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Catalyst

Catalyst. Pick up your graded binders from one of the lab tables. On a sheet of notebook paper, put these things in order from LARGEST TO SMALLEST: A blue whale Mount Everest A polar bear An electron The Milky Way Galaxy Jupiter Earth An atom A loaf of bread Red Blood Cells

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Catalyst

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  1. Catalyst Pick up your graded binders from one of the lab tables. On a sheet of notebook paper, put these things in order from LARGEST TO SMALLEST: A blue whale Mount Everest A polar bear An electron The Milky Way Galaxy Jupiter Earth An atom A loaf of bread Red Blood Cells A molecule

  2. Summary of Atomic Models • Dalton's model • Atoms are billiard ball-like spheres • Thomson's model • Electrons are imbedded in a positive sphere. • Rutherford's model • Positive dense tiny nucleus is surrounded by electrons in empty space. • Bohr's Model • Electrons orbit the nucleus. • Electron-cloud model • Electrons do not travel in orbits but fill space like a cloud with no definite position, but definite energy levels.

  3. Atomic Models

  4. Atomic Models

  5. Objective 2.1: The Bohr Model and Subatomic Particles • The discovery that the atom has parts, or subatomic particles was an important breakthrough in science. Bohr's model of an atom shows a positively charged nucleus and negatively charged electrons. Today we know that even the nucleus of the atom has particles. The nucleus is made up of protons and neutrons. Protons have a positive charge, whereas neutrons are neutral, or have no charge. Most of the mass of an atom is in the nucleus where the protons and neutrons are located. Electrons have almost no mass.

  6. Each element has a unique number of protons in its atoms. This is called the atomic number. For example, helium has two protons, or an atomic number of 2. Lithium has three protons, so its atomic number is 3, and carbon has six protons, so its atomic number is 6. • For every positively charged proton in the nucleus, there is a negatively charged electron to balance it out. In other words, there are as many negative particles as there are positive particles. So an atom, as a whole, is neutral.

  7. Objective 2.2: Periodic Table and Proton Number • The modern Periodic Table is organized so that the elements are arranged in ascending order of atomic number. The atomic number is the number of protons in the nucleus and is also the number of electrons in the neutral atom. • The present day symbols for the elements are a combination of ancient and modern symbols, from several different languages. Latin, English, and German are some of the languages from which symbol names have come. All of them consist of one or two letters, with the first letter capitalized, and the second lower case.

  8. Objective 3: Energy Levels of the Atom • While it is difficult to predict where electrons will be at any given time, it is known that they move within specific energy levels. The negatively charged electrons at each level have a certain amount of energy. Electrons in the first energy level have lower total energy than the electrons farther away from the nucleus. • Remember that the atomic number of an atom also is the number of electrons in the atom. Each atom has one or more energy levels, and each level has a maximum number of electrons that it can hold. The first level can hold a maximum of two electrons. After the first level, the maximum number of electrons that a level can hold increases, but the outermost level always holds a maximum of eight electrons.

  9. The number of energy levels in each atom depends on its number of electrons. Each level fills before the next level is occupied. For example, hydrogen has only one electron, so it has one energy level. Helium has only two electrons, so it also has one energy level. Lithium has three electrons, so it has two energy levels. Two electrons fill the first level. The remaining electron is in the second level. And magnesium has 12 electrons, so it has three energy levels, with two electrons in the first, eight electrons in the second, and two in the third. • The electrons in the outermost energy level of an atom are known as valence electrons. For example, the single electron in hydrogen's first energy level is its valence electron. The single electron in lithium's second energy level is its valence electron. And the two electrons in magnesium's third energy level are its valence electrons.

  10. Objective 4: The Periodic Table • Our modern Periodic Table is arranged with the elements in rows and columns. The rows are called periods. Elements in a period are arranged in order of increasing atomic number. The columns in the Periodic Table are called groups or families. Elements in the same group have the same number of valence electrons. • Group 1 is called the alkali metals. They have only one valence electron and react readily with other elements. Examples of alkalis are lithium, sodium, and potassium. The alkali metals are soft, silver-white metals. They react quickly with oxygen or water and will burn your skin if you touch them. That's why, in their pure form, they are kept under oil.

  11. The family of elements in Group 2 have two valence electrons. They are known as the alkaline earth metals. This group isn't usually found in a free state in nature because these elements, like the alkalis, are also very active. Beryllium, magnesium, and calcium are examples of alkaline earth metals. Magnesium and beryllium are used in fireworks. Magnesium provides bright light and beryllium and other elements create the color.

  12. Group 17 has seven valence electrons and is called the halogen family. Fluorine, chlorine, and bromine are examples of halogens. They react with alkali metals to form salts. For example, sodium and chlorine form table salt, and potassium chloride is a common substitute for table salt.

  13. Group 18 is called the noble gas family. They are inert, or inactive, and don't react easily with other elements because their outer energy levels are full. All the noble gases have the maximum number of valence electrons in their outer energy level. Examples of noble gases are helium, neon, argon, and krypton. Neon and argon are used in lighted signs. They are stable and won't ignite.

  14. Objective 5: Mass Number • You have learned that almost all of the mass of an atom is concentrated in the nucleus. Protons and neutrons make up this mass. The mass of a neutron is almost the same as the mass of a proton, so scientists say that each has a mass of one atomic mass unit. The mass number of an atom is the total number of atomic mass units or the number of neutrons and protons. If you know the number of neutrons and the number of protons (the atomic number), you can calculate the mass number by adding the two together. • For example, we know that nickel has an atomic number of 28. A nickel nucleus usually contains 31 neutrons, so its mass number is 28 + 31 = 59. Conversely, if we know the mass number of zinc is 65, and its atomic number is 30, then we can calculate the number of neutrons to be 65 - 30 = 35. So zinc has 35 neutrons.

  15. The number of protons in an atom gives the atom its identity. For an atom to be chlorine, it must have 17 protons. However, the number of neutrons can vary without affecting the identity of the atom. Atoms of the same element having different numbers of neutrons are called isotopes. Isotopes of the same element have the same chemical properties because they still have the same number of protons and electrons. • Isotopes are written with a special type of notation. For example, the following is an isotope of iodine. 131 53 • The superscript, 131, is the mass number and the subscript, 53, is the atomic number (number of protons). To determine the number of neutrons in this isotope, the atomic number is substracted from the mass number. 131 - 53 74 • Thus, there are 74 neutrons in this isotope. Isotopes can also be written with the mass number following the symbol of the element. I - 131

  16. Objective 6: Atomic Mass • The atomic mass of each element is provided on the Periodic Table. If you look at the atomic masses of elements on the Periodic Table you can see that they are not whole numbers. One of the reasons for this is that all of the elements have several isotopes. The atomic mass of an element is an average of the mass numbers of all the naturally occurring isotopes.

  17. Objective 7: Metals and Nonmetals • In addition to classifying elements according to families, we can classify them as metals or nonmetals. Metals are made up of the alkali metals and a group of families called the transition metals. The noble gases, halogens , and a few other families comprise the nonmetals. Notice the bold line stretched across the Periodic Table from Boron (13) to Polonium (Po). This line separates the metals on the left from the nonmetals on the right. • Metals are good conductors of heat and electricity. They are malleable and ductile, have metallic lusters, and most of them are solids. Nonmetals are poor conductors of heat and electricity. Their appearance is dull instead of lustrous. They are not malleable. They break or shatter, when bent. Nonmetals may exist as gases, liquids, and solids.

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