Transcript File
Smallest unit of matter Three subatomic particles Protons Neutrons Electrons Positively charged Are part of the nucleus Have a mass of 1 amu Number of protons = atomic number Defines the atom Have a neutral charge Also part of the nucleus Have a mass of 1 amu neutrons + protons = atomic mass Have a negative charge Moving around the nucleus Have little mass Number of electrons = number of protons Variant forms of an atom Atoms with same number of protons (C = 6) have different number of neutrons 12C has 6 protons and 6 neutrons; 14C has 6 protons and 8 neutrons. Some isotopes (radioactive) are unstable and decay into more stable atoms Used to date rocks and fossils Used as tracers to follow atom through reactions or through body Radioisotopes are radioactive isotopes They are not stable Emit particles and energy as they decay spontaneously into other elements Decays at a constant rate into the same products Example: 14C → 14N Tracer Molecule with a detectable substance attached PET scans Electrons & Energy Levels Full Shells = Happy Shells Unfilled Shells = Reactive Atoms Molecules Electrons are attracted to protons but are repelled by other electrons Orbitals are volumes of space around nucleus where electrons are found Each orbital hold 2 electrons Shells Are levels or orbitals Closest to nucleus = 1 orbital = 2 electrons Next shell = 4 orbitals = 8 electrons Any atom with a vacant orbital will tend to fill it by forming a bond with other atom(s) Chemical bonds are unions between electron structures of atoms May give up , gain, or share electrons Chemical bond Distribution of electrons changes if the atom gives up, gains, or shares electron(s) Molecules “2 or more atoms of the same or different elements join in chemical bond” One element Oxygen Hydrogen Nitrogen Compound 2 or more elements H2O = Water CO2 = Carbon dioxide Mixture Blend without chemical bond Sugar water Ionic Bond Covalent Bond Hydrogen Bond Electrons are transferred Forms ions atoms with a net electrical charge +/ Gained Lost Gain electrons = - charge Lose electrons = + charge Positive and negative ions attract each other NaCl HCl KBr Sodium ion Chloride ion a A crystal of table salt is a cubic lattice of many sodium ions and chloride ions. b The mutual attraction of opposite charges holds the two kinds of ions together closely in the lattice. Fig. 2.8, p. 23 Electrons shared Non-polar covalent Equally shared Polar covalent Unequally shared Slight positive & negative charge to opposite “poles” of the molecule Charge areas attract Hydrogen bond Form between a hydrogen atom and an electronegative atom Each with separate polar covalent bonds Are not chemical bonds Do not make atoms into molecules Individually weak Collectively stabilize structures of large molecules Water molecules are polar Form hydrogen bonds with other polar molecules Hydrophilic substances (water-loving) Hydrophobic substances (water-dreading) Polarity gives liquid water unique properties that make life possible: Resistance to temperature changes Internal cohesion Dissolves polar and ionic substances Absorbs heat without changing temperature Evaporation = cooling Freezing hydrogen bonds resist breaking Crystal structure is less dense than water Hydrogen bonding Cohesion (stickiness) Cohesion pulls water through plants Capillary action Solvent is a substance, usually liquid, that dissolves other substances Solutes are dissolved substances Water is an excellent solvent Will dissolve most polar molecules Is the most nearly universal solvent Form spheres of hydrogen Clusters of water molecules around a solute A substance is said to be dissolved after solvent molecules cluster around its ions or molecules & keep them disapersed Arrange substances from acid to base 0-14 7 = Neutral Power of hydrogen (negative exponent) Acids 0-7 on pH scale (Protons) H+ ions Red in litmus Sour taste React with metals Bases 7-14 on pH scale OH- ion Blue in litmus Bitter taste Weak acid and the base that forms in water H2CO3 HCO3- + H+ Carbonic acid Bicarbonate Prevents swings in pH. Form from an acid and a base Hydrochloric acid + Sodium hydroxide = Sodium chloride + water HCl + NaOH NaCl + H2 Useful ions in solution