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Welcome to this set of flashcards about genetics. Here’s how it works:
- Click ‘Check answer’ to see the answer to each card.
- If you don’t know it as well as you’d like to, click ‘Need more practice,’ and that card will go to the bottom of the stack so you can practice it again.
- If you know it, click ‘Got it.’
- ‘Shuffle’ lets you shuffle the deck.
[start]
[q] The structure Of Water
To understand water’s chemistry and properties, we need to understand its internal structure. To review how to draw a molecule’s structure, let’s start with the simplest molecule in the universe, hydrogen gas (H2).
Remember that a hydrogen atom has one proton and one electron.
Your first diagram should be an electron distribution model (showing the atomic nuclei and the electron energy levels). The second should be a structural formula.
[a]
[q] Molecule of water
Now let’s look at a molecule of water.
Water’s chemical formula is H2O.
Hydrogen has one proton and one electron.
Oxygen has 8 protons, 8 neutrons, and 8 electrons.
Use that information to draw a diagram of a water molecule that shows electron sharing between the single oxygen and the two hydrogens. Then, draw the structural formula. When you’re done, click below to see the solution.
[a]
[q]
If you orient water so that the hydrogens are on top,
you should be reminded of a very famous Disney cartoon character.
[a] Mickey Mouse molecule!
[q] We’ll begin with the concept of polarity.
The Earth is polar. What that means is that it has two poles .. A north and a south pole.
Magnets are also polar.
Like the Earth, a bar magnet has a north and a south pole. The north pole of one magnet is attracted to the south pole of another magnet. Two magnetic south poles, by contrast, push each other apart (as do two magnetic north poles).
[a] The rules for magnets are
- Like poles repel (push away)
- Opposite poles attract.
[q] Like Magnet Water is Also Polar
Look at this electron distribution model of water, and see where there’ll be a more negatively charged side, and where there’ll be a more positively charged side.
[a]
[q]
Let’s dig a little bit deeper so we can understand why water is a polar molecule.
- The nucleus of the oxygen atom has eight protons: eight charges.
- The two hydrogen nuclei each have only one Proton. one positive charge.
- Those eight protons in the oxygen nucleus are going to pull on the 10 electron in the molecule with a lot more force than the single proton in each hydrogen nucleus.
- As a result, the oxygen side of the molecule will tend to have more electrons and have a slight negative charge. By contrast, the region around the two hydrogen nuclei will tend to have less electrons and have a slight positive charge.
- In sum, water isn’t just a covalently bonded molecule. Because electron sharing is unequal, and results in polarity, the bonds have special name: they’re called Polar Covalent bonds.
[a] Water Polarity Leads to Hydrogen Bonding
Because water molecules are polar, weak bonds will form between any two water molecules that get close to one another. The dotted line below represents one of these weak bonds.
[q] hydrogen bond.
Water molecules, as you can see here, are “sticky.” Remember that this stickiness is on a molecular level. Here are two key points to keep in mind.
- The oxygen end of one water molecule, with its partially _Negative charge, will temporarily bond with the _hydrogen end of another water molecule, with its partially positive charge.
- The bond that forms between one water molecule and the next is called a hydrogen bond.
[a]
Hydrogen bonds are weak and temporary. But, in any body of water — anything from the tiniest droplet to an ocean — they have enormous consequences. We’ll look at these consequences in the next tutorial. Before that, though, let’s compare water to another molecule that you might be familiar with: methane: CH4.
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