Hydrogen bonding in water | Water, acids, and bases | Biology | Khan Academy

Summary

The script delves into the vital role of water in biological processes, highlighting its composition as H2O and the molecular structure that gives rise to its unique properties. It explains the electronegativity of oxygen, creating partial charges within the molecule, which leads to hydrogen bonding between water molecules. These bonds are crucial for water's fluidity, heat absorption, temperature regulation, and its ability to act as a universal solvent, essential for life and biological systems.

Takeaways

• 💧 Water is fundamental to life, with all significant biological processes in the human body occurring in or dependent on water.
• 🧬 The cytoplasm inside cells is primarily composed of water, highlighting its role in cellular structure and function.
• 🌊 The human body, including the speaker, consists of 60% to 70% water, emphasizing the importance of water in our physical composition.
• 🌍 The search for life on other planets often focuses on the presence of water, as it is considered essential for life as we know it.
• 🔬 Water's molecular structure, H2O, is made up of one oxygen atom and two hydrogen atoms bonded by covalent bonds.
• 🌀 The electron configuration of water results in a tetrahedral shape, with the hydrogen atoms on one side of the oxygen atom.
• 🚫 The lone electron pairs on oxygen repel each other, influencing the molecule's three-dimensional arrangement.
• ⚫ Oxygen's high electronegativity causes a partial negative charge on the oxygen side and a partial positive charge on the hydrogen side of the water molecule.
• 🔗 The partial charges lead to the formation of hydrogen bonds between water molecules, which are weaker than covalent bonds but crucial for water's properties.
• 🌡 Hydrogen bonds give water its fluidity, allowing for cohesion and the ability to flow, which is important for its behavior under normal temperatures and pressures.
• 🌡️ Hydrogen bonds are responsible for water's ability to absorb heat, regulate temperature, and prevent lakes from freezing over.
• 🧪 Water's polarity and hydrogen bonding make it an excellent solvent, capable of dissolving polar molecules, which is vital for biological systems.

Q & A

Why is water considered essential to life?

Water is essential to life because all significant biological processes in the body are dependent on it, most of which occur inside of water. It is a major component of cells, and life as we know it is dependent on it, which is why signs of water are sought when searching for life on other planets.

What percentage of a human body is made up of water?

A human body is composed of 60% to 70% water, making it a significant part of our biological makeup.

What is the molecular structure of water?

Water, chemically known as H2O, is made up of one oxygen atom and two hydrogen atoms bonded together by covalent bonds.

Why do the hydrogen atoms in a water molecule not appear on opposite sides of the oxygen atom?

The hydrogen atoms do not appear on opposite sides of the oxygen atom because oxygen also has two lone electron pairs, which repel each other, leading to a tetrahedral shape in three dimensions.

What is a covalent bond and how does it relate to the structure of water?

A covalent bond is a chemical bond formed by the sharing of a pair of electrons between atoms. In water, the oxygen atom shares a pair of electrons with each hydrogen atom, forming the H2O structure.

Why is the shape of the water molecule described as tetrahedral?

The shape of the water molecule is described as tetrahedral because of the arrangement of the two hydrogen atoms and two lone pairs of electrons around the oxygen atom, which positions them at the vertices of a tetrahedron.

What is the significance of the electron cloud model in describing the behavior of electrons in a water molecule?

The electron cloud model signifies the probability of where electrons might be found around the atoms. It shows that electrons are not fixed in place but are in constant motion, which is important for understanding the dynamic nature of chemical bonds.

Why is oxygen described as electronegative in the context of water molecules?

Oxygen is described as electronegative because it has a stronger attraction to electrons compared to hydrogen. This causes the electrons in the covalent bonds to spend more time near the oxygen atom, creating a partial negative charge on the oxygen side of the molecule.

What is the result of the electronegativity difference between oxygen and hydrogen in a water molecule?

The electronegativity difference results in a partial negative charge on the oxygen side and a partial positive charge on the hydrogen side of the water molecule, setting the stage for hydrogen bonding between water molecules.

What is a hydrogen bond and how does it affect the properties of water?

A hydrogen bond is an attraction between a partially negative charge on one water molecule and a partially positive charge on another. This bond is weaker than a covalent bond but is responsible for water's unique characteristics, such as its fluidity, cohesion, and ability to act as a solvent for many substances.

How do hydrogen bonds contribute to water's role as a solvent for polar molecules?

Hydrogen bonds allow water to surround and interact with polar molecules, pulling them apart and dissolving them within the water. This is due to the polarity of water molecules and their ability to form hydrogen bonds with other polar substances.