ATOM, MOLECULE AND ION

    I. ATOMAtom is the smallest particle that still has the properties of the elements. According to the physicists, the radius of an atom about 3-15 nm (1 nm = 10-9 m). Until now there is no tool that can magnify atoms so that it can be clearly observed. Although atoms can not be seen clearly, the experts can make an estimate based on an idea of ​​atomic experimental data and theoretical studies were done. Estimates about the picture of the atom is called the atomic model. That is why the model of the atom has been amended several times in accordance with the development of science.Atomic theory was first proposed by John Dalton in 1803, the atom is the smallest particle that can not be subdivided. Then it is known that atoms turned out to consist of particles smaller ie protons, electrons, and neutrons. Subatomic particles called subatomic particles atoms or elementary particles. Protons are positively yangbermuatan subatomic particles, discovered by Eugen Goldstein in 1886. Electrons are negatively charged subatomic particles, discovered by Joseph John Thomson in 1897. Neutrons are uncharged subatomic particles, discovered by James Chadwick padatahun 1932. Atomic model continues to evolve from the atomic model of Dalton, Thomson, Rutherford, Bohr, to the modern atomic model that we use today.

    A. ATOM MODEL DEVELOPMENTThe term stems from the time Leukipos atom and Democritus who say that it is the smallest atom. Atoms derived from the Greek that atomos, a meaning not and Tomos shared meaning. Atomic models have evolved along with the development of science and factual experiments. Although the atomic model has been modified, but the main idea of ​​the model of the atom is still accepted today. The development of atomic models of Dalton atomic model of quantum mechanics to atomic model is as follows:

    Dalton's atomic modelTahum In 1803, John Dalton proposed his theory as follows:

    each element is composed of tiny particles that can not be divided again called atoms.
    atoms of the same element will have the same properties, but the atoms of different elements have different properties.
    in a chemical reaction no atoms are lost, but only changes the arrangement of the atoms in the substance.
    when atoms form molecules, atoms are joined by a round andsimple comparative figures, such as 1: 1, 2: 1, 2: 3.Dalton atomic model has some drawbacks. Some weaknesses include

    Unable to explain the electrical properties of materials
    Unable to explain the affinity elements. For example, why in the formation of water (H2O) one oxygen atom bound to two atoms of hydrogen.Atomic Model Dalton

    Thomson atom modelAfter J.J. Thomson found that there are electrons in the atom, the Thomson atom model as follows:

    Atom is an spherical solid materials and in which a positively charged electron-scattered electron (model raisin bread).Thomson Atomic Model

    Neutral atom, the number of positive charges equal to the amount of negative charge.Thomson atomic model did not last long. This is because the model does not explain the Thomson atomic nuclei.

    Rutherford model of the atomAfter Rutherford discovered the atomic nucleus and the positively charged atomic mass centered on the nucleus, the Rutherford atomic model as follows:

    atom consists of a positively charged nucleus and negatively charged electrons that surround the nucleus of an atom;
    atom is neutral;
    radius of the nucleus and atomic radii can be determined.Rutherford Atom ModelWith the development of science, it also has its drawbacks Rutherford model. Fundamental weaknesses of Rutherford's atomic model is not able to explain why electrons orbit around the nucleus does not fall into the nucleus as there are attractive forces between the nucleus and the electrons. And according to classical physics at mass (Maxwell theory), electrons moving around the nucleus of an atom releases energy in the form of radiation.

    Bohr model of the atomBased on the observations on the spectrum of the hydrogen atom, Neils Bohr Rutherford atomic model repair, by constructing an atomic model as follows:

    Atoms consist of a nucleus that contains positively charged protons and negatively charged electrons surrounding the nucleus of an atom; Electron empty space surrounding the core nucleus (positively charged).Bohr Atom Model

    Quantum mechanical model of the atomAtomic model of quantum mechanics is based on:

    electrons are waves and particles, by Louis de Broglie (1923);
    the wave function of electrons in atoms, by Erwin Schrodinger; (1926)
    uncertainty principle, by Werner Heisenberg (1927).Quantum mechanical model of the atomAccording to the atomic theory of quantum mechanics, the electron does not move in a certain trajectory. Under these conditions, the atomic model of quantum mechanics are as follows:

    Atoms consist of a nucleus containing protons and neutrons, and electrons surrounding the nucleus of an atom are in orbitals membentukkulit particular atom, it is called the orbital concept.
    By combining the uncertainty principle of Werner Heisenberg and wave mechanics of Louis de Broglie, Erwin Schrödinger formulated the concept of orbitals as a space where the chance of an electron can be found.
    Position of the electrons in the orbital-orbital quantum numbers stated.

    B. DEVELOPMENT OF ATOMIC PARTICLESIf a plastic ruler rubbed-rub on dry hair, a ruler can attract small pieces of paper. This incident proves that the ruler has electrical properties, because the ruler is a material composed of atoms. It can be concluded that the atom has electrical properties. The investigation of the electrical properties of an atom made over the years by some of them JJ Thompson, Eugen Goldstein, Rutherford, and Bathe & Becker.

    1. ElectronElectron was discovered by Joseph John Thomson in 1897. The discovery begins with the discovery of the electron by William Crookes tube cathode. Then J.J. Thomson researching more about cathode rays and it is certain that this is a cathode ray particles, because they can rotate the propeller is placed between the cathode and the anode.The nature of the cathode rays, among others:

    propagating perpendicularly from the surface of the cathode towards the anode;
    particle radiation that is proven to play a propeller;
    electrically charged negative that was deflected into the positive electric pole;
    be casting different types of substances, including glass.Cathode ray tubeThomson experiment to determine the price (Brown & LeMay, 1977)From the results of these experiments, J.J. Thomson stated that cathode rays are subatomic particles that are negatively charged and later called electrons. J.J. Thomson managed to determine the ratio between the mass of the electron charge (e / m) of 1.76 × 108 C / g. Then in 1909, Robert Millikan of the University of Chicago, succeeded in determining the amount of a charge of 1 electron of 1.6 × 10-19 C. Thus, the price of one electron mass can be determined from the price comparison with the mass of the electron charge (e / m). The value of e / m = 1.76 x 108 C / g,So Mass 1 electron === 9.11 x 10-28 gAfter the discovery of the electron, the Dalton atomic model is no longer acceptable. According J.J. Thomson, atoms are neutral particles. Since electrons are negatively charged particles then there must be others that can neutralize the negative charge that is positively charged particles. From these findings, J.J. Thomson argued that atomic theory known as Thomson's atomic theory, namely: Atom is a positively charged solid sphere and over which the electrons are negatively charged. Since the spread of the electrons in the atom like raisins, so called atomic model of raisin bread.Thomson Atomic Model

    2. The nucleus
        ProtonWith the discovery of the electron by Thomson, experts are increasingly convinced that the atom is composed of particles smaller. In 1886, Eugen Goldstein modify the cathode-ray tube with a hole in the plate katodenya and gas behind the plate cathode becomes incandescent. These events indicate radiation from the anode through the holes in the plate cathode. These rays are called anode rays or positive rays. The nature of anode rays, among others:

    Is particle radiation that can rotate a propeller;
    In an electric field / magnetic deflected to the negative pole, so it is positively charged radiation;
    Anode ray particles depends on the type of gas in the tube.Smallest particles obtained from hydrogen gas. These particles are then called protons. Mass of 1 proton = 1 smp = 1.66 × 10-24 gCharge of 1 proton = +1 = 1.6 × 10-19 CIn 1910, Ernest Rutherford and two of his assistants, namely Hans Geiger and Ernest Marsden, conducted a series of experiments to determine the position of the particles in the atom. Their experiment is known as the scattering of alpha rays on a thin plate of gold. From their observations, it was found the fact that the particle is fired at a thin gold metal plates, mostly passed, and there is a small part that dibelokan there are even some of them are reflected. It was very surprising for Rutherford. This discovery led to the death of Thomson's atomic theory. Reflected particles is estimated to have hit something solid in the atom. Thus the atom is not homogeneous as described by Thomson. Even according to Marsden observations, obtained the fact that one in 20,000 particles will be banked at an angle of 90 ° or more.Rutherford experiment. Shooting a thin metal plateGold with lightBased on these symptoms, obtained several conclusions, among others:

    Atom is not a solid ball, because almost all of the particles passed. Meaning, most of the volume of an atom is empty space.
    Particles that undergo deflection particle is approaching the atomic nucleus. This is due to both positively charged.
    The reflected particles are particles hitting the right nucleus.Based on facts obtained from these experiments, Rutherford proposed a model of the atom states that atoms consist of a nucleus of an atom is very small and positively charged, surrounded by negatively charged electrons. The number of protons in the nucleus equals the number of electrons surrounding the nucleus ynag, so the atom is neutral. Rutherford also suspect that in the nucleus are neutral particles that serve to bind the particles so as not to repel positive. From these experiments, Rutherford can estimate the atomic radius of approximately 10-8cm and core radius of approximately 10-13cm.

    NeutronIn 1930, W. Bothe and H. Becker did another experiment, the firing of beryllium nucleus with particles and radiation they found an article that has great penetrating power. Later in 1932, James Chadwick proved that radiation consists of neutral particles with masses similar to the mass of a proton. Because these particles are neutral, then called neutrons. The experiments further prove that the neutron is also a core constituent particles.Table 1.1Drafting Basic Atomic ParticlesCoat particle mass Inventor(Sma)Mass (g) Contentexact(Coloumb)Loadrelative(Sme)Electron e J.J. Thomson 0.00055 9.1100 × 10-28 -1.6 × 10-19 -1Proton p Goldstein 1.00728 1.6726 +10-24 +1.6 × 10-19 +1Neutron n Chadwick 1.00866 1.6750 × 10-24 0 0

    C. ATOMIC NUMBER NUMBER AND MASS
        Atomic numberThe atomic number indicates the number of positive charges in the nucleus (the number of protons). By HENRY Moseley (1887-1915) the number of positive charges is characteristic of each element, so the different elements will have different atomic numbers. For the amount of positive charge (atomic number) given the symbol Z. If the atom is neutral, then the number of positive charges (protons) in the atom must equal the number of negative charges (electrons). So, atomic number = number of protons = number of electrons.Z = np = nen = number of

    The mass numberAtoms consist of protons, neutrons, and electrons. Thus, atomic mass = (mass p + mass n) + e mass.Electron mass is much smaller than the mass of the proton and neutron masses, the electron mass can be neglected.Thus:Atomic mass = mass p + mass nAtomic mass expressed as mass numbers and given the symbol A. So:The mass number = number of protons = number of neutronsAll of the atomic nucleus consists of protons and neutrons. Both core constituent particles are called nucleons. The atoms of an element have different numbers of protons with atoms of other elements. The number of protons is called the atomic number. Since only protons are charged particles in the nucleus, then the number of protons also expressed nuclear charge. The composition of the core is expressed by the following notation:By:X = element atom signsZ = atomic number (number of protons (p) in the nucleus of an atom)A = mass number (number of protons (p) + number of neutrons (n))As we know, the atom is said to neutral if the number of electrons equals the number of protons. We need to know also that an atom can receive (absorb) or release electrons. If you accept one electron atom, then the atom is excess negative charge as much as 1 atom and is called the charged -1. Conversely, if the atom releases one electron, it will lack the negative charge as much as 1 atom or an excess positive charge as much as 1 atom and called charged +1, and so on.






    3. Isotopes, Isobar, AND IsotonThe atoms of an element can have different atomic mass number, because the number of neutrons in an atom is different. In addition, atoms of different mass numbers and can have the same number of neutrons.

    IsotopeIsotopes are atoms that have the same atomic number, but different atomic masses. The atomic number is the identity of the atom, so each atom having the same atomic number elements were the same.Examples of isotopes:

    Isotopes of carbon atoms,, And,; same atomic number, namely 6.

    Isotopes of oxygen atoms,, And; same atomic number, ie 8

    IsobarIsobar are atoms that have different atomic numbers but the same atomic mass.Examples of atoms isobar:a. and; same atomic mass, which is 14.b. and; same atomic mass, which is 39.

    IsotonIsoton are atoms that have the same number of neutrons of different elements.Examples of atoms isoton:a. and; neutrons together with 15b. and; neutrons together with 20

    4. ATOM MOLECULE MASS AND RELATIVE MASSAtom is an extremely small particles and a thing that is not possible if we determine the mass of an atom by using a balance or weigh scales. How do we know the mass of an atom?

    The relative atomic mass (Ar)Since 1961, after the discovery of the mass spectrometer, the standard of comparison for determining the relative atomic mass is replaced with the new standard, which is the mass of 1 atom of C-12 (= 1 sma). Determination of the mass of the atom as a comparison standard, the carbon atom is an atom due to the most stable than other atoms. Each element consists of several isotopes, it is the relative atomic mass (Ar) is the ratio of the average mass of one atom of an element of the mass of one atom of C-12. IUPAC (international body chemistry) from the current definition of relative atomic mass as follows:The relative atomic mass (Ar) elements X = x mass of 1 atom C-12Atomic mass units (sma) = x 1.99268 x 10-23gram= 1.66057 × 10-24 grams

    Relative molecular mass and relative formula mass (Mr)Relative molecular mass (Mr) is the ratio between the average mass of a single molecule of an element or compound to the mass of the atom C-12.Mr substance X = the number of Ar substance XThus, the number of relative atomic mass (Ar) of all atoms making upmolecular substances were:Mr =For ionic compounds, used the term relative formula mass for ionic compounds composed of molecules but not ions. Relative formula mass is also represented by Mr. Calculation is the same as the relative molecular mass.

    5. ELECTRON CONFIGURATIONFurther experiments on the atomic model aims to determine how partikal subatomic particles are arranged in an atom. According to the quantum mechanical model of the atom, the electrons are in orbitals. Orbitals with the same energy level or nearly equal to form shells. The composition of atomic shells is similar to the Niels Bohr model of the atom. Bohr through experiments on the hydrogen atom spectrum failed to provide an overview on the state of the electrons occupy the area around the atomic nucleus. According to the Bohr model of the atom, the electrons around the nucleus in certain paths called shells or energy levels. Skin that is occupied by electrons depends on energy. The lowest energy level is atomic shell which is located in or closest to the core, the outside skin and the bigger the number the greater the energy level.Describe the electron configuration deployment or arrangement of electrons in atoms. Completion of the electrons in the atom shells meet certain rules, namely:

    The maximum number of electrons in the shell meets 2N2 formula, with n = number of skinK shell (n = 1) Maximum 2. 12 = 2 electronsSkin L (n = 2) a maximum of 2. 22 = 8 electronsLeather M (n = 3) maximum 2. 32 = 18 electronsLeather N (n = 4) a maximum of 2. 42 = 32 electrons, and so on.

    The maximum number of electrons in the outer shell is 8Electron configuration examples:11Na: 2 8 120Ca: 2 8 8 235Br: 2 8 18 7The number of electrons menempiti outer shell called valence electrons. Thus, the electronvalence for the Na atom is 1, the Ca atom valence electrons is 2, and the Br atom valence electron is 7.Table 1.2Electron configuration of elements Atomic Number 1 to 20Atomic Number Element K L M NHHeyLiBeBCNOFNeNaMgAlThePSClArKCa12345678910th11th12th13th14th15th16th17th18th19th20th12345678910th11th12th13th14th15th16th17th18th19th20th123456788888888888123456788812II. MOLECULESMany of the smallest particle of a substance in nature are not atoms, but a combination of two or more atoms of element, either from the same or different elements. Combination of two or more atoms from the same or different elements are called molecules. If the atoms are of the same element the molecule is called molecular elements. If a molecule is composed of two or more atoms of different elements is called molecular compounds. Unlike metallic element smallest particles composed of atoms, the smallest particles of nonmetal elements can be either atoms or molecules. The elements of the noble gas group (VIIIA) is composed of the smallest particles of the atom. The halogen group elements (VIIA) elements are composed of molecules.To establish an understanding of the differences between the molecular elements and molecular compounds, we take the example of oxygen and carbon dioxide gas (see Figure beside). From the figure it is seen that the oxygen gas molecule composed of two atoms of the same element, the oxygen atom oxygen molecules, including molecules that element (formula O2), whereas molecules of carbon dioxide gas including molecular compound because it is composed of atoms of different elements , ie one carbon atom and two oxygen atoms (CO2 formula).Another example of molecular elements are molecules formed by atoms of the element hydrogen. Two atoms of the element hydrogen form diatomic molecules of elements (composed by two atoms) with the chemical formula H2. In addition to halogen group elements, oxygen elements, and the element hydrogen, nitrogen is also composed of diatomic molecules with molecular formula N2.Aside from being able to form diatomic molecules, some nonmetallic elements are also able to form polyatomic molecules (molecules composed of elements which three or more atoms). For example, ozone (O3) is a molecule composed of three oxygen atoms of the element. The elemental sulfur is able to form molecules composed of eight atoms of sulfur (S8).Examples of substances that constitute the smallest particle is a water molecule compounds. The usual water we drink contains the smallest particles called molecules of water. The water molecule is composed of two atoms of hydrogen and one atom of the element oxygen element (formula H2O). Because water molecules are composed of atoms of different elements including the water molecule molecule compounds. Water molecules can be produced from a reaction between hydrogen molecules and molecular elements of the element oxygen.The oxygen molecule reacts with two molecules of hydrogen to form two molecules of water.In the picture above shows that the molecules of the element hydrogen molecules react with molecular oxygen to form compounds the elements of water. Each element of the oxygen molecules will react with hydrogen to form two molecules elements compounds 2 molecules of water. If one molecule of molecular oxygen requires two elements of hydrogen to react perfectly to form two molecules of water compounds the 2 molecules of oxygen element requires 4 molecules of the element hydrogen to react perfectly to form four molecules of water.This reaction can be seen that the chemical reaction there is no loss of atoms. The number of H and O atoms on the right equal to the number of H and O atoms on the left. The difference, ie each atom that binds to the left of the atom of the same element, while on the right are bonded to atoms of other elements to form molecules compounds. The number of atoms in a reaction resulting in the phenomenon will remain the Law of Conservation of Mass (mass quantities of substances that react with mass amounts of substances the reaction) can be understood. In addition to the substances mentioned above, there are many substances around us are the smallest particles in the form of molecules. Examples are white sugar (C12H22O11) is a mixture of substances used to make coffee. Another example is carbon monoxide (CO) and ethanol (C2H5OH). Carbon monoxide is a gas that can poison our blood causing death. As ethanol is a substance that can be used for various purposes, such as sterilization, mixed liquor, and fuel. All substances are made up of the smallest particles of matter called molecules.




    III. IONAt the beginning of the 19th century, Dalton reveals that the smallest particles of matter are atoms. In the mid-19th century, a lot of research showing that many substances are not composed by atoms but by charged particles called ions. The particle size is about the size of atoms and molecules. Example: people already know that the molten salt and the salt solution in water can conduct electricity. In the event, an electrical charge to flow in a different way than in the metal. In metals, the electrical charge carried by electrons. Conversely, in a molten salt or a salt solution in water, the electrical charge carried by the ions (positive and negative ions).Thus, the smallest particles of matter not only in the form of atoms and molecules, but can also form ion. Electron charge is the smallest amount of charge is called the elementary charge (e). Ion charge is a one-time or multiple times the elementary charge. Therefore, the ion charge number is only written with one or multiple of the charge. Metals form positively charged ions (cations). Ions most nonmetallic elements form a negatively charged ion (anion).The atoms in neutral containing positive and negative charges of the same amount. Atoms turn into ions when receiving or releasing electrons (see the picture). Alkali metal ions (IA) always form positively charged ions one, such as lithium ion (Li +), sodium ions (Na +) and potassium ions (K +). Ions of alkaline earth metals (IIA) has two positive charges, such as calcium ions (Ca2 +) and magnesium (Mg 2 +).As with ions of metals, ions of nonmetal elements can be estimated based on the location of the load these elements in the periodic system of elements. The ions of the halogen group elements (VIIa) is always negatively charged one, namely fuorida ion (F-), chloride ions (Cl-), bromide ion (Br-), and iodide ions (I-). The ions of the VIA group, such as oxygen to form two negatively charged ions, oxide (O2-) or sulfur which also form two negatively charged ions, sulfda (S2-). Of elements of group VA, people familiar with the elements nitrogen capable of forming three negatively charged ions, nitride (N3-). The elements of group VIIIA noble gases do not form ions ion.Di aside from a single element atoms (monatomic), there are also ions derived from the combinedtwo or more atoms of different elements (polyatomic). For example, sulfate ions negatively charged two (SO42-), ion nitrate negatively charged one (NO3-), acetate ions negatively charged one (CH3COO-), ammonium ions are positively charged one (NH +) and hydroxyl ions are negatively charged one ( OH-).Substances that are composed of ions have a neutral electrical charge. It is caused by a number of positive and negative charges are equal. Example: sodium chloride (NaCl) is composed of a positively charged sodium ion and a negatively charged chlorine ions in the ratio 1: 1, magnesium chloride (MgCl2) is composed of a positively charged magnesium ions two and two negatively charged chlorine ions in the comparison of the amount of magnesium ions and the amount of chlorine ions is 1: 2. Thus, the amount of positive charge from the magnesium ions equal to the amount of negative charge from the chlorine ions. In aluminum chloride (AlCl3), a positively charged aluminum ion three neutralized by three negatively charged chlorine ion one. Between positive ions and negative construct a salt mutual attraction to one another to form a crystal lattice. Crystal lattice is various types, depending on the range of proportions of positive and negative ions that bind. Here is described a model of the crystal lattice of the compound salt or sodium chloride (NaCl).NaCl crystal lattice modelIn the picture above shows that the sodium ion is surrounded by six chlorine ions. Conversely, a chlorine ion is surrounded by six sodium ions. Regularity is owned by each ion of sodium and chlorine ions. Thus, the two reactions do not form molecules but form a crystal lattice. Each ion remains in place. This could explain why the solid salt can not conduct electricity, while the discharge can conduct electric current. When sodium chloride (NaCl) is dissolved in water the NaCl crystal lattice will decompose to form sodium ions and ionklor.Both of these ions will interact with water molecules, as shown in the picture. Charged ions have opposite electrical attraction force is strong. Chemical bonding that occurs because the force of electric attraction is called an ionic bond. Compounds are formed due to ionic bonds are called ionic compounds. The existence of strong gravity could explain why the salts or ionic compounds generally have high melting and boiling points are high, much higher than substances composed of molecules.