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Chapter 3, Section 1 Inside an Atom Tuesday, November 3, 2009 Pages 76 -- 80 Objectives Describe the structure of an atom and define protons, neutrons, and electrons. Explain the role of valence electrons in forming chemical bonds. Vocabulary Words Nucleus Proton Neutron Electron Atomic number Atomic mass unit (amu) Valence electron Electron dot diagram Structure of an Atom Atoms are extremely small. An atom consists of a nucleus surrounded by one or more electrons. – The nucleus is the core of an atom. – The nuclei contain particles called protons and neutrons. Protons Protons have a positive charge. It is indicated by this symbol “+”. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Neutrons Neutrons have no charge. They are neutral. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Electrons These particles are energetic. Moves in all direction around the nucleus. Electrons carry a negative charge. It is indicated by this symbol “-”. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Atomic Number Every atom of a particular element contains the same number of protons. The atomic number is equal to the number of protons in that element. The atomic number is a unique identifying characteristic. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Atomic Mass Because of its size, atoms cannot be measured with everyday units. The atomic mass unit (amu) was created to measure the particles in atoms. The majority of the atom’s mass is in the nucleus. Valence Electrons Not all electrons in an atom are the same distance from the nucleus. Valence electrons are electrons farthest away from the nucleus. A chemical bond forms between 2 atoms when valence electrons move between them. – Valence electrons can be transferred from one atom to another or shared between atoms. Electron Dot Diagram Electron Dot Diagram is made up of the symbol for an element surrounded by dots. Each dot represents one valence electron. QuickTime™ and a decompressor are needed to see this picture. Homework Workbook 3.1 (due 11/5) Vocabulary quiz 3.1 (on 11/5)