The Chemical Basis of Life

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CHEMICAL BASIS OF LIFE ATOM • Fundamental structural units of matter. Smallest particle in existence. • Unit of measure = Angstrom (Å) • Consists of two integral units: Proton (+), Neutron, (+/-). • Electron is found in the orbital (outer shell) of an atom. • Estimated size of an atom: 1.67 × 10−27 • Atomic number refers to the number of protons. • Atoms are electrically neutral. • Atomic weight refers to the available neutrons in an atom. • Reactivity of an atom is dependent on the number of electrons in orbit. Atomic Structure (-) (+) CHEMICAL ELEMENTS • All matter on Earth is composed of combinations of chemical elements. • Elements cannot be broken down by chemical processes into simpler substances. • There are over 90 naturally-occurring chemical elements. • The most common chemical elements in living things are: • S, P, O, N, C, H! MOLECULES • Atoms joined by bonds are called molecules. • Molecules are categorized according to their structure often called molecular geometry. • Reactivity of an molecule based on its structure is called isomers. • Two basic principles of chemical interaction: Inert and Reactive. • Two basic type of molecules are essential to support life: Inorganic and organic. FORMATION OF COMPOUNDS & MOLECULES • relies on its number of electrons in its outer shell (energy level): the outer shell. Electron Energy Levels: First energy level holds up to 2 electrons Second energy level holds up to 8 electrons Third energy level holds up to 8 electrons ATOM STABILITY • Refers to the readiness of availability of an atom to engage in a chemical reaction. • Some atoms already have a full outer energy level, such that atoms do not react with other atoms to form molecules. • The noble gases: These include the inert or noble gases: Helium, Argon, Neon, Krypton, Xenon, and Radon. ATOM

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