Question

Explain how to use the periodic table to determine that there are two chloride ions for every magnesium ion in magnesium chloride and one chloride ion for every sodium ion in sodium chloride. Then write the formulas for calcium oxide and potassium oxide and explain how you got them.

Short answer

In the periodic table, elements form ions with specific charges. Magnesium (Mg^(2+)) has a charge of +2, and chloride (Cl^(-)) has a charge of -1, so two chloride ions balance one magnesium ion in MgCl2. Sodium (Na^(+)) and chloride have charges of +1 and -1, respectively, forming NaCl with a 1:1 ratio. Calcium oxide (CaO) forms with a 1:1 ratio between Ca^(2+) and O^(2-) ions. Potassium oxide (K2O) forms with a 2:1 ratio between K^(+) and O^(2-) ions.

Step-by-step solution

Understand ions and how they relate to the periodic table

An ion is an atom or a molecule with an unequal number of electrons and protons, which results in a net electric charge. Elements in the periodic table form ions with a specific charge based on their position in the table. Main group elements tend to form ions that have the same number of valence electrons as the nearest noble gas atom, either by losing or gaining electrons.

Identifying the ions formed by magnesium, sodium, and chloride

Magnesium (Mg) is in group 2 of the periodic table, which means it has 2 valence electrons. To achieve a stable configuration like the nearest noble gas, neon, it will lose these 2 electrons, forming a +2 charged ion: Mg^(2+). Sodium (Na) is in group 1, with 1 valence electron. It will lose this electron to become like the nearest noble gas, neon, forming a +1 charged ion: Na^(+). Chlorine (Cl) is in group 17,, with 7 valence electrons. To achieve the electron configuration of the nearest noble gas, argon, it will gain 1 electron, forming a -1 charged ion: Cl^(-).

Determining the stoichiometric relationship between ions in magnesium chloride and sodium chloride

In magnesium chloride, the magnesium ion (Mg^(2+)) has a charge of +2, and the chloride ion (Cl^(-)) has a charge of -1. To balance these charges and create a neutral compound, we need two chloride ions for every magnesium ion. So, the formula for magnesium chloride is MgCl2. In sodium chloride, the sodium ion (Na^(+)) has a charge of +1, and the chloride ion (Cl^(-)) has a charge of -1. The positive and negative charges balance each other, forming a neutral compound with the ratio of 1:1 for sodium and chloride ions. So, the formula for sodium chloride is NaCl.

Writing the formulas for calcium oxide and potassium oxide

First, we identify the ions formed by calcium (Ca), potassium (K), and oxygen (O). Calcium (Ca) is in group 2, with 2 valence electrons. To achieve the electron configuration of the nearest noble gas, argon, it will lose both electrons, forming a +2 charged ion: Ca^(2+). Potassium (K) is in group 1, with 1 valence electron. It will lose this electron to become like the nearest noble gas, argon, forming a +1 charged ion: K^(+). Oxygen (O) is in group 16, with 6 valence electrons. To achieve the electron configuration of the nearest noble gas, neon, it will gain 2 electrons, forming a -2 charged ion: O^(2-). Now, we can determine the stoichiometric relationship for calcium oxide and potassium oxide. In calcium oxide, the calcium ion (Ca^(2+)) has a charge of +2, and the oxide ion (O^(2-)) has a charge of -2. The positive and negative charges balance each other, forming a neutral compound with the ratio of 1:1 for calcium and oxygen ions. So, the formula for calcium oxide is CaO. In potassium oxide, the potassium ion (K^(+)) has a charge of +1, and the oxide ion (O^(2-)) has a charge of -2. To balance these charges and create a neutral compound, we need two potassium ions for every oxygen ion. So, the formula for potassium oxide is K2O. In conclusion, the formulas for the requested compounds are: - Magnesium chloride: MgCl2 - Sodium chloride: NaCl - Calcium oxide: CaO - Potassium oxide: K2O

Key concepts

Ion Formation

When atoms gain or lose electrons, they form ions, which are atoms with an electric charge. This happens because an ion's electron count doesn't match its proton count. Ions are crucial in creating chemical compounds. The electrons involved are usually the valence electrons since they're the outermost ones and can be lost or gained easily.

For instance:

• Magnesium (Mg) in group 2 of the periodic table has 2 valence electrons. To achieve stability like the noble gas, neon, it tends to lose these electrons, forming a Mg\(^{2+}\) ion.
• Sodium (Na) in group 1 has just 1 valence electron that it loses to become similar to neon, forming a Na\(^{+}\) ion.
• Chlorine (Cl), located in group 17, has 7 valence electrons and gains 1 electron to become like argon, turning into a Cl\(^{-}\) ion.

Understanding how elements form ions is key to predicting how they will combine into compounds.

Chemical Formulas

Chemical formulas are like a recipe that shows how elements combine to form compounds. They provide the ratio of different ions in a compound. The subscripts in a formula denote the number of atoms or ions present.

For example:

• Magnesium chloride (MgCl\( _2 \)) indicates two chloride ions for every magnesium ion, which balances the charges between Mg\(^{2+}\) and two Cl\(^{-}\).
• Sodium chloride (NaCl) shows a 1:1 ratio between sodium ions (Na\(^{+}\)) and chloride ions (Cl\(^{-}\)).

Formulas are determined by combining ions in a way that balances their charges, resulting in a neutral compound. Remember, the total positive charge must equal the total negative charge.

Stoichiometry

Stoichiometry involves calculating the relationships between the amounts of reactants and products in chemical reactions. It relies heavily on the concept of balanced chemical equations, indicating the stoichiometric ratios of elements or compounds involved.

In the context of forming compounds from ions:

• In magnesium chloride, the ratio is 1 magnesium ion (Mg\(^{2+}\)) to 2 chloride ions (Cl\(^{-}\)), forming MgCl\( _2 \).
• For sodium chloride, the ratio is straightforward, 1:1 for Na\(^{+}\) to Cl\(^{-}\).

By adjusting these ratios according to their charges, we ensure that the compound is electrically neutral. This balance is the essence of stoichiometry in ionic compounds.

Valence Electrons

Valence electrons are the outer electrons of an atom, and they're key players in chemical bonding. These electrons determine how an element will react, as they are the ones that can be gained, lost, or shared when forming substances.

Let's consider a few examples:

• Calcium (Ca), in group 2, has 2 valence electrons. It loses both to achieve stability akin to the nearest noble gas, forming a Ca\(^{2+}\) ion.
• Potassium (K) has 1 valence electron. By losing this electron, it forms a K\(^{+}\) ion, reflecting noble gas configuration.
• Oxygen (O), with 6 valence electrons in group 16, gains 2 electrons to fulfil the octet rule, becoming O\(^{2-}\).

Knowing the number of valence electrons helps predict these elemental actions and the ions they form, which is crucial when writing chemical formulas and understanding compound formation.