Matter
The matter is defined as anything that occupies space and has weight; that is, the weight and dimensions of matter can be measured.
Elements and Compounds
- An ELEMENT is a substance that cannot be reduced to a simpler substance by chemical means.
- A compound is a chemical combination of elements that can be separated by chemical but not by physical means.
- A mixture, on the other hand, is a combination of elements and compounds, not chemically combined, that can be separated by physical means.
Compounds are made up of 2 or more different kinds of elements. Elements are made up of 1 type of atom.
For example, chlorine is an element. It is made up of 1 chlorine atom. Sodium is also an element. It is made up of a sodium atom.
Now, let's see a compound of these 2. Sodium chloride (NaCl), or table salt, is made up of sodium and chlorine. It is a compound because it contains 2 different elements, thus containing 2 different kinds of atoms.
Molecules
A molecule is a chemical combination of two or more atoms.
Atoms
An atom is the smallest particle of an element that retains the characteristics of that element.
A molecule is Any particle that is a chemical combination of two or more atoms.
The atoms of each element are made up of electrons, protons, and, in most cases, neutrons, which are collectively called subatomic particles.
the electrons, protons, and neutrons of one element are identical to those of any other element. The reason that there are different kinds of elements is that the number and the arrangement of electrons and protons within the atom are different for the different elements.
The electron is considered to be a small negative charge of electricity
The proton has a positive charge of electricity equal and opposite to the charge of the electron.
The electron and proton each have the same quantity of charge, although the mass of the proton is approximately 1837 times that of the electron.
In some atoms, there exists a neutral particle called a neutron. The neutron has a mass slightly greater than that of a proton, but it has no electrical charge.
electrons, protons, and neutrons arranged in a manner similar to a miniature solar system.
Elements are classified numerically according to the complexity of their atoms.
The atomic number of an atom is determined by the number of protons in its nucleus.
In a neutral state, an atom contains an equal number of protons and electrons.
Energy Levels
Since an electron in an atom has both mass and motion, it contains two types of energy.
By virtue of its motion, the electron contains kinetic energy. Due to its position, it also contains potential energy.
The total energy contained by an electron (kinetic plus potential) is the factor which determines the radius of the electron orbit.
In order for an electron to remain in this orbit, it must neither GAIN nor LOSE
energy.
It is well known that light is a form of energy, but the physical form in which this energy exists is not known.
One accepted theory proposes the existence of light as tiny packets of energy called photons. Photons can contain various quantities of energy. The amount depends upon the color of the light involved.
a photon of sufficient energy collide ( tabrakan) with an orbital electron, the electron will absorb the photon's energy, as shown in the figure.
The electron, which now has a greater than normal amount of energy, will jump to a new orbit farther from the nucleus.
An electron cannot exist in the space between energy levels. This indicates that the electron will not accept a photon of energy unless it contains enough energy to elevate itself to one of the higher energy levels. Heat energy and collisions with other particles can also cause the electron to jump orbits.
Once the electron has been elevated to an energy level higher than the lowest possible energy level, the atom is said to be in an excited ( aktif) state. The electron will not remain (tetap) in this excited condition for more than a fraction of a second ( sepersekian detik) before it will radiate (memancarkan) the excess energy and return to a lower energy orbit.
To illustrate this principle, assume that a normal electron has just received a photon of energy sufficient to raise it from the first to the third energy level. In a short period of time, the electron may jump back to the first level emitting a new photon identical to the one it received.
A second alternative would be for the electron to return to the lower level in two jumps; from the third to the second, and then from the second to the first. In this case, the electron would emit two photons, one for each jump. Each of these photons would have less energy than the original photon which excited the electron.
This principle is used in the fluorescent light where ultraviolet light photons (lampu neon photon cahaya ultraviolet) , which are not visible (tidak terlihat) to the human eye, bombard a phosphor coating (lapisan) on the inside of a glass tube. The phosphor electrons, in returning to their normal orbits, emit (memancarkan) photons of light that are visible (tidak terlihat) . By using the proper chemicals for the phosphor coating, any colour of light may be obtained, including white.
Shells and Sub-shells
In general, the electrons reside in groups of orbits called shells.
Pauli's exclusion principle, this principle specifies that each shell will contain a maximum of 2n2 electrons, where n corresponds to the shell number starting with the one closest to the nucleus. By this principle, the second shell, for example, would contain 2(2)2 or 8 electrons when full.
Starting with the shell closest to the nucleus and progressing outward, the shells are labeled K, L, M, N, O, P, and Q, respectively. The shells are considered to be full, or complete, when they contain the following quantities of electrons: two in the K shell, eight in the L shell, 18 in the M shell, and so on, in accordance with the exclusion principle.
Each of these shells is a major shell and can be divided into sub-shells, of which there are four, labeled s, p, d, and f.
the "s" sub-shell is complete when it contains two electrons, the "p" sub-shell when it contains 6, the "d" sub-shell when it contains 10, and the "f" sub-shell when it contains 14 electrons.
Valence
The number of electrons in the outermost shell determines the valence of an atom. For this reason, the outer shell of an atom is called the valence shell; and the electrons contained in this shell are called valence electrons.
An atom that is lacking only one or two electrons from its outer shell will easily gain electrons to complete its shell, but a large amount of energy is required to free any of its electrons. An atom having a relatively small number of electrons in its outer shell in comparison to the number of electrons required to fill the shell will easily lose these valence electrons.
Compounds
Note that a compound:
- consists of atoms of two or more different elements bound together,
- can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means),
- has properties that are different from its component elements, and
- always contains the same ratio of its component atoms
Ionization
ionization is the process by which an atom loses or gains electrons.
negative ion An atom having more than its normal amount of electrons acquires a negative charge
positive ion The atom that gives up some of its normal electrons is left with less negative charges than positive charges
Conductors, Semiconductors, and Insulators
conductors are elements which conduct electricity very readily, insulators have an extremely high resistance to the flow of electricity. All matter between these two extremes may be called semiconductors.
Normally, conductors have three or fewer valence electrons; insulators have five or more valence electrons, and semiconductors usually have four valence electrons.
The fewer the valence electrons, the better conductor of electricity it will be. Copper, for example, has just one valence electron.
When not under the influence of an external force, these electrons move in a haphazard manner within the conductor. This movement is equal in all directions so that electrons are not lost or gained by any part of the conductor. When controlled by an external force, the electrons move generally in the same direction. The effect of this movement is felt almost instantly from one end of the conductor to the other. This electron movement is called an electric current.
Silver, copper, gold, and aluminum are materials with many free electrons and make good conductors. Silver is the best conductor, followed by copper, gold, and aluminum. Copper is used more often than silver because of cost. Aluminum is used where weight is a major consideration, such as in high-tension power lines, with long spans between supports. Gold is used where oxidation or corrosion is a consideration and good conductivity is required.
Non-conductors have few free electrons. These materials are called insulators. Some examples of these materials are rubber,
plastic, enamel, glass, dry wood, and mica. Just as there is no perfect conductor, neither is there a perfect insulator. Some materials are neither good conductors nor good insulators since their electrical characteristics fall between those of conductors and insulators. These in-between materials are classified as semiconductors. Germanium and silicon are two common semiconductors used in solid-state devices.
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