Problem 16 - Chemistry: The Central Science

Question

(a) Use Lewis symbols to represent the reaction that occurs between Ca and F atoms. (b) What is the chemical formula of the most likely product? (c) How many electrons are transferred? (d) Which atom loses electrons in the reaction?

Step-by-Step Solution

Answer

(a) The Lewis symbols for the reaction are: Ca •• + 2F ••••••• ⟶ Ca²⁺ + 2F⁻ (b) The chemical formula of the most likely product is CaF₂. (c) Two electrons are transferred in the reaction. (d) Calcium (Ca) atom loses electrons in the reaction.

Step 1: Recognize the Lewis symbols for Ca and F

Calcium (Ca) is in group 2 of the periodic table and has two valence electrons. As a result, it will have a Lewis symbol of Ca with two dots around it. Fluorine (F) is in group 17 of the periodic table and has seven valence electrons. Consequently, its Lewis symbol is F with seven dots around it.

Step 2: Represent the reaction using Lewis symbols

When Ca reacts with F, Ca loses two electrons to achieve a stable octet configuration like noble gases and forms Ca²⁺ ion. F gains one electron to achieve stability and becomes F⁻ ion. Since two F atoms are needed to accept the two electrons from Ca, the reaction will be between one Ca atom and two F atoms. Lewis symbols of the reaction: Ca •• + 2F ••••••• ⟶ Ca²⁺ + 2F⁻

Step 3: Determine the chemical formula of the product

Since we have a Ca²⁺ ion and two F⁻ ions, they combine to form the ionic compound calcium fluoride. The chemical formula is CaF₂.

Step 4: Calculate the number of electrons transferred

In this reaction, Ca loses two electrons to form Ca²⁺ ion, and each F atom gains one electron to form F⁻ ions. Therefore, a total of two electrons are transferred.

Step 5: Identify the atom that loses electrons

In the reaction, Calcium (Ca) loses two electrons to achieve a stable configuration. Thus, Calcium (Ca) is the atom that loses electrons in the reaction. In summary: (a) The reaction between Ca and F atoms can be represented using Lewis symbols as: Ca •• + 2F ••••••• ⟶ Ca²⁺ + 2F⁻ (b) The most likely chemical formula of the product is CaF₂. (c) Two electrons are transferred in the reaction. (d) Calcium (Ca) atom loses electrons in the reaction.

Key Concepts

Understanding Chemical Formulas

Chemical formulas are essential in chemistry as they succinctly express the composition of molecules and ionic compounds. They show the types and numbers of atoms involved in a substance. In our exercise, the chemical formula CaF₂ describes the ionic compound calcium fluoride, consisting of one calcium (Ca) atom and two fluoride (F) atoms. The subscript '2' in the chemical formula indicates that there are two fluoride ions for every calcium ion, reflecting the charge balance necessary for the ionic compound to be electrically neutral.

When you're trying to figure out the chemical formula for a compound, count the total number of positive and negative charges to ensure they cancel out. Since the calcium ion carries a +2 charge (Ca²⁺) and each fluoride ion carries a -1 charge (F⁻), two fluoride ions are needed to balance out the charge of one calcium ion. This results in the stable formula CaF₂.

Electron Transfer in Ionic Bonding

Electron transfer is the movement of electrons from one atom to another, a process that is fundamental to forming ionic bonds. In our exercise, calcium (Ca) gives up two electrons to achieve a stable octet, reminiscent of the nearest noble gas configuration. This electron donation transforms the neutral calcium atom into a positively charged ion (Ca²⁺).

On the other side of the reaction, each fluorine atom (F) accepts one electron, which leads to the formation of two negatively charged fluoride ions (F⁻). The acceptance and donation of electrons result in a transfer of two total electrons from calcium to the fluorine atoms. Visualizing the electron transfer can be simplified by using Lewis symbols, which provide a clear depiction of the valence electrons involved in bond formation.

Ionic Compounds and Their Properties

Ionic compounds, such as calcium fluoride in the given exercise, are formed when positively charged ions (cations) and negatively charged ions (anions) come together to create a neutral compound. These bonds are the result of electrostatic force—the attraction between oppositely charged ions. Ionic compounds generally have high melting and boiling points, and they conduct electricity when melted or dissolved in water because their ions are free to move.

Ionic compounds also form crystal lattice structures, which gives them their characteristic solid form. In the case of calcium fluoride, the Ca²⁺ and F⁻ ions lock into a repeating pattern that extends in all three dimensions, creating the solid structure observed in the actual compound. These stable structures and the strong electrostatic forces within ionic compounds are essential for their unique properties and uses in various applications.