Why does carbonate
have a -2 charge and not -1?
Why does phosphate have a
-3 charge and not -2 or -1?
Why does nitrate have a
-1 charge and not -2 or -3?
My answer: Based on the Lewis structure, these ions need a certain number of electrons in order to be stable...the octet rule allows the atoms to achieve a noble gas configuration. Is this explanation conceptually correct?
Yes, your explanation is conceptually correct. The charges of carbonate, phosphate, and nitrate ions can be understood by looking at their Lewis structures and applying the octet rule.
The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a stable electron configuration with a full outer shell of electrons, similar to the noble gases. For most atoms, this usually means having eight valence electrons.
Carbonate (CO3 2-) consists of one carbon atom bonded to three oxygen atoms. Each oxygen atom needs two electrons to complete its octet, while carbon only has four valence electrons. To achieve a stable configuration, carbon can form two additional bonds and gain two electrons from the oxygen atoms, resulting in a charge of -2 for the carbonate ion.
Phosphate (PO4 3-) contains one phosphorus atom bonded to four oxygen atoms. Each oxygen atom requires two electrons to fill its octet. Phosphorus has five valence electrons, so it can form three additional bonds and gain three electrons from the oxygen atoms to achieve a stable configuration as a phosphate ion with a charge of -3.
Nitrate (NO3 -) includes one nitrogen atom bonded to three oxygen atoms. Each oxygen atom needs two electrons to meet the octet rule. Nitrogen has five valence electrons, so it can form two additional bonds and receive one electron from each oxygen atom to achieve a stable configuration. This results in a nitrate ion with a charge of -1.
In summary, the charges of these ions are determined by the number of electrons that need to be gained or lost in order to achieve a stable electron configuration in accordance with the octet rule.