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Atomic Structure Atom- The building blocks of matter. All matter is made up of atoms. An atom is like a tiny solar system. In the center of the atom is the nucleus which is a cluster of protons and neutrons. The protons have a positive electric charge while the neutrons are electrically neutral. The nucleus makes up almost all of an atom's mass or weight. Whirling at fantastic speeds around the nucleus are smaller and lighter particles called electrons which have a negative electric charge. An atom has the same number of electrons (- ve charge) and protons (+ ve charge) to make the atom electrically neutral. An extremely powerful force, called the nuclear force, holds the protons together in the nucleus as they naturally repelled one another electrically. The atoms of each chemical element have a different nucleus. An atom of hydrogen has one proton and no neutrons. An atom of nitrogen has 7 protons and 7 neutrons. Heavy elements have a large number of protons and neutrons. For example, the most common isotope of uranium, uranium-238 has 92 protons and 146 neutrons in its nucleus. The Nucleus Almost the entire mass of the atom is concentrated in the nucleus, which occupies only a tiny fraction of the atom's volume. The nucleus of an atom consists of neutrons and protons, the neutron being an uncharged particle and the proton a positively charged one. Their masses are almost equal. Atoms containing the same number of protons but different numbers of neutrons represent different forms, or isotopes, of the same element. The Electrons Surrounding the nucleus of an atom are its electrons; for a neutral atom, the number of electrons is equal to the atomic number. The outermost electrons of an atom determine its chemical and electrical properties. An atom may combine chemically with another atom in various ways, either by giving up or receiving electrons, thus setting up an electrical attraction between the atoms (see ion), or by sharing one or more pairs of electrons (see chemical bond). Because metals have few outermost electrons and tend to give them up easily, they are good conductors of electricity or heat Atomic Theory In chemistry and physics, atomic theory is a scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms. It began as a philosophical concept in ancient Greece and entered the scientific mainstream in the early 19th century when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up of atoms. The word atom comes from the Ancient Greek adjective atomos, meaning "indivisible". 19th century chemists began using the term in connection with the growing number of irreducible chemical elements. While seemingly apropos, around the turn of the 20th century, through various experiments with electromagnetism and radioactivity, physicists discovered that the so-called "indivisible atom" was actually a conglomerate of various subatomic particles (chiefly, electrons, protons and neutrons) which can exist separately from each other. In fact, in certain extreme environments, such as neutron stars, extreme temperature and pressure prevents atoms from existing at all. Since atoms were found to be divisible, physicists later invented the term "elementary particles" to describe the 'indivisible', though not indestructible, parts of an atom. The field of science which studies subatomic particles is particle physics, and it is in this field that physicists hope to discover the true fundamental nature of matter. Dalton's Atomic Theory 1. Each chemical element is composed of extremely small particles that are indivisible and cannot be seen by the naked eye, calledatoms. Atoms can neither be created nor destroyed. Pictured below is a helium atom. The purple and red dots represent the neutrons and protons in the nucleus. The black area around the nucleus represent the electron cloud. The following sections discuss this further. 2. All atoms of an element are alike in mass and other properties, but the atoms of one element differ from all other elements. For example, gold and silver have different atomic masses and different properties. Gold Atomic Mass: 196.97 Silver Atomic Mass: 107.87 3. For each compound, different elements combine in a simple numerical ratio. The illustration below describes this rule. The second equation for the reaction is incorrect because half of an atom does not exist. Atomic theory can be used to answers the questions presented above. A pure gold necklace is made up of atoms. A pure gold necklace and a pure silver necklace are different because they have different atoms. Pure gold mixed with pure copper forms rose gold. The gold and copper atoms combine in a simple numerical ratio. Dalton's theory has not proven to be correct under all circumstances. The first rule was proven incorrect when scientists divided atoms in a process called nuclear fission. The second rule was proven incorrect by the discovery that not all atoms of the same element have the same mass; there are different isotopes. However, these failures do not justify discarding the atomic theory. It correctly explains the law of conservation of mass: if atoms of an element are indestructible, then the same atom must be present after a chemical reaction as before and, and the mass must constant. Dalton’s atomic theory also explains the law of constant composition: if all the atoms of an element are alike in mass and if atoms unite in fixed numerical ratios, the percent composition of a compound must have a unique value without regards to the sample analyzed. The atomic theory led to the creation of the law of multiple proportions. Law of Multiple Proportions The law of multiple proportions states that if two elements form more than one compound between them, the masses of one element combined with a fixed mass of the second element form in ratios of small integers. The illustration of the third rule of the atomic theory correctly depicts this law. Discovering Electrons The first cathode-ray tube (CRT) was invented by Michael Faraday (1791-1867). Cathode rays are a type of radiation emitted by the negative terminal, the cathode, and were discovered by passing electricity through nearly-evacuated glass tubes. The radiation crosses the evacuated tube to the positive terminal, the anode. Cathode rays produced by the CRT are invisible and can only be detected by light emitted by the materials that they strike, called phosphors, painted at the end of the CRT to reveal the path of the cathode rays. These phosphors showed that cathode rays travel in straight lines and have properties independent of the cathode material (whether it is gold, silver, etc.). Another significant property of cathode rays is that they are deflected by magnetic and electric fields in a manner that is identical to negatively charged material. Due to these observations, J.J. Thompson (1856-1940) concluded that cathode rays are negatively charged particles that are located in all atoms. It was George Stoney who first gave the term electrons to the cathode rays. The below figures depict the way that the cathode ray is effected by magnetics. The cathode ray is always attracted by the positive magnet and deflected by the negative magnets. The Plum Pudding Model After Thompson discovered the electron, he proposed the plum pudding model of an atom, which states that the electrons float in positively-charged material. This model was named after the plum-pudding dessert. Discovery of the Proton In 1909, Ernest Rutherford (1871-1937) performed a series of experiments studying the inner structure of atoms using alpha particles. Rutherford knew that alpha particles are significantly more massive than electrons and positively charged. Using the plum-pudding model for reference, Rutherford predicted that particles in an alpha beam would largely pass through matter unaffected, with a small number of particles slightly deflected. The particles would only be deflected if they happened to come into contact with electrons. According to the plum pudding model, this occurrence would be very unlikely. In order to test his hypothesis, Rutherford shot a beam of alpha particles at a thin piece of gold foil. Around the gold foil Rutherford placed sheets of zinc sulfide. These sheets produced a flash of light when struck by an alpha particle. However, this experiment produced results that contradicted Rutherford's hypothesis. Rutherford observed that the majority of the alpha particles went through the foil; however, some particles were slightly deflected, a small number were greatly deflected, and another small number were thrown back in nearly the direction from which they had come. Figure 10 shows Rutherford's prediction based off of the plum-pudding model (pink) and the observed large deflections of the alpha particles (gold). To account for these observations, Rutherford devised a model called the nuclear atom. In this model, the positive charge is held in an extremely small area called the nucleus, located in the middle of the atom. Outside of the nucleus the atom is largely composed of empty space. This model states that there were positive particles within the nucleus, but failed to define what these particles are. Rutherford discovered these particles in 1919, when he conducted an experiment that scattered alpha particles against nitrogen atoms. When the alpha particles and nitrogen atoms collided protons were released. The Discovery of the Neutron In 1933, James Chadwick (1891-1974) discovered a new type of radiation that consisted of neutral particles. It was discovered that these neutral atoms come from the nucleus of the atom. This last discovery completed the atomic model. Chemical bond A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electrostatic force of attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction. The strength of chemical bonds varies considerably; there are "strong bonds" such as covalent or ionic bonds and "weak bonds" such as dipole–dipole interactions, the London dispersion force and hydrogen bonding. Since opposite charges attract via a simple electromagnetic force, the negatively charged electrons that are orbiting the nucleus and the positively charged protons in the nucleus attract each other. An electron positioned between two nuclei will be attracted to both of them, and the nuclei will be attracted toward electrons in this position. This attraction constitutes the chemical bond. Due to the matter wave nature of electrons and their smaller mass, they must occupy a much larger amount of volume compared with the nuclei, and this volume occupied by the electrons keeps the atomic nuclei relatively far apart, as compared with the size of the nuclei themselves. This phenomenon limits the distance between nuclei and atoms in a bond. In general, strong chemical bonding is associated with the sharing or transfer of electrons between the participating atoms. The atoms in molecules, crystals, metals and diatomic gases— indeed most of the physical environment around us— are held together by chemical bonds, which dictate the structure and the bulk properties of matter. Types of Chemical Bond 1. Ionic Compound: A compound resulting from a positive ion (usually a metal) combining with a negative ion (usually a non-metal). Example: M+ + X- Covalent Bond: Electrons are shared by nuclei. Example: H-H Polar Covalent Bond: Unequal sharing of electrons by nuclei. Example: H-F Hydrogen fluoride is an example of a molecule that has bond polarity. QUESTIONAIRE 1. 2. 3. 4. 5. Cylinder comes from the Greek words _________. What do you call the two ends of cylinder? ____________. What is the shape formed if you were to unroll the cylinder? _____________. It is the perpendicular distance between the bases. _______________. A line joining the center of the base. Solve for the following: 1. Calculate the lateral area of a rectangular prism with a base with measure of 5.6in and 4.3in and a height of 10 inches? Answer: The formula for lateral area of a rectangular prism is Ph where P is the perimeter of the base so P = 2L + 2W. In this case P = 2(5.6) + 2(4.3) = 11.2+8.6 = 19.8. The h = 10. Lateral area is 19.8 * 10 = 198 square inches. 2. Calculate the surface area of rectangular prism whose given measures are: length=4cm width= 3cm and whose height is 5cm. SA = 2 • Top + 2 • Front + 2 • Left SA = 2lw + 2lh + 2wh SA = 2 • 4 • 3 + 2 • 4 • 5 + 2 • 3 • 5 SA = 24 + 40 + 30 SA = 94cm2 3. Find the volume of rectangular prism whose measures given are: length= 10cm width = 5cm and height is 7cm. V= Bh = (10x5)7 =350cm3 4. Calculate the volume of A can of Pringles whose measures are 10 cm for the base and its height is 10cm. use 3.14 for pi V=pir2h = 3.14(28)2 x 10cm = 3,140cm3 5. Calculate the surface area of a cylinder. Given: radius-10cm height-28cm. let pi 3.1416 SA= 2piR(r + h) = 2(3.1416)(10)(10+28) = 2,387.62 Fact or Bluff 1. The world’s smallest book is 1cm wide, 1cm tall and 4mm deep. Bluff – The smallest book in 2008 measured 2.4 x 2.9 mm and was presented in a wooden box with a magnifying glass. 2. "Copyrightable" is the longest word in the English language that can be written without repeating a letter? Bluff (it's "uncopyrightable") 3. Taphephobia is the fear of losing your teeth? Bluff (it's the fear of being buried alive) 4. India gave us the word “shampoo” and pajamas Fact 5. Lesson plan is the other word for Lexicon. Bluff 6. Cory Aquino’s favorite color is Yellow. Bluff 7. The terms kuya and ate came from Chinese. Fact Most experts point to Chinese origins. Kuya is said to be a combination of two Chinese words: ko (elder brother) and a (a term of kinship); ate from the same a plus chi (elder sister). 8. The typical Filipino breakfast is not tapsilog (tapa, sinangag and itlog). Bluff: It's kankamtuy: kanin, kamatis and tuyo. 9. A person will die from total lack of sleep faster than from starvation. Fact 10. Squidward is not a squid. Fact