How many valence electrons are there in the compound HCO3-? How stable is a compound with so many valence electrons?

Answer

Bicarbonate is a polyatomic anion with one central carbon atom bonded to three oxygen atoms.  One of the oxygen atoms is also bonded to a hydrogen atom.  The entire ion has a single negative charge.  Let's calculate how many valence electrons are present:  

  • Hydrogen (H):  1 valence electron x 1 atom = 1 valence electron
  • Carbon (C):  4 valence electrons x 1 atom = 4 valence electrons
  • Oxygen (O):  6 valence electrons x 3 atoms = 18 valence electrons
  • Negative charge (-):  The -1 charge indicates one extra electron = 1 valence electrons

      Adding these up:  1+ 4 +18 + 1 = 24 valence electrons

The reactivity of a compound is not solely determined by the total number of valence electrons it possesses.  Reactivity is primarily governed by the arrangement of these valence electrons; specifically how close the atoms are to achieving a stable electron configuration (usually an octet or a duet for hydrogen and lithium). 

Factors influencing reactivity: the octet rule--atoms tend to gain, lose, or share electrons to achieve a full outer shell of 8 valence electrons (like the noble gases, which is a very stable configuration.  Presence of lone pairs--lone pairs of electrons can make a molecule more reactive, as there are regions of high electron density.  Formal charges--molecules with positive or negative charges on atoms tend to be more reactive as they seek to become neutral. Bond polarity--polar bonds are more susceptible to reactions with charged or polar species.  

Other compounds with 24 valence electrons and varying reactivityNitrate ion (NO3-)--all atoms in the nitrate ion achieve an octet through resonance structures.  It is a relatively stable ion.  Formaldehyde (CH2O)-- all atoms achieve an octet.  Formaldehyde is a reactive molecule due to the polar C=O double bond.  Nitric acid (HNO3)--nitric acid is a strong acid and a powerful oxidizing agent, making it highly reactive.  

 

  • Last Updated Apr 29, 2025
  • Views 3
  • Answered By Tamiko Kemp

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