INTRODUCTION TO CHEMICAL BONDS

INTRODUCTION TO CHEMICAL BONDS

Chemical Bonds A general comparison of metals and nonmetals.

Chemical Bonds Types of Chemical Bonding 1. Metal with nonmetal: electron transfer and ionic bonding 2. Nonmetal with nonmetal: electron sharing and covalent bonding 3. Metal with metal: electron pooling and metallic bonding

Chemical Bonds The three models of chemical bonding.

For main group elements - Chemical Bonds Lewis Electron-Dot Symbols The A group number gives the number of valence electrons. Place one dot per valence electron on each of the four sides of the element symbol. Pair the dots (electrons) until all of the valence electrons are used. Example: Nitrogen, N, is in Group 5A and therefore has 5 valence electrons. :. N... : N.... N :... N. :

Chemical Bonds Lewis electron-dot symbols for elements in Periods 2 and 3.

Ionic Bonds Electron configurations Li 1s 2 2s 1 + F 1s 2 2s 2 2p 5 Li + 1s 2 + F - 1s 2 2s 2 2p 6 Li Orbital diagrams 1s 2s 2p Li + 1s 2s 2p + F + F - 1s 2s 2p 1s 2s 2p Lewis electron-dot symbols. Li. + : F : Li+ + : F : - : : : Three ways to represent the formation of Li + and F - through electron transfer.

Ionic Bonds Electron configurations Li 1s 2 2s 1 + O 1s 2 2s 2 2p 4 Li + 1s 2 + O -2 1s 2 2s 2 2p 6 Orbital diagrams Li 1s 2s 2p Li + 1s 2s 2p Li + 1s 2s 2p + O 1s 2s 2p + O -2 1s 2s 2p Lewis electron-dot symbols 2Li. + : O : 2Li+ + : O : - : : : Three ways to represent the formation of Li + and O -2 through electron transfer.

Sample Problem Use condensed electron configuration and Lewis electron dot symbols to depict the monatomic ions formed from each of the following atoms, and predict the formula of the compound the ions produced: a) Ba and Cl b) Sr and O c) Al and F d) Rb and O Answers: a) BaCl 2 b) SrO c) AlF 3 d) Rb 2 O

Worksheet #4-0.1 Use Lewis electron dot symbols to depict the ionic compounds formed from each of the following atoms. 1. Calcium and phosphorus 2. Aluminum and oxygen 3. Magnesium and chlorine

A bond created by the sharing of electrons between atoms Occurs between two nonmetals (resulting in a neutral overall charge) Figure 8.2 Electrons typically shared in pairs Weaker bonds than ionic bonds 3-11

When two nonmetals form a bond, the bond is covalent. They are both close to the noble-gas electron configuration, so sharing will allow both to obtain it. In a covalent bond, each shared electron interacts simultaneously with two nuclei. Figure 8.12 3-12

The atoms of CO 2 molecules are held together by strong covalent bonds. No bonds connect the molecules, so CO 2 molecules separate from each other into the gas state at room temperature. Figure 8.13 Figure from p. 28 3-13

Just as in ionic bonding, covalent bonds are formed so that each atom can have the noble-gas electron configuration. Noble gases have 8 valence electrons, an octet. Figure 8.14 3-14

Octet rule - tendency of an atom to achieve an electron configuration having 8 valence electrons Covalently bonded atoms achieve 8 valence electrons by sharing electrons The 8 electrons exist in 4 pairs 3-15

How does hydrogen obtain a noble-gas electron configuration? H atoms bond with other atoms to obtain a total of 2 electrons like He. 3-16

Do the atoms in each of these molecules have an octet? Why do the halogens exist as diatomic molecules? Figure 8.16 3-17

How many valence electrons does an oxygen atom have? How many does it need to obtain an octet? O 2 has a double bond, two pairs of shared electrons Figure 8.17 3-18

Multiple Bonds How many valence electrons does a nitrogen atom have? How many does it need to obtain an octet? N 2 has a triple bond, three pairs of shared electrons 3-19

How do phosphorus and sulfur obtain an octet in P 4 and S 8? 3-20

How many bonds do each of the following atoms tend to form? a) H b) Cl c) O d) N e) C 1 1 2 3 4 3-21 8-21

Draw the Lewis structures for each of the following based on the number of bonds that each tends to form. Remember to include the nonbonding electrons so that all have octets (except H). 1. C 2 H 6 2. C 2 H 4 3. C 2 H 2 4. HCN 3-22 8-22

Sample Problem: Answers 3-23 8-23

Worksheet #4-0.2 Draw the Lewis structures for each of the following based on the number of bonds that each tends to form. 1. CO2 2. H2S 3. O3 4. SO2 5. NNO

Electronegativity Electronegativity - The tendency of an atom in a molecule to attract electrons to itself

Electronegativity The Pauling electronegativity (EN) scale.

Electronegativity Electronegativity and atomic size.

Electronegativity

Sample Problem Using the periodic table only, arrange the elements in each set in order of increasing EN: a) S, O, Si b) Ca, P, As Answer: a) Si < S < O b) Ca < As < P

Worksheet #4-0.3 Arrange the following elements in order of increasing electronegativities. 1. Cl, At, Br, F, I 2. Al, Cs, Mg, P 3. O, P, S, Si 4. Mg, Be, C, Ca 5. Br, In, Te, Rb

Electronegativity Figure 9.21 Electron density distributions in H 2, F 2, and HF.

Electronegativity 3.0 DEN 2.0 0.0 Boundary ranges for classifying ionic character of chemical bonds.

Electronegativity Percent ionic character of electronegativity difference (DEN).

Electronegativity Properties of the Period 3 chlorides.

Electronegativity Figure 9.25 Electron density distributions in bonds of the Period 3 chlorides.

Sample Problem Are the bonds in each of the following substances ionic, nonpolar covalent or polar covalent? Arrange the substances with polar covalent bonds in order of increasing bond polarity: a) S 8 d) SCl 2 b) RbCl e) F 2 c) PF 3 f) SF 2 Answers: a) nonpolar covalent b) ionic c) polar covalent d) polar covalent e) nonpolar covalent f) polar covalent SCl 2 < SF 2 < PF 3

Worksheet #4-0.4 Arrange the bonds in each of the following sets in increasing polarity. 1. HBr, HF, HI, H2, HCl 2. Cl2, BeCl2, BrCl, BCl3 3. H2S, PH3, AsCl3, SbCl3 4. CCl4, CF4, CBr4, CI4 5. H2S, H2O, H2Se, H2Te