Problem 123 - Chemistry The Molecular Science

Question

Write the formula for a compound formed by chlorine and element \(X\), if element \(X\) has the electronic configuration \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{1}\).

Step-by-Step Solution

Answer

The compound formed is NaCl.

Step 1: Determine the Element 'X'

The electronic configuration given for element 'X' is \(1s^2 2s^2 2p^6 3s^1\). Adding up the electrons: 2 (from \(1s^2\)) + 2 (from \(2s^2\)) + 6 (from \(2p^6\)) + 1 (from \(3s^1\)) equals 11 electrons. This corresponds to the element sodium (Na) on the periodic table.

Step 2: Identify Valence Electrons

Element 'X' (sodium) has its outermost electron in the 3s subshell, denoted by 3s1, indicating it has 1 valence electron.

Step 3: Determine Chlorine's Valence Electrons

Chlorine has the electronic configuration \(1s^2 2s^2 2p^6 3s^2 3p^5\), with the outer shell having 7 electrons. Chlorine needs one more electron to complete its outer shell (8 electrons for stability).

Step 4: Determine Charges of the Ions

Sodium (Na) will lose one electron to achieve a stable electronic configuration resulting in a \(Na^+\) ion. Chlorine (Cl) will gain one electron, forming a \(Cl^-\) ion.

Step 5: Write the Chemical Formula

Since sodium forms a \(Na^+\) ion and chlorine forms a \(Cl^-\) ion, they combine in a 1:1 ratio to balance each other's charge, forming the compound \(NaCl\).

Key Concepts

Electron Configuration

Electron configuration is a method used to denote the arrangement of electrons among the various orbitals in atoms. It is written by listing the energy levels, orbitals, and the number of electrons in each orbital. For example, the electron configuration of sodium is given as \(1s^2\, 2s^2\, 2p^6\, 3s^1\). This tells us:

• The first number represents the energy level (shell).
• The letter indicates the type of orbital (s, p, d, f).
• The superscript shows the number of electrons in those orbitals.

By summing the superscripts, you can find the total number of electrons, which corresponds to the atomic number on the periodic table. In our example, sodium has 11 electrons, which matches its atomic number.

Valence Electrons

Valence electrons are the electrons found in the outermost shell of an atom. They play a crucial role in chemical bonding because they can be gained, lost, or shared with other atoms to achieve stability. For an element like sodium, which has the electron configuration \(1s^2\, 2s^2\, 2p^6\, 3s^1\), the single electron in the 3s orbital is its valence electron.
The number of valence electrons determines how an element will react. Elements with one valence electron, such as sodium, tend to lose that electron in reactions to achieve a stable electronic configuration. Chlorine, with a configuration of \(1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^5\), has seven valence electrons, meaning it's one electron short of a full outer shell.

Ionic Compounds

Ionic compounds form when atoms transfer electrons to achieve full outer shells, resulting in positive and negative ions. These ions are held together by the electrostatic forces known as ionic bonds. Sodium chloride (\(NaCl\)) is a classic example of an ionic compound. Sodium loses an electron, becoming a positively charged \(Na^+\) ion. Chlorine gains an electron to become a negatively charged \(Cl^-\) ion.
In the ionic bond between \(Na^+\) and \(Cl^-\), the transfer of one electron from sodium to chlorine satisfies both elements, resulting in a compound that is electrically neutral overall. This transfer leads to the compound's stability as both ions achieve a stable electron configuration.

Periodic Table

The periodic table is an organized layout of all known elements according to increasing atomic number, which represents the number of protons in an atom's nucleus. The table helps predict how elements will react with each other.

• Elements are grouped together based on similar properties, which often relate to the number of valence electrons.
• For instance, elements in Group 1, like sodium, have one valence electron and are highly reactive metals.
• In contrast, elements in Group 17, like chlorine, have seven valence electrons and are reactive nonmetals.

The periodic table is a valuable tool that helps us understand both the physical and chemical properties of elements, guiding us in predicting the formation of compounds.

Stable Electronic Configuration

Stable electron configurations are characterized by filled outer electron shells. Atoms will often lose or gain electrons to achieve stability, resembling the electron configuration of the nearest noble gas. This is known as the octet rule, where atoms seek to have eight electrons in their outermost shell.
In the formation of \(NaCl\):

• Sodium loses one electron to attain the stable configuration of neon, leaving it with an octet in the previous shell.
• Chlorine gains an electron to achieve an octet, mirroring the configuration of argon.

This transition toward stable electronic configurations explains the formation and stability of many ionic compounds in chemistry, as elements strive to satisfy the octet rule.