Understanding the Periodic Table of Elements

Posted on Feb 23, 2025 in Chemistry

ITEM 8 – Periodic Table

  • Pure Substance: A substance that consists of a single component, has characteristic properties and a fixed, unchanging chemical composition. It cannot be separated into other components by physical methods.
  • Mixture: A combination of two or more substances in a way that does *not* produce a chemical reaction. The individual components maintain their identity and chemical properties.
  • Chemical Element: Pure substances that cannot be decomposed into any other simpler pure substance by chemical or physical methods.
  • Chemical Compound: A substance composed of one or more elements in the periodic table that can be decomposed/separated only by chemical, not physical, means.
  • Atom: An extremely small particle of matter that is part of the molecule in chemical elements. It consists of a nucleus of neutrons, protons, and electrons. It possesses an overall neutral electrical charge.
  • Molecule: The smallest part of a substance that can exist in a free state.

Atom Structure

  1. Nucleus: The center of the atom, consisting of protons (p+), which are positively charged, and neutrons (n), which have a neutral charge. Therefore, the nucleus is positively charged.
  2. Electron Cloud: Surrounds the nucleus and is formed by electrons (e–), particles that are in constant motion.
  • The mass of atoms is expressed in atomic mass units (u). The mass of a proton and a neutron is equal to 1u, and the mass of an electron is negligible.
  • The electric charge of the electron is the same as the proton’s electric charge and is called elementary charge.
  • Proton: electric charge: +1.6 × 10-19C, mass: 1.67 × 10-27kg
  • Electron: charge: -1.6 × 10-19C, mass: 9.10 × 10-31kg
  • Neutron: electric charge: 0; mass: 1.67 × 10-27kg
  • Atomic Number: This is the number of protons in the nucleus of a particular element and is represented by the letter Z.
  • Mass Number: The sum of protons and neutrons present in the nucleus. It is represented by the letter A.
  • Isotopes: Atoms with the same atomic number but different atomic mass. That is, their atomic nuclei have the same number of protons but different numbers of neutrons.
  • Atomic Mass: The total mass of protons and neutrons in a single atom in a state of rest. For example, 12C (98.89%) and 13C (1.11%) are calculated by multiplying the mass number of each isotope by its abundance: (12 * 98.89) + (13 * 1.11). The result is then divided by 100.
  • Atomic Radius: The distance from the center of the nucleus to the outer electron orbital of an atom that is in balance. Usually measured in picometers (1 pm = 10-12 m) or Angstroms (1 Å = 10-10 m). The atomic radius of an element increases from top to bottom and from *right* to *left* in the periodic table.
  • Ionization Potential: The energy required to remove an electron from the outermost layer of a neutral atom in its ground state and in gaseous form. This energy is measured in Joules. X(g) + Energy → X+(g) + 1 e–. The ionization energy increases from left to right and from bottom to top.
  • Electronegativity: The tendency of an atom to attract electrons from other atoms when they combine to form a molecule. Electronegativity increases from left to right and from bottom to top.