Problem 36 - College Physics

Question

Use the electron configurations of Si and O to explain why these atoms combine chemically in a one-to-two ratio to form sand.

Step-by-Step Solution

Answer

Si and O form SiO2 because Si shares its 4 electrons with 2 O atoms, each receiving 2 electrons to complete their octets.

Step 1: Identify Electron Configurations of Si and O

Silicon (Si) has an atomic number of 14. Its electron configuration is \([\text{1s}^2 \text{2s}^2 \text{2p}^6 \text{3s}^2 \text{3p}^2]\). Oxygen (O) has an atomic number of 8, and its electron configuration is \([\text{1s}^2 \text{2s}^2 \text{2p}^4]\). These configurations show how electrons are arranged in atomic orbitals for these elements.

Step 2: Determine Valence Electrons

The valence electrons are found in the outermost shell. For Si, the valence electrons are in the 3rd shell, with a configuration of \(3s^2 3p^2\), totaling 4 valence electrons. For O, the valence electrons are in the 2nd shell, with a configuration of \(2s^2 2p^4\), totaling 6 valence electrons.

Step 3: Explain the Formation of Bonds

Atoms combine to complete their octets for a stable configuration. Oxygen needs 2 electrons to fill its outer shell and reach a stable \(2p^6\) configuration. Silicon can share its 4 valence electrons, allowing each oxygen atom to "take" 2 electrons per bond.

Step 4: Explain the SiO2 Ratio

To satisfy the octet rule for both elements, two oxygen atoms chemically combine with one silicon atom. Each oxygen atom uses two electrons from silicon. This results in the compound \(\text{SiO}_2\), commonly known as sand.

Key Concepts

Electron Configuration

Electron configuration is like a map that shows where electrons live around an atom's nucleus. It tells us in which energy level or shell certain electrons can be found.
For example, if we look at silicon (Si), it has an atomic number of 14. This means it has 14 electrons, and its electron configuration is \[\text{1s}^2 \text{2s}^2 \text{2p}^6 \text{3s}^2 \text{3p}^2\].

What does this mean? Let's break it down:

• The first energy level, with shells "1s," is filled with 2 electrons.
• The second energy level, containing "2s" and "2p" shells, holds 8 electrons.
• The third level starts filling up with the "3s" and "3p" shells holding 4 electrons in total.

Oxygen (O), with an atomic number of 8, has an electron configuration of \[\text{1s}^2 \text{2s}^2 \text{2p}^4\]. This shows:

• The first shell "1s" holds 2 electrons.
• The second shell "2s" and "2p" holds 6 electrons total, almost filling it entirely.

This arrangement is crucial because it affects how atoms like Si and O interact with each other.

Valence Electrons

Valence electrons are the magic electrons that live in the outermost shell of an atom. They decide how atoms will bond with each other.
In silicon (Si), these valence electrons are the 4 electrons in the "3s" and "3p" orbitals.
These 4 valence electrons mean Si can form several bonds to achieve a stable structure.

For oxygen (O), with valence electrons located in the "2s" and "2p" orbitals, there are a total of 6:

• 2 in the "2s" orbital
• 4 in the "2p" orbital

These sets of electrons play a huge role when oxygen wants to bond because it needs 2 more electrons to fill its outer shell.

Understanding where these electrons reside helps explain why atoms join together, like pieces of a puzzle, to form compounds such as SiO₂.

Octet Rule

The octet rule is like a goal that atoms try to achieve to be happy and stable.
They aim to have 8 electrons in their outer shell, just like the noble gases, which are the happiest and most stable elements around.

Oxygen, for instance, has 6 valence electrons and thus needs 2 more to reach the perfect 8.
Silicon has 4 valence electrons. By sharing these, each oxygen atom can "borrow" 2 electrons from silicon, fulfilling their octet quest.

When these exchanges happen:

• Each oxygen achieves its octet by getting 2 electrons.
• Silicon satisfies the needs of 2 oxygens by sharing its 4 valence electrons.

This explains why they form a compound in a 1:2 ratio, resulting in SiO₂, where silicon "coordinates" with two oxygen atoms, completing their electronic destinies according to the octet rule.