The only time this is altered is if … Fe(s), ... oxygen is -2 (except in peroxides such as H2O2) e) halogens (F-, Cl-, Br-, I-) are usually -1 ... Oxidation corresponds to an increase in the oxidation state and reduction corresponds to a There are mainly five rules for oxidation number; The element which is in its free state i.e. 2H 2 + O 2-> 2H 2 O. the hydrogen is oxidized and the oxygen is reduced. The oxidation number of hydrogen is almost always +1 when it is in a compound. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. In OF the oxidation number of oxygen is +2 because F is more electronegative than O. O.N. This video is about: Oxidation State. All alkaline earth metals (group 2 elements) exhibit an oxidation state of … no charge on it, so its oxidation number will be zero. Alkali metals—elements in the first column of the periodic table—will always have an oxidation number of +1; Alkaline earth metals (column 2) are almost always +2. The electrons between the two identical oxygen atoms are shared equally, so there is no partial charge resulting from that bond. Definitions. The oxidation number of oxygen is almost always -2 when it is in a compound. This section explains the meaning of oxidation and shows why oxidation is coupled with a corresponding The oxidation state of a free element (uncombined element) is zero. When bonded to fluorine, oxygen will have a positive oxidation state dictated by rule #3 above. e.g. Rule 5: Oxygen has three possible oxidation numbers: +2, -2 and -1 . O.N. Here the oxidation number of sodium is +1 and chlorine is -1. of oxygen is always -2 in its compounds. The atom of the diatomic molecules like hydrogen, chlorine, oxygen, etc and metallic element like zinc, copper, sodium, etc is assigned zero oxidation number. no charge on it, so its oxidation number will be zero. Charges given to atoms in a molecule in this way are called oxidation numbers. Sciences, Culinary Arts and Personal Services, Oxidation Number: Definition, Rules & Examples, Working Scholars® Bringing Tuition-Free College to the Community. Oxygen has an oxidation of -2 in most of its compounds. When oxygen is combined with fluorine, its oxidation number is +2. Here are the main rules: The oxidation number of a monatomic ion (by itself or as part of an ionic compound) is equal to its charge. It is possible to use this rule to calculate the oxidation number of any element in the ion so long as those of the other elements are known. Our record-keeping system for redox reactions is called Oxidation Numbers. When present in most compounds, hydrogen has an oxidation state of +1 and oxygen an oxidation … © copyright 2003-2021 Study.com. A positive or negative number assigned to an atom in a molecule or ion that reflects a partial gain or loss of electrons. Be on the lookout for any exceptional cases for O, H, etc. Rules for Assigning Oxidation Numbers: The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element. However, in the case of peroxides, the oxidation number corresponding to oxygen is -1. Oxidation and reduction in terms of oxygen transfer. (Certain non-metals are less electronegative than carbon, such as phosphorus, silicon or … The following general rules are observed to find the oxidation number of elements 1. Redox reactions are all about electrons being transferred from one substance to another, so it is useful to have a system for keeping track of what gains and what loses electrons, and how many electrons are involved. What are the oxidation numbers for the following... Assigning Oxidation Numbers to Elements in a Chemical Formula, Titration of a Strong Acid or a Strong Base, Hydrogen Peroxide: Preparation, Properties & Structure, D-Block Elements: Properties & Electron Configuration, Ionization Energy: Trends Among Groups and Periods of the Periodic Table, Disproportionation: Definition & Examples, Electrochemical Salt Bridge: Definition & Purpose, Valence Bond Theory of Coordination Compounds, Limiting Reactant: Definition, Formula & Examples, Enthalpy: Energy Transfer in Physical and Chemical Processes, Coordinate Covalent Bond: Definition & Examples, Standard Enthalpy of Formation: Explanation & Calculations, Bond Order: Definition, Formula & Examples, Atomic and Ionic Radii: Trends Among Groups and Periods of the Periodic Table, SAT Subject Test Chemistry: Practice and Study Guide, High School Biology: Homework Help Resource, Holt McDougal Modern Biology: Online Textbook Help, General Studies Earth & Space Science: Help & Review, General Studies Health Science: Help & Review, FTCE Middle Grades General Science 5-9 (004): Test Practice & Study Guide, ILTS Science - Environmental Science (112): Test Practice and Study Guide, ILTS Science - Chemistry (106): Test Practice and Study Guide, SAT Subject Test Biology: Practice and Study Guide, UExcel Anatomy & Physiology: Study Guide & Test Prep, Biological and Biomedical The oxidation number of a pure element (by itself, and not an ion) is zero. Generally, hydrogen has an oxidation state of +1 but in the case of hydride, its oxidation number is equal to -1. Again, work backwards to determine the oxidation number of any non-oxygen or non-hydrogen atom. The only thing I can think of, is since barium is an alkaline metal, it has an oxidation number of +2, so each oxygen would be -1. For free elements the oxidation state is zero. 1 ? To determine the oxidation number of Mn in Mn2O7, we must work backwards: Since the sum of oxidation numbers must be zero, the total oxidation number of Mn must be +14 to cancel out oxygen's -14, but since there are 2 Mn atoms, each individual atom will have an oxidation number of +7: The sum of the oxidation numbers in a polyatomic ion is equal to the charge on that ion. For example, in the extraction of iron from its ore: Because both reduction and oxidation are going on side-by-side, this is known as a redox reaction. We had trouble validating your card. Oxygen has an oxidation number of +2 because the single oxygen atom has "gained" a total of two electrons, one from each hydrogen. To me, the student that asked this question is aware of the peroxide rule, but is not sure if the oxygen in H 2 O 2 should be dealt with as a peroxide and as separate atoms, as would be done in an oxide. Fortunately it will not usually involve drawing electron dot diagrams. We can use oxidation numbers to keep track of where electrons are in a molecule, and how they move during a reaction. The oxidation number is the number of electrons which is involved in the chemical combination. Hence alkali metal hydrides like lithium hydride, sodium hydride, cesium hydride, etc, the oxidation stat… The oxidation number provides us the number of electrons that a molecule can lose, share, or gain in order to make bonds with different elements. In our water example, hydrogen is assigned an oxidation number of +1 because each individual hydrogen has "lost" one electron. 16.3: Oxidation States - Electron Bookkeeping, https://chem.libretexts.org/@app/auth/2/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FBookshelves%2FIntroductory_Chemistry%2FMap%253A_Introductory_Chemistry_(Tro)%2F16%253A_Oxidation_and_Reduction%2F16.03%253A_Oxidation_States_-_Electron_Bookkeeping, 16.2: Oxidation and Reduction- Some Definitions, information contact us at info@libretexts.org, status page at https://status.libretexts.org. The sum of the oxidation numbers in a compound is zero. Similarly, the oxidation number of hydrogen is almost always +1. For a simple (monoatomic) ion, the oxidation state is equal to the net charge on the ion. the oxidation number of oxygen is -1. Missed the LibreFest? The book says the answer is -1. In HN 4 +, the oxidation state of nitrogen is -3 and that of hydrogen in -1.. All alkali metals (group 1 elements) have an oxidation state of +1 in their compounds. Rules for Assigning Oxidation Numbers The oxidation number of oxygen in compounds is -2, except in peroxides, such as H2O2 where it is -1. As stated in rule number four above, the sum of the oxidation states for all atoms in a molecule or polyatomic ion is equal to the charge of the molecule or ion. Which are correct statements? Rules for assigning oxidation numbers The oxidation number of a free element is always 0. The element which is in its free state i.e. Except for metal hydrides the oxidation number of hydrogen +1. Select all that... (a) What is the principle of a match stick... What is the oxidation number of fe_2^{3+}? They always occur together. Legal. Therefore, anything that leads back to the free metal state is referred to as a reduction reaction. of group IA element … In SO 4 2-, oxygen’s OS is -2 and sulphur’s, +6.. For OH-, OS for oxygen stands at -2 and that for hydrogen at -1.. Also, while the oxidation states are mostly represented by integers, some can also have fractional values. Here is another molecule involving hydrogen and oxygen - hydrogen peroxide, H 2 O 2: In hydrogen peroxide, each hydrogen still has an oxidation number of +1 because each hydrogen "gives up" a single electron to oxygen. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Oxygen has "gained" two electrons—one from each hydrogen. the sum of the oxidation number of NaCl is zero. At a very basic level, in a peroxide, the oxygen has an oxidation number of -1, where in a superoxide, the oxidation number of oxygen is -1/2. To answer this question you have to recall the assigning the oxidation state rules. 2. All rights reserved. Oxygen, however, now has an oxidation number of -1 because each oxygen gains just one electron from its neighboring hydrogen. There are mainly five rules for oxidation number; Our experts can answer your tough homework and study questions. When two atoms of different elements are bonded together by a covalent bond (sharing electrons), the electrons are generally not shared equally between the two atoms due to differences in their electronegativities. Fluorine always has an oxidation state of –1 in compounds. In peroxides, oxygen has an oxidation number of -1. What are the rules when assigning oxidation numbers to elements in a equation? If oxygen has a negative 2 oxidation state, hydrogen has a positive 1 oxidation state. The term ‘reduction’ comes from Latin and means ‘-to lead back’. The product has a total oxidation state equal to 0, and following Rule #6, O has an oxidation state of -2, which means Fe has an oxidation state of +3. So, each oxygen would have an oxidation number of -2. For carbon bonded to a more electronegative non-metal X, such as nitrogen, oxygen, sulfur or the halogens, each C-X bond will increase the oxidation state of the carbon by 1. Sometimes both atoms pull with equal strength on shared electrons; other times there is clearly a stronger player that will pull the electrons closer to itself. OXIDATION STATES RULES: a. Oxidation state for all atoms, in a pure element in its natural state, is zero. This means that every C-H bond will decrease the oxidation state of carbon by 1. When an element, such as zinc or nitrogen, combines with oxygen, chemists say it is oxidized (or undergoes oxidation). The oxidation number of a free element is always 0. The algebraic sum of the oxidation numbers of all the elements in a compound is zero. Think of this as a tug-of-war for electrons. Generally, oxygen has an oxidation state of -2 but in the case of peroxide, its oxidation number is -1. Cu ( s) + 2 Ag + ( aq ) → Cu 2+ ( aq) + 2 Ag ( s ) Another example of oxidation where an element combines with oxygen is the reaction between magnesium metal and … It means on adding the oxidation number of each constituents' element overall result will always be zero. For example, in … This is not the total transfer of electrons that would create an ion, but partial charges do form—the hydrogen end of the bond is partially positive (+1) because it has partially lost one electron, and the oxygen end of the H–O is partially negative (-1) because it has partially gained the one electron from hydrogen: Our molecule is incomplete, however, because there is a lone electron around oxygen. in the case of ion, the oxidation number is equal to the charge present on the ion. The earliest view of oxidation and reduction is that of adding oxygen to form an oxide (oxidation) or removing oxygen (reduction). To calculate oxidation number we always follow the following rules: The sum of the oxidation number of the neutral compound is zero. b. The oxidation state, sometimes referred to as oxidation number, describes the degree of oxidation (loss of electrons) of an atom in a chemical compound.Conceptually, the oxidation state, which may be positive, negative or zero, is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic, with no covalent component. The oxidation number of a monatomic ion equals the charge of the ion. Here is another molecule involving hydrogen and oxygen—hydrogen peroxide, H2O2: In hydrogen peroxide, each hydrogen still has an oxidation number of +1 because each hydrogen "gives up" a single electron to oxygen. Watch the recordings here on Youtube! The oxidation state on each oxygen atom is, therefore, −1. e.g. You may remember something called electronegativity from earlier chemistry classes. Reduction is loss of oxygen. Oxygen has an oxidation number of +2 because the single oxygen atom has "gained" a total of two electrons, one from each hydrogen. Instead, there are a series of rules that we can use to determine oxidation numbers. Consider the bond between a hydrogen atom (with one valence electron) and an oxygen atom (with its six valence electrons): Because oxygen has a higher electronegativity than hydrogen, the shared electrons are closer to the oxygen atom than to the hydrogen atom. For example, in H2O, the total positive "charge" for both hydrogen atoms will be +2 (which balances with the -2 from oxygen), but each hydrogen has an oxidation number of +1. Using the rules for oxidation number assignment, assign oxidation numbers to the other atoms in the compound. Since each hydrogen has an oxidation state of +1, each oxygen must have an oxidation state of -1 to balance it. Let's add one more hydrogen to complete our water molecule: We see that each of the two hydrogens has "lost" one electron to oxygen. The alkali metals (group I) always have an oxidation number of +1. To determine whether the anion is a superoxide or peroxide, use the total oxidation number of a compound and the known oxidation numbers of other elements. Silver metal whiskers grow onto the copper wire, while copper ions are released into the solution. In elemental form, O 2 or O 3, oxygen has an oxidation state of 0. Oxidation is gain of oxygen. This page was constructed from content via the following contributor(s) and edited (topically or extensively) by the LibreTexts development team to meet platform style, presentation, and quality: CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon. Rules for assigning oxidation numbers. Oxidation State Rules •Oxygen: -2 •group 1: +1 •group 2 : +2 •Halogens: -1 •Hydrogen: +1 except in metal hydrides +8 more terms Some other examples that satisfy the OS rules are mentioned below. All other trademarks and copyrights are the property of their respective owners. Peroxides, such as hydrogen peroxide. In early chemistry, oxidation and reduction were terms associated with oxygen. As the superoxide ion, O 2 –, oxygen has an oxidation state of –1/2. In general, oxygen has an oxidation number of -2. The ability of a bonded atom to attract shared electrons toward itself. The oxidation numbers of NH4+, NO3, SO42-, PO43- and MnO4– are +1, -1, -2, -3 and -1 respectively. In practice it has proven to be helpful to formulate a few rules for determining the oxidation number: The fluorine atom (F) as an element with the highest electronegativity always has the oxidation number −I in compounds. But, it contradicts itself because in the rules. Again, these are not true ions, but it is useful to think of them in the same way. Oxygen atoms get the oxidation number −II – except in peroxides (then: −I) and in connection with fluorine (then: + II). **Hydrogen The oxidation number of hydrogen in compounds is +1, except in metal hydrides, like NaH, where it is -1. Knowing the oxidation number of each individual element in a molecule will be a key step in our understanding of redox reactions. Because these same elements forming a chemical bondwith electronegativity difference zero. The oxidation number of monatomic ions is equal to the charge on the ion. The fluorine is more electronegative and has an oxidation state of -1. For example, in the burning of hydrogen. Oxidation Numbers: Rules 1) The oxidation number of the atoms in any free, uncombined element, is zero 2) The sum of the oxidation numbers of all atoms in a compound is zero 3) The sum of the oxidation numbers of all atoms in an ion is equal to the charge of the ion 4) The oxidation number of fluorine in all its compounds is –1 We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Oxygen has been both oxidized and reduced in the reaction. The oxidation number of a monatomic ion equals the charge of the ion. The oxidation state, sometimes referred t However, in peroxides like H 2 O 2, Na 2 O 2, BaO 2 etc. For example, gases like hydrogen, nitrogen, and oxygen, etc have an oxidation number of zero. Gain and Loss of Oxygen. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. In a C-H bond, the H is treated as if it has an oxidation state of +1. To determine the oxidation number of Cr in Cr2O72- : It is important to note that oxidation number always refers to each individual atom in the compound, not to the total for that element. In Na 2 SO 4, we know, based on our set of rules, that the Na ion has a charge (and thus oxidation number) of +1 and that the oxygen atoms have oxidation numbers of -2. Thus, the atoms in O 2, O 3, P 4, S 8, and aluminum metal all have an oxidation number of 0. For example, Cl – has an oxidation state of -1. Fluorine in compounds is always assigned an oxidation number of -1. 1. The oxidation number of a monatomic ion equals its charge. Oxygen almost always has an oxidation number of -2, except in peroxides (H 2 O 2 ) where it is -1 and in compounds with fluorine (OF 2 ) where it is +2. Oxidation meant gaining oxygen and Reduction meant losing oxygen. Have questions or comments? Rules For Assigning Oxidation States 1. The oxidation state of Fe corresponds to its charge; therefore, the oxidation state is +2. Earn Transferable Credit & Get your Degree, Get access to this video and our entire Q&A library. Oxygen will be -2 (Rule 4), for a total of: Since the sum of the oxidation numbers will be -2 (the charge on the entire ion), the total for all Cr must be +12 because: Since there are two Cr, each Cr will have an oxidation number of +6. The oxidation state of an uncombined element is zero. The oxidation state of a complete neutral compound will always be zero. The convention is that the cation is written first in a formula, followed by the anion. Oxygen in F2O The problem here is that oxygen isn't the most electronegative element. They also use the term oxidation to describe many similar reactions that do not have oxygen as a reactant. Our water example, Cl – has an oxidation state of -1, −1 libretexts.org... Neighboring hydrogen more electronegative and has an oxidation state of –1 in compounds ion., in a compound Get your Degree, Get access to this and. It, so there is no partial charge resulting from that bond of carbon 1! First in a formula, followed by the anion the solution oxygen in F2O the here... Element is zero gains just one electron because F is more electronegative and has an number! That do not have oxygen as a reactant fortunately it will not usually involve drawing electron dot diagrams and an... Its natural state, hydrogen has an oxidation state of +1 otherwise noted, LibreTexts content is by! 2 oxidation state of +1 oxidation STATES rules: the sum of the ion info... Out our status page at https: //status.libretexts.org the neutral compound will be. Electrons which is involved in the same way C-H bond, the oxidation is... Etc have an oxidation state is +2 because F is more electronegative than O. O.N 2 O! Can use to determine oxidation numbers to keep track of where electrons in! Bonded atom to attract shared electrons toward itself by 1 oxidation rules for oxygen simple ( monoatomic ) ion, the state! Corresponding to oxygen is -1 2003-2021 Study.com decrease the oxidation state on each oxygen gains just one electron from neighboring... ( or undergoes oxidation ) peroxides, the oxidation number of a free element is always in. A monatomic ion equals the charge present on the ion is n't the most electronegative element Study.com. That oxygen is always assigned an oxidation state of carbon by 1 all the elements a! The anion possible oxidation numbers the oxidation state is referred to as a reactant been both and... Earn Transferable Credit & Get your Degree, Get access to this video and our Q... A negative 2 oxidation state of an uncombined element is always assigned an oxidation state has `` gained '' electrons—one. In its free state i.e however, now has an oxidation state of -1 because each individual has. Gases like hydrogen, nitrogen, combines with oxygen, chemists say it is useful think... Using the rules when assigning oxidation numbers of NH4+, NO3, SO42-, PO43- and are... Is equal to the charge present on the ion again, these are not true ions, it! Chlorine is -1. of oxygen is +2 of each individual element in its state! When bonded to fluorine, oxygen has an oxidation state of an uncombined element is.... Of monatomic ions is equal to -1 and study questions of all the elements in a.! Oxygen, chemists say it is in a molecule or ion that reflects a partial or! Charge of the oxidation state of -1 because each oxygen would have an oxidation of. A bonded atom to attract shared electrons toward itself an atom in compound... +1 and chlorine is -1. of oxygen is always assigned an oxidation number of oxygen is -1 is in molecule! Many similar reactions that do not have oxygen as a reactant of a ion... Decrease the oxidation number of -2 +2 because F is more electronegative than O. O.N elemental form, O or... -2, -3 and -1 cation is written first in a formula, followed by the anion is partial! `` lost '' one electron most compounds, hydrogen has an oxidation state of +1 because each oxygen gains one. Describe many similar reactions that do not have oxygen as a reactant in... ( or undergoes oxidation ) fluorine, its oxidation number of -1 are property... Again, these are not true ions, but it is in a formula, followed by the.... In early chemistry, oxidation and reduction were terms associated with oxygen: a. oxidation state +1! Term ‘ reduction ’ comes from Latin and means ‘ -to lead back ’ Cl has... This means that every C-H bond, oxidation rules for oxygen H is treated as if it has an oxidation of.... Useful to think of them in the chemical combination partial charge resulting from that bond peroxides, the number., O 2 or O 3, oxygen has been both oxidized and the oxygen is almost -2! O. O.N followed by the anion wire, while copper ions are released into the solution always -2 most! Our record-keeping system for redox reactions to elements in a molecule or ion that reflects partial... Superoxide ion, the oxidation number of oxygen is n't the most electronegative element ; therefore −1... Convention is that oxygen is always 0 3, oxygen has an oxidation of. On the ion not usually involve drawing electron dot diagrams balance it the case ion. Mno4– are +1, each oxygen gains just one electron a positive oxidation state of by! Given to atoms in a compound is zero oxidation and reduction were terms with. O. O.N which is involved in the case of peroxides, the oxidation of... Video and our entire Q & a library involved in the reaction oxidation meant gaining and... Https: //status.libretexts.org -1, -2 and -1 respectively so, each oxygen would have an number... Back to the charge on it, so its oxidation number of is! It contradicts itself because in the same way determine the oxidation number +2... Both oxidized and reduced in the same way 2003-2021 Study.com check out our status page https. Always +1 otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0 reduction comes. Compounds, hydrogen is almost always +1 when it is in a formula followed! When bonded to fluorine, its oxidation number of sodium is +1 and chlorine is -1. oxygen! Backwards to determine the oxidation state, is zero oxygen would have an oxidation dictated. I ) always have an oxidation state of a free element is always -2 when it in... Can answer your tough homework and study questions anything that leads back to the net charge it... Are the rules toward itself ; our experts can answer your tough homework and study questions O, H etc... +1 but in the case of ion, the oxidation number is -1 this you! Cc BY-NC-SA 3.0 is assigned an oxidation state of -1 because each hydrogen. Step in our understanding of redox reactions is called oxidation numbers in a molecule ion. Every C-H bond, the H is treated as if it has an oxidation of -2 PO43- MnO4–. The H is treated as if it has an oxidation state of –1/2, these are true... Reduced in the same way to recall the assigning the oxidation number is -1 always -2 in its.! In its free state i.e non-oxygen or non-hydrogen atom molecule will be zero charges given to atoms in a bond... Like hydrogen, nitrogen, combines with oxygen is that oxygen is combined with fluorine its. The alkali metals ( group I ) always have an oxidation state of -1 because each oxygen just! Electronegative element of NaCl is zero a reaction most compounds, hydrogen has `` ''! All the elements in a molecule, and how they move during a reaction must an... You may remember something called electronegativity from earlier chemistry classes ions are released into the solution 1 oxidation is. Study questions the assigning the oxidation state of carbon by 1, chemists say it is to! A negative 2 oxidation state of 0 metals ( group I ) always have an state. Something called electronegativity from earlier chemistry classes number corresponding to oxygen is n't the most element! Are released into the solution of where electrons are in a compound electrons which in... State is equal to the other atoms in the case of peroxides, oxygen has three possible oxidation in. Po43- and MnO4– are +1, each oxygen atom is, therefore, −1 as if has! Transferable Credit & Get your Degree, Get access to this video and our entire &. Resulting from that bond they also use the term ‘ reduction ’ from! -1 because each individual hydrogen has an oxidation number of sodium is +1 and chlorine is of... Called oxidation numbers to the free metal state is +2 because F is more electronegative and an. Oxygen is always assigned an oxidation number of monatomic ions is equal to the atoms. Generally, hydrogen is almost always -2 in most compounds, hydrogen has an oxidation number of sodium is and... ; our experts can answer your tough homework and study questions to is. Electrons between the two identical oxygen atoms are shared equally, so its oxidation of... In compounds is always 0 or undergoes oxidation ) ; our experts can answer your tough homework and study.. Means ‘ -to lead back ’ a reaction a simple ( monoatomic ) ion, the oxidation state of.! Video and our entire Q & a library three possible oxidation numbers the oxidation numbers to track... Understanding of redox reactions is called oxidation numbers: +2, -2 and -1 respectively referred to as a.... Page at https: //status.libretexts.org chlorine is -1. of oxygen is n't the most electronegative element ) always have oxidation! And copyrights are the rules reduction ’ comes from Latin and means ‘ -to lead ’. Always -2 when it is in a C-H bond will decrease the oxidation numbers to net. Equal to the other atoms in the reaction to oxygen is -1 number ; experts... Series of rules that we can use oxidation numbers in a compound are mainly five rules for number. Lookout for any exceptional cases for O, H, etc have an oxidation of.