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Atoms, Bonding and The Periodic Table Chapter 5, Section 1 Pg.’s 176-182 Remember!!!! The nucleus of an atom contains protons and neutrons and is surrounded by electrons in orbit. Electrons are in specific orbital's, some closer to the nucleus than others. The electrons that are furthest from the nucleus, in the highest energy level, are valence electrons. How the Periodic Table Works The periodic table reveals the underlying atomic structure of atoms, including the arrangement of atoms. As the atomic number increases, the number of electrons also increases. Valence Electrons The electrons in the highest energy level, furthest from the nucleus. (fig. 1, pg. 176) Are held most loosely. The number of Valence electrons in an atom of an element determines many properties of that element, including the way in which the atom can bond with other atoms. Electron Dot Diagrams Depicts the number of valence electrons an element has. (fig. 2, pg. 177) Includes the symbol for the element surrounded by dots. Each dot stands for one valence electron. Atoms of most elements Valence are more stable (less likely Electrons and to react) when they have 8 Element valence electrons. Reactivity The noble gases all have 8 valence electrons in their outer orbital. Some smaller atoms, such as Helium, are stable with only 2 valence electrons. Chemical Bonds and Stability Atoms usually react to become more stable. They do this in 2 different ways. They increase their number of valence electrons to 8. They give up their loosely held valence electrons. Atoms that react like this can become chemically combined, creating a chemical bond. Chemical Bonds and Group Patterns The force of attraction that holds 2 atoms together as a result of the rearrangement of electrons between them is a chemical bond. (fig.’s 3 & 4, pg.’s 178 & 179) Notice the Valence electron group pattern: Group 1 elements have 1 valence electron. Group 2 elements have 2 valence electrons. Group 13 elements have 3 valence electrons. What is the pattern (minus groups 3-12)? Reactivity of Halogens and Alkali Metals Group 17, the halogens, need to gain just 1 electron to have 8. As a result they react easily with other elements whose atoms can give up or share 1 electron. Group 1, the alkali metals, have only 1 valence electron. This property makes them very reactive because they only need to lose 1 electron to become chemically stable. Why do Halogens react violently with Alkali metals? The other Metals??? The reactivity of metals decreases from left to right across the periodic table. Groups 2-12 have 1, 2, or 3 valence electrons. They react by losing these electrons. Why do they give up their electrons instead of trying to gain more? The Semimetals??? The semimetals have 3-6 valence electrons and can lose or share electrons depending on the conditions. They can behave as either Metals or Nonmetals. The other Nonmetals?? All of the nonmetals have 4 or more valence electrons. They react by gaining or sharing electrons to have a set of 8 valence electrons. Why do they gain electrons instead of losing them? Any Questions??? Complete your notes, summaries, and questions.
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