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“BASICS OF CHEMISTRY” • ATOMS: Everything in the world is composed of MATTER. Atoms are the smallest particle of matter that exist. What do atoms generally look like? • A) NUCLEUS: Contains protons and neutrons. • B) RINGS: aka Orbitals/shells/ • Electron clouds. Electrons are generally found in the rings The most important ring is the one on the outside. Called Valence shell. (Holds Valence electrons) • The number of electrons found on the outer ring allows atoms to combine with other atoms. What does an atom look like? Fig. 3.1 e- determine the chemical behavior of atoms Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sodium atom • The number of rings an element has depends on its row on the periodic table. • Because this element has 11 protons, it is sodium. Sodium is in the third row (PERIOD) of the P. table, it has 3 orbital rings. • KEY!!! • There is no limit to the number of Protons and Neutrons to be found in a nucleus. The number of electrons allowed on each ring is different! • 2 electrons on the first (MAX), 8 electrons on all of the rest (GENERALLY). This is known as the OCTET RULE. PERIODIC TABLE INFORMATION • ATOMIC NUMBER: This is the number of Protons and can also be the number of electrons if the atom is neutral. • ATOMIC MASS: This is the number of Protons and Neutrons. How do you find the number of Neutrons? • Atomic Mass-Atomic number. • (AM-AN) • Number of • neutrons • in Sodium? Ions and Isotopes IONS • Number of Electrons are not equal to the number of Protons. How is a sodium ion different? • It is missing an electron from the last ring. • This happens a lot with elements that are metals. (Left of the stairs). The number they can lose corresponds to their column. (Family) on table. Types of Ions • A) Cations: Lose electrons…. causing their overall charge to now be positive when comparing protons and electrons. • B) Anions: Gain electrons…. Causing them to have an overall negative charge when comparing protons and electrons. ISOTOPES • These differ from neutral atoms because when COMPARING them to the Neutral atom, they do not have the same number of neutrons as the neutral atom has. • EX: How many neutrons does a carbon have in its neutral atom? SIX! • How many neutrons would an isotope of carbon have? Carbon Isotopes • Isotopes of carbon are now written as Carbon-13, Carbon14. • The number 13, 14 refer to the atomic mass. Biological importance of Isotopes • Radioactive Decay: Isotopes that exist in nature are not stable and so they will periodically break up into smaller particles. Biological Importance of Isotopes continued • Uses of these particles: • A) Medicine: Harmless isoptopes that emit radioactivity can be used as TRACERS for following or identifying internal problems. (Thyroid issues.) • B) Dating fossils: There are some isotopes that decay at a specific rate. We can use this known rate (half life) to help determine the age of fossils. Carbon Dating example: • If a fossil contains only 12.5% of the carbon that the organism originally had right before becoming a fossil, how old is the fossil? • 100% to 50%= 1 half life (5680 years) • 50% to 25%= another half life (another 5680 years.) • 25% to 12.5 %= yet another half life (additional 5680 years) • Age of fossil: 5680+5680+5680= 17040 years! Carbon dating… • How do you get the atoms to “stick together”? • • • • • Bonding! Three types of Bonds: A) Ionic Bonds B) Covalent Bonds C) Hydrogen Bonds Ionic Bonds • Form when atoms that were neutral and then gained or lost electrons from the outer shell are now attracted to each other because of charge differences. (Like opposites attract!) • KEY: Elements that generally form ionic bonds contain at least one metal and one non-metal! Not as strong as Covalent bonds. Covalent Bonds • Form when atoms have incomplete outer shells and have NOT gained/lost electrons, instead decide to SHARE electrons to reach the octet rule. • KEY: Elements that generally form covalent bonds contain two or more nonmetals. STRONG! Strength increases with number of shared electrons. Covalent Bonds Fig. 3.9 Water molecules contain two covalent bonds Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Hydrogen Bonds • These are very different from the previous two bonds. Ionic and covalent bonds combine atoms into a compound/molecule. Hydrogen Bonds form between already formed compounds/molecules thus making larger molecules. The bonding occurs between a hydrogen atom and either an oxygen or nitrogen atom. WEAK! Hydrogen Bonds Fig. 3.10 Hydrogen bonding in water molecules Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display