Respuesta :
Answer: D
- Cation: [tex]\text{Ca}^{2+}[/tex]
- Anion: [tex]\text{Cl}^{-}[/tex]
- Formula: CaCl₂
Explanation
- Cations are ions that carry one or more positive charges.
- Anions are ions that carry one or more negative charges.
Electrons have negative charges. Atoms are originally neutral. They turn positive and form cations when they lose electrons. They turn negative and form anions when they gain electrons.
The superscript next to an ion shows its charge. By convention, the size of the charge is written in front of the sign of the charge. For example, "[tex]1-[/tex]" indicates a negative charge of one. "[tex]2+[/tex]" indicates a positive charge of two.
The choices include only elements from the s block and the p block. They are main group elements. Charges of their ions can be predicted.
- In case the name of the element ends in -ium. The element is likely to be a metal. It tends to lose electrons to form a cation. It will lose all its valence electrons in most cases. The number of valence electrons in a main group metal atom (1, 2, 3, etc.) is the same as the last digit of its IUPAC group number. As a result, that number will also be the charge of the ion that it forms.
- Otherwise, the element is likely to be a nonmetal. It seeks to have eight valence electrons. However, most nonmetals have less than that number. It tends to gain the missing electron or electrons. By doing so, it will form an anion. All of the known nonmetals are in the main group. Like metals from the main group, the number of valence electrons in a nonmetal atom (4, 5, 6, 7, or 8) is the same as the last digit of its IUPAC group number. Subtracting that number from eight will give the number of electrons added to the atom when it forms an anion. The result will also be the charge on the anion that it forms. For example, chlorine Cl has IUPAC group number 17. It has 7 valence electrons. [tex]8 - 1 = 7[/tex]. It will accept one extra electron. As a result, its anion [tex]\text{Cl}^{-}[/tex] will have a charge of -1.
- The rule above does not work for hydrogen H. An H atom has only one valence electron. It tends to lose that electron to form the [tex]\text{H}^{+}[/tex] ion, with a charge of +1.
Also by convention, cations shall go in front of anions in a chemical formula. Their should balance the charge on each other. For example, [tex](+2) + 2 \times (-1) = 0[/tex]. Two ions of charge -1 would combine with one ion of charge +2 to form a neutral compound.
Choice A:
[tex]\text{Cl}^{-}[/tex] is an anion, not a cation.
Choice B:
Magnesium Mg is in IUPAC group 2. It has two valence electrons. It tends to lose both of them to form an [tex]\text{Mg}^{2+}[/tex] ion with a charge of +2. The [tex]\text{Mg}^{+}[/tex] ion with a charge of +1 might be too unstable to become part of an ionic compound.
Choice C:
[tex]\text{Na}^{+}[/tex] is a cation and has a positive charge. By convention, it should go in front of [tex]\text{Cl}^{-}[/tex], which is an anion and has a negative charge. The formula should be NaCl.
Choice D:
Calcium Ca is also in IUPAC group 2. Similar to Mg, it has two valence electrons and tends to form a [tex]\text{Ca}^{2+}[/tex] ion. Each [tex]\text{Ca}^{2+}[/tex] ion shall combine with two [tex]\text{Cl}^{-}[/tex] ions for their charges to balance. Hence the formula CaCl₂.
