CHEMISTRY - BONDS MODULE #8

BONDING

Bonding Basics

You must first learn why atoms bond together. We use a concept called "Happy Atoms." We figure that most atoms want to be happy, just like you. 

The idea behind Happy Atoms is that atomic shells like to be full. That's it. If you are an atom and you have a shell, you want your shell to be full. Some atoms have too many electrons (one or two extra). These atoms like to give up their electrons. Some atoms are really close to having a full shell. Those atoms go around looking for other atoms who want to give up an electron. 

Let's take a look at some examples. 

We should start with the atoms that have atomic numbers between 1 and 18. 

There is a 2-8-8 rule for these elements. 

• The first shell is filled with 2 electrons
• the second is filled with 8 electrons
• third is filled with 8. 

You can see that sodium (Na) and magnesium (Mg) have a couple of extra electrons. They, like all atoms, want to be happy. They have two possibilities: they can try to get to eight electrons to fill up their third shell, or they can give up a few electrons and have a filled second shell.

•  It is always easier to give away one or two electrons than it is to go out and find six or seven to fill your shells. 

What a coincidence! Many other atoms are interested in gaining a few extra electrons. 

Oxygen (O) and fluorine (F) are two good examples. Each of those elements is looking for a couple of electrons to make a filled shell. They each have one filled shell with two electrons, but their second shells want to have eight. There are a couple of ways they can get the electrons. 

• They can share electrons, making a covalent bond, or they can just borrow them, and make an ionic bond (also called electrovalent bond). 

So, let’s say we've got a sodium atom that has an extra electron. We've also got a fluorine atom that is looking for one. 

When they work together, they can both wind up happy! Sodium gives up its extra electron. The sodium then has a full second shell and the fluorine (F) also has a full second shell. Two happy atoms! When an atom gives up an electron, it becomes positive like the sodium ion (Na⁺). When an atom gets an extra electron, it becomes negatively charged like the fluorine ion (F^-). 
The positive and negative charges continue to attract each other like magnets. The attraction of opposite charges is the way they form and maintain the bond. 

• Any atoms in an ionic/electrovalent bond can get or give up electrons. 

CHEMISTRY - COMPOUNDS MODULE #9

COMPOUNDS

Compound Basics

Compounds are groups of two or more elements that are bonded together. You have also seen us use the word molecule. 
Molecule is the general term used to describe atoms connected by chemical bonds. 

• Every combination of atoms is a molecule. 
• Compounds happen with atoms from different elements. So, all compounds are molecules, because they have bonds between the atoms, like in water (H₂O).      
• However, not all molecules are compounds because sometimes the atoms are of the same element. 
• Hydrogen gas (H₂) is a good example of a molecule that is not a compound. 

There are two main types of chemical bond that hold atoms together covalent and electrovalent/ionic bonds. 

• Covalent compounds happen when the atoms share the electrons, and
• Ionic compounds happen when electrons are donated from one atom to another. 

When we discuss phase changes in matter, physical forces create the changes. 
When we talk about compounds, bonds are built and broken down by chemical forces. Physical forces alone (unless you're inside of the Sun or something extreme) cannot break down compounds. Chemical forces are forces generated by other compounds or molecules that act on substances. You can apply the physical force of heat to melt an ice cube and there is no change to the water molecules. You can also pour a liquid acid on a solid and watch the solid melt, but that is a chemical change because molecular bonds are being created and destroyed. 

There are millions of different compounds around you. Probably everything you can see is one type of compound or another. When elements join and become compounds, they lose many of their individual traits. 

• Sodium (Na) alone is very reactive. But when sodium and chlorine (Cl) combine, they form a non-reactivesubstance called sodium chloride (salt, NaCl). The compound has few or none of the traits of the original elements. The new compound is not as reactive. It has a new life of its own. 

Different Bonds Abound

Most compounds are made up of combinations of bonds. If you look at sodium chloride, it is held together by one ionic/electrovalent bond. What about magnesium chloride (MgCl₂)? It contains one magnesium (Mg) and two chlorine atoms. There are two ionic bonds. There's a compound called methane (CH₄) that is made up of one carbon (C) and four hydrogen (H) atoms. There are four bonds and they are all covalent. Those examples are very simple compounds, but most compounds are combinations of ionic and covalent bonds. 

Let's look at sodium hydroxide (Na-OH)... 

You can see the sodium (Na) part on the left and the hydroxide (-OH) part on the right. The bond that binds the hydrogen (H) to the oxygen (O) is covalent. The sodium is bonded to the hydroxide part of the compound with an ionic/electrovalent bond. This is a very good example of how there can be different types of bonds within one compound. 


REVIEW: 

A compound is a substance made up of two or more elements combined chemically. 

•  This combination is similar to a recipe for a dessert in which one combines the different ingredients in specific amounts to one another to create a delicious treat!

• Compounds are made up of elements which are a kind of atom or of a combination of compounds. 
• When they are combined chemically, it is very difficult to separate out the different elements just as it is very difficult once a cake is baked to separate out the eggs, flour, sugar and other ingredients.

• Compounds often have common names such as water or salt - but are also named by their formula which tell what elements make up the compound and in what proportion. 
• For example, the smallest bit of water, a molecule of water, is made up of two hydrogen atoms for every one oxygen atom. 
• A formula is similar to a very precise recipe for a compound.

• Compounds are made up of many, many molecules of that compound.

CHEMISTRY - COMPOUND NAMES MODULE #10

COMPOUND NAMES

Whole Lotta Rules Going On

The process of naming compounds is just a set of rules. We're going to show you some of the basics. There are some advanced ways of naming things that we're going to skip right now. 

When you have two different elements, there are usually only two words in the compound name. The first word is the name of the first element. The second word tells you the second element and how many atoms there are in the compound. The second word usually ends in IDE. That's the suffix. When you are working with non-metals likeoxygen (O) and chlorine (Cl), the prefix (section at the beginning of the word) of the second element changes based on how many atoms there are in the compound. It's like this... 

Do you notice anything about the chalkboard? You can see that the prefixes are very similar to the prefixes of geometric shapes. You know what a triangle is. Right? Well the prefix tri- means three. So when you have three chlorine atoms, you would name it trichloride. 

Look at the other names too. You may know about a pentagon, a hexagon, or an octagon. The naming system in chemistry works the same way! 

Let's put these ideas together! Remember, we're only talking about simple compounds with no metal elements. Most simple compounds only have two words in their names. Let's start with carbon monoxide (CO). That name tells you that you have one carbon (C) atom and one oxygen (O) atom (you can also use the prefix MONO to say one atom). Remember that the second word ends in -ide. So... 

(1) Carbon + (1) Oxygen = Carbon monoxide (CO)

Now we'll build on that example. What if you have one carbon (C) and two oxygen (O) atoms? 

(1) Carbon + (2) Oxygen = Carbon dioxide (CO₂)

One last example and we'll call it quits. Now you have one carbon (C) and four chlorine (Cl) atoms. 

(1) Carbon + (4) Chlorine = Carbon tetrachloride (CCl₄)

You should be getting the idea now. The compound name can tell you how many atoms are inside. Take a look at some of the examples and see if you understand what is happening in the name. 

SCIENCE NEWS - SUPERGLUE #20

CHEMISTRY - ELEMENT OF THE DAY - MAGNESIUM

12

Mg

Magnesium

24.3050

Atomic Number: 12

Atomic Weight: 24.3050

Phase at Room Temperature: Solid

Element Classification: Metal

Period Number: 3    Group Number: 2    

Group Name: Alkaline Earth Metal

What's in a name? For Magnesia, a district in the region of Thessaly, Greece.

Say what? Magnesium is pronounced as mag-NEE-zhi-em.

History and Uses:

Although it is the eighth most abundant element in the universe and the seventh most abundant element in the earth's crust, magnesium is never found free in nature. Magnesium was first isolated by Sir Humphry Davy, an English chemist, through the electrolysis of a mixture of magnesium oxide (MgO) and mercuric oxide (HgO) in 1808. Today, magnesium can be extracted from the minerals dolomite (CaCO₃·MgCO₃) and carnallite (KCl·MgCl₂·6H₂O), but is most often obtained from seawater. Every cubic kilometer of seawater contains about 1.3 billion kilograms of magnesium (12 billion pounds per cubic mile).

Magnesium burns with a brilliant white light and is used in pyrotechnics, flares and photographic flashbulbs. Magnesium is the lightest metal that can be used to build things, although its use as a structural material is limited since it burns at relatively low temperatures. Magnesium is frequently alloyed with aluminum, which makes aluminum easier to roll, extrude and weld. Magnesium-aluminum alloys are used where strong, lightweight materials are required, such as in airplanes, missiles and rockets. Cameras, horseshoes, baseball catchers' masks and snowshoes are other items that are made from magnesium alloys.

Magnesium oxide (MgO), also known as magnesia, is the second most abundant compound in the earth's crust. Magnesium oxide is used in some antacids, in making crucibles and insulating materials, in refining some metals from their ores and in some types of cements. When combined with water (H₂O), magnesia forms magnesium hydroxide (Mg(OH)₂), better known as milk of magnesia, which is commonly used as an antacid and as a laxative.

Hydrated magnesium sulphate (MgSO₄·7H₂O), better known as Epsom salt, was discovered in 1618 by a farmer in Epsom, England, when his cows refused to drink the water from a certain mineral well. He tasted the water and found that it tasted very bitter. He also noticed that it helped heal scratches and rashes on his skin. Epsom salt is still used today to treat minor skin abrasions.

Other magnesium compounds include magnesium carbonate (MgCO₃) and magnesium fluoride (MgF₂). Magnesium carbonate is used to make some types of paints and inks and is added to table salt to prevent caking. A thin film of magnesium fluoride is applied to optical lenses to help reduce glare and reflections.

CHEMISTRY - ISOTOPES - MODULE #7

ISOTOPES

Neutron Madness

We have already learned that ions are atoms that are either missing or have extra electrons. Let's say an atom is missing a neutron or has an extraneutron. That type of atom is called an isotope. An atom is still the same element if it is missing an electron. The same goes for isotopes. They are still the same element. They are just a little different from every other atom of the same element. 

For example, there are a lot of carbon (C) atoms in the Universe. The normal ones are carbon-12. Those atoms have 6 neutrons. There are a few straggler atoms that don't have 6. Those odd ones may have 7 or even 8 neutrons. As you learn more about chemistry, you will probably hear about carbon-14. Carbon-14 actually has 8 neutrons (2 extra). C-14 is considered an isotope of the element carbon. 

Messing with the Mass

If you have looked at a periodic table, you may have noticed that the atomic mass of an element is rarely an even number. That happens because of the isotopes. If you are an atom with an extra electron, it's no big deal. Electrons don't have much of a mass when compared to a neutron or proton. 

Atomic masses are calculated by figuring out the amounts of each type of atom and isotope there are in the Universe. For carbon, there are a lot of C-12, a couple of C-13, and a few C-14 atoms. When you average out all of the masses, you get a number that is a little bit higher than 12 (the weight of a C-12 atom). The average atomic mass for the element is actually 12.011. Since you never really know which carbon atom you are using in calculations, you should use the average mass of an atom. 

Bromine (Br), at atomic number 35, has a greater variety of isotopes. The atomic mass of bromine (Br) is 79.90. There are two main isotopes at 79 and 81, which average out to the 79.90amu value. The 79 has 44 neutrons and the 81 has 46 neutrons. While it won't change the average atomic mass, scientists have made bromine isotopes with masses from 68 to 97. It's all about the number of neutrons. As you move to higher atomic numbers in the periodic table, you will probably find even more isotopes for each element. 

Returning to Normal

If we look at the C-14 atom one more time, we find that C-14 does not last forever. There is a time when it loses its extra neutrons and becomes C-12. The loss of those neutrons is called radioactive decay. That decay happens regularly like a clock. For carbon, the decay happens in a few thousand years (5,730 years). Some elements take longer, and others have a decay that happens over a period of minutes. Archeologists are able to use their knowledge of radioactive decay when they need to know the date of an object they dug up. C-14 locked in an object from several thousand years ago will decay at a certain rate. With their knowledge of chemistry, archeologists can measure how many thousands of years old an object is. This process is called carbon dating.