Chem 1075 Chapter 12 Chemical Bonding Lecture Outline Slide 2 Chemical Bond Concept Recall that an atom has and electrons. Core electrons are found to the nucleus. Valence electrons are found in the s and p energy subshells. It is electrons that are responsible for holding two or more atoms together in a. Slide 3 Octet Rule The states that atoms bond in such a way so that each atom acquires electrons in its outer shell. There are two ways in which an atom may achieve an octet. (a) By of electrons from one atom to another (b) By one or more pairs of electrons Slide 4 Types of Bonds Ionic Bonds are formed from the of electrons between atoms to form compounds. Covalent Bonds are formed when two atoms electrons to form compounds. Slide 5 Ionic Bonds An ionic bond is formed by the between charged cations and charged anions. This is similar to the attraction between opposite poles on two magnets. Slide 6 Ionic Bonds The ionic bonds formed from the combination of anions and cations are and result in the formation of a rigid, structure. The structure for ordinary table salt, is shown here.
Slide 7 Formation of Cations are formed when an atom valence electrons to become charged. Most main group achieve a noble gas electron configuration by their valence electrons and are with a noble gas. Magnesium (Group IIA/2) loses its valence electrons to become Mg 2+. A magnesium ion has (12 2=10e-) and is isoelectronic with. See also Ch.6 Slide 25 for discussion of Positive Ionic Charge Slide 8 Formation of Cations We can use electron dot formulas to look at the formation of. Each of the metals in Period 3 form cations by losing 1, 2, or 3 electrons, respectively. Each metal atom becomes with the preceding noble gas,. Slide 9 Formation of Anions are formed when an atom electrons and becomes charged. Most achieve a noble gas electron configuration by electrons to become with a noble gas. Chlorine (Group VIIA/17) gains valence electron and becomes Cl. A chloride ion has 18 electrons (17 + 1 = 18 e-) and is isoelectronic with. See also Ch.6 Slide 26 for discussion of Negative Ionic Charge Slide 10 Formation of Anions We can also use electron dot formulas to look at the formation of. The nonmetals in Period 3 gain 1, 2, or 3 electrons, respectively to form anions. Each nonmetal ion is with the following noble gas,.
Slide 11 Lewis Dot Structures of Molecules In Ch.6 Slide 21 we drew electron dot formulas for atoms. The number of around each atom is equal to the number of electrons the atom has. We will now draw electron dot formulas for molecules (also called Lewis Dot structures). A Lewis structure shows the between atoms and helps us to visualize the of atoms in a molecule. Slide 12 Lewis Dot Structures of Molecules Drawing the following out on board, Consider H 2 : The bond in H 2 is called a bond. Consider O 2 : The bond in O 2 is called a bond. Consider N 2 : The bond in N 2 is called a bond. Slide 13 Guidelines for Drawing Lewis Dot Structures of Molecules 1. Hydrogen has only 2 e- or. 2. Beryllium has 4 e- or. 3. Boron can have 6 e- or and be happy. 4. Elements the 2nd Period can their octet (have more than e-) 5. Halogens prefer bonds if possible Slide 14 Steps for Drawing Lewis Dot Structures of Molecules 1. Count the number of electrons for the structure. 2. Arrange atoms and connect with bonds. 3. Left-over electrons fill octets first, then octet. 4. Multiple-bond if of electrons and for central atom. Slide 15 Lewis Dot Structures 1. H 2 O 2. PCl 3 3. SO 2
4. CO 2 5. HCN (C is central) 6. PCl 5 7. NO 3 1-8. ClO 2 1-9. Cl 2 CO (C is central) Slide 16 Polar Covalent bonds bonds result from the of valence electrons. Often, the two atoms do not share the electrons. One of the atoms holds on to the electrons than the other. When one of the atoms holds the shared electrons more tightly, the bond is. A is one in which the electrons are shared equally. Slide 17 Electronegativity Each element has an innate to valence electrons. is the ability of an atom to in a chemical. Linus Pauling devised a method for measuring the electronegativity of each of the elements. Fluorine is the electronegative element. Slide 18 Electronegativity
Slide 19 Electronegativity Differences The electronegativity of H is and of Cl is. Since there is a in electronegativity between the two elements ( ), the bond in H Cl is polar. Since Cl is electronegative, the bonding electrons are attracted the Cl atom and from the H atom. This will give the Cl atom a charge and the H atom a charge. Slide 20 Delta Notation for Polar bonds We use the Greek letter delta, δ, to indicate a bond. The charged atom is indicated by the symbol, and the charged atom is indicated by the symbol. This is referred to as for polar bonds. δ+ H Cl δ Slide 21 Delta Notation for Polar bonds The hydrogen halides, HF, HCl, HBr, and HI all have bonds. The halides are all electronegative than hydrogen and are designated with a. Slide 22 Nonpolar Covalent Bonds What if two atoms in a covalent bond have the electronegativities? The bond is polarized and it is a. If the electronegativity difference is, it is usually considered a bond. The diatomic halogen molecules have bonds.
Slide 23 Shapes of Molecules Electron pairs surrounding an atom repel each other. This is referred to as Valence Shell Electron Pair Repulsion (VSEPR) theory. The indicates the arrangement of and electron pairs around the central atom. The gives the arrangement of (ignoring lone pairs of electrons) around the central atom as a result of electron repulsion. Slide 24 Tetrahedral Molecules Methane, CH 4, has pairs of around the central carbon atom. The four bonding pairs (and therefore ) are repelled to the four corners of a tetrahedron. The geometry is. Slide 25 The shape is also tetrahedral. Trigonal Pyramidal Molecules In ammonia, NH3, the central nitrogen atom is surrounded by pairs and pair. The geometry is and the shape is. Slide 26 Bent Molecules In water, H 2 O, the central O atom is surrounded by pairs and pairs. The electron pair geometry is and the molecular shape is. Slide 27 Linear Molecules In carbon dioxide, CO 2, the central C atom is bonded to each oxygen by two electron pairs (a double bond). There are bonded to C. According to VSEPR, the electron pairs will each other, and they will be at of the C atom. The electron pair geometry and the molecular shape are both.