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Atoms and Molecules Macromolecule –a Protein Caffeine molecule The atom • Neutral in charge. • Composed of nucleus with protons (+) and neutrons (0). • Electrons (-) found in energy levels around the nucleus. • Atoms are most stable when outer (valence) energy level is full. Lithium: Atomic # = 3, Atomic mass = 6 Compounds • Composed of atoms of two or more elements. • Held together by chemical bonds. • Chemical bonds require energy to form. • Chemical bonds result from outer electrons (valence electrons) interacting. Methane gas molecule CH4 Remember: elements are specific types of atoms. The atomic # (# of protons) determines the identify of an atom. i.e. Hydrogen has 1 proton. Types of bonds Water: two hydrogen atoms plus an oxygen atom. • Covalent bonds – Two or more atoms share electrons. – Example: water • Ionic bonds – Formed when electrons are transferred. – Atoms become charged (ions) – Opposite charged ions attract each other. – Example: salt Salt: one chlorine atom plus one sodium atom. Water: a special molecule • Water is the most common molecule on Earth & in living organisms. • Chemistry of living organisms takes place water. Structure of The Water Molecule • H20 is polar: it has a negative end and a positive end. – Oxygen is negative – Hydrogen is positive – Polarity makes water a good solvent. Hydrogen Bonds • Water molecules are attracted to each other. • (-) oxygen is attracted to (+) hydrogen. • The attraction is called a hydrogen bond. Hydrogen bonds are very weak Cohesion & adhesion • Cohesion: Molecules of the same type are attracted to each other. – Surface tension is a result of cohesion. • Adhesion: Molecules of different types are attracted to each other. – Plants move water up stems in part due to adhesion. High heat capacity of water • Heat capacity is the amount of energy it take to raise the temperature of a substance 1°C. • Water must gain or lose a lot of energy for its temperature to change. • Results in stable aquatic environment & the internal environment of cells. Note: aquatic means water, the ocean is an aquatic environment. Energy • Ability to work or cause change. • Energy is never lost, it only changes form. • Different forms of energy. – Chemical – Thermal – Mechanical – electrical Chemical Reactions Reactions have: • Reactants – starting chemicals • Products – ending chemicals 2 H2O2 ---> 2 H2O + O2 Photosynthesis Respiration Reduction-Oxidation Reactions • Don’t Panic! • This is a fancy way to talk about electron transfers between products and reactants • Oxidation: A substance gives up an electron and becomes more positive • Reduction: A substance gains an electron and becomes more negative To get a deeper understanding of this concept view this series of videos on the Khan Academy website: www.khanacademy.org/science/chemistry /oxidation-reduction/v/introduction-tooxidation-states Suggested Summary When writing the summary for this lecture contrast the following pairs: Atom/ element Molecule/ compound Ionic/ covalent Energy/ matter Adhesion/cohesion Reactant/ product Reduction/ oxidation