CONTENT Contents IONIC BOND 2 METALLIC BOND 9 The "Sea of Electrons" Theory 14 Conductors‚ Insulators and Semiconductors 16 25 IONIC BOND Ionic bond is formed when electron transferred from a valence shell of an atom to the valence shell of another atom. Ionic bond involves electron transfer across two atoms. The atom which donates the electron is called cation which is a positive ion whereas the atom which gains the electron is called anion which is a negative ion. The opposite charge
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between metals and nonmetals. Remember that metal atoms lose one or more valence electrons in order to achieve a stable electron arrangement. When a metal atom loses electrons it forms a positive ion or cation. When nonmetals react they gain one or more electrons to reach a stable electron arrangement. When a nonmetal atom gains one or more electrons it forms a negative ion or anion. The metal cations donate electrons to the nonmetal anions so they stick together in an ionic compound. This means
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Electricity is a form of energy. Electricity is the flow of electrons. All matter is made up of atoms‚ and an atom has a center‚ called a nucleus. The nucleus contains positively charged particles called protons and uncharged particles called neutrons. The nucleus of an atom is surrounded by negatively charged particles called electrons. The negative charge of an electron is equal to the positive charge of a proton‚ and the number of electrons in an atom is usually equal to the number of protons. When
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metals do not conduct electricity quite as good as copper. The electrons of different types of atoms have different degrees of freedom to move around. With some types of materials‚ such as metals‚ the outermost electrons in the atoms are so loosely bound that they chaotically move in the space between the atoms of that material by nothing more than the influence of room-temperature heat energy. Because these virtually unbound electrons are free to leave their respective atoms and float around in the
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Since the ancient times‚ people like the Greeks were acknowledged of the existence of elements‚ but only knew of common ones like gold‚ tin‚ and copper. It wasn’t until the middle of the nineteenth century when about 50 elements were discovered and scientists began to wonder if the elements vary from each other or if a pattern is represented in the arrangement of the elements. A number of scientists tried different kinds of patterns. For example‚ the German scientist Johann Wolfgang Döbereiner tried
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poor conductor of electricity. If the electrons in an atom can’t be moved from their orbits at all‚ the material is an insulator. If at least some of the electrons can be moved‚ the material is a resistor. Two of the best-known conductors of electricity are silver and copper. The atomic structures of the silver and copper atom are compared in Figure 6. Note that both atoms have only one electron in the outermost orbit. This makes silver and copper excellent conductors of electricity. Silver
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nucleus contains positively charged protons and uncharged neutrons. The electron cloud is composed of negatively charged electrons. Elements in the same row are similar in size. Elements in the same column have similar electronic and chemical properties. An s orbital has a sphere of electron density and is lower in energy than the other orbitals of the same shell. A p orbital has a dumbbell shape and contains a node of electron density at the nucleus. It is higher in energy than an s orbital.
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c. Insulator • Number of valence electrons is 1-3 with very high conductivity • Number of valence electrons is 4 with intermediate conductivity • Number of valence electrons is 5-8 with very low conductivity Semiconductor Conductors • Has more electrons that are free to move • Supports charge carriers to flow • Support flow of electricity • Has very low resistance allowing easy flow of electron current • Has less than 4 valence electrons – Examples: metals‚ electrolytes and
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MANIPULATIONS: Cathode rays can be manipulated in a number of ways: 1) SPEED a. The speed the rays travel can be changed by changing the voltage between the anode and cathode. The voltage change changes the potential energy of the electrons. As it travels between the anode and the cathode‚ this energy is transformed into kinetic energy‚ therefore changing the speed of the particles. 2) NUMBER OF RAYS b. The number of cathode rays can be further manipulated by the introduction
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a molecule or ion‚ follow these steps: •Step 1: Count up the number of valence electrons for each atom‚ and total them up to give the total number of electrons for the molecule. If the molecule is an ion‚ include that charge in the count. For example‚ for a +1 ion‚ subtract one electron‚ and for a -2 ion add two electrons to the total count. (For more information about how to count the number of valence electrons per atom‚ see the related questions link to the left of this answer). •Step
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