Question

Contact Lenses Soft contact lenses are made of silicon and oxygen atoms bonded together. Create a table listing the atomic and ionic electron configurations, and the atomic and ionic radii for silicon and oxygen. When silicon bonds with oxygen, which atoms become larger and which become smaller? Why?

Short answer

In summary, the atomic electron configurations for silicon and oxygen are 1s^2 2s^2 2p^6 3s^2 3p^2 and 1s^2 2s^2 2p^4, respectively. Silicon forms a Si^4+ ion with an electron configuration of 1s^2 2s^2 2p^6, and oxygen forms an O^2- ion with an electron configuration of 1s^2 2s^2 2p^6. The atomic radii for silicon and oxygen are 111 pm and 66 pm, while their ionic radii are 40 pm (Si^4+) and 140 pm (O^2-), respectively. When silicon bonds with oxygen, silicon becomes smaller while oxygen becomes larger. This is because silicon loses electrons, which decreases electron repulsion and increases effective nuclear charge, while oxygen gains electrons, which increases electron repulsion and expands the electron cloud.

Step-by-step solution

Determine the Atomic Number and Electron Configuration

First, we need to find the atomic number for both silicon and oxygen in the periodic table. - Silicon (Si) has an atomic number of 14. - Oxygen (O) has an atomic number of 8. Now we can write the electron configuration for each atom: - Silicon (Si): 1s^2 2s^2 2p^6 3s^2 3p^2 - Oxygen (O): 1s^2 2s^2 2p^4

Determine the Ionic Electron Configuration

When an atom gains or loses electrons to form ions, the electron configuration changes. Silicon typically forms a +4 ion by losing 4 electrons, and oxygen forms a -2 ion by gaining 2 electrons. Ionic electron configuration: - Silicon (Si^4+): 1s^2 2s^2 2p^6 - Oxygen (O^2-): 1s^2 2s^2 2p^6

Find the Atomic and Ionic Radii

By referring to the periodic table or any reliable source, we can find the atomic and ionic radii for silicon and oxygen. - Silicon atomic radius: 111 pm - Silicon ionic radius (Si^4+): 40 pm - Oxygen atomic radius: 66 pm - Oxygen ionic radius (O^2-): 140 pm

Create the Table

Here is the requested table for Silicon and Oxygen: | Element | Atomic Electron Configuration | Atomic Radius | Ionic Electron Configuration | Ionic Radius | |----------|-------------------------------|---------------|-----------------------------|--------------| | Silicon | 1s^2 2s^2 2p^6 3s^2 3p^2 | 111 pm | 1s^2 2s^2 2p^6 | 40 pm | | Oxygen | 1s^2 2s^2 2p^4 | 66 pm | 1s^2 2s^2 2p^6 | 140 pm |

Determine Which Atoms Become Larger and Which Become Smaller

When silicon bonds with oxygen, silicon loses 4 electrons to become a Si^4+ ion, and oxygen gains 2 electrons to become an O^2- ion. Looking at the ionic radii in the table: - Silicon becomes smaller (from 111 pm to 40 pm). - Oxygen becomes larger (from 66 pm to 140 pm).

Explain Why the Sizes Change

When silicon loses 4 electrons, it has fewer electron shells, which results in a decreased repulsion between electrons. So, the effective nuclear charge increases, and the remaining electrons are pulled closer to the nucleus, causing the ion size to decrease. In contrast, when oxygen gains 2 electrons, the electron repulsion within the outermost shell increases due to the added electrons. This causes the electron cloud to expand, and the ionic radius increases.

Key concepts

Atomic Radius

The concept of atomic radius refers to the size of an atom, which is the distance from the center of the nucleus to the outer edge of the electron cloud. Understanding the atomic radius is crucial for analyzing how atoms come together to form molecules, such as the silicon and oxygen in soft contact lenses.

In the step-by-step solution, we see that when comparing the atomic radius of silicon (111 pm) to its ionic radius (40 pm), there is a significant reduction in size when silicon forms a Si⁴⁺ ion. This happens because the loss of electrons reduces electron-electron repulsion and the atoms draw in closer to the nucleus, leading to a smaller atomic radius.

Ionic Radius

Ionic radius, on the other hand, is the measurement of an atom's size after it has become an ion. This can either increase or decrease depending on whether the atom gains or loses electrons. The periodic table and the discussion of ionic radii are essential when predicting the sizes of ions in chemical compounds.

For example, when oxygen gains two electrons to become an O^2- ion, its ionic radius increases to 140 pm due to increased electron-electron repulsion causing the electron cloud to expand. The exercise provided uses this concept to demonstrate how atomic size changes in the formation of ions, which is a cornerstone of chemical bonding.

Periodic Table

The periodic table is a comprehensive chart that organizes all known elements according to their atomic number and other chemical properties. It helps us predict how elements will behave in chemical reactions, including their electron configurations and trends in atomic and ionic radii. As seen in the presented exercise, by understanding the periodic trends, we can deduce that as we move across a period, atoms typically become smaller because they gain more protons, which increases the effective nuclear charge. This charge pulls the electron cloud tighter toward the nucleus, reducing the atomic radius.

Hence, the periodic table not only aids in finding atomic numbers and electron configurations but also serves as a guide for understanding how atoms will interact with each other, as displayed in the case of silicon and oxygen combining to form silicon dioxide in contact lens material.