Chemistry (including Biochemistry)/electrons


thank you, please tell me, since reduction is about the addition of electrons and oxidation is taking electrons away, then why is superoxide and peroxide so reactive as an oxidiser if it has more electrons then oxygen? should it not be satisfied with the extra electrons it already has since oxygen usually takes an electron or two to become an oxide but superoxide and peroxide it already has these, why does it need more, where do they go if not to fill the electron spaces already filled?
thank you,

Hi Gene!

My students often complain about oxidation and reduction, because the terminology can be confusing.

Oxidation - the noun, or process, describes removing electrons from something.
Reduction - the noun, is the process of adding electrons to something. (It helps to remember this as 'reducing the charge by adding -1's.)

The element that gains electrons is referred to as an oxidizing agent. So if oxidize is a verb or an adjective, the element in question has been reduced.
An element that loses electrons is referred to as a reducing agent. If reduce is a verb or adjective, the element in question has been oxidized.

Superoxide (one extra electron on an oxygen) and peroxide (two extra electrons on oxygen) are great oxidizing agents. They want to give up those extra electrons to someone else. (Typically, any local double bond is a great candidate for soaking up extra electrons.)

As to 'why does oxygen need more electrons'... it wants to cover its nucleus. (Insert appropriate butt-covering joke here.)

Molecular orbital theory tells us that the lowest energy state (least interference state) in three dimensions for electrons involves eight electrons more-or-less in a sphere around an atom. While they actually arrange themselves in balloonlike shapes, the original idea proposed a mental image similar to an onion; the nucleus at the center and stacked spheres of eight electrons each going outward. When completely surrounded, the nucleus is shielded from strange electrons coming in and taking up space next to the nucleus. Because of this, chemists may say that atoms 'want' either eight (or for hydrogen, lithium, and beryllium, two)  outermost electrons around a nucleus at all times, and will gain or lose electrons to achieve this state.

Bond formation between atoms is essentially a pair of electrons occupying a shared space between nuclei. If the electrons surrounding a nucleus cannot cover the entire nucleus, another electron pair may move in and 'claim' that nucleus, forming a new bond. In this case other electrons are displaced onto a leaving element or molecule. (Where did the extra electrons go? With the leaving group!)

For example, a lone oxygen floating in a vacuum would have six electrons in its outermost sphere.  This is not enough to provide a stable electron cover - the electrons have too much area to cover well, and so there are 'weak areas' in the electron shield. Oxygen seeks to gain two electrons to cover itself completely, so it enters into two bonds with other elements. A shared electron acts as adding one electron. Oxygen may steal or share these electrons to fill the space surrounding it to its satisfaction..

In the case of O2, two oxygen atoms each share two electron pairs, which draws the two oxygen nuclei together in a double bond. The closeness of the two nuclei give the shielding electrons less area to cover in total, which makes the molecule stable. When you add one more electron to this system (superoxide), suddenly one of the oxygens only needs to share one electron pair, and is pushed away from its partner because the extra electron needs space. (Electrons are lousy roommates.) The partner oxygen still wants two extra pairs of electrons and to remain close, so it pulls four electrons towards it. This asymmetric tug-of-war is especially unstable, meaning that the odd-numbered electron state doesn't last long.

If you add two extra electrons to O2 (peroxide), these electrons take up space between the two oxygen nuclei and force them apart a little bit. Both nuclei have seven electrons to themselves, and are sharing two, so no tug-of-war to keep the extra electron to just one atom. This symmetric distribution is somewhat more stable than a superoxide, though more reactive than a double bond.

Because peroxides are somewhat more stable than superoxides - there's no weird stretching of the double bond - a superoxide may accept another electron to become a peroxide, and thus be either an oxidizing reagent or a reducing reagent.

Does this help?


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Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. My chemistry weaknesses are that I do not know organic or inorganic synthesis well, nor am I familiar with advanced inorganic reactions. I will attempt quantum mechanics and thermodynamics questions, but primarily as they relate to biological systems. Furthermore, I cannot tell you if a skin photograph is cancerous, or otherwise diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab (PhD, DDS), studying gelatinase A and oral carcinoma.

2001 American Association for the Advancement of Science
2007 American Chemical Society
2007 Protein Society
2011 UTHSCSA Women’s Faculty Association

Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019)
Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913)
Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835)
Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477)

Poster Abstracts:
Robichaud TK, Carruthers. A "Mutagenesis of the Human type 1 glucose transporter exit site: A functional study." ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007
Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Catalytic Domain Exosites Contribute to Determining Matrix Metalloproteinase Triple Helical Collagen Specificities” Dental Science Symposium. UTHSCSA 2011
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

Oakland University, Auburn Hills MI BS, Biochemistry 1998
University of Massachusetts Medical School, Worcester MA PhD, Biochemistry & Molecular Pharmacology 2001-2008
University of Texas Health Science Center, San Antonio TX Postdoc, Biochemistry 2009-Present

Awards and Honors
1998 Honors College Graduate, Oakland University
2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446
2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars:
Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010)
Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011)
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

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