Wednesday, December 14, 2011

The Periodic Table of the Elements

The Periodic Table of the Elements contains every known element in the universe. It is used by chemists to learn about these atoms. It is made up of tiny squares, each containing a certain element. The boxes are various colors as well. Blue indicates a gas when in its natural state, a yellow square indicates a solid when in its natural state, orange identify liquids when in their natural state, and green show that the element has been discovered by man in a laboratory. Inside each square is a one or two letter abbreviation of the name of the element, the symbol. Most of these abbreviations come from the Latin or Greek names of the elements. Above the symbol for the element is the elements atomic number.

The atomic number indicates the number of protons within the nucelus of a given element. Hydrogen only has one proton, so it's number one on the Periodic Table. Helium has two protons, so it is number two, and so on. The number that appears below the symbol is the elements atomic mass number. Protons and Neutrons are each both about one atomic mass unit. Neutrons have no electrical charge, so they don't affect the electrical balance of an atom, and there can be varying numbers of them. Each one of these with a varying number of neutrons is called an isotope.

Tuesday, December 6, 2011

Ionic Bonds

There are three sorts of changes in matter - nuclear, physical, and chemical. Nuclear changes occur in the nucleus, or center, of atoms. Physical changes occur when a substance undergoes change, but retains its chemical composition. When chemical changes occur, there is an actual chemical change in the substance. The original atoms remain, but a new substance is created, with a different chemical composition. This is how items such as plastic are created. The substances used to make it cannot be separated, which is what distinguishes between these and mixtures, such as muddy water. If given enough time, mud and water will separate. In a compound, however, the valence electrons (the electrons in the outer energy level) are lost, gained, or shared between the different elements to create unique substances. They are held together by bonds, either ionic or covalent. I'll talk about ionic bonds today.

If an atom looses a negatively charged electron, it becomes a positive ion, because it has more positively charged protons than negatively charged electrons. If the opposite happens, and the atom looses a positively charged proton, it becomes a negatively charged ion. A positive ion and a negative ion will attract. Sodium has only one valence electron. Chlorine is an atom that is missing only one electron in order to become stable. If both come close together, the sodium's valence electron will join the chlorine atom, completing an ionic bond and forming sodium chloride, or table salt. This sort of bond is common in chemistry and has given rise to the Octet rule, which states that atoms tend to gain, loose, or share electrons in order to acquire a full set of valence electrons.

Ionic bonds share similar properties, which include high melting points, a tendency to be brittle, and dissolve in water.