[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:14.50,0:00:16.56,Default,,0000,0000,0000,,How come some insects are able to walk
Dialogue: 0,0:00:16.56,0:00:18.14,Default,,0000,0000,0000,,on the surface of a pond,
Dialogue: 0,0:00:18.14,0:00:19.82,Default,,0000,0000,0000,,but you quickly sink to the bottom
Dialogue: 0,0:00:19.82,0:00:21.42,Default,,0000,0000,0000,,when you try to walk on water?
Dialogue: 0,0:00:21.42,0:00:24.81,Default,,0000,0000,0000,,And why do lakes freeze from the top down in winter?
Dialogue: 0,0:00:24.81,0:00:28.82,Default,,0000,0000,0000,,In a word, the answer to all these questions is polarity.
Dialogue: 0,0:00:28.82,0:00:30.49,Default,,0000,0000,0000,,Water is a simple molecule
Dialogue: 0,0:00:30.49,0:00:33.95,Default,,0000,0000,0000,,made up of one oxygen atom and two hydrogen atoms,
Dialogue: 0,0:00:33.95,0:00:35.86,Default,,0000,0000,0000,,but it is essential to life.
Dialogue: 0,0:00:35.86,0:00:39.32,Default,,0000,0000,0000,,In fact, water makes up approximately 60%
Dialogue: 0,0:00:39.32,0:00:41.95,Default,,0000,0000,0000,,of the adult human being's body weight.
Dialogue: 0,0:00:41.95,0:00:44.37,Default,,0000,0000,0000,,The polarity within those water molecules
Dialogue: 0,0:00:44.37,0:00:46.62,Default,,0000,0000,0000,,gives this common substance the properties
Dialogue: 0,0:00:46.62,0:00:49.41,Default,,0000,0000,0000,,that make it unique and life-sustaining.
Dialogue: 0,0:00:49.41,0:00:51.54,Default,,0000,0000,0000,,Polarity refers to the unequal sharing
Dialogue: 0,0:00:51.54,0:00:53.60,Default,,0000,0000,0000,,of electrons within a molecule.
Dialogue: 0,0:00:53.60,0:00:56.55,Default,,0000,0000,0000,,For water, the bonding between the oxygen atom
Dialogue: 0,0:00:56.55,0:00:59.64,Default,,0000,0000,0000,,and two hydrogen atoms within a single water molecule
Dialogue: 0,0:00:59.64,0:01:03.02,Default,,0000,0000,0000,,is like a tug-of-war between a big, strong football player
Dialogue: 0,0:01:03.02,0:01:05.19,Default,,0000,0000,0000,,and a cute little toddler.
Dialogue: 0,0:01:05.19,0:01:07.06,Default,,0000,0000,0000,,Oxygen is a larger atom,
Dialogue: 0,0:01:07.06,0:01:09.77,Default,,0000,0000,0000,,with more protons in its nucleus than hydrogen.
Dialogue: 0,0:01:09.77,0:01:13.17,Default,,0000,0000,0000,,These positive charges are like a person's physical strength.
Dialogue: 0,0:01:13.17,0:01:14.48,Default,,0000,0000,0000,,They're able to attract
Dialogue: 0,0:01:14.48,0:01:16.86,Default,,0000,0000,0000,,the negatively charged electrons in the bond,
Dialogue: 0,0:01:16.86,0:01:19.45,Default,,0000,0000,0000,,just like a strong individual is able to overpower
Dialogue: 0,0:01:19.45,0:01:22.02,Default,,0000,0000,0000,,a weaker individual in a tug of war.
Dialogue: 0,0:01:22.02,0:01:24.20,Default,,0000,0000,0000,,So, oxygen is able to attract
Dialogue: 0,0:01:24.20,0:01:27.12,Default,,0000,0000,0000,,more than its fair share of electrons.
Dialogue: 0,0:01:27.12,0:01:30.27,Default,,0000,0000,0000,,Because hydrogen is smaller and has less strength,
Dialogue: 0,0:01:30.27,0:01:31.55,Default,,0000,0000,0000,,or fewer protons,
Dialogue: 0,0:01:31.55,0:01:33.55,Default,,0000,0000,0000,,it loses the tug of war
Dialogue: 0,0:01:33.55,0:01:36.73,Default,,0000,0000,0000,,and attracts fewer than its fair share of electrons.
Dialogue: 0,0:01:36.73,0:01:39.72,Default,,0000,0000,0000,,So, the oxygen in water behaves as though it's negative,
Dialogue: 0,0:01:39.72,0:01:43.14,Default,,0000,0000,0000,,and the hydrogens behave as though they're positive.
Dialogue: 0,0:01:43.14,0:01:45.85,Default,,0000,0000,0000,,The bonds within a single water molecule
Dialogue: 0,0:01:45.85,0:01:48.16,Default,,0000,0000,0000,,are called polar covalent bonds.
Dialogue: 0,0:01:48.16,0:01:50.86,Default,,0000,0000,0000,,Covalent means that the electrons are shared.
Dialogue: 0,0:01:50.86,0:01:52.94,Default,,0000,0000,0000,,But, as we just learned,
Dialogue: 0,0:01:52.94,0:01:56.28,Default,,0000,0000,0000,,polar means that these electrons are not shared equally.
Dialogue: 0,0:01:56.28,0:01:58.94,Default,,0000,0000,0000,,In water, the oxygen acts negative
Dialogue: 0,0:01:58.94,0:02:01.66,Default,,0000,0000,0000,,and the hydrogens act positive.
Dialogue: 0,0:02:01.66,0:02:03.70,Default,,0000,0000,0000,,Since negative and positive attract,
Dialogue: 0,0:02:03.70,0:02:06.50,Default,,0000,0000,0000,,that oxygen is attracted to the hydrogen atoms
Dialogue: 0,0:02:06.50,0:02:08.15,Default,,0000,0000,0000,,in neighboring water molecules.
Dialogue: 0,0:02:08.15,0:02:11.93,Default,,0000,0000,0000,,A special type of bond forms between water molecules,
Dialogue: 0,0:02:11.93,0:02:13.96,Default,,0000,0000,0000,,known as a hydrogen bond.
Dialogue: 0,0:02:13.96,0:02:16.77,Default,,0000,0000,0000,,Hydrogen bonds don't just happen in water either.
Dialogue: 0,0:02:16.77,0:02:18.96,Default,,0000,0000,0000,,They can form between a water molecule
Dialogue: 0,0:02:18.96,0:02:22.47,Default,,0000,0000,0000,,and different substances that are polar or ionic.
Dialogue: 0,0:02:22.47,0:02:25.60,Default,,0000,0000,0000,,Water's ability to stick to itself is called cohesion,
Dialogue: 0,0:02:25.60,0:02:28.32,Default,,0000,0000,0000,,while water's ability to stick to other substances
Dialogue: 0,0:02:28.32,0:02:30.56,Default,,0000,0000,0000,,is called adhesion.
Dialogue: 0,0:02:30.56,0:02:32.99,Default,,0000,0000,0000,,Now, think back to the initial questions.
Dialogue: 0,0:02:32.99,0:02:36.90,Default,,0000,0000,0000,,First, why are some insects able to walk on water?
Dialogue: 0,0:02:36.90,0:02:39.57,Default,,0000,0000,0000,,Surface tension due to hydrogen bonding
Dialogue: 0,0:02:39.57,0:02:41.70,Default,,0000,0000,0000,,creates a thin film on the surface of water
Dialogue: 0,0:02:41.70,0:02:43.16,Default,,0000,0000,0000,,that gives enough resistance
Dialogue: 0,0:02:43.16,0:02:45.59,Default,,0000,0000,0000,,for super-light insects to walk on.
Dialogue: 0,0:02:45.59,0:02:46.77,Default,,0000,0000,0000,,You can't walk on it
Dialogue: 0,0:02:46.77,0:02:48.80,Default,,0000,0000,0000,,because the hydrogen bonds aren't strong enough
Dialogue: 0,0:02:48.80,0:02:50.54,Default,,0000,0000,0000,,to hold you up.
Dialogue: 0,0:02:50.54,0:02:52.92,Default,,0000,0000,0000,,Why does ice float on top of liquid water?
Dialogue: 0,0:02:52.92,0:02:54.68,Default,,0000,0000,0000,,For most other substances,
Dialogue: 0,0:02:54.68,0:02:57.89,Default,,0000,0000,0000,,the solid state is more dense than the liquid state,
Dialogue: 0,0:02:57.89,0:03:00.39,Default,,0000,0000,0000,,but that is not the case for water!
Dialogue: 0,0:03:00.39,0:03:02.60,Default,,0000,0000,0000,,Hydrogen bonds keep water molecules
Dialogue: 0,0:03:02.60,0:03:05.55,Default,,0000,0000,0000,,farther apart in frozen water than in liquid water.
Dialogue: 0,0:03:05.55,0:03:07.52,Default,,0000,0000,0000,,The farther apart the molecules are,
Dialogue: 0,0:03:07.52,0:03:09.77,Default,,0000,0000,0000,,the less dense that solid is.
Dialogue: 0,0:03:09.77,0:03:13.23,Default,,0000,0000,0000,,So ice is about 9% less dense than water,
Dialogue: 0,0:03:13.23,0:03:15.44,Default,,0000,0000,0000,,which means it floats on the top.
Dialogue: 0,0:03:15.44,0:03:17.94,Default,,0000,0000,0000,,That's why lakes freeze from the top down
Dialogue: 0,0:03:17.94,0:03:19.86,Default,,0000,0000,0000,,and aquatic life is able to survive
Dialogue: 0,0:03:19.86,0:03:21.95,Default,,0000,0000,0000,,through a cold winter every year.
Dialogue: 0,0:03:21.95,0:03:24.66,Default,,0000,0000,0000,,It is the polarity of the water molecule
Dialogue: 0,0:03:24.66,0:03:26.91,Default,,0000,0000,0000,,and the resulting hydrogen bonding
Dialogue: 0,0:03:26.91,0:03:29.100,Default,,0000,0000,0000,,that account for water's unique properties.
Dialogue: 0,0:03:29.100,0:03:33.13,Default,,0000,0000,0000,,So, the reason that water is so special,
Dialogue: 0,0:03:33.13,0:03:34.44,Default,,0000,0000,0000,,from inside your cells
Dialogue: 0,0:03:34.44,0:03:35.88,Default,,0000,0000,0000,,to the world's oceans,
Dialogue: 0,0:03:35.88,0:03:40.83,Default,,0000,0000,0000,,is simply because it is a polar molecule.