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Ch. 2 Chemical Basis of Life Atomic Structure ! Nucleus ! Protons (p+) ! Neutrons (n0) ! Outside of nucleus ! Electrons (e-) Figure 2.1 Atomic Structure of Smallest Atoms Figure 2.2 Identifying Elements ! Atomic number- equal to the number of protons that the atom contains ! Atomic mass number- sum of the protons and neutrons Isotopes and Atomic Weight ! Isotopes ! Have the same number of protons ! Vary in number of neutrons Figure 2.3 Isotopes and Atomic Weight ! Atomic weight ! Close to mass number of most abundant isotope ! Atomic weight reflects natural isotope variation Molecules and Compounds ! Molecule—two or more like atoms combined chemically ! Compound—two or more different atoms combined chemically Figure 2.4 Chemical Reactions ! Atoms are united by chemical bonds ! Atoms dissociate from other atoms when chemical bonds are broken Electrons and Bonding ! Electrons occupy energy levels called electron shells ! Electrons closest to the nucleus are most strongly attracted ! Each shell has distinct properties ! The number of electrons has an upper limit ! Shells closest to the nucleus fill first Bonding ! Electrons occupy energy levels called electron shells ! Bonding involves interactions between electrons in the valence shell (outer shell). ! All atoms want a full outer shell- 8 electrons Ionic Bonds ! Ionic bonds: Form when electrons are completely transferred from one atom to another ! Ions: Charged particles ! Anions: negative ! Cations: positive Ionic Bonds Na Cl Sodium atom (Na) (11p+; 12n0; 11e–) Chlorine atom (Cl) (17p+; 18n0; 17e–) + – Na Cl Sodium ion (Na+) Chloride ion (Cl–) Sodium chloride (NaCl) Figure 2.6 Ionic Bonds Na Cl Sodium atom (Na) (11p+; 12n0; 11e–) Chlorine atom (Cl) (17p+; 18n0; 17e–) Figure 2.6, step 1 Ionic Bonds Na Cl Sodium atom (Na) (11p+; 12n0; 11e–) Chlorine atom (Cl) (17p+; 18n0; 17e–) Figure 2.6, step 2 Ionic Bonds Na Cl Sodium atom (Na) (11p+; 12n0; 11e–) Chlorine atom (Cl) (17p+; 18n0; 17e–) + – Na Cl Sodium ion (Na+) Chloride ion (Cl–) Sodium chloride (NaCl) Figure 2.6, step 3 Covalent Bonds ! Covalent bonds: Atoms get “full” outer shell by sharing electrons ! Single covalent bonds share one pair of electrons ! Double covalent bonds share two pairs of electrons Examples of Covalent Bonds Figure 2.7a Examples of Covalent Bonds Figure 2.7b Examples of Covalent Bonds Figure 2.7c Polarity ! Non-polar covalently bonded molecule: electrically neutral as a molecule ! Polar covalently bonded molecule: has a positive and negative side Figure 2.8 Chemical Bonds ! Hydrogen bonds: weak chemical bonds in which hydrogen is attracted to the negative portion of a polar molecule, providing attraction between molecules. Patterns of Chemical Reactions ! Synthesis reaction (A + BàAB) ! Atoms or molecules combine ! Energy is absorbed for bond formation ! Decomposition reaction (ABàA + B) ! Molecule is broken down ! Chemical energy is released Synthesis and Decomposition Reactions Figure 2.10a Synthesis and Decomposition Reactions Figure 2.10b Patterns of Chemical Reactions ! Exchange reaction (AB + CàAC + B) ! Involves both synthesis and decomposition reactions ! Switch is made between molecule parts and different molecules are made Patterns of Chemical Reactions Figure 2.10c