Ions, Ionic Bonding and Ionic Formulas

An anion is defined as a negatively charged ion that results from an atom gaining one or more electrons. This process increases the number of electrons relative to protons, resulting in an overall negative charge. Unlike cations, which are formed by the loss of electrons and carry a positive charge, anions are typically formed by nonmetals, which have a greater tendency to gain electrons to achieve a stable electron configuration.

Ionic compounds are formed when atoms transfer electrons, resulting in the creation of positively charged cations and negatively charged anions. The strong electrostatic attraction between these oppositely charged ions is what holds them together, creating a stable ionic bond. This attraction is significantly stronger than other types of interactions, such as covalent bonds or magnetic forces, making ionic compounds distinct in their properties and structure.

Magnesium and oxygen form an ionic compound because magnesium is a metal that readily loses two electrons to achieve a stable electron configuration, while oxygen is a non-metal that gains two electrons to complete its outer shell. This transfer of electrons creates positively charged magnesium ions (Mg²⁺) and negatively charged oxide ions (O²⁻), which are held together by strong electrostatic forces of attraction, characteristic of ionic bonds. In contrast, the other pairs involve elements that either do not readily transfer electrons or are of the same type, leading to covalent bonding instead.

When an oxygen atom gains 2 electrons, it becomes negatively charged because electrons carry a negative charge. The addition of two electrons to the neutral oxygen atom, which originally has 8 protons and 8 electrons, results in a total of 10 electrons. This results in an overall charge of -2, leading to the formation of the O²⁻ ion. Thus, the ion formed is the oxide ion, O²⁻.

Calcium carbonate is formed from the combination of calcium ions (Ca²⁺) and carbonate ions (CO₃²⁻). To achieve electrical neutrality, one calcium ion combines with one carbonate ion, resulting in the formula CaCO₃. This indicates that for every calcium ion, there is one carbonate ion, reflecting the 2:1 charge balance between the ions. Other options either misrepresent the stoichiometry or suggest incorrect ratios of ions, making CaCO₃ the accurate representation of calcium carbonate.

When an aluminium atom loses 3 electrons, it results in a positively charged ion. Since electrons carry a negative charge, losing them increases the overall positive charge of the atom. The atomic number of aluminium is 13, so when it loses 3 electrons, it has 10 electrons left, leading to a charge of +3. Thus, the ion formed is Al³⁺, indicating that it has lost three electrons and has a charge of +3.

Ammonium nitrate is a salt formed from the combination of the ammonium ion (NH₄⁺) and the nitrate ion (NO₃⁻). When these ions combine, they form a single unit without any additional ions or molecules involved. The chemical formula reflects this combination, where one ammonium ion pairs with one nitrate ion, resulting in NH₄NO₃. This formula indicates the presence of one ammonium group and one nitrate group, which is characteristic of ammonium nitrate as a compound.

Ionic compounds consist of cations (positively charged ions) and anions (negatively charged ions). For the compound to be stable, the overall charge must be neutral, meaning the total positive charge from the cations must equal the total negative charge from the anions. This balance ensures that there is no net charge, allowing the compound to exist in a stable form. If the charges did not cancel out, the compound would be unstable and unable to maintain its structure.

Group 7 of the periodic table, also known as the halogens, typically forms ions with a charge of −1. This is because halogens have seven electrons in their outermost shell and require one additional electron to achieve a stable octet configuration. By gaining one electron, they attain a full outer shell, resulting in a negatively charged ion (anion). This characteristic behavior distinguishes them from other groups, such as Group 1 and Group 2, which form positively charged ions.

An atom with 12 protons and 10 electrons has a net positive charge because protons are positively charged and electrons are negatively charged. The number of protons (12) exceeds the number of electrons (10) by 2. This results in an overall charge of +2, indicating that the atom is a positively charged ion, or cation, due to the loss of two electrons.

Sodium sulfate is formed from the combination of sodium ions (Na⁺) and sulfate ions (SO₄²⁻). Each sulfate ion carries a charge of -2, while each sodium ion has a charge of +1. To balance the charges, two sodium ions are required for each sulfate ion, resulting in the formula Na₂SO₄. This ensures that the overall charge of the compound is neutral, with two positive charges from sodium balancing the single negative charge from sulfate. Thus, the correct formula for sodium sulfate is Na₂SO₄.

NO₃⁻, known as the nitrate ion, is classified as a polyatomic ion because it consists of more than one atom. Specifically, it is made up of one nitrogen atom covalently bonded to three oxygen atoms, resulting in a charged species. In contrast, Na⁺, Cl⁻, and Mg²⁺ are all monatomic ions, consisting of single atoms with a positive or negative charge. Polyatomic ions like NO₃⁻ play significant roles in various chemical reactions and compounds, particularly in biological and environmental contexts.

In the reaction between sodium and chlorine, sodium donates an electron to chlorine. Sodium, having one electron in its outer shell, seeks to achieve a stable electron configuration by losing that electron. Chlorine, on the other hand, has seven electrons in its outer shell and needs one more to complete it. When sodium transfers its electron to chlorine, it forms sodium ions (Na⁺) and chloride ions (Cl⁻), resulting in the formation of sodium chloride (NaCl). Therefore, the particle transferred during this reaction is the electron.

The sulfate ion (SO₄²⁻) carries a charge of −2. This is because sulfur, which is the central atom, is bonded to four oxygen atoms. Each oxygen typically has a charge of −2, and the overall structure of the sulfate ion balances to a total charge of −2. Therefore, the sulfate ion is commonly recognized as having a net charge of −2.

Calcium hydroxide is composed of one calcium ion (Ca²⁺) and two hydroxide ions (OH⁻) to balance the charge. Since the calcium ion has a +2 charge, two hydroxide ions, each with a -1 charge, are needed to achieve electrical neutrality. This results in the formula Ca(OH)₂, indicating one calcium ion bonded to two hydroxide ions, which is the standard representation for this compound in chemical nomenclature.

Iron is classified as a transition metal, which is characterized by its ability to form multiple oxidation states. Transition metals have partially filled d-orbitals, allowing them to lose different numbers of electrons. In the case of iron, it can lose two electrons to form Fe²⁺ or three electrons to form Fe³⁺. This versatility in oxidation states is a defining feature of transition metals, distinguishing them from other groups in the periodic table.

Aluminium oxide is formed when aluminium ions (Al³⁺) combine with oxide ions (O²⁻). To achieve electrical neutrality, two Al³⁺ ions, which contribute a total charge of +6, must bond with three O²⁻ ions, which contribute a total charge of -6. This results in the formula Al₂O₃, indicating that two aluminium ions and three oxide ions create a stable compound, balancing the overall charges.

To determine the formula for the ionic compound formed between magnesium (Mg²⁺) and chloride (Cl⁻), we apply the swap-and-drop rule. Magnesium has a charge of +2, and each chloride ion has a charge of -1. To balance the charges, two chloride ions are needed to neutralize one magnesium ion. Thus, the formula is MgCl₂, indicating one magnesium ion combines with two chloride ions to form a stable ionic compound.

Nitrogen, being in Group 5 of the periodic table, has five valence electrons. To achieve a stable electron configuration similar to that of noble gases, it tends to gain three additional electrons. This results in the formation of a nitride ion (N³⁻), which has a full outer shell with eight electrons, thereby increasing its stability. The other options, such as N⁵⁺ or N³⁺, would require nitrogen to lose electrons, which is less favorable due to its electronegativity and position in the periodic table.

A cation is formed when an atom loses one or more electrons. Electrons carry a negative charge, so when they are removed, the number of positively charged protons in the nucleus exceeds the number of negatively charged electrons. This imbalance results in a net positive charge, which defines the cation. In contrast, gaining protons or neutrons does not lead to a positive charge in the same way, as protons are located in the nucleus and do not change in number during the formation of a cation.