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Basic Atomic Structure and Chemical Bonding Goals: Understand and explain basic atomic structure. Be able to determine number of subatomic particles. Form chemical bonds. Subatomic Particles Protons are positively charged Neutrons have no charge Electrons are negatively charged Protons and neutrons are found in the center of the atom (nucleus) and together, make up nearly all the mass of the atom. Protons determine the physical qualities of the element Electrons determine the chemical properties of the element Determining the number of subatomic particles In a NEUTRAL atom the number of subatomic particles can be found like this: The number of protons for an element can be determined by that elements atomic number. The number of electrons will equal the number of protons The number of neutrons can be found by subtracting the atomic number from the atomic mass. Isotopes. There are many elements that have multiple forms. Being the same element, they will all have the same number of protons. However, they have differing atomic masses, due to differences in their number of neutrons. Determining the number of subatomic particles of an Ion. Sometimes atoms will become charged, or ionized. This occurs when the number of electrons is different than the number of protons. To find the number of electrons, you must consider the charge. If an atom is positively charged, the number of electrons will be less than the number of protons. If it is negatively charged, the number of electrons will be greater. Valence Electrons. While larger elements will have greater numbers of electrons, there are only a few that we actually care about. The electrons on the very outside of the atom are the ones that we will focus on. They are the ones involved with chemical bonding, and therefore the most important. The number of valence (outermost) electrons can be determined by the periodic group to which the element belongs. Dot Structures. Dot structures serve as a visual representation of the valence electrons. When forming dot structures, remember that no two electrons may be paired until the total number of valence electrons is greater than four. Ionic Bonds. Ionic bonds exist between a metal and a non-metal. The metal literally and physically “gives” its electrons to the non-metal, which “takes” the electrons donated by the metal. This results in both becoming ionized, and the bond is formed due to the opposite charges. Covalent Bonds. Covalent bonds are formed by two or more non-metals. Because these elements have no great desire to give up electrons, they opt instead to “share” valence electrons. It is the sharing of electrons and the resulting overlapping of electron clouds that holds the elements together.