Name: 離子鍵和共價鍵、氫鍵、範德華--生物學中的4種化學鍵。 (Ionic and Covalent Bonds, Hydrogen Bonds, van der Waals - 4 types of Chemical Bonds in Biology)
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There are four types of chemical bonds essential for life to exist: Ionic Bonds, Covalent Bonds,

Hydrogen Bonds, and van der Waals interactions.

All of these bonds represent an emergent property of atoms.

Individually, we can study the makeup of atoms - how many protons, neutrons,

But when atoms come in to close proximity with each other, a new characteristic becomes apparent.

If an atom doesn’t have a filled valence shell of electrons, it can either share electrons

with another atom, or it can completely transfer electrons.

This way, an atom can gain enough electrons to fill its outermost shell, or shed enough

electrons to empty its outermost shell, leaving a complete valence shell underneath at the

The interactions between atoms that take place as a result are called chemical bonds.

So this is an example of an emergent property.

You don’t know anything about an atom’s chemical behavior until it comes in close

contact with another atom - then the chemical behavior EMERGES.

One thing that determines what kind of bond an atom will be involved in is its Electronegativity.

Think of electronegativity as the degree to which an atom pulls on an electron

If two atoms come together and they have fairly similar electronegativities, they will share

This especially makes sense when the two atoms are identical.

Like - a hydrogen and a hydrogen share an electron and become an H2 molecule.

Neither one has a complete valence shell of electrons.

The outermost valence shell in oxygen has 6 electrons.

So it needs two electrons to fill up that valence shell and become more stable.

When two oxygen atoms come into close proximity, they can share two electrons and so form a

They have the same electronegativity, since they’re identical, so the electrons are

Now, if there IS a difference in the electronegativities, the electrons will spend a greater amount

of time next to the atom with a higher Electronegativity.

Remember, electrons are always in motion, moving around in kind of cloudlike regions

For instance, in a water molecule, H2O,Oxygen has a higher electronegativity than Hydrogen.

So in both of the bonds in this molecule, the electrons will spend a greater part of

their time closer to the oxygen atom versus next to the hydrogen atoms.

This results in a water molecule having a partial negative charge around the oxygen

atom, and a partial positive charge around the hydrogen atoms.

We call this kind of chemical interaction a POLAR COVALENT BOND.

Now if the electronegativities are different enough, one atom will actually donate one

or more electrons to the more electronegative atom.

This results in two charged species - ions.

The atom that donates one or more electrons is called a cation.

The atom that takes on electrons becomes negatively charged.

As a result of becoming oppositely charged, these ions are now attracted to each other

That attraction holding the two ions together is called an IONIC BOND.

Now here’s a funny thing about ionic bonds in biology.

When you learn about ionic bonds in chemistry, like say, the bonds holding the salt NaCl

together, we think of it as quite a strong bond.

But in biology/ biochemistry, you must remember that everything - all these chemical interactions

- are taking place in the context of water.

In water, ionic bonds quickly dissociate.

So for this reason, in biochemistry, we consider ionic bonds weaker than most covalent bonds.

In chemistry, we always discuss the range of strengths of the bonds.

You can learn more in a video we have called ionic bonds vs covalent bonds in our chemistry

This may surprise you, but it’s really important that we have the capability to make bonds

There are some cases where we want very strong bonds.

But there are other cases where it makes more sense to have weak bonds.

Bonds that can be used for REVERSIBLE interactions.

Let’s say we have a receptor, and a signalling molecule that binds it - like a hormone or

We don’t want that signalling molecule to bind to the receptor once, and get stuck there,

We want it to bind REVERSIBLY - to bind, send the signal, and then fall off.

In fact, there are some poisons that work this way - they bind permanently to a receptor

and don’t fall off, so they mess up signalling in your body.

The next weaker bond is the Hydrogen bond.

People often get confused about hydrogen bonds because the one example you’ll always hear

We use that example because it’s incredibly important for why water is essential to life...and

But meanwhile, the confusion comes because we just said there are polar covalent bonds

In INDIVIDUAL water molecules, those bonds are polar covalent bonds.

There are hydrogen bonds that hold different water molecules together.

For example, why water forms drops that kind of bunch up instead of lying flat.

The hydrogen bond is the very weak attraction between one hydrogen atom that is already

covalently bonded to something else (so it has a partial positive charge) and something

This is usually an oxygen, nitrogen, or fluorine atom that is bonded to something else.

So in the case of water, you have the hydrogen from one water molecule attracted to the oxygen

Notice that these bonds are written differently from covalent bonds.

Rather than a solid line joining the two atoms, it’s a dotted line.

That’s to remind you that this is a very weak interaction.

Now, let’s talk about the very weakest kind of bond, the van der Waals interactions.

To understand these, you must keep in mind that idea that electrons are

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離子鍵和共價鍵、氫鍵、範德華--生物學中的4種化學鍵。 (Ionic and Covalent Bonds, Hydrogen Bonds, van der Waals - 4 types of Chemical Bonds in Biology)

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