IM for SE 203

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What is inside the Atom What is an Atom How did our present day concept of the atom evolve? What are some important atomic Terms that we need to know? What is an isotopes Do radioisotopes remain Unstable or radioactive all the time? Welcome to the world of the atom!

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Look around you. What do you see? Trees, water, cars, other people. There are also things we can’t see but know are there, like air. There are many, many thousands of things around us -- things we call matter. Some matter are solid, such as a piece of paper, wood and glass. Some are liquid, such as juice, milk and soft drinks. And some are gases such as exhaust from a car and carbon dioxide which makes the bubbles in soft drinks. Matter, whether in the form of solid, liquid or gas, is made up of tiny and invisible groups of particles called molecules. Molecules are strongly held together so as to function as a single unit. All molecules in turn are made up of smaller and invisible units called atoms. Atoms are the building blocks of everything around us. What is an Atom? What is a Molecule?

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They are so small that it takes millions of them to make a drop of water or even a speck of dust. There are many different kinds of atoms which occur in nature. Combining atoms of the same kind or different kinds makes molecules. The kind of molecules depends on which atoms combine. Pure Elements — When the molecule contains only one kind of atoms (atoms that are alike), we have a pure element or elemental type of matter or substance. Examples are hydrogen, carbon, gold and the oxygen gas that we breathe.

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Compound — When the molecule contains two or more kinds of atoms, we have what is called a compound. In compounds, atoms of different kinds are actually linked together in a chemical bond. Water is an example of a compound type of matter. Each oxygen atom in water is chemically bonded to two hydrogen atoms to form the water molecule.

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Mixture — When the molecules are simply jumbled together (and are not chemically combined), we have what is called a mixture. Air, for instance, is a mixture of oxygen and nitrogen molecules and other gases.

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Matter, for example water, is made up of molecules Matter, Molecules and Atoms

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Atoms Molecules are made up of atoms. Matter, Molecules and Atoms

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All molecules in turn are made up of smaller units called atoms. Matter, Molecules and Atoms

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There are many different kinds of atoms. Matter, Molecules and Atoms

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Two or more of these atoms can join together to form a molecule. Matter, Molecules and Atoms

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Gold Atom: when the molecule contains only one kind of atoms ( atoms that are alike), we have a pure element or elemental type of matter or substance. Example: Gold molecules Make up a gold bar Matter, Molecules and Atoms

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Example: Sodium and chloride atoms make up sodium chloride, also known as table salt. When the molecule contains two or more kinds of atoms, we have what is called a compound (e.g. table salt). In compounds, atoms of different kinds are linked together in a chemical bond. Matter, Molecules and Atoms

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Examples of Compounds

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Although the atom is extremely small, it is made up of even smaller units or particles. These particles are the protons, neutrons and electrons. The electron is a particle with a negative electric charge. It is approximately 1837 times lighter than a neutron or proton. The proton is a particle with a positive electrical charge. It is approximately 1837 times heavier than the electron. The neutron is a neutral particle. It has no electrical charge. It has about the same mass as a proton and an electron combined. What is inside the atom?

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The three subatomic particles of an atom are arranged like a miniature solar system. The protons and neutrons together form the nucleus or center of the atom. The electrons orbit around the atom's nucleus in much the same way as the planets revolve around the sun. In general, an atom usually contains an equal number of positively charged protons in the nucleus and negatively charged electrons in orbit. This makes the atom electrically neutral.

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Structure of an Atom

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Structure of an Atom

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Structure of an Atom

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Structure of an Atom

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For example, the element oxygen has 8 electrons Orbiting the nucleus…. …and 8 protons in the nucleus Structure of an Atom

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Ancient Greek Philosophers The ancient Greek philosophers thought a great deal about the nature of matter. A number of them wondered what would happen if a piece of matter--like a stone--was split into smaller and smaller particles. Some said that no matter how tiny the particles became, it would be possible to break them up into still smaller particles. How did our present-day concept of the atom evolve? A brief historical perspective of the atom

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Some, however, like the Greek philosopher named Democritus argued that no matter how hard or long you divide a piece of matter, you will eventually come to a piece so very small that it could not be divided or split further. He called this indivisible particle an atom. The word atom comes from the Greek word “atomos” meaning “can’t be cut” or "indivisible".

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The atom is the last particle that cannot be divided any further Democritus believed that the atom is the ultimate indivisible particle of matter. Democritus’ Concept of the Atom

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J.J. Thomson’s “Plum Pudding” Model British chemist J.J. Thomson suggested that the atom could be compared to a positively-charged sphere with electrons embedded on it. ‘Sea” of positive charge Negatively charged particles

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Bohr’s Concept of the Atom Electrons orbit Around nucleus Small nucleus Electrons move in specific layers or shells.

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Atoms absorb or give off energy when the electrons move from one shell to another. Set orbits for electrons in Energy levels Empty space Bohr’s Concept of the Atom

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Rutherford’s Concept of the Atom Empty space Electrons in orbits circling the nucleus randomly (not to scale) The atom is like a solar system. The nucleus corresponds to the sun and the electrons correspond to the planets moving around the sun. Small positive nucleus

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Chadwick’s Concept of the Atom Electrons orbit around nucleus British physicist James Chadwick discovered the neutron in 1932. The existence of the neutron explained why atoms were heavier than the total mass of their protons and electrons. Neutrons and protons in nucleus

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The Modern Concept of the Atom neutrons protons The modern model of the atom shows the electrons forming a negatively charged cloud around the nucleus.

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The model also shows that the subatomic particles can be divided further into particles called quarks. The Modern Concept of the Atom

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Each atom is identified by an atomic number which is represented by the symbol “Z”. The atomic number is the number of protons in the nucleus of an atom. This number determines the chemical identity of an atom. • For example: hydrogen, the lightest atom, has one proton; helium has two protons; lithium has three; and so on. A chart (periodic table) of the chemical elements has been included in this topic as basis for the classification of the elements. The atomic number Some important atomic terms we need to know…

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The atomic mass or mass number A nuclide is any atomic species characterized by the number of protons and number of neutrons. The atomic mass or mass number of an atom is represented by the symbol “A”. It is equal to the total number of protons (Z) and neutrons (N) in the nucleus of an atom. • Nuclide

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Atoms of the same element have the same number of protons in their nucleus. The number of neutrons, however, in combination with the fixed number of protons, may vary for a given element. Atoms of the same element having different number of neutrons, in combination with the fixed number of protons, are called isotopes. Practically, all elements have more than one isotope. Isotopes of a given element have the same chemical properties, but they may differ in their nuclear properties. What is an isotope and a radioisotope?

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• Unstable isotopes or radioisotopes Some isotopes of an element have unstable nuclei. These unstable nuclei stabilize themselves by emitting or shooting energy rays called gamma rays, similar to X-rays. Others may emit particles from their nuclei and change to different elements. Conceptually, the source of the instability of atoms is due to the unbalanced number of protons and neutrons in their nuclei. If the nucleus of an atom has too many neutrons or protons as compared to the optimum ratio of neutrons to protons, then this atom becomes unstable. Isotopes may be categorized into: · Stable isotopes Some isotopes of an element have stable nuclei and do not spontaneously emit energy in the form of rays or particles.

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An unstable or radioactive isotope is called a radioisotope or radionuclide. Some of the other radioisotopes are found in nature. Two important natural radioisotopes are carbon-14 and potassium-40. Most radioisotopes are produced artificially in special nuclear devices such as a nuclear reactor. Radioisotope Production by Neutron Bombardment Radioisotopes may be produced artificially by neutron bombardment in special devices such as a nuclear research reactor. When stable elements are allowed to capture neutrons, the elements become unstable or radioactive.

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Radioisotopes do not remain unstable atoms all the time. Unstable (radioactive) atoms undergo spontaneous decay into a more stable form (usually a different element) by emitting or shooting out gamma rays (similar to X-rays) or particles from their nucleus. These rays and particles are called ionizing radiation. The property of radioisotopes which emit radiation spontaneously is known as radioactivity. Any material that exhibits the property of radioactivity is called a radioactive material. The process of emitting ionizing radiation is termed as radioactive decay. Do radioisotopes remain unstable or radioactive all the time?

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If unstable atoms are decaying to stable states, the total number of unstable atoms subject to decay will decrease with time. We use the term half-life as a measure of the time it takes for an original number of atoms in a sample of radioactive material to decay or disintegrate to one half this number. Half-Life

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 In 7 more days, half of the remaining half will decay. In 7 more days, half of the remaining half will decay, and so on. Each specific radioisotope has its own half-life which varies from a tenth of a second to billions of years. Some naturally - occurring radioisotopes, such as those of uranium, have half-lives of millions of years. That is why up to now, they still exist in the earth. Radioactive decay is unaffected by the physical and chemical state of the radioactive material, temperature, pressure and other physical changes. For example : if a radioactive substance has a half-life of 7 days, half of its radioactive atoms will have decayed within 7 days.

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Half life is the amount of times it takes for one half of the unstable nuclei to decay. Parent material (unstable)

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 The half-lives of certain radioactive isotopes are useful in determining the ages of rocks and the fossils found in them. As plants grow, they use carbon dioxide (CO2) from the air during photosynthesis. Half-Lives in Radioactive Dating  Some carbon dioxide contains radioactive carbon-14. This becomes part of the plant’s structures the same way carbon-12 does.  From the data, scientists can calculate how many half-lives have passed since the plant was alive. Thus, they can estimate the age of the plant and its surrounding rock. This process is called radioactive dating.  After the plant dies, it stops taking in carbon dioxide. If the plant’s remains are preserved as a fossil, the ratio of carbon-14 to carbon-12 decreases due to radioactive decay of carbon-14.

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The half-life of carbon-14 is short compared to some other radioactive isotopes. It cannot be used to find the ages of objects older than about 60,000 years. Other isotopes, such as potassium-40 and uranium-238, are used to study older fossils, rocks and objects used by early humans.

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thank you for listening...... have a nice day.... by: ms. merced m. gutierrez Do not conform yourselves to the standards of this world, but let God transform you inwardly by a complete change of your mind.