Download Attraction between 2 or more atoms or ions. Bonding and more Schemes and Mind Maps Chemistry in PDF only on Docsity! Mr. Kovscek Period 1 & 3 Int. Chemistry Chapter 6 section 3 Page 1 6-3-1 Compare and contrast a chemical formula for a molecular compound with one for an ionic compound. Bond: Attraction between 2 or more atoms or ions. Bonding occurs because it lowers the energy of the system. Chemical Bonding is also referred to as valence bond Bonding involves electrons in valence shell (outermost electron shell; has highest principal quantum number (n) Electrons on atom that are not valence electrons are called core electrons Two broad classifications Ionic (attraction between cations & anions; Metal- Nonmetal) Covalent (electron sharing; Nonmetal - Nonmetal) Caution! The idea of a "pure ionic bond" is an oversimplification, even if you consider very strongly ionic species such as NaCl or NaF Ionic bond is the attraction between cations and anions with a lowest energy arrangement (like covalent bonds, the lowest potential is sought). The pattern is repeated throughout the crystal or Lattice Also see lattices on page 177 of text. Mr. Kovscek Period 1 & 3 Int. Chemistry Chapter 6 section 3 Page 2 An ionic compound is composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal. A formula unit is the simplest collection of atoms from which an ionic compound’s formula can be established. It represents the ratio of atoms in an ionic bond. For example: sodium chloride, the ions (Na+ and Cl - ions) combine in a one-to-one ratio the formula unit is written simply as NaCl (the ones are understood). In Calcium Fluoride (Ca2+ and F – ions) the ions combine in a 1 to 2 ratio, the formula unit is CaF2 . (See fig 6 – 10 page 170 of text). Ions form to reach an octet The Octet Rule: Cations: Group 1 elements lose 1 electron and form cations with +1 charge X + EXAMPLE Na + Group 2 elements lose 2 electrons and form cations with +2 charge X 2+ EXAMPLE Mg 2+ Some group 13 elements lose 3 electrons and form cations with +3 charge X 3+ example Al 3+ The formation of Group 1, 2 , and selected 13 cations results in Noble gas electron configuration, when their valence electrons are given away, they acquire the outer shell configuration of the Nobel gas one level lower. Mg 2+ has the electron configuration 1s 2 2s 2 2p 6 just like Neon. All of group 1 and group 2 ions will follow this example. Some group 13 elements will lose d orbital electrons (Ex Sn), thus may not achieve NG Configuration. The Octet Rule: Anions: Group15 (-3), 16 (-2) and 17 (-1) gain electrons to reach their NG configuration Lewis formula for ionic compounds metal-Nonmetal Consider NaCl; it consists of an array of Na+ and Cl- ions. Na+ is the Lewis symbol for sodium ions. There are no dots on the symbol because Na has given away its valence electrons Note! Cl – Note! Cl – has 8 valence electrons so when it is drawn it must have 8 dots around it. It also has a negative charge, as a result anion Lewis dot looks a little different. Square brackets are place on both sides of the ion and the charge is expressed as a superscript:
