chemical behavior

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How Will an Element Behave?orIt’s All About Electrons.

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KCS 8th Grade Science CSO 8th Grade Science Content Standards and Objectives: SC.O.’s 8.2.11; 8.2.12; 8.2.13; 8.2.14; 8.2.16; & 8.2.17 The student knows relationships exist between properties of matter and its components. The student is expected to (D) relate the chemical behavior of an element, including bonding, to its placement on the periodic table.

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First, a quick review… Atoms are composed of protons, neutrons, and electrons.

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Element Symbols Each element is represented on the periodic table by a symbol. Atomic Number (number of protons) Atomic Mass (average mass of all isotopes)

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But as we have said… It’s all about electrons! Part I: Electron Configuration Electrons are arranged in a predictable pattern. Part II: The Periodic Table The layout of the periodic table is determined by the electron configurations of the elements. Part III: Chemical Bonds Electrons influence the chemical properties of an element and how it combines with other elements.

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Electrons occur in discrete energy levels around the nucleus of an atom. These energy levels are often represented as circles. Within an energy level, electrons can be found in orbitals. The first, or innermost, energy level can hold two electrons. The second and third energy levels can each hold eight. Part I: Electron Configuration Energy Levels

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Valence Electrons are defined as… the electrons in the outermost energy level that are involved in chemical bonding. Example: An atom of chlorine has 7 valence electrons. Octet Rule – To become more stable, atoms will gain, lose, or share valence electrons in order to obtain an octet (8 valence electrons). Valence Electrons Part I: Electron Configuration

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7 valence electrons Lewis Dot Diagrams Valence electrons are the most important in forming chemical bonds. Lewis dot diagrams show only the valence electrons as dots surrounding the element symbol. Part I: Electron Configuration

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Lewis Dot Diagrams The chart below shows the Lewis dot diagrams for several elements in their position on the periodic table. Notice that the elements within each group, or column, have the same dot diagram. Part II: The Periodic Table

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When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. Part II: The Periodic Table Periodic Law

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Metalloids have properties that are intermediate between the metals and nonmetals. Part II: The Periodic Table Metals vs. Non-Metals

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A period is a row on the periodic table. As you go from left to right across a period, there is a regular, or periodic, change in properties. With the start of each new period, a similar pattern begins again. Everyday Analogy During a class period at school, you have roll call, collection of homework, lecture, practice problems, and assignments. When that ‘period’ is over you go to another class ‘period’ and the same general pattern starts over, even though it’s not exactly the same. Part II: The Periodic Table Periods

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A group is a column on the periodic table. Elements within a group have similar chemical properties. Because of these similarities, they are also called chemical families. Everyday Analogy A group on the periodic table is like a family. Members of a family share many characteristics, even though each member has a unique identity. The Noble Gases are in the last group on the table. Just as “nobility” (kings and queens) don’t interact with “regular people,” these elements don’t react easily with other elements. Part II: The Periodic Table Groups

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Back to Electrons… Groups – Elements in the same group have the same number of valence electrons. Periods – Each period represents an energy level. Notice how the first period contains 2 electrons, the second contains 8 electrons, and so on. Part II: The Periodic Table

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Intro to Chemical Bonds What is a chemical bond? A chemical bond is a strong attractive force between atoms or ions in a molecule or compound. Why do chemical bonds form? Atoms form bonds in order to become more stable. According to the Octet Rule, atoms will form bonds by gaining, losing, or sharing valence electrons in order to obtain an octet (8 valence electrons). What are the three main types of chemical bonds? Metallic Ionic Covalent Part III: Chemical Bonds

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Metallic Bond A metallic bond is formed when metal atoms give up their valence electrons to form an “electron sea.” Part III: Chemical Bonds Magnesium

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Metallic Bond The attraction between the loose electrons and the positively charged metal cations creates the chemical bond. Part III: Chemical Bonds Magnesium

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Ionic Bond Part III: Chemical Bonds An ionic bond is formed when an electron is transferred from a metal atom to a nonmetal atom.

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Ionic Bond Part III: Chemical Bonds The metal becomes a positively charged cation and the nonmetal becomes a negatively charged anion. The attraction between the opposite charges creates the chemical bond. Notice that both ions now have 8 valence electrons.

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Covalent Bond A covalent bond is formed when electrons are shared between two nonmetals. The overlapping orbitals create the chemical bond. Notice that both atoms now have 8 valence electrons. Part III: Chemical Bonds

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Conclusion You have discovered that the behavior of an element is dependent on its valence electrons. These electrons determine the position of elements on the periodic table. Valence electrons can also be used to predict bond types between elements. Once the chemical behavior of an element is known, the type of compounds and mixtures it forms can be predicted. Continue on to the next lesson to learn more about the classification of matter.