Houston Community College System Chemistry 1405 Chapter 3 Molecules and Chemical Bonds By Mounia Elamrani Blei / Odian ’ s General, Organic, and Biochemistry

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Objectives Ionic and covalent bonds Octet rule and the formation of ions Formulas of binary ionic compounds Naming ionic and covalent compounds Lewis structures Bond polarity VSEPR theory and molecular shape

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds The Octet Rule and Chemical Bonding Noble gases are very stable elements and virtually non-reactive Noble gases have an octet (8) of electrons in their valence shell Other Elements try to achieve an octet by forming chemical bonds and compounds There are two types of chemical bonds: Ionic Bonds Covalent Bonds

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.1 Ionic vs. Covalent Bonds Ionic bond: forms between a positive ion and a negative ion There is a complete transfer of electrons from one element to the other Strong electrostatic forces hold the ions together Mostly formed between metals and nonmetals Covalent bond: Forms between elements sharing electrons Mostly formed between nonmetals Electron affinity and ionization energy help determine the type of bond formed

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.1 Electron Affinity and Ionization Energy Electron Affinity (EA) measures the ability of an atom to attract an electron: The higher the EA, the stronger the attraction Elements with high EA tend to gain electrons, forming negative ions EA increases up in a group and to the left of a period Ionization Energy (IE) measures the ability of an atom to loose an electron from the outer shell The lower the IE, the easier it is to loose the electron Elements with low IE tend to loose electrons, forming positive ions IE increases up in a group and to the left of a period

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.2 Lewis Symbols and Formulas of Ionic Compounds Lewis Symbols represent the valence electrons as dots around the chemical symbol of the element Lewis Symbols are used to depict how elements can transfer or share electrons to form chemical bonds Ionic compounds result when metals react with nonmetals We can write the formula of the compound formed using simple rules: Determine the charges on each ions Balance positive and negative charges Write a formula with the metal first then the nonmetal

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Formation of Ions from Metals Metals will lose electrons to nonmetals to form ionic compounds Li gives 1 e - to F  Li + and F - Group 1A metals  ion 1+ Mg gives 1e - each to two F  Mg 2+ and two F - Group 2A metals  ion 2+ Al gives 1e - each to three F  Al 3+ and three F - Group 3A metals  ion 3+

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Ions from Nonmetal Ions In ionic compounds, nonmetals in 5A, 6A, and 7A gain electrons from metals Nonmetal add electrons to achieve the octet F, Cl, Br … gain 1e -  F -, Cl -, … Group 7A metals  ion 1- O, S … gain 2e -  O 2-, S 2- … Group 6A metals  ion 2- N, P gain 3e -  N 3-, P 3- Group 5A metals  ion 3-

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check A. Why does Ca form a Ca 2+ ion and Na form a Na + ion? B. Why does F form a F - ion and O form a O 2- ion?

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Formation of Ionic Compounds Attraction between + ions and - ions Electrons go from metals to nonmetals electron transfer metal + nonmetal ion + + ion – Electrons lost = Electrons gain

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Formulas of Ionic Compounds Formulas of ionic compounds are determined from the charges on the ions atoms ions     – Na  +  F :  Na + + : F :  NaF     sodium fluorine sodium fluoride formula Charge balance: = 0

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Writing a Formula Write the formula for the ionic compound that will form between Ba 2+ and Cl . Solution: 1. Balance charge with + and – ions 2. Write the positive ion of metal first, then the negative ion Ba 2+ Cl  Cl  3. Write the number of ions needed as subscripts BaCl 2

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Write the correct formula for the compounds containing the following ions: A. Na +, S 2- 1) NaS 2) Na 2 S3) NaS 2 B. Al 3+, Cl - 1) AlCl 3 2) AlCl 3) Al 3 Cl C. Mg 2+, N 3- 1) MgN 2) Mg 2 N 3 3) Mg 3 N 2

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.3 Naming Binary Ionic Compounds Binary compounds contain 2 different elements Name the metal first, then the nonmetal as -ide. Examples: NaClsodium chloride ZnI 2 zinc iodide Al 2 O 3 aluminum oxide

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Complete the names of the following binary compounds: Na 3 Nsodium ________________ KBrpotassium________________ Al 2 O 3 aluminum ________________ MgS_____________________________

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Transition Metals Many form 2 or more positive ions :

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Names of Variable Ions Use a roman number after the name of a metal that forms two or more ions: FeCl 2 (Fe 2+ ) iron (II) chloride CuCl(Cu + ) copper (I) chloride SnF 4 (Sn 4+ ) tin (IV) fluoride PbCl 2 (Pb 2+ )lead (II) chloride Fe 2 S 3 (Fe 3+ )iron (III) sulfide

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Complete the names of the following binary compounds with variable metal ions: FeBr 2 iron (_____) bromide Cu 2 Ocopper (_____) oxide SnCl 4 _____(___ ) _______________ Fe 2 O 3 _____(____)_______________ CuS_____(____)_______________

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Name the following compounds: A. CaO 1) calcium oxide2) calcium(I) oxide 3) calcium (II) oxide B. SnCl 4 1) tin tetrachloride2) tin(II) chloride 3) tin(IV) chloride C. Co 2 O 3 1) cobalt oxide 2) cobalt (III) oxide 3) cobalt trioxide

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.4 Polyatomic Ions Ions consisting of 2 or more atoms combined, with a total charge that is not zero Consider these ions as one unit, similar to the monoatomic ions NH 4 + ammoniumOH - hydroxide NO 3 - nitrateNO 2 - nitrite CO 3 2- ______________ HCO 3 - hydrogen carbonate (bicarbonate)

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.4 More Polyatomic Ions Sulfur SO 4 2- sulfate SO 3 2- sulfite HSO 4 - hydrogen sulfate HSO 3 - hydrogen sulfite Phosphorous PO 4 3- phosphatePO 3 3- ____________ HPO 4 2- _______________________________ H 2 PO 4 - dihydrogen phosphate

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Match each set with the correct name: A. Na 2 CO 3 1) magnesium sulfite MgSO 3 2) magnesium sulfate MgSO 4 3) sodium carbonate B.Ca(HCO 3 ) 2 1) calcium carbonate CaCO 3 2) calcium phosphate Ca 3 (PO 4 ) 2 3) calcium bicarbonate

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check A. aluminum nitrate 1) AlNO 3 2) Al(NO) 3 3) Al(NO 3 ) 3 B. copper(II) nitrate 1) CuNO 3 2) Cu(NO 3 ) 2 3) Cu 2 (NO 3 ) C. Iron (III) hydroxide 1) FeOH2) Fe 3 OH3) Fe(OH) 3 D. Tin(IV) hydroxide 1) Sn(OH) 4 2) Sn(OH) 2 3) Sn 4 (OH)

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.6 Covalent Bonds and There Nomenclature Covalent bonds form between two nonmetals Nonmetals have high electronegativity values Electrons are shared single bond shares one pair electrons double bond shares two pairs electrons triple bond shares three pairs electrons

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Indicate whether a bond between the following would be 1) Ionic2) covalent ____A. sodium and oxygen ____B. nitrogen and oxygen ____C. phosphorus and chlorine ____D. calcium and sulfur ____E. chlorine and bromine

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Covalent Bonds Two nonmetal atoms form a covalent bond because they have less energy after they bonded H  +  H H : H = H  H = H 2 Hydrogen atomsHydrogen molecule

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Diatomic Molecules Gases that exist as diatomic molecules are H 2, F 2, N 2, O 2, Cl 2, Br 2, I 2 octets          N  +  N   N ::: N   triple bond

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Use the name of the element to name the following diatomic molecules. H 2 hydrogen N 2 nitrogen Cl 2 _______________ O 2 _______________ I 2 _______________

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Covalent Bonds in NH 3 Bonding pairs H  H : N : H  Lone pair of electrons

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Naming Binary Covalent Compounds Two nonmetals Name each element End the last element in -ide Add prefixes to show more than 1 atom Prefixes mono1 tetra4 di2 penta5 tri3 hexa6

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Fill in the blanks to complete the following names of covalent compounds. CO carbon ______oxide CO 2 carbon _______________ PCl 3 phosphorus _______chloride CCl 4 carbon ________chloride N 2 O_____nitrogen _____oxide

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check A.P 2 O 5 1) phosphorus oxide 2) phosphorus pentoxide 3) diphosphorus pentoxide B.Cl 2 O 7 1) dichlorine heptoxide 2) dichlorine oxide 3) chlorine heptoxide C. Cl 2 1) chlorine 2) dichlorine 3) dichloride

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Electronegativity Electronegativity is defined as the ability of an atom in a molecule to attract electrons to itself. Electronegativity of an atom is related to its IE and EA. Electronegativity is a scale from 0.7 (Cs) to 4.0 (F)

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Bond Polarity In a covalent bond, electrons are shared. Sharing of electrons to form a covalent bond does not imply equal sharing of those electrons. There are some covalent bonds in which the electrons are located closer to one atom than the other. Unequal sharing of electrons results in polar covalent bonds. If the difference in electronegativity is large enough, an ionic bond is formed.

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Bond Polarity Nonpolar covalent bond Electrons are shared between atoms with the same electronegativity values. Difference = 0 Examples: N 2 Br 2 Polar covalent bond Electrons are shared between different nonmetal atoms Examples:O-Cl O-SN-Cl Ionic bond Electrons are transferred between metal and nonmetal atoms Examples: NaClKF

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Bond Polarity a) The electrons are shared equally between the two H atoms in H 2, which gives a nonpolar covalent bond. b) The electrons of the bond in HCl are pulled towards the Cl end of the molecule giving a polar covalent bond.

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Identify the type of bond between the following atoms A. K-N 1) nonpolar 2) polar3) ionic B. N-O 1) nonpolar2) polar3) ionic C. Cl-Cl 1) nonpolar2) polar3) ionic

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Drawing Lewis Structures add the valence electrons from all atoms. If ions, then add negative charge and subtract positive charge Identify the central atom Place the central atom in the center of the molecule and add all other atoms around it. Place one bond (two electrons) between each pair of atoms. Complete the octet for all atoms surrounding the central atom. Complete the octets for the central atom. Use double bonds if necessary.

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Draw the Lewis Structures of the following compounds: PCl 3 SCl 2 CO 2 NH 4 + IF 4 -

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds D Molecular Structures, VSEPR Lewis structures do not indicate the shapes of molecules; they simply show the # and types of bonds between atoms. The shape of a molecule is determined by its bond angles. In CCl 4, experimentally all Cl-C-Cl bond angles are 109.5°.

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.10 VSEPR In order to predict molecular shape, we assume the valence electrons repel each other. Therefore, the molecule adopts whichever 3D geometry minimizing this repulsion. We call this process Valence Shell Electron Pair Repulsion (VSEPR) theory.

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.10 VSEPR To determine the electron pair geometry: 1. draw the Lewis structure. 2. count the total number of electron domains around the central atom and arrange them in the way (geometry) that minimizes e - -e - repulsion. 3. multiple bonds (double or triple bond), and lone pairs count as one electron domain when predicting geometry # electron domain = # of atoms bonded to central atom + # of nonbonding pairs on the central atom.

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.10 Molecular Geometry (no lone pairs)

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.10 Molecular Geometry (with lone pairs) NH 3 has: 3 bonds + 1 lone pair = 4 electron domains 4 electron domains = Tetrahedral geometry Tetrahedral geometry with one missing bond = Trigonal Pyramidal geometry

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds 3.10 Molecular Geometry (with lone pairs)

Mounia ElamraniChapter 3 – Molecules and Chemical Bonds Learning Check Draw the 3-D structure of the following compounds: CCl 4 NI 3 OF 2