes affect its atomic mass?

  The high relative abundance of these isotopes gives tellurium a greater relative atomic mass
• What is the atomic number of tellurium?

  52
• How are iodine and tellurium positioned in the modern periodic table?

  They are in the correct order based on their atomic numbers
• What is the atomic number of iodine?

  53