Nature of Matter

Notes Section 2.1 The Nature of Matter Why do we study chemistry in biology class?  Life depends on chemistry  Chemical reactions maintain life  What is the study of chemistry in living things called?  biochemistry Chemistry Basics  Matter: substance of which any physical thing is composed.  Basic unit of matter = atom  The word atom means “unable to be cut”  Named by Democritus Atoms are composed of 3 main types of subatomic particles 1. Proton - positively charged particle 2. Neutron – neutral particle – no charge 3. Electron – negatively charged particle Protons and neutrons are together in the nucleus  Electrons orbit around the nucleus Why? They are attracted by:  the positive charge of the proton(s)  the mass of the nucleus Interesting Tidbits  The charge of a proton (+) is equal to and opposite the charge of an electron (-)  The mass of a proton is over 1800 times larger than that of an electron  The neutron also has a mass similar to that of the proton More on the Atom o Neutral Atom – equal # protons and electrons o Atomic Number - # protons in nucleus o Mass Number - # protons and neutrons Elements  Substance composed of only 1 type of atom    Over 100 known About 2 dozen found in living things Represented by 1 – 2 letter symbols C = carbon He = helium Most Common Elements in Living Organisms Oxygen Hydrogen Carbon Nitrogen Isotopes  Atoms of same element with differing numbers of neutrons  This alters the atom’s mass but NOT its chemical properties Isotopes are distinguished by the mass number on their symbol 12C 13C 14C Radioactive Isotopes  Unstable nuclei  Breakdown at constant rate  Emit radiation  Uses:     Determine the age of rocks and fossils Treat cancer Tracers in living tissue Kill bacteria in food Chemical Compounds  2 or more elements chemically combined in fixed amounts • Elements change properties when they combine in a compound!!! • e.g. NaCl = enhance the taste of food • • Na = explosive silvery metal Cl = poisonous green gas Compounds are represented by formulas  Symbols of elements present and the ratio in which they occur H2SO4 H2O NaCl  Molecule = smallest unit of a compound Chemical Bonds  Forces holding atoms together in compounds  Formed by specific interactions of electrons  Two main types of chemical bonds:   1. Covalent (weak, and share electrons) 2. Ionic (strong, and transfer electrons) Covalent Bonds Sharing of electrons between atoms o Single bond = sharing two electrons Fluorine molecule = F2 o Double bond = sharing four electrons o Triple bond = sharing six electrons o Example = H2O Ionic Bonds Transfer of 1 or more electrons Atom becomes electrically charged Charged atom = Ion Opposite charges hold atoms together in a compound Example: NaCl Weak Chemical Bonds  Van der Waals Forces   Slight attraction between different molecular surfaces Due to positive and negative regions on the molecules Geckos feet show Van der Waals forces at work in strong adhesion of two hydrophobic surfaces to adhere in air. Chemistry Basics (cont’d)  Chemical Reactions – interaction of molecules to yield new molecules Reactants yield products  Total # atoms of each element is the same on each side of the equation  A look at an atom Neutrons are in red A look at an atom Periodic Table of Elements