THE CHEMISTRY OF LIFE CHAPTER 2.1The Nature of Matter
Atoms • Basic unit of matter • Greek atomos, which means “unable to cut” • Proposed by Democritus 2500 years ago
Subatomic Particles • Nucleus- held together by strong forces • Protons (+) • Neutrons (0) • Electrons (-) • 1/1840th the mass of a proton
Elements and Isotopes • Element- pure substance that consists of entirely one atom • Isotopes- atoms of an element with different numbers of neutrons • Because they have the same number of e-, all isotopes of an element have the same chemical properties • Isotopes are identified by their mass numbers • C-12, C-13, C-14 • Atomic mass is the weighted average of the isotopes found in nature (abundance)
Radioactive Isotopes • Contain unstable nuclei that breakdown at a constant rate over time • Radiation can be used to… • Date rocks and fossils • Treat cancer • Kill bacteria in food • As “tracers” • Can be harmful!
Chemical Compounds • A substance by the chemical combination of two or more elements in definite proportions • Properties of compounds are usually different than the elements that make it up • Sodium- silvery soft metal, reacts explosively with cold water • Chlorine- greenish poisonous gas
E-dot diagrams and bonds • The electron dot diagrams express the element’s symbol and number of valence electrons available for bonding. • Try these… • Na • Mg • B • C • P • S • F • Ne • He
Formation of Ions • When a neutral atom gains/loses electrons, its overall charge becomes + or - • When you gain an electron the ion is known as an anion which is negative. • When you lose an electron the ion is known as a cation which is positive.
Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.
Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)
Van der Waals Forces • Weak force of intermolecular attraction • Due to uneven charges that exist in covalent bonding • Helps geckos grip smooth surfaces!