Problem 15 - Chemistry The Central Science

Question

(a) Using Lewis symbols, diagram the reaction between magnesium and oxygen atoms to give the ionic substance MgO. (b) How many electrons are transferred? (c) Which atom loses electrons in the reaction?

Step-by-Step Solution

Answer

(a) The Lewis symbols for the reaction between magnesium and oxygen are: Mg •• → Mg^(2+) + 2e^(-) O••• + 2e^(-) → O^(2-) •• The reaction forms magnesium oxide (MgO): Mg^(2+) + O^(2-) → MgO. (b) 2 electrons are transferred in this reaction. (c) The magnesium atom (Mg) loses electrons in the reaction.

Step 1: Determine the Lewis symbols of Magnesium and Oxygen atoms.

Recall that Lewis symbols represent the valence electrons of an atom as dots surrounding its chemical symbol. Magnesium is in group 2 of the periodic table and has 2 valence electrons, so its Lewis symbol is Mg with two dots around it. Oxygen is in group 16 (or 6A) and has 6 valence electrons, so its Lewis symbol is O with six dots (in 4 groups of lone pairs) surrounding it. Mg: •• O: ••• ••

Step 2: Use Lewis symbols to show the electron transfer.

Ionic substances are formed when one atom transfers its valence electrons to another atom, creating a complete octet (8 valence electrons) for both atoms. In the reaction between magnesium and oxygen, magnesium will lose its 2 valence electrons to oxygen. The Lewis symbols for this reaction are: Mg •• → Mg^(2+) + 2e^(-) O••• + 2e^(-) → O^(2-) ••

Step 3: Show the formation of the ionic substance MgO.

Now that the electron transfer has occurred, the magnesium ion (Mg^(2+)) and the oxygen ion (O^(2-)) are attracted to each other by electrostatic forces. This attraction forms the ionic substance magnesium oxide (MgO). Mg^(2+) + O^(2-) → MgO

Step 4: Answer part (b) and (c) of the exercise.

(b) Count the number of electrons transferred during the reaction. In our case, magnesium transferred 2 electrons to oxygen. Therefore, 2 electrons were transferred. (c) Magnesium (Mg) loses its 2 valence electrons during the reaction, becoming positively charged (Mg^(2+)).

Key Concepts

Electron Transfer

Electron transfer is a fundamental concept in chemistry, particularly in the formation of ionic compounds. It refers to the movement of electrons from one atom to another during a chemical reaction, leading to the creation of ions.

For example, consider the reaction between magnesium and oxygen to form magnesium oxide (MgO). Magnesium has two electrons in its outermost energy level, also known as its valence shell. Oxygen, on the other hand, has six valence electrons, but it needs eight to achieve a stable electron configuration. During the reaction, magnesium donates its two valence electrons to oxygen, transforming into a positively charged magnesium ion (Mg^(2+)), while oxygen becomes a negatively charged oxide ion (O^(2-)).

Significance of Electron Transfer

The process of electron transfer has profound importance as it not only dictates the type of bond that forms between atoms but also affects the electrical conductivity, magnetic properties, and chemical reactivity of substances. Ultimately, electron transfer leads to the creation of ionic compounds, which are essential in various industries and biological systems.

Ionic Substances

Ionic substances are chemical compounds composed of positively and negatively charged ions held together by strong electrostatic forces known as ionic bonds. These substances usually form when metals react with nonmetals, with the metal atoms donating electrons to the nonmetal atoms.

Following electron transfer, the resulting ions—cations (positively charged) and anions (negatively charged)—are attracted to each other due to their opposite charges, creating a regular spatial arrangement known as a crystal lattice. This lattice is a defining property of ionic substances, contributing to their high melting and boiling points, solid state at room temperature, and ability to conduct electricity when dissolved in water or melted.

Properties of Ionic Substances

Ionic substances have distinctive characteristics: they tend to be hard and brittle, have high melting and boiling points, and can conduct electricity when in a liquid state or aqueous solution. The ionic substance magnesium oxide, formed by the reaction between magnesium and oxygen, showcases these properties, making it useful in refractory materials, electrical insulators, and more.

Valence Electrons

Valence electrons are the electrons located in an atom's outermost shell and are involved in chemical bonding. An atom's chemical behavior is primarily dictated by these electrons since they can be lost, gained, or shared during reactions to form molecules or ionic compounds.

The number of valence electrons in an atom is determined by its position in the periodic table. For instance, magnesium (Mg), a group 2 element, has two valence electrons, which are easily lost to become a Mg^(2+) ion. Oxygen (O), on the other hand, is in group 16, meaning it has six valence electrons, and tends to gain two electrons to achieve a full octet.

Octet Rule

Understanding valence electrons is crucial because of the octet rule, which postulates that atoms tend to bond in a way that leaves them with eight valence electrons, resembling the electron configuration of a noble gas. This quest for electronic stability leads to the diverse range of chemical compounds seen in nature and is a cornerstone of predicting an atom's reactivity and the types of bonds it can form.