CHAPTER 2

• anything that takes up space and has mass

  Matter
• the smallest chemical units of matter

  Atoms
• negatively charged subatomic particles circling a nucleus

  Electrons
• structure containing neutrons and protons

  Nucleus
• uncharged particles


  neutrons
• positively charged particles


  protons
• composed of a single type of atom


  Element
• equal to the number of protons in the nucleus

  Atomic number
• sum of masses of protons, neutrons, and electrons

  atomic mass
• Atoms of a given element that differ in the number of neutrons in their nuclei


  Isotopes
• Release energy during radioactive decay

  Radioactive isotopes
• Only the electrons of atoms interact, so they determine

  atom's chemical behavior
• Electrons occupy electron shells
• electrons in outermost shell that interact with other atoms

  valence electrons
• combining capacity of an atom

  Valence
• Positive if atom has electrons to give up
• Negative if atom has spaces to fill
• Stable when outer electron shells contain eight electrons
• atoms combine by sharing or transferring valence electrons

  chemical bonds
• two or more atoms held together by chemical bonds

  molecule
• a molecule composed of more than one element

  compound
• sharing of a pair of electrons by two atoms

  covalent bond
• attraction of atom for electrons

  electronegativity
• The more electronegative an atom, the greater the pull its nucleus exerts on electrons
• Shared electrons spend equal amounts of time around each nucleus

  Non-polar bonds
• • Atoms with similar electronegativities • No poles exist • Carbon atoms form four nonpolar covalent bonds with other atoms

  non-polar bonds
• Organic compounds contain carbon and hydrogen atoms
• Unequal sharing of electrons due to significantly different electronegativities(non metal + metal / metalloids)

  Polar covalent bonds
• Most important polar covalent bonds involve hydrogen
• Occur when two atoms with vastly different electronegativities come together

  Ionic bonds
• Atoms have either positive (cation) or negative (anion) charges
• Cations and anions attract each other and form ionic bonds (no electrons shared)
• Ionic bonds typically form crystalline ionic compounds known as salts
• Electrical attraction between partially charged H+ and full or partial negative charge on same or different molecule

  Hydrogen bonds
• Weaker than covalent bonds but essential for life . Help to stabilize 3-D shapes of large molecules

  Hydrogen bonds
• • The making or breaking of chemical bonds • Involve reactants and products

  Chemical reactions
• • Involve the formation of larger, more complex molecules • Require energy (endothermic) • Common type is dehydration synthesis • Water molecule formed


  Synthesis reaction
• All the synthesis reactions in an organism are called-

  Anabolism
• Break bonds within larger molecules to form smaller atoms, ions, and molecules • Release energy (exothermic) • Common type is hydrolysis • Ionic components of water are added to products


  Decompression reaction
• All the decomposition reactions in an organism are called-

  catabolism