Question

Draw a Lewis structure for each of the following ionic compounds. What chemical formula does Lewis theory predict? a. sodium oxide b. aluminum sulfide c. magnesium chloride d. beryllium oxide

Short answer

The Lewis structures for the given ionic compounds indicate that sodium oxide has a formula of Na2O, aluminum sulfide has a formula of Al2S3, magnesium chloride has a formula of MgCl2, and beryllium oxide has a formula of BeO.

Step-by-step solution

Valence Electrons of Sodium and Oxygen

Identify the valence electrons for sodium (Na) and oxygen (O). Sodium, being in group 1, has 1 valence electron. Oxygen, being in group 16, has 6 valence electrons.

Lewis Structure for Sodium Oxide (Na2O)

Since sodium loses an electron and oxygen gains two electrons, two sodium atoms will transfer their electrons to one oxygen atom. The resulting structure will show oxygen with a full octet and each sodium with an empty valence shell.

Valence Electrons of Aluminum and Sulfur

Identify the valence electrons for aluminum (Al) and sulfur (S). Aluminum, in group 13, has 3 valence electrons. Sulfur, in group 16, has 6 valence electrons.

Lewis Structure for Aluminum Sulfide (Al2S3)

For aluminum sulfide, two aluminum atoms will together provide six electrons to three sulfur atoms. Each sulfur atom requires two additional electrons to complete its octet, which they get from the aluminum atoms.

Valence Electrons of Magnesium and Chlorine

Identify the valence electrons for magnesium (Mg) and chlorine (Cl). Magnesium, in group 2, has 2 valence electrons. Chlorine, in group 17, has 7 valence electrons.

Lewis Structure for Magnesium Chloride (MgCl2)

One magnesium atom will transfer its two electrons to two separate chlorine atoms. Subsequently, magnesium will have an empty valence shell and each chlorine will have a complete octet.

Valence Electrons of Beryllium and Oxygen

Identify the valence electrons for beryllium (Be) and oxygen (O). Beryllium, in group 2, has 2 valence electrons. Oxygen, in group 16, has 6 valence electrons.

Lewis Structure for Beryllium Oxide (BeO)

Beryllium oxide consists of one beryllium atom which will provide its two electrons to one oxygen atom, completing the octet of oxygen and the valence shell of beryllium will become empty.

Key concepts

Valence Electrons

Learning about valence electrons is fundamental when studying chemistry. Valence electrons are the outermost electrons of an atom and are primarily responsible for the chemical properties of the element. These electrons participate in bonding because their position allows other atoms to interact with them. For instance, an atom like sodium (Na), which is in group 1 of the periodic table, possesses a single valence electron.

This lone valence electron is relatively easily lost since sodium is a reactive metal. Conversely, oxygen (O), which is in group 16, has six valence electrons. It tends to gain electrons to fill its outer shell, following the octet rule. The interaction between atoms to lose or gain electrons leads to the formation of ionic bonds. To visualize these interactions, the Lewis dot structure is a convenient tool. It shows the representation of valence electrons around the symbol of an element, providing insight into the possible chemical bonds an element can form.

Electron Transfer

The concept of electron transfer is central to the formation of ionic compounds. During the formation of an ionic bond, one atom donates electrons, usually to achieve a full valence shell, while another atom accepts them to complete its own valence shell. This transfer leads to the creation of ions: cations, which are positively charged due to the loss of electrons, and anions, negatively charged due to the gain of electrons.

For example, in sodium oxide (Na2O), each sodium atom loses one electron to form Na⁺, while the oxygen atom gains two electrons to form O^2-. This transfer of electrons from metal to non-metal allows the atoms to follow the octet rule and achieve a more stable electronic arrangement similar to the noble gases.

Chemical Formula Prediction

When it comes to chemical formula prediction, understanding the charges on the ions formed by electron transfer is key. The chemical formula of an ionic compound must reflect the balance of these charges so that the net charge of the compound is zero.

To predict the formula, one must consider the number of electrons lost by the cation(s) and gained by the anion(s). For instance, in magnesium chloride (MgCl2), magnesium loses two electrons and each chlorine atom gains one electron. Thus, two chlorine atoms are needed to balance the two positive charges of a single magnesium ion, which results in the formula MgCl2. This stoichiometry ensures charge neutrality, a fundamental principle in chemical formula prediction.

Octet Rule

The octet rule is a chemical principle stating that atoms tend to form compounds in ways that give them eight electrons in their valence shell, resembling the electron configuration of a noble gas. The octet rule explains the stability of most chemically bound atoms as they all seek to either lose, gain or share electrons to achieve eight electrons in the outer shell.

Take the formation of beryllium oxide (BeO). Beryllium has two valence electrons and needs to lose them to comply with the octet rule. Oxygen needs two additional electrons to make eight. The process of beryllium transferring its electrons to oxygen leads to a stable ionic compound where both elements have complete octets, consistent with the rule. Not all elements follow the octet rule strictly, but for main group elements, it is a reliable guideline for understanding chemical bonding behavior.