ATOMS!
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Let's look REALLY close now, to better understand how atoms are arranged.
See those little balls? Those are atoms, increased by 100 million times!
While it is easier to draw an atom as a flat, still structure, the reality is, each electron moves so fast that it could be at any time around a nucleus, and it is hard to predict where it is. It's a little like the blades of a fan; you know that at any point in time, they are somewhere in that gray area, but you are never sure where.
What we do know, however, is that electrons are organized a certain way around the nucleus. Not all electrons have the same level of energy; so, they organize in layers of possibility, a little bit like an onion. We call each layer a shell.
While it is easier to draw an atom as a flat, still structure, the reality is, each electron moves so fast that it could be at any time around a nucleus, and it is hard to predict where it is. It's a little like the blades of a fan; you know that at any point in time, they are somewhere in that gray area, but you are never sure where.
What we do know, however, is that electrons are organized a certain way around the nucleus. Not all electrons have the same level of energy; so, they organize in layers of possibility, a little bit like an onion. We call each layer a shell.
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After experimenting with atoms, a scientist named Niels Bohr discovered that the electrons choose their layers in a very predictable way.
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Bohr discovered the maximum number of electrons on an electron shell can be determined by the following formula:
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Where e is the number of electrons within the shell, and n is the shell number.
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This is why we call the models for the atoms we build Bohr's models.
What element do you think is represented on the model to the right? |
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What happens with the leftovers?
Now we know that there is a maximum number of atoms in each layer; but what happens when an atom does not have enough eletrons to fill their last shell?
It turns out, most atoms are not balanced unless they are interacting, or sharing energy with other atoms. This is because most atoms are missing electrons on their last shell... because Bohr's formula is not only the formula for maximum electrons on a layer, but for stability.
Most atoms need to have at least two atoms interacting with each other; the gas Hydrogen, for instance, is actually made of two atoms of Hydrogen combined.
The atoms combine with each other by sharing energy. Think of the onion -- the very last layer has the most energy, and it's that outer layer that melds together to form molecules, such as proteins.
Below is a model molecule of the gas Oxygen. There are two lines between them because they share the energy of two of their most external atoms.
The atoms combine with each other by sharing energy. Think of the onion -- the very last layer has the most energy, and it's that outer layer that melds together to form molecules, such as proteins.
Below is a model molecule of the gas Oxygen. There are two lines between them because they share the energy of two of their most external atoms.
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What would be the exception to this rule -- which elements don't need another atom to become stable?
What is an Ion?
When elements are around in nature, they sometimes interact in unusual ways. For instance, when they bond, they can lose electrons to each other, or gain electrons from each other.
Let's look at Potassium, for instance. When its layers are organized, it turns out to have a single electron on its last layer, but the one right underneath has 8 electrons -- which is super stable. These atoms are desperate to lose an electron, so they can be stable.
Meanwhile, Chlorine has 7 electrons on the last layer. It only needs one, and so it is quite desperate for that last electron.
When Potassium gets near Chlorine, the atoms react immediately.
Potassium loses an electron; now, it has the original 19 protons, but only 18 electrons. Potassium is now more towards the positive. Meanwhile, Chlorine now has one more electron; it has 17 protons, but 18 electrons. It's more toward the negative.
We call these atoms with inbalanced number of electrons and protons IONS.
A negative Ion is called an ANION. Chlorine is almost always an ANION.
A positive Ion is called a CATION. Potassium is almost always a CATION.
Under the right circumstances, ANY element can be an ion.
Cations and anions are named based on the Greek words for "down" and "up"!
Let's look at Potassium, for instance. When its layers are organized, it turns out to have a single electron on its last layer, but the one right underneath has 8 electrons -- which is super stable. These atoms are desperate to lose an electron, so they can be stable.
Meanwhile, Chlorine has 7 electrons on the last layer. It only needs one, and so it is quite desperate for that last electron.
When Potassium gets near Chlorine, the atoms react immediately.
Potassium loses an electron; now, it has the original 19 protons, but only 18 electrons. Potassium is now more towards the positive. Meanwhile, Chlorine now has one more electron; it has 17 protons, but 18 electrons. It's more toward the negative.
We call these atoms with inbalanced number of electrons and protons IONS.
A negative Ion is called an ANION. Chlorine is almost always an ANION.
A positive Ion is called a CATION. Potassium is almost always a CATION.
Under the right circumstances, ANY element can be an ion.
Cations and anions are named based on the Greek words for "down" and "up"!
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Have you ever heard of Lithium Ion batteries? Do you wonder why they are called that? Let's watch the video below and check it out!!!
Valence
Valence is what we call the electrons on the last layer of an atom. Protons and neutrons don’t really do much; they just hold each other tight and hope for the best. But electrons are the wild cards.
One thing that is important is, the inner layers of atoms can’t really connect with the outside world. Why? Ok, imagine you go to a race car event. Would you try to cross the street when all the superfast cars are going? No? Same reason. Electrons are extremely fast and completely fill their layers with movement and energy, and so the only layer that can be touched and interact with other atoms is the outer layer.
Of course, as we saw in a couple of examples, sometimes the layer right below the last kicks some electrons out to make the last layer. Example: an atom that has 11 electrons on the last layer, for instance, will kick off 3 electrons to create a new layer, which will then try to find an atom that needs 3 electrons. This will be usually an ionic bond except for some exception compounds.
Let’s see the trick to figure out valences once and for all!
One thing that is important is, the inner layers of atoms can’t really connect with the outside world. Why? Ok, imagine you go to a race car event. Would you try to cross the street when all the superfast cars are going? No? Same reason. Electrons are extremely fast and completely fill their layers with movement and energy, and so the only layer that can be touched and interact with other atoms is the outer layer.
Of course, as we saw in a couple of examples, sometimes the layer right below the last kicks some electrons out to make the last layer. Example: an atom that has 11 electrons on the last layer, for instance, will kick off 3 electrons to create a new layer, which will then try to find an atom that needs 3 electrons. This will be usually an ionic bond except for some exception compounds.
Let’s see the trick to figure out valences once and for all!
The Valence Trick
On the table above, groups 1, 2, 13, 14, 15, 16, 17 and 18 are pretty special.
Their valences are 1, 2, 3, 4, 5, 6, 7 and 8, respectively!
You can prove this by figuring out the Bohr’s models for every one of the very top atoms (they are very easy).
If you know the valence of an atom, and you know how many electrons makes a stable atom (2 in some instances, 8 in most instances) then you can tell how many electrons are needed to make each atom happy.
So, looking at Mg, you see that it has 2 electrons on the last layer; it wants to dump those and become a positive ion (+2). This way it can bind with Oxygen, which has a valence 6. How does this happen? A valence 6 means it has 6 electrons on the last layer, and so it needs two electrons to feel good about itself. That means Oxygen is a -2 in terms of bond.
Does it always mean ions will be formed? No! But you will be able to tell what will happen by looking at the atoms you are using. Depending on them, you will be able to tell if it is an ionic bond or a covalent bond.
The rule is: An ionic bond will always bind a metal to a non metal (like NaCl), while a covalent bond will bind two non-metals (think H2O).
Let’s check out the charges for the elements:
Their valences are 1, 2, 3, 4, 5, 6, 7 and 8, respectively!
You can prove this by figuring out the Bohr’s models for every one of the very top atoms (they are very easy).
If you know the valence of an atom, and you know how many electrons makes a stable atom (2 in some instances, 8 in most instances) then you can tell how many electrons are needed to make each atom happy.
So, looking at Mg, you see that it has 2 electrons on the last layer; it wants to dump those and become a positive ion (+2). This way it can bind with Oxygen, which has a valence 6. How does this happen? A valence 6 means it has 6 electrons on the last layer, and so it needs two electrons to feel good about itself. That means Oxygen is a -2 in terms of bond.
Does it always mean ions will be formed? No! But you will be able to tell what will happen by looking at the atoms you are using. Depending on them, you will be able to tell if it is an ionic bond or a covalent bond.
The rule is: An ionic bond will always bind a metal to a non metal (like NaCl), while a covalent bond will bind two non-metals (think H2O).
Let’s check out the charges for the elements:
As you can see, some elements can form more than one charge; usually this will be defined by the problem, so no need to worry about it. The basic thought process is that the charge will be positive until it reaches group 14; as this group has 4 electrons on the last layer, it can either give or take 4 electrons, and very commonly likes to do a covalent bond with other elements, so that it can easily reach 8.
Covalent and Ionic Bonds
So, how does the oxygen above actually interact with the other oxygen?
What do those bridges mean?
If you looked what is actually happening on the last shell of both atoms, you would see the following image:
What do those bridges mean?
If you looked what is actually happening on the last shell of both atoms, you would see the following image:
The part in between the two atoms is most important. Both atoms of Oxygen have six electrons on their last shell, which is shell n=2; following Bohr's formula, we see that both would be balanced with 8 electrons on their last shell.
They need 2 electrons to balance. Instead of a straight donation, they each bring two atoms and share it with the other atom. These shared atoms form the bridges that we use on our models.
This is called Covalent Bond.
So, a covalent bond is a chemical bond between two atoms share one or more pairs of electrons. This happens because the atoms are trying to fill their outermost energy level, or valence shell, with a full complement of electrons. When the atoms share electrons in this way, they become more stable and less likely to react with other substances.
Covalent bonds occur between two non-metals or a non-metal, and a metalloid.
Sometimes, two atoms form a bond where electrons are (mostly) transferred from one atom to another. We say mostly because they still hang around each other, like they are still holding hands with the donated electron; but still, the donation is unequal, unline the covalent bond where each atom brings one electron to form a pair.
This is called Ionic Bond.
The less equal the sharing of the electrons, the more ionic character the bond has.
Ionic bonds occur between a metal and a non-metal.
They need 2 electrons to balance. Instead of a straight donation, they each bring two atoms and share it with the other atom. These shared atoms form the bridges that we use on our models.
This is called Covalent Bond.
So, a covalent bond is a chemical bond between two atoms share one or more pairs of electrons. This happens because the atoms are trying to fill their outermost energy level, or valence shell, with a full complement of electrons. When the atoms share electrons in this way, they become more stable and less likely to react with other substances.
Covalent bonds occur between two non-metals or a non-metal, and a metalloid.
Sometimes, two atoms form a bond where electrons are (mostly) transferred from one atom to another. We say mostly because they still hang around each other, like they are still holding hands with the donated electron; but still, the donation is unequal, unline the covalent bond where each atom brings one electron to form a pair.
This is called Ionic Bond.
The less equal the sharing of the electrons, the more ionic character the bond has.
Ionic bonds occur between a metal and a non-metal.
Build Molecules
Before we build molecules, let's review how to write them.
A molecule is composed of at least two atoms; if they are the same atom, like Oxygen, then we just need to put the symbol of the molecule and then add a 2 on the bottom right. This indicates that there are two of the same atom.
A molecule is composed of at least two atoms; if they are the same atom, like Oxygen, then we just need to put the symbol of the molecule and then add a 2 on the bottom right. This indicates that there are two of the same atom.
The formula for water is H2O -- how does that look?
Read the formula as "Hydrogen 2, Oxygen 1" -- If there is nothing under a letter, then it is always 1!
That was easy, right? But some molecules can get quite complex.
How many atoms of Nitrogen are in a molecule of Caffeine, for instance?
Caffeine: C8H10N4O2
There are 4 molecules of Nitrogen!
Carbon 8, Hydrogen 10, Nitrogen 4, Oxygen 2.
Read the formula as "Hydrogen 2, Oxygen 1" -- If there is nothing under a letter, then it is always 1!
That was easy, right? But some molecules can get quite complex.
How many atoms of Nitrogen are in a molecule of Caffeine, for instance?
Caffeine: C8H10N4O2
There are 4 molecules of Nitrogen!
Carbon 8, Hydrogen 10, Nitrogen 4, Oxygen 2.
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Let's build some ATOMS, and then... MOLECULES!
Before we build molecules, let's get real comfortable building atoms.
Try to build Li, B, C, O, Ne, K, Ca, Si, Kr and Mg, using some BIG paper, or the sheet below!
Try to build Li, B, C, O, Ne, K, Ca, Si, Kr and Mg, using some BIG paper, or the sheet below!
| build_atoms_sheet.pdf |
Let's build some Molecules!!!!
For your reference, the number of electrons is:
K=19, Cl = 17, C=6, H=1, N = 7, O=8, S =16
K=19, Cl = 17, C=6, H=1, N = 7, O=8, S =16
KCl (Potassium Chloride)
CH4 (Methane)
CO2 (Carbon Dioxide)
Sulphuric Acid (H2SO4)
Glucose (C6H12O6)
Ammonia (NH3)
Ethanol (C2H6O)
Nitrogen Gas (N2)
CH4 (Methane)
CO2 (Carbon Dioxide)
Sulphuric Acid (H2SO4)
Glucose (C6H12O6)
Ammonia (NH3)
Ethanol (C2H6O)
Nitrogen Gas (N2)
