Polar & Non-Polar Molecules: Crash Course Chemistry #23

CrashCourse

22 Jul 201310:45

EducationalLearning

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TLDRThe script discusses molecules and their polarity, explaining how the difference in electronegativity between atoms in a molecule along with its asymmetrical geometry determine polarity. It covers how polar molecules interact with other polar substances but not nonpolar ones, using the example of washing butter off hands with water. Concepts touched on include intermolecular forces, hydrogen bonding, and hybrid polar/nonpolar molecules. Overall the narrator argues polar molecules are more interesting despite their asymmetry, and provides examples of how the polarity of water enables many key life processes on Earth.

Takeaways

😀 The script discusses molecules and chemical compounds, focusing on categorizing them as polar or nonpolar.
👩‍🔬 A molecule's polarity depends on having asymmetrical electron distribution and geometrical asymmetry.
🔬 Electronegativity differences between elements in a molecule cause charge asymmetry.
🚰 Water's polarity makes it very useful for dissolving other polar and ionic compounds.
⛸ Water's hydrogen bonding capabilities give it unique thermal properties that are critical for life.
🧽 Surfactants like soap have hybrid polar/nonpolar structures that allow them to dissolve oils and fats in water.
🍚 Nonpolar oils don't dissolve in water because water molecules hydrogen bond with each other, excluding the oil.
⚛ The polarity of cell membrane phospholipids allows them to form bilayers in aqueous bodily fluids.
🧬 Water's versatility to dissolve so many compounds makes it invaluable for biological systems.
🎥 The video aims to explain molecular polarity in an engaging way to viewers.

Q & A

What are the two requirements for a molecule to be polar?
-A molecule needs to have both asymmetrical electron distribution (difference in electronegativity of 0.5 or more) and geometrical asymmetry in order to be polar.
How does water interact with non-polar substances like oil?
-Water molecules hydrogen bond with each other, forming an orderly structure. Non-polar substances like oil disrupt this structure, so water molecules minimize contact with oil, causing it to bead up.
Why does ice float on liquid water?
-The hydrogen bonding between water molecules forces them slightly apart in ice, making its density lower than liquid water. So ice floats.
What causes the phenomenon of like dissolves like?
-Polar molecules are attracted to other polar molecules, and non-polar molecules are attracted to other non-polar molecules, due to the interactions between their partial charges.
How do surfactants like soap work to wash away grease?
-Surfactants have both a polar end to interact with water and dissolve, and a non-polar end to dissolve grease. This allows grease to be suspended in water and washed away.
Why is water such a good solvent?
-Water can dissolve ionic compounds due to the attraction between its partial charges and ionic charges. It can also dissolve many non-polar compounds due to its polarity.
What is hydrogen bonding and why is it important?
-Hydrogen bonding describes the attraction between the partially positive hydrogen atom on one water molecule and the partially negative oxygen atom on another. This attraction gives water many anomalous properties critical for life.
What causes surface tension in liquids?
-Cohesive intermolecular forces between liquid molecules pull surface molecules inward, resulting in the liquid minimizing its surface area and exhibiting surface tension.
How does electronegativity vary across the periodic table?
-Electronegativity increases from left to right as the number of protons and pull on electrons increases. It decreases from top to bottom as electrons shield each other from proton pull.
Why can water dissolve so many substances without dissolving us?
-Cell membranes have non-polar tails shielded from water and polar heads that interact with water, allowing cells to be suspended without dissolving.

Outlines

00:00

😮 Introduction to Molecules and Polar vs Nonpolar

Introduces molecules and how we classify them as polar or nonpolar based on symmetry of charge. Explains requirements for polarity - asymmetrical electron distribution caused by differences in electronegativity of 0.5+ between elements, and geometric asymmetry. Examples of nonpolar molecules like CO2. Polar molecules have partial charges and are asymmetrical. Water is used to demonstrate interaction of polar and nonpolar substances.

05:01

👍 Attraction Between Polar Molecules

Explains intermolecular forces and interaction between polar molecules. Polar molecules orient to align charges and minimize energy. This attraction allows surface tension in water. When nonpolar oil is added, water minimizes contact. Polar solids dissolve when water molecules interact with ions. Polarity allows hydrogen bonding which impacts water's density and heat capacity.

10:03

🧪 Recap and Applications of Polarity

Recaps key learnings - requirements for polarity, denoting dipole moments, like dissolves like. Applications like solubility of sugars, proteins, ions and temperature regulation on Earth due to hydrogen bonding. Hybrid polar/nonpolar molecules like soap. Thanks viewers for watching.

Mindmap

Keywords

💡polarity

Polarity refers to the separation of charge in a molecule, creating partial positive and negative poles. It is an important molecular property. The video discusses requirements for polarity such as charge asymmetry from differences in electronegativity and geometric asymmetry in the molecule.

💡electronegativity

Electronegativity refers to an atom's tendency to attract electrons in a covalent bond. Differences in electronegativity (>0.5) between atoms in a molecule cause charge asymmetry and polarity.

💡dipole moment

A dipole moment results from the charge separation in a polar molecule, with the positive and negative poles marked using delta plus (δ+) and delta minus (δ-).

💡hydrogen bond

A hydrogen bond is a special electrostatic attraction between a hydrogen atom covalently bonded to an electronegative atom (especially O or N) and another electronegative atom nearby.

💡cohesion

Cohesion refers to the intermolecular attractive forces that hold molecules of a liquid together. For water, these are primarily hydrogen bonds.

💡specific heat capacity

Specific heat capacity measures the amount of energy needed to raise the temperature of 1 gram of a substance by 1°C. Water has an exceptionally high specific heat capacity due to extensive hydrogen bonding.

💡surfactant

Surfactants like those in soap have hybrid polar/nonpolar structures, allowing them to dissolve fats and oils and emulsify them in water by orienting the polar regions outward.

💡phospholipid

Phospholipids with polar heads and nonpolar tails similarly allow cell membranes to interact favorably with the aqueous environment while maintaining integrity against dissolving.

💡solvent

A solvent dissolves a solute. Water is called "the universal solvent" for its unparalleled ability to dissolve polar and ionic compounds, sugars, proteins etc. - a property enabled by its polarity.

💡like dissolves like

The maxim "like dissolves like" summarizes that polar compounds tend to dissolve well in polar solvents like water, while nonpolar compounds dissolve better in nonpolar solvents - based on favorable intermolecular interactions.

Highlights

Classifying molecules as polar or nonpolar is important for understanding their properties

Asymmetrical electron distribution and geometrical asymmetry make a molecule polar

Electronegativity differences cause asymmetrical electron distribution

Nonpolar molecules can have polar bonds but still be nonpolar overall

A dipole moment indicates separation of charge in a polar molecule

Partial charges are marked with delta plus and delta minus

Polar liquids dissolve ionic and polar solids well

Liquid interactions minimize surface area like cohesion forces

Water likes itself more than nonpolar molecules

Hydrogen bonding makes water unique

Hydrogen bonds affect water's volume and heat capacity

Water dissolves many compounds due to polarity

Hybrid polar/nonpolar molecules enable soap cleaning

Cell membranes have polar and nonpolar regions

Water's polarity and capabilities enable life on Earth

Transcripts

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Polar & Non-Polar Molecules: Crash Course Chemistry #23

Takeaways

Q & A

What are the two requirements for a molecule to be polar?

How does water interact with non-polar substances like oil?

Why does ice float on liquid water?

What causes the phenomenon of like dissolves like?

How do surfactants like soap work to wash away grease?

Why is water such a good solvent?

What is hydrogen bonding and why is it important?

What causes surface tension in liquids?

How does electronegativity vary across the periodic table?

Why can water dissolve so many substances without dissolving us?