Valence Electrons and Chemical Properties

Valence Electrons and Blocks

• Valence Electrons: Electrons in the outermost energy level (shell) of an atom.

• Octet Rule: Atoms tend to gain, lose, or share electrons to achieve 8 valence electrons (a full outer shell). Exceptions include hydrogen and helium (duplet rule—2 electrons).

• Family Numbers (Representative Elements): Valence electrons determine the group number for elements in groups A (representative elements).

  • 1A: 1 valence electron
  • 2A: 2 valence electrons
  • 3A: 3 valence electrons
  • 4A: 4 valence electrons
  • 5A: 5 valence electrons
  • 6A: 6 valence electrons
  • 7A: 7 valence electrons
  • 8A: 8 valence electrons (stable, noble gases)

• Orbital/Electron Distribution: The table correlates valence electrons with the filling order of the s and p orbitals.

  • s orbital can hold 2 electrons
  • p orbital can hold up to 6 electrons

• Charges and Stability:

  • Loss of electrons → positive charge (cation): Easier way to reach a noble gas configuration. Thus, elements with 1-4 valence electrons gain stability by losing those electrons.
  • Gain of electrons → negative charge (anion): Easier way to reach a noble gas configuration.
  • Elements in Group 8A (noble gases) have a charge of 0, because they already have a full valence electron shell.

Periodic Table Blocks

• Blocks: The periodic table is divided into blocks (s, p, d, f) based on the type of orbital where valence electrons reside.

  • s-block: Groups 1 and 2 (alkali metals and alkaline earth metals); valence electrons occupy the s orbital

  • p-block: Groups 13-18; valence electrons occupy the p orbital

  • d-block (Transition Metals): Groups 3-12; valence electrons occupy the d orbital

  • f-block (Inner Transition Metals): Lanthanides and Actinides; valence electrons occupy the f orbital

Determining Electron Configuration and Properties Using Group and Period Information

• Period number correlates to energy level (n): The highest energy level (principal quantum number) occupied by electrons.

• Group number and valence electrons are linked: The number of valence electrons determines the group number (for elements in groups A, or s and p blocks)

• Example: To determine the electron configuration of an element in period 2 and group 8A:

  • Identify the period (2) and recognize the highest energy level (2).
  • Identify the group (8A) meaning the element has 8 valence electrons.
  • Determine the appropriate orbitals (using the table): The first two valence electrons go in the s orbital(s) and the remaining 6 in p orbitals: 1s²2s²2p⁶

• Example Yttrium (39):

  • Determine the electron configuration ([Ar] 4s23d104p65s24d1).
  • The valence electrons are 2+1=3, which means the element is in the 3B family (add valence electrons of s and d orbitals).
  • The highest energy level is 5, suggesting the element is in period 5.

• Exceptions (transition metals such as Copper): The expected electron configuration isn't always the actual configuration Use the expected electron configuration in these cases to determine the group number and valence electrons.