Chapter 4 Chemical Bonds John Singer, Jackson Community College Chemistry for Changing Times, Thirteenth Edition Lecture Outlines © 2013 Pearson Education, Inc.

2 Chapter 4 © 2013 Pearson Education, Inc. The Ties that Bind Carbon exists commonly as soot. When soot is subjected to high temperature and pressure, it can form diamond. This process can be explained by understanding the chemical bonds that hold the atoms together.

3 Chapter 4 © 2013 Pearson Education, Inc. Stable Electron Configurations Fact: Noble gases, such as helium, neon, and argon are inert, they undergo few if any, chemical reactions. Theory: The inertness of noble gases results from their electron structures; each (except helium) has an octet of electrons in its outermost shell. Deduction: Elements become less reactive when they alter their electron structures to that of a noble gas.

4 Chapter 4 © 2013 Pearson Education, Inc. Sodium can lose a valence electron. After doing so, its core electrons are configured like the noble gas neon. Stable Electron Configurations

5 Chapter 4 © 2013 Pearson Education, Inc. Chlorine can gain an electron, and in doing so, its electron structure becomes like argon. Stable Electron Configurations

6 Chapter 4 © 2013 Pearson Education, Inc. Lewis (Electron Dot) Symbols G. N. Lewis developed a method of visually representing the valence electrons as dots around the symbol of an atom.

7 Chapter 4 © 2013 Pearson Education, Inc. Lewis (Electron Dot) Symbols

8 Chapter 4 © 2013 Pearson Education, Inc. Sodium Reacts with Chlorine (Fact)

9 Chapter 4 © 2013 Pearson Education, Inc. Sodium Reacts with Chlorine (Theory)

10 Chapter 4 © 2013 Pearson Education, Inc. Na + ions and Cl - have opposite charges and attract each other. The resulting attraction is an ionic bond. Ionic compounds are held together by ionic bonds and exist as crystal lattice. Sodium Reacts with Chlorine (Theory)

11 Chapter 4 © 2013 Pearson Education, Inc. Atoms and Ions: Distinctively Different

12 Chapter 4 © 2013 Pearson Education, Inc. Octet Rule In chemical reactions, atoms tend to gain, lose, or share electrons so as to have eight valence electrons. This is known as the octet rule.

13 Chapter 4 © 2013 Pearson Education, Inc. Octet Rule Metals lose electrons to take on the electron structure of the previous noble gas. In doing so, they form positive ions (cations). Nonmetals tend to gain electrons to take on the electron structure of the next noble gas. In doing so, they form negative ions (anions).

14 Chapter 4 © 2013 Pearson Education, Inc. Octet Rule

15 Chapter 4 © 2013 Pearson Education, Inc. Formulas and Names of Binary Ionic Compounds Cation Charge: The charge of a cation from the representative elements is the same as the family number. The name of a cation is simply the name of the element. Examples: Na + = sodium ion Mg 2+ = magnesium ion

16 Chapter 4 © 2013 Pearson Education, Inc. Anions: The charge of an anion from the representative elements is equal to the family number minus eight. The name of an anion is the root name of the element plus the suffix –ide. Examples: Cl - = chloride ion O 2- = oxide ion Formulas and Names of Binary Ionic Compounds

17 Chapter 4 © 2013 Pearson Education, Inc. To name binary ionic compounds, simply name the ions. Examples: NaCl=sodium chloride MgO=magnesium oxide Formulas and Names of Binary Ionic Compounds

18 Chapter 4 © 2013 Pearson Education, Inc. Many transition metals can exhibit more than one ionic charge. Roman numerals are used to denote the charge of such ions. Examples: Fe 2+ =iron(II) ion Fe 3+ = iron(III) ion Cu 2+ =copper(II) ion Cu + =copper(I) ion Formulas and Names of Binary Ionic Compounds

19 Chapter 4 © 2013 Pearson Education, Inc. Commonly Encountered Ions Formulas and Names of Binary Ionic Compounds

20 Chapter 4 © 2013 Pearson Education, Inc. Covalent Bonds Many nonmetallic elements react by sharing electrons rather than by gaining or losing electrons. When two atoms share a pair of electrons, a covalent bond is formed. Atoms can share one, two, or three pairs of electrons, forming single, double, and triple bonds.

21 Chapter 4 © 2013 Pearson Education, Inc. Binary covalent compounds are named by using a prefix to denote the number of atoms. Names of Binary Covalent Compounds

22 Chapter 4 © 2013 Pearson Education, Inc. Binary covalent compounds have two names: 2.Second name = prefix + root name of second element + suffix –ide. 1. First name = prefix + name of 1 st element (Note: If the first element has only one atom, the prefix mono- is dropped.) Names of Binary Covalent Compounds

23 Chapter 4 © 2013 Pearson Education, Inc. Examples: SBr 4 sulfur tetrabromide P2O3P2O3 diphosphorus trioxide Names of Binary Covalent Compounds

24 Chapter 4 © 2013 Pearson Education, Inc. Electronegativity Electronegativity is a measure of an atom’s attraction for the electrons in a bond.

25 Chapter 4 © 2013 Pearson Education, Inc. Polar Covalent Bonds When two atoms with differing electronegativities form a bond, the bonding electrons are drawn closer to the atom with the higher electro-negativity. Such a bond exhibits a separation of charge and is called a polar covalent bond.

26 Chapter 4 © 2013 Pearson Education, Inc. Bond Polarity Bond polarity can be represented on a Lewis structure with either the partial symbol or with the arrow as shown below:

27 Chapter 4 © 2013 Pearson Education, Inc. The difference in electronegativity between two bonded atoms can be used to determine the type of bond. Use the adjacent table as a rule of thumb. Δ ENType of Bond < 0.5Nonpolar covalent Between 0.5 and 2.0 Polar covalent Greater than 2.0 Ionic Bond Polarity

28 Chapter 4 © 2013 Pearson Education, Inc. Polyatomic Ions Polyatomic ions are groups of covalently bonded atoms with a charge.

29 Chapter 4 © 2013 Pearson Education, Inc. Writing Formulas Using Polyatomic Ions When writing formulas for compounds containing polyatomic ions, it may be necessary to use parentheses to denote the proper number of the ions. Example: calcium nitrate Ca 2+ NO 3 - Ca(NO 3 ) 2

30 Chapter 4 © 2013 Pearson Education, Inc. Naming Compounds with Polyatomic Ions When naming compounds with polyatomic ions, simply name the ions in order. Example:(NH 4 ) 2 SO 4 ammonium sulfate

31 Chapter 4 © 2013 Pearson Education, Inc. Rules for Sketching Lewis Structures 1.Count valence electrons. 2.Sketch a skeletal structure. 3.Place electrons as lone pairs around outer atoms to fulfill the octet rule. 4.Subtract the electrons used so far from the total number of valence electrons. Place any remaining electrons around the central atom. 5.If the central atom lacks an octet, move one or more lone pairs from an outer atom to a double or triple bond to complete an octet.

32 Chapter 4 © 2013 Pearson Education, Inc. Sketching Lewis Structures

33 Chapter 4 © 2013 Pearson Education, Inc. Odd Electron Molecules: Free Radicals An atom or molecule with an unpaired electron is known as a free radical. Examples include: NONO 2 ClO 2

34 Chapter 4 © 2013 Pearson Education, Inc. Molecular Shapes: The VSEPR Theory The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the shape of molecules and polyatomic ions based on repulsions of electron pairs on central atoms.

35 Chapter 4 © 2013 Pearson Education, Inc. Molecular Shapes: The VSEPR Theory

36 Chapter 4 © 2013 Pearson Education, Inc. Molecular Shapes: The VSEPR Theory

37 Chapter 4 © 2013 Pearson Education, Inc. Shapes and Properties: Polar and Nonpolar Molecules In order for a molecule to be polar, two conditions must be met: 1. It must have polar bonds. 2. The bonds must be arranged such that a separation of charge exists.

38 Chapter 4 © 2013 Pearson Education, Inc. Shapes and Properties: Polar and Nonpolar Molecules

39 Chapter 4 © 2013 Pearson Education, Inc. Shapes and Properties: Polar and Nonpolar Molecules

40 Chapter 4 © 2013 Pearson Education, Inc. Shapes and Properties: Polar and Nonpolar Molecules

41 Chapter 4 © 2013 Pearson Education, Inc. Chemical Vocabulary