CHAPTER 2.1 The Nature of Matter THE CHEMISTRY OF LIFE CHAPTER 2.1 The 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- ions Bond formed between two ions by the transfer of electrons
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 BOND- Molecules Bond formed by the sharing of electrons
Covalent Bonds
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!