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ATOMS: WHAT THE WORLD IS MADE OF! ELEMENTS • Element – a substance made of only ONE kind of an atom – Cannot be broken down into simpler substances – Represented on the Periodic Table of Elements Example: ATOMS • Smallest particle of an element that still retains the properties of that element • Mostly open space! • Made up of a central Nucleus orbited by one or more electrons • Too small to be seen. Models are used to study the atom – Bohr model (planetary model) – Electron cloud model – Lewis Structure diagram BOHR MODEL OF SODIUM ELECTRON CLOUD MODEL LEWIS STRUCTURE (a.k.a. Electron Dot Diagram) These models only show the valence electrons – the electrons on the outer most shell of an atom. (Example: Sodium, Na, has 11 electrons total but only 1 valence electron) Valence electrons are involved in chemical bonds & reactions between atoms. STRUCTURE OF THE ATOM • Nucleus – tiny central core of the atom Subatomic particles found inside the nucleus – – 1) Protons – have a positive (+) charge – 2) Neutrons – have no charge (0) neutral • Electron Cloud – area outside of the nucleus – (aka “shells” or “energy levels”) Subatomic particles outside the nucleus: 3) Electrons – have a negative (-) charge and orbit rapidly around the nucleus Subatomic Particles • Sub = “smaller than” • Subatomic particles are particles that are smaller than an atom • Protons, Neutrons and Electrons are all examples of subatomic particles ATOMIC CHARGES • Atoms are normally electrically neutral (0). WHY? – For every positive (+) charge, there is a negative (-) charge. In other words: Equal number of protons (+) and electrons(-) gives the atom an overall neutral (0) charge. MORE ABOUT ELECTRONS!! • Electrons move rapidly around the nucleus. • Smallest of the sub-atomic particles – Too small to count towards an atom’s mass! • Electrons move so fast that they look like moving fan blades! It’s Electric! • Electrons near the nucleus are held tight to the atom (opposites attract!) • Electrons further out are not & can be made to move out of their orbits. • Moving electrons create electricity! ATOMIC NUMBER • Atomic number Identifies an element. • Equal to the number of protons an element has. • EX: Every atom of carbon has 6 protons – Therefore, carbon’s atomic number is 6 Every atom of oxygen has 8 protons What is oxygen’s atomic number? ___ All atoms of the same element have the same chemical properties and the same number of protons. If the number of protons changes, then you have a DIFFERENT element. ATOMIC MASS • Most of an atom’s mass is in the nucleus (where the protons and neutrons are) • AMU – Atomic Mass Unit – used to measure the mass of an atom – Mass of a proton or neutron = 1 amu – Mass of an electron = about 0.0005 amu • It takes almost 2,000 electrons to = 1 amu! • Electrons are generally ignored when calculating an atom’s mass because they are so tiny • Atomic Mass = Protons + Neutrons Mass & Volume • Most of an atom’s mass comes from the protons (+) and neutrons (0) in the nucleus. • Most of an atom’s volume comes from the space where the electrons move. ISOTOPES • Atoms of an element always have the same number of protons, but the number of neutrons can be different. • This is called an isotope of an element – Isotopes: atoms of the same element with different numbers of neutrons than average • EXAMPLE: Carbon always has 6 protons, but it could have 5, 6, or 7 neutrons. – (Known as isotopes C-5, C-6, or C-7). • Question: How many electrons would an isotope of carbon have? Common Isotopes of Carbon: VALENCE ELECTRONS • Farthest away from the nucleus – on the outer most shell – Not held as tightly by the atom • Determine the properties and reactivity of the atom. • Form the chemical bonds between atoms – Chemical bonds are the force that holds the atoms together in a compound (atomic glue) Next time….. The Periodic Table of Elements!!!