3 Electron Shells and Chemical Bonding Valence electronsFull capacity of a shell = 2n2Group 1AGroup 7A
4 Show one dot for each valence electron in the atom Fig 12.3Show one dot for each valence electron in the atom
5 Fig 8.20 Electron dot notation for representative elements 1 8 34567Valence electrons – outermost electrons in an atomOctet rule – atoms attempt to acquire 8 valence electrons
6 Closer look at the inert gases Inert gas atoms have filled valence shellsExcept for He, all have 8 valence electrons in4 nonbonding pairsOctet rule: An atom will gain. lose, or sharevalence electrons until it is surroundedby 8 valence electrons.
8 Three Types of Chemical Bonds Ionic bondsElectrons are transferred from one atom to anotherOccur between a metal atom and a nonmetal atom(2) Covalent bondsElectrons are shared between two atomsOccur between two nonmetal atomsMetallic bondsMetal atoms share many electrons in a “sea” that is free to move throughout the metal
9 The Ionic Bonds and Ionic Compounds NaNa+ + e-e- +Cl-Cl-Na+ClNa+NaClOpposite charges hold ions togetherForm between metals and nonmetals
10 This energy is called the heat of formation Formation of an ionic bondNa11 protons11 electronsNa+11 protons10 electrons+ e−Cl-17 protons18 electronsCl17 protons17 electronsNet reaction: Na + Cl → Na+Cl− + energyThis energy is called the heat of formation
11 Fig. 12.7(a) Model of the sodium chloride crystal No molecules in an ionic compound!Formula unit+−Na+ ionsCl− ions
12 Fig. 12.7(b) The crystal structure of sodium chloride
13 Ionic compounds consist of a combination of Ionic compounds consist of a combination of positive ions and negative ionsIons are formed as nonmetal atoms gain and metal atoms lose electrons to achieve stable noble gas structureThe sum of the charges on the positive ions and negative ions in each formula unit must equal zeroHow do we determine the formula for an ionic compound?