Compounds are groups of two or more ELEMENTS bonded together. There are two main types of bonds which hold those atoms together. There are COVALENT and IONIC/ELECTROVALENT compounds. Covalent compounds happen when the electrons are shared by the atoms and ionic compounds happen when electrons are donated from one atom to another.
We talked about compounds and molecules in the matter section. When we discuss changes to matter, the changes are because of physical forces. When we talk about compounds, bonds are formed and broken down by chemical forces. Compounds cannot be broken down by physical forces. Chemical forces are forces caused by other compounds, or molecules.
There are millions of compounds everywhere. Chances are, everything you can see is one type of compound or another. When elements join together and become compounds they lose their individual traits. Sodium alone is very reactive. But when sodium combines with chlorine (another reactive element) they form a non-reactive substance called Sodium chloride (Salt). The compound has none of the traits or the original elements. It has a new life of its own.
DIFFERENT BONDS IN MOST COMPOUNDS
Most compounds are made up of combinations of bonds. If you look at Sodium chloride it is held together by one ionic bond. What about Magnesium chloride? One Magnesium and two Chloride atoms. So that's two ionic bonds. There's a compound called methane. It is made up of one Carbon and four Hydrogens. Four bonds, all covalent. Those 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 that on the left is the Sodium part and the right has the Oxygen/Hydrogen part. The bond which binds the Hydrogen to the Oxygen is covalent. The Sodium is bonded to the HYDROXIDE part of the compound with an ionic bond. This is a very good example of how there can be different types of bonds within one compound.
FUSING IDEAS TOGETHER
Where can we begin? 1967 Nobel Prize. One of the chiefs of the Manhattan Project (First Atomic Bomb). Leader in fusion research and how stars make their energy. He studied Cosmic Rays when he was 90. Born in Alsace-Lorraine in 1906, he received his Ph.D. at 22. Like many other scientists, he left Europe during World War 2. He came to Cornell.
More than just a scientist, Hans Bethe has worked to make the world a better place. He worked to make sure that governments were responsible with their new atomic weapons. He worked with Clinton, when he was 90, to create the Comprehensive Test Ban Treaty (it limits nuclear weapons testing). More than anything, he was always a great guy. When you look on the web, you will find tons of information praising Dr. Bethe for his work and his great attitude towards life.