Let's evaluate the given formulas:
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Cu(NO3)2: This is the correct formula for copper(II) nitrate, which consists of one copper ion (Cu²⁺) and two nitrate ions (NO3⁻).
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CaCl3: This formula is incorrect because calcium (Ca) typically forms a +2 oxidation state, and thus would bond with only two chloride ions (Cl⁻) to produce CaCl2, not three.
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MgO: This is the correct formula for magnesium oxide, which consists of one magnesium ion (Mg²⁺) and one oxide ion (O²⁻).
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H3O: This is actually correct and represents the hydronium ion, which is formed when water (H2O) gains a proton (H⁺), resulting in H3O⁺.
Correct Formula Explanation: Cu(NO3)2
Let's explain why Cu(NO3)2 is a correct formula.
Copper typically has a valence electron configuration of [Ar] 3d10 4s1, and can lose either one or two electrons to form cations. In the case of copper(II) nitrate, copper loses two valence electrons to form the Cu²⁺ ion.
The nitrate ion (NO3⁻) consists of one nitrogen atom bonded to three oxygen atoms. The nitrogen has five valence electrons and forms three bonds (sharing electrons with oxygen), which allows it to achieve a stable octet configuration. On the other hand, each oxygen atom contributes two valence electrons (each has six valence electrons), and collectively they facilitate the formation of a nitrate ion with a total of 24 valence electrons distributed for stability.
In summary, the formula Cu(NO3)2 is correct as it shows the correct cation (Cu²⁺) pairing with the appropriate number of nitrate ions (-1 charge each) to balance the charge (2 from Cu²⁺ and 2 from two NO3⁻), achieving charge neutrality.
Therefore, the presence of valence electrons plays a critical role in both the formation of the copper and the nitrate ions, leading to the final composition of copper(II) nitrate, represented as Cu(NO3)2.
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