Chapter 6 Chemical Bonding Classic joke of the

Chapter 6 Chemical Bonding Classic joke of the day: Two atoms walking down the street, one atom gets bumped by another. He shouts “Hey he stole my electron”. His friend asks “Are you sure? !” to which he replies “ Yes, I’m positive” Hey. . That’s Ionic!!! Pre-AP Chemistry 1

Chapter 6 Vocabulary 1. chemical bond 2. ionic bonding 3. covalent bond 4. nonpolar-covalent bond 5. polar-covalent bond

Section 6. 1 Intro to Chemical Bonding l 3 Main Ideas: – Atoms Form Compounds by gaining, losing, or sharing electrons. – Atoms tend to form bonds to follow the octet rule – Atoms will bond in order to lower their potential energy. – Ionic bonds form from gaining and losing electrons – Covalent bonds form from shared electrons

Valence Electrons are…? l The electrons responsible for the chemical properties of atoms, and are those in the outer energy level. l Valence electrons - the s and p electrons in the outer energy level – the highest occupied energy level l Core electrons – are those in the energy levels below.

The Octet Rule l l l In Chapter 5, we learned that noble gases are unreactive in chemical reactions In 1916, Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules The Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer level (s and p) is stable l Each noble gas (except He, which has 2) has 8 electrons in the outer level

Chemical Bond l A link between atoms that results from the mutual attraction of their nuclei for electrons – Electrostatic attraction between proton and electron – Classified by the way the valence e- are distributed around nuclei of combined atoms 6

l Ionic Types of Bonds – A chemical bond resulting from electrostatic attraction between cations and anions – In a pure ionic bond, one atom completely gives up one or more e- to another atom (rarely happens) – Illustration: A + B A+ + B - 7

l Covalent – Chemical bond resulting from the sharing of valence electrons between two atoms – In a pure covalent the electrons are shared equally between the two atoms (called nonpolar covalent) – Most covalent result in the electrons being shared unequally between atoms (called polar covalent) 8

Covalent bonds l l 9 Nonmetals hold on to their valence electrons. They can’t give away electrons to bond. – But still want noble gas configuration. Get it by sharing valence electrons with each other = covalent bonding By sharing, both atoms get to count the electrons toward a noble gas configuration.

l No bond is completely ionic and is rarely completely covalent – Bonds range between the two extremes – Degree of ionic or covalent estimated by comparing electronegativities (ionic character) 10

Ionic Bonds Ionic - Greater the difference (≥ 50%), the more ionic the bond – Range of 1. 71 - 4. 0 considered ionic – Example: Cs + F 4. 0 ( F electroneg) - 0. 7 (Cs electroneg) = 3. 3 Ionic bond formed Cs becomes cation, F becomes anion 11

– Covalent bonds occur if the difference is less than 50% • A bond between 2 identical atoms is completely covalent (7 diatomics: H, N, O, F, Cl, Br, I) • Types of covalent – Nonpolar – Polar 12

Nonpolar-covalent Bonds – Nonpolar • Pole= unequal distribution of charge • nonpolar-covalent bond- the bonding electrons are shared equally by bonded atoms, with a resulting balanced distribution of electrical charge • Occur between 0% to 5% ionic character • Range of difference 0 - ~0. 3 13

Polar-covalent Bonds – Polar • Pole= unequal distribution of charge • Polar covalent bond is a bond where united atoms have an unequal attraction for the shared electrons • Occur between 5%-~50% ionic character • Range of difference ~0. 3 -1. 7 14

Examples l l H-H 2. 1 -2. 1= 0 nonpolar covalent bond H - Cl 3. 0 -2. 1= 0. 9 polar covalent bond Because Cl is more electronegative, it has a stronger attraction for the e-, thus an uneven pull of electrons occurs—however e- still shared Uneven sharing causes a partial positive, partial negative pole 15

l 16 Metallic Bonding – In a liquid or solid state, metals readily give up electrons – When only other metal atoms are around, electrons are not accepted and held, they are free to move – Free moving electrons called an electron sea—reason for metallic properties of luster, malleability, ductility, and conductivity

Why do atoms bond? 17 l Atoms will bond in order to lower their potential energy. (most atoms at high potential energy) l Atoms strive to reach an octet by bonding (ie: can take on the configuration of a noble gas)

Quick Trick 18 l Polar covalent and nonpolar covalent bonding most readily occurs between nonmetals l Ionic most readily occurs between metals and nonmetals l Metallic occurs between metals

Chemical Bond ü. . a mutual electrical attraction between nuclei and valence electrons of different atoms that binds the atoms together ü Two types: 1. Ionic bonds – transfer of electrons (gained or lost; makes formula unit) -usually metal-nonmetal bond -forms cations and anions -range of 1. 71 - 4. 0 2. Covalent bonds – sharing of electrons. The resulting particle is called a “molecule” -usually nonmetal-nonmetal bond a) nonpolar - range of difference 0 - ~0. 3 b) polar- range of difference ~0. 3 -1. 7 19

Sec 6. 1 Practice Problems textbook p. 200 #6, 7 Complete chart. (Hint: See Sample A page 167) Electronegativity Difference Bonded Elements More Electronegative Atom Bond Type a. H, I b. S, O c. K, Br d. Si, Cl e. K, Cl f. Se, S g. C, H 7. List the bonding pairs described in item 6 in order of increasing covalent character (Hint: decreasing ionic)