Formal Charge vs Oxidation Number Flashcards: Electron Accounting

Question 1

Formal charge: how are a bond's electrons assigned?

Accepted Answer

Half to each bonded atom, regardless of electronegativity.

Question 2

Electron accounting: how many nonbonding electrons are in three lone pairs?

Accepted Answer

Six electrons. Each lone pair contains two electrons.

Question 3

Lewis counting: how many bonding electrons are in a single, double, and triple bond?

Accepted Answer

Two, four, and six, respectively. Each bond line represents one electron pair.

Question 4

Oxidation number: how are electrons allocated in an ordinary bond between different elements?

Accepted Answer

Assign the entire bonding pair to the more electronegative atom. Nonbonding electrons stay with their atom.

Question 5

Electron accounting: what must the sum of all atom formal charges, or all atom oxidation numbers, equal?

Accepted Answer

The charge of the whole species. For a neutral molecule, each sum is zero.

Question 6

Formal charge: what's the calculation for a specified Lewis structure?

Accepted Answer

Neutral valence electrons − nonbonding electrons − half the bonding electrons. Read the target atom's counts from that particular structure.

Question 7

NH4+ (charge +1): four N–H single bonds; no lone pairs on N or H. N formal charge? N has 5 valence electrons.

Accepted Answer

+1 — N receives 4 bonding electrons: 5 − 0 − 4 = +1.

Question 8

Neutral H–F: one single bond; F has 3 lone pairs, H none. F is more electronegative than H. H oxidation number? H has 1 valence electron.

Accepted Answer

+1 — the bonding pair goes to F, leaving H assigned 0 electrons: 1 − 0 = +1.

Question 9

Neutral O=C=O: C has no lone pairs; each O has 2. C formal charge? C has 4 valence electrons.

Accepted Answer

Zero — two double bonds assign C 4 bonding electrons: 4 − 0 − 4 = 0.

Question 10

OH− (charge −1): one O–H single bond; O has 3 lone pairs, H none. O formal charge? O has 6 valence electrons.

Accepted Answer

−1 — O receives 1 bonding electron: 6 − 6 − 1 = −1.

Question 11

Neutral N≡N: each N has 1 lone pair. Either N oxidation number? N has 5 valence electrons.

Accepted Answer

Zero — each N is assigned 2 nonbonding electrons and 3 bonding electrons: 5 − 2 − 3 = 0.

Question 12

Neutral CH3Cl: C has 3 C–H single bonds and 1 C–Cl single bond; C and H have no lone pairs, Cl has 3. Cl > C > H in electronegativity. C oxidation number? C has 4 valence electrons.

Accepted Answer

−2 — C gets 6 electrons from the C–H bonds and none from C–Cl: 4 − 6 = −2.

Question 13

Neutral H–C≡N: N has 1 lone pair; C and H have none. N formal charge? N has 5 valence electrons.

Accepted Answer

Zero — N receives 3 electrons from the triple bond: 5 − 2 − 3 = 0.

Question 14

Neutral H2C=CH2: each C has 2 C–H single bonds and the C=C double bond; no atom has lone pairs. C > H in electronegativity. Either C oxidation number? C has 4 valence electrons.

Accepted Answer

−2 — C gets 4 electrons from C–H and 2 from half the C=C bond: 4 − 6 = −2.

Question 15

CN− (charge −1): C≡N; each atom has 1 lone pair. N is more electronegative than C. C oxidation number? C has 4 valence electrons.

Accepted Answer

+2 — C keeps only its 2 nonbonding electrons: 4 − 2 = +2.

Question 16

Neutral CH3F: four single bonds around C; C and H have no lone pairs, F has 3. F formal charge? F has 7 valence electrons.

Accepted Answer

Zero — F receives 1 bonding electron: 7 − 6 − 1 = 0.

Question 17

Neutral CH3–O–H: all bonds are single; O has 2 lone pairs, C and H none. O formal charge? O has 6 valence electrons.

Accepted Answer

Zero — O receives 1 electron from each of its two bonds: 6 − 4 − 2 = 0.

Question 18

Neutral H2C=O: C has 2 C–H single bonds and 1 C=O double bond; O has 2 lone pairs, C and H none. O > C > H in electronegativity. C oxidation number? C has 4 valence electrons.

Accepted Answer

Zero — C gets 4 electrons from C–H and none from C=O: 4 − 4 = 0.

Question 19

NH2− (charge −1): two N–H single bonds; N has 2 lone pairs, H none. N formal charge? N has 5 valence electrons.

Accepted Answer

−1 — N receives 2 bonding electrons: 5 − 4 − 2 = −1.

Question 20

Neutral H–C≡C–H: no atom has lone pairs. C > H in electronegativity. Either C oxidation number? C has 4 valence electrons.

Accepted Answer

−1 — C gets 2 electrons from C–H and 3 from half the C≡C bond: 4 − 5 = −1.

Question 21

H3O+ (charge +1): three O–H single bonds; O has 1 lone pair, H none. O formal charge? O has 6 valence electrons.

Accepted Answer

+1 — O receives 3 bonding electrons: 6 − 2 − 3 = +1.

Question 22

Neutral F–O–F: both bonds are single; O has 2 lone pairs and each F has 3. O formal charge? O has 6 valence electrons.

Accepted Answer

Zero — O receives 2 bonding electrons: 6 − 4 − 2 = 0.

Question 23

Neutral H2N–NH2: all bonds are single; each N has 1 lone pair, H none. N > H in electronegativity. Either N oxidation number? N has 5 valence electrons.

Accepted Answer

−2 — N keeps 2 nonbonding electrons, gets 4 from N–H, and 1 from N–N: 5 − 7 = −2.

Question 24

Neutral F–F: one single bond; each F has 3 lone pairs. Either F oxidation number? F has 7 valence electrons.

Accepted Answer

Zero — each F keeps 6 nonbonding electrons and half the bond: 7 − 6 − 1 = 0.

Question 25

NH4+ (charge +1): four N–H single bonds, no lone pairs. N > H in electronegativity. Giving N all 8 bonding electrons yields −3. Which accounting label belongs on that result?

Accepted Answer

Oxidation number. Equal sharing instead gives N formal charge +1: 5 − 4 = +1.

Question 26

Neutral H–O–H: O has 2 lone pairs; H none. A formal-charge calculation subtracts 2 for O's nonbonding electrons. What count should replace it?

Accepted Answer

Four electrons. Two lone pairs contain 4 electrons, so O formal charge is 6 − 4 − 2 = 0.

Question 27

Neutral O=C=O: C has no lone pairs; each O has 2. A formal-charge calculation assigns C only 2 bonding electrons because it has two neighbors. What count should replace it?

Accepted Answer

Four electrons. Each double bond assigns C 2 electrons, giving 4 − 4 = 0.

Question 28

Neutral F–F: each F has 3 lone pairs. An oxidation-number calculation gives both bonding electrons to the left F. How should this bond be allocated?

Accepted Answer

One electron to each F. Identical-element bonds are split equally, so both F oxidation numbers are zero.

Question 29

OH− (charge −1): O–H single bond; O has 3 lone pairs, H none. A formal-charge calculation gives O both bonding electrons. How many should O receive?

Accepted Answer

One bonding electron. Formal charge splits the pair, giving O: 6 − 6 − 1 = −1.

Question 30

Neutral H2N–NH2: all bonds single; each N has 1 lone pair, H none. N > H in electronegativity. Does the N–N bond contribute +1 or −1 to either N's oxidation number?

Accepted Answer

Neither; its contribution is zero. The N–N electrons are shared equally; the two N–H bonds give each N oxidation number −2.

Question 31

Neutral H–C≡N: N has 1 lone pair; C and H none. A formal-charge calculation assigns N only 1 electron from C≡N. What count should replace it?

Accepted Answer

Three electrons. A triple bond contains 6 electrons; N receives half, so 5 − 2 − 3 = 0.

Question 32

Neutral F–O–F: O has 2 lone pairs, each F has 3. F > O in electronegativity. A learner uses 'oxygen is always −2.' What is O's oxidation number here?

Accepted Answer

+2 — both O–F bonding pairs go to F; O keeps 4 electrons: 6 − 4 = +2.

Question 33

Neutral CH3–O–H: all bonds single; O has 2 lone pairs, C and H none. O > C > H in electronegativity. A learner copies C's formal charge of zero as its oxidation number. What should C's oxidation number be?

Accepted Answer

−2 — C gets 6 electrons from its three C–H bonds and none from C–O: 4 − 6 = −2.

Question 34

CN− (charge −1): C≡N; each atom has 1 lone pair. N > C in electronegativity. Must C have a negative oxidation number because the ion is negative?

Accepted Answer

No; C is +2. C keeps 2 nonbonding electrons, while N receives 8 electrons and is −3; +2 − 3 = −1.

Question 35

A neutral molecule's atom formal charges add to +1. Can that be a complete, consistent charge assignment?

Accepted Answer

No. A neutral species requires a total of zero; recheck the counts and any omitted atoms.

Question 36

Neutral H–O–O–H: all bonds single; each O has 2 lone pairs, H none. O > H in electronegativity. Either O oxidation number? O has 6 valence electrons.

Accepted Answer

−1 — O keeps 4 nonbonding electrons, gets 2 from O–H and 1 from O–O: 6 − 7 = −1.

Question 37

Neutral O=C=O: C has no lone pairs; each O has 2. O > C in electronegativity. Labels C +4 and each O −2 sum to zero. Does that make them correct formal charges?

Accepted Answer

No. Those are oxidation numbers; this Lewis structure has formal charge zero on every atom. A correct total doesn't identify the method.

Question 38

NO3− (charge −1), one specified resonance form: N=Oa, N–Ob, N–Oc; N has no lone pairs, Oa has 2, Ob and Oc have 3 each. Ob formal charge? O has 6 valence electrons.

Accepted Answer

−1 — Ob is singly bonded with 6 nonbonding electrons: 6 − 6 − 1 = −1.

Question 39

H3O+ (charge +1): three O–H single bonds; O has 1 lone pair, H none. O formal charge is +1 and each H is zero. What is their total?

Accepted Answer

+1 — add one O and three H: +1 + 3(0) = +1.

Question 40

Does an atom's formal charge specify its measured local electric charge inside a molecule?

Accepted Answer

No. Formal charge follows a counting convention; electron-density-based partial charges require a stated method and are a different quantity.

Question 41

CO3²− (charge −2): C oxidation number +4, each of the three O atoms −2. What is the oxidation-number total?

Accepted Answer

−2 — +4 + 3(−2) = −2, matching the ion charge.

Question 42

Only the neutral formula C2H4O2 is supplied. Can it uniquely determine the oxidation number of each individual carbon atom?

Accepted Answer

No. Connectivity matters: the formula alone doesn't say which bonds belong to each carbon atom.

Question 43

Neutral C≡O: each atom has 1 lone pair; O > C in electronegativity. C has 4 valence electrons. C formal charge and oxidation number, respectively?

Accepted Answer

−1 and +2. Formal charge: 4 − 2 − 3 = −1. Oxidation number: the triple-bond electrons go to O, so 4 − 2 = +2.

Question 44

NH4+ has overall charge +1. Does that tell you that every atom has formal charge +1?

Accepted Answer

No. The +1 is the total for the ion. In its four-single-bond Lewis structure with no lone pairs, N is +1 and each H is zero.

Question 45

Neutral H–H: one single bond; no lone pairs. Each H has 1 valence electron. Does H having zero for both formal charge and oxidation number make the two methods interchangeable?

Accepted Answer

No. Both methods split this identical-element bond equally, but they allocate ordinary different-element bonds differently.

Question 46

NO3−: in each of its three equivalent Lewis resonance forms, the O formal charges are 0, −1, and −1. Is −2/3 the formal charge of an O atom in one of those forms?

Accepted Answer

No. It is the average across equivalent forms; in any specified form an O formal charge is either 0 or −1.

Question 47

A prompt gives an atom's element and bond orders but omits its nonbonding electrons and overall species charge. Is that enough to determine its formal charge uniquely?

Accepted Answer

No. You need the nonbonding-electron count or enough additional information to deduce it.

Question 48

Neutral F–O–F: O has 2 lone pairs, each F has 3; F > O in electronegativity. O has 6 valence electrons. O formal charge and oxidation number, respectively?

Accepted Answer

Zero and +2. Formal charge: 6 − 4 − 2 = 0. Oxidation number: both bonding pairs go to F, so 6 − 4 = +2.

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Formal Charge vs Oxidation Number Flashcards: Electron Accounting