The Composition of Matter

Chemistry is defined as an organized body of knowledge concerning the composition of matter and how matter interacts and changes . Matter can be defined as anything that possesses the properties of mass and volume. Mass is the measure of a chunk of matter's ability to resist a change in movement or direction. The chemist calls this "inertia". Volume is the three dimensional space occupied by matter. It is a universal axiom that two chunks of matter can not occupy the same space simultaneously. All matter is composed of basic particles of atoms, molecules or ions.

What are atoms?

The basic of these particles are the atom. Atoms are particles that are composed of three sub-atomic particles. The three sub-atomic particles are the proton, neutron, and the electron. The proton is a positively charged particle that has the mass approximately equal to a hydrogen atom. It is said to have the mass of 1 atomic mass unit (amu). The protons reside in the nucleus or center of the atom. The neutron is a neutrally charged particle that is approximately the mass of a proton. The neutron does not have an electrical charge, but it also resides in the nucleus. The particles of the nucleus are called nucleons. The third particle of an atom is the electron. The electron is a negatively charged particle of negligible but finite mass. It resides on the outer edges of the atom with an enormous amount of space between the nucleus and the electrons.

Because the protons and the neutrons are relatively well protected in the nucleus and the electron is on the periphery of the atom, it is the electrons that undergo change during a chemical reaction. It is the electrons that the chemist focuses upon. It takes millions of times more energy for the nucleus to be penetrated so the nucleus is not affected in normal chemical reactions. Atoms are neutral so that means that the positive protons and the negative electrons must be equal for the atom to be neutral. There are some 111 known different atoms that are differentiated by two numbers, atomic number and mass number. The atomic number is equal to the number of protons found in the nucleus. For a neutral atom that would also be the number of electrons in the atom. The mass number is defined as the sum of the protons and the neutrons in the nucleus of an atom. In other words, the mass number is the number of nucleons found in the atom. If I know the atomic number of an atom and the mass number then I can determine the number of electrons, protons, and neutrons that the atom has.

What are molecules?

Molecules are clusters of atoms that are held together by strong electrical forces called bonds. Molecules are neutral like atoms. Substances that form molecular units are called molecular substances. Just as elements can be symbolized by a symbol, molecules can be symbolized by the symbols of the elements that make up the compound. These are called formulas. Non-metallic elements react with other non-metallic elements to form molecular compounds

What are ions?

Ions are the third basic particle of matter. Ions are charged atoms or groups of atoms possessing an electrical charge. Atoms are neutral possessing equal numbers of negative electrons and positive protons. However some atoms have a tendency to lose one or more negative electrons during a Chemical change. If the atom loses electrons that would mean that the atom would have more positive protons than negative electrons and the atom would become positively charged. These ions are called "cations". Metallic elements tend to lose electrons and become cations.

Other atoms prefer to gain one or more negative electrons. This would give such an atom more negative electrons than protons and the atom would be negatively charged. These are referred to as "anions". Non-metallic elements have atoms that tend to gain electrons to become anions.

Why do atoms lose or gain electrons?

The whole motivation of why some atoms lose and some gain electrons is to make the atoms chemically more stable. They gladly sacrifice their electrical neutrality in favor of a more stable state. The more stable state is an ion that has the same number of electrons as one of the noble gases found in the last column of elements on the right of the periodic table. This condition is referred to as being "isoelectronic" to a Noble gas. These elements used to be called the "inert gases" because there were no known compounds of these elements. These elements are still relatively inert which is a testament of their great stability. All other elements have atoms that would like to emulate these noble gases. In other words, to be isoelectronic to a Noble Gas. The Noble gases were found to react with certain very chemically reactive elements like Fluorine and Oxygen and only Xenon has been known to form compounds of Fluorine and Oxygen. It is not surprising that such relatively stable elements would react with these two non-metals (Fluorine and Oxygen) If they were to react it would be the two most reactive non-metals in the universe.

Why do elements lose or gain different numbers of electrons?

All atoms would like to have the same number of electrons as a Noble gas because of their great stability. In order to accomplish that, some atoms must lose one and some more than one electron in order to have the same number of electrons as the nearest Noble Gas in the Periodic Table. For the first column of elements called Group 1 located in the first column on the left side of the Periodic Table each element in this Group have atoms that have only one electron that needs to be lost in order to reach this isoelectronic state with the nearest Noble Gas located on the last column on the extreme right of the Table called Group 18. The second column of elements in the Periodic Table called Group 2 has elements whose atoms have two electrons that must be lost to become isoelectronic to the nearest Noble Gas. On the other end of the Periodic Table, there are Groups of elements like Group 15 where atoms must gain three electrons in order to become isoelectronic to the nearest Noble Gas. Group 16 elements have atoms that must gain only two electrons to become isoelectronic to the nearest Noble Gas. Group 17 elements which are only one column to the left of the Noble Gas Group requires that its atoms need only to gain one electron.