Chapter 4 Compounds and Their Bonds

Chapter 4 Compounds and Their Bonds
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Ionic and Covalent Bonds
Atoms that are not noble gases form octets to become more stable by losing, gaining, or sharing valence electrons by forming ionic bonds or covalent bonds Ionic bonds occur when atoms of one element lose valence electrons and the atoms of another element gain valence electrons. Covalent bonds occur when nonmetal atoms share electrons to attain a noble gas arrangement. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

The Octet Rule An octet is eight valence electrons
is associated with the stability of the noble gases (except He) The octet rule states that elements gain or lose electrons and become ions to attain noble gas arrangement. valence electrons He Ne 2, 8 8 Ar 2, 8, 8 8 Kr 2, 8, 14, 8 8 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Ionic and Covalent Bonds

Metals Form Positive Ions
by a loss of their valence electrons with the electron configuration of the nearest noble gas that have fewer electrons than protons Group 1A metals ion 1+ Group 2A metals ion 2+ Group 3A metals ion 3+ Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Formation of Magnesium Ion, Mg2+

Nonmetals Form Negative Ions
by a gain of valence electrons with the electron configuration of the nearest noble gas with fewer protons than electrons Group 5A nonmetals ion 3− Group 6A nonmetals ion 2− Group 7A nonmetals ion 1− Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Formation of Chloride Ion, Cl−

Formulas and Names of Common Ions

Ionic Charges from Group Numbers

Properties of Ionic Compounds
consist of positive and negative ions have attractions called ionic bonds between positively and negatively charged ions have high melting points are solid at room temperature Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Formulas of Ionic Compounds
An ionic formula consists of positively and negatively charged ions is neutral has charge balance total positive charge = total negative charge The symbol of the metal is written first, followed by the symbol of the nonmetal. metal symbol, nonmetal symbol Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Subscripts in Formulas

Writing Ionic Formulas from Ion Charges
Subscripts in ionic compound represent the number of positive and negative ions that give an overall charge of zero. total positive charge + total negative charge = 0 therefore, total positive charge = total negative charge Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Charge Balance for Na2S In Na2S
2 Na atoms lose their valence electrons to become Na+ ions an S atom gains 2 electrons to become an S2− ion subscripts indicate number of each ions to give charge balance total positive charge = total negative charge Na+ Na+ + S2− = Na2S 2(1+) = 2− Write the symbol of the metal first followed by a subscript of 2 and then the symbol of the nonmetal. 2 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Writing an Ionic Formula for Na3N
Charge balance is used to write the formula for sodium nitride, a compound containing Na+ and N3−. Na+ 3 Na N3− = Na3N 3(+1) (3−) = 0 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Naming and Writing Ionic Formulas
4.3 Naming and Writing Ionic Formulas

Names of Some Ionic Compounds

Naming Ionic Compounds

Learning Check Write the names of the following compounds.
A. CaO ___________ B. Al2O3 ___________ C. MgCl2 ___________

Learning Check Write the formulas and names for compounds of the following ions: Br− S2− N3− Na+ Al3+

Metals That Form More Than One Cation
Transition metals except for Zn2+, Cd2+, and Ag+ form two or more positive ions (cations). We use a Roman numeral to identify ionic charge. Cu2+ copper(II) Pb2+ lead(II) Cu+ copper(I) Pb4+ lead(IV) Fe2+ iron(II) Cr3+ chromium(III) Fe3+ iron(III) Cr6+ chromium(VI) Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Metals with Variable Charge

Metals Form Positive Ions; Nonmetals Form Negative Ions

Naming Compounds with Variable Charge Metals

Learning Check Name the following ionic compounds containing metals that form two kinds of positive ions: A. Fe2O3 B. SnCl2

Writing Formulas from the Name of an Ionic Compound

Formula for Chromium(III) Bromide
29 Step 1 Identify the cation and anion. The Roman numeral (III) indicates that the charge on the chromium ion is 3+, Cr3+. Step 2 Balance the charges. Cr3+ Br− Br− 1(3+) + 3(1−) = 0 Step 3 Write formula, cation first, using subscripts from the charge balance CrBr3

Learning Check Write chemical formulas for the following compounds:
A. Nickel(II) sulfide B. Zinc chloride C. Iron(III) oxide

4.4 Polyatomic Ions

Polyatomic Ions Polyatomic Ions
are a group of atoms with an overall charge often consist of a nonmetal such as phosphorus, sulfur, carbon, or nitrogen and oxygen usually have a 1−, 2−, or 3− charge

Names of Polyatomic Ions
1. Names of most common polyatomic ions end in ate. SO42− sulfate PO43− phosphate NO3− nitrate 2. When a related ion has one less oxygen, its name ends in ite. SO32− sulfite PO33− phosphite NO2− nitrite

3. Exceptions to these rules are: CN− cyanide OH− hydroxide NH4+ ammonium 4. Add an H+ and reduce negative charge. CO32− + H+ = HCO3− carbonate + H+ = bicarbonate or hydrogen carbonate SO42− + H+ = HSO4− sulfate + H+ = bisulfate or hydrogen sulfate Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

5. Halogens form 4 polyatomic ions with oxygen each have a 1 charge. ClO4− perchlorate ClO3− chlorate ClO2− chlorite ClO− hypochlorite

Compounds Containing Polyatomic Ions
When writing formulas for ionic compounds containing polyatomic ions, we use the same rules of charge balance as those for simple ionic compounds. Consider the formula for magnesium nitrate: Mg NO3− NO3− (2+) (1−) = 0 Mg NO3− = Mg(NO3)2 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Select the correct formula for each.
A. aluminum nitrate 1) AlNO3 2) Al(NO)3 3) Al(NO3)3 B. copper(II) nitrate 1) CuNO3 2) Cu(NO3)2 3) Cu2(NO3) C. iron(III) hydroxide 1) FeOH 2) Fe3OH 3) Fe(OH)3 D. tin(IV) hydroxide 1) Sn(OH)4 2) Sn(OH)2 3) Sn4(OH)

Guide to Naming Ionic Compounds with Polyatomic Ions

Learning Check Name each of the following compounds containing polyatomic ions. A. MgSO3 B. MgSO4 C. Ca(ClO3)2

Learning Check Name each of the following compounds: A. Fe2(SO4)3
B. Ba3(PO3)2 C. PbCO3

Covalent Compounds and Their Names
4.5 Covalent Compounds and Their Names

Covalent Bonds Covalent compounds form
when atoms share electrons to complete octets between nonmetal atoms from Groups 4A, 5A, 6A, and 7A Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Formation of Octets in Molecules – F2
In a fluorine, F2,, molecule, each F atom shares one electron to attain an octet. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Writing Electron-Dot Formulas
To draw the electron-dot formula for methane, CH4, we start with the electron-dot symbols for carbon and hydrogen we need four hydrogen atoms to complete carbon’s octet Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Double and Triple Covalent Bonds
A double bond: occurs when atoms share two pairs of electrons forms when there are not enough electrons to complete octets A triple bond: occurs when atoms share three pairs of electrons Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Guide to Drawing Electron-Dot Formulas

Electron-Dot Formulas for Some Covalent Compounds – CO2
Step 1 Determine the arrangement of atoms. O C O Step 2 Determine the total number of valence electrons. C 2(O) = CO2 4e− + 2(6−) = 16e− Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Electron-Dot Formulas for Some Covalent Compounds – CO2
Step 3 Attach each bonded atom to the central atom with a pair of electrons. Step 4 Place the remaining electrons using single or multiple bonds to complete octets. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Triple Bond – N2 In a nitrogen molecule, N2,
each N atom shares three electrons to gain an octet the multiple bond formed is called a triple bond the name is the same as the element Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Names and Formulas of Covalent Compounds
When naming covalent compounds: the first nonmetal in the formula is named by its element name the second nonmetal is named by using the first syllable of its name followed by ide if a subscript is used in the formula a prefix is used in front of its name when vowels o and o or a and o appear together, the first vowel is omitted Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Guide to Naming Covalent Compounds

Prefixes Used in Naming Covalent Compounds

Learning Check Select the correct name for each compound.
A. SiCl4 1) silicon chloride 2) tetrasilicon chloride 3) silicon tetrachloride B. P2O5 1) phosphorus oxide 2) phosphorus pentoxide 3) diphosphorus pentoxide C. Cl2O7 1) dichlorine heptoxide 2) dichlorine oxide 3) chlorine heptoxide Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Write the name of each covalent compound. A. CO B. NO2
C. PF3 D. CCl4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Writing Formulas for Covalent Compounds

Learning Check Write the correct formula for each of the following:
A. phosphorus pentachloride B. dinitrogen trioxide C. sulfur hexafluoride Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Summary to Naming Simple Compounds

Learning Check Identify each compound as ionic or covalent, and give its correct name. A. SO3 B. BaCl2 C. (NH4)3PO3 D. Cu2CO3 E. N2O4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Study Tip: Ionic or Covalent
A compound is ionic if the first element in the formula or the name is a metal or the polyatomic ion NH4+ K2O K is a metal; compound is ionic; potassium oxide covalent if the first element in the formula or the name is a nonmetal N2O N is a nonmetal; compound is covalent; dinitrogen oxide Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Identify each compound as ionic or covalent and give its correct name. A. SO3 covalent – sulfur trioxide B. BaCl2 ionic – barium chloride C. (NH4)3PO3 ionic – ammonium phosphite D. Cu2CO ionic – copper(I) carbonate E. N2O4 covalent – dinitrogen tetroxide Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Electronegativity The electronegativity value
of an element indicates the attraction of an atom for the shared electrons in a bond increases from left to right going across a period on the periodic table is high for the nonmetals, with fluorine as the highest is low for the metals Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Electronegativity and the Periodic Table

Comparing Ionic, Polar, and Nonpolar Covalent Bonds

Comparing Nonpolar and Polar Bonds
In the nonpolar covalent bond of H2, electrons are shared equally. In the polar covalent bond of HCl, electrons are shared unequally. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Nonpolar Covalent Bonds
A nonpolar covalent bond occurs between nonmetals is an equal or almost equal sharing of electrons has a very small electronegativity difference Examples: Electronegativity Atoms Difference Type of Bond N-N  3.0 = 0.0 Nonpolar covalent Cl-Br 3.0  2.8 = 0.2 Nonpolar covalent H-Si 2.1  1.8 = 0.3 Nonpolar covalent Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Polar Covalent Bonds A polar covalent bond
occurs between nonmetal atoms is an unequal sharing of electrons has a moderate electronegativity difference Examples: Electronegativity Atoms Difference Type of Bond O-Cl  3.0 = 0.5 Polar covalent Cl-C 3.0  2.5 = 0.5 Polar covalent O-S  2.5 = 1.0 Polar covalent Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Ionic Bonds An ionic bond occurs between metal and nonmetal ions
is a result of electron transfer has a large electronegativity difference (1.8 or more) Examples: Electronegativity Atoms Difference Type of Bond Cl-K – 0.8 = 2.2 Ionic N-Na 3.0 – 0.9 = 2.1 Ionic S-Cs 2.5 – 0.7 = 1.8 Ionic Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check Use the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following: A. K-N B. N-O C. Cl-Cl D. H-Cl Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution Use the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following: Difference Type of bond A. K-N ionic (I) B. N-O polar covalent (P) C. Cl-Cl 0.0 nonpolar covalent (NP) D. H-Cl 0.9 polar covalent (P)

VSEPR Theory Valence Shell Electron-Pair Repulsion Theory (VSEPR)
describes the orientation of electron groups around the central atom states that electron groups are arranged as far apart as possible around the central atom states that specific shape of a molecule is determined by the number of atoms attached to the central atom Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Central Atom with Two Electron Groups
In a molecule of BeCl2 there are only two electron groups around the central atom, Be, which is an exception to octet rule repulsion is minimized by placing the two groups on opposite sides of the Be atom, giving this a linear arrangement with bond angles of 180° the shape with two electron groups around the central atom is linear Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Central Atom with Three Electron Groups
In a molecule of BF3 there are only three electron groups around the central atom, B, which is an exception to octet rule repulsion is minimized by placing the three groups as far apart as possible at bond angles of 120° the shape with three electron groups around the central atom is trigonal planar Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Central Atom with Three Electron Groups
In a molecule of SO2 there are three electron groups around the central atom S: a single-bonded O atom, a double-bonded O atom, and a lone pair of electrons repulsion is minimized by placing the three groups as far apart as possible since one group is a lone pair, the shape is determined by the two O atoms bonded to S, giving the molecule its bent shape Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Central Atom with Four Electron Groups
In a molecule of CH4 there are four electron groups attached to H atoms around the central atom, C repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109° the shape with four bonds on the central atom is called tetrahedral Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

In a molecule of NH3 there are three electron groups attached to H atoms and a lone pair around the central atom, N repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109° the shape with three bonds on the central atom is called trigonal pyrimidal Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

In a molecule of H2O there are two electron groups attached to H atoms and two lone pairs around the central atom, O repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109° the shape with two bonds on the central atom is called bent Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Molecular Shapes for Molecules

Guide to Predicting Molecular Shape

Learning Check State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. A. PF3 B. H2S C. CCl4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. Step 1 Draw the electron-dot formula. A. PF3 B. H2S C. CCl4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution State the number of electron groups, and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. Step 2 Arrange electron groups around the central atom to minimize repulsion. A. PF3 To minimize repulsion electron groups have a tetrahedral arrangement. B. H2S To minimize repulsion electron groups have a tetrahedral arrangement. C. CCl4 To minimize repulsion electron groups have a tetrahedral arrangement. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. Step 3 Use the atoms bonded to the central atom to determine the molecular shape. A. PF3 With three bonds and one lone pair, the shape is trigonal planar. B. H2S With two bonds and two lone pairs, the shape is bent. C. CCl4 With four bonds the shape is tetrahedral.

Nonpolar Molecules Nonpolar molecules
such as H2, Cl2, and O2 are nonpolar because they contain nonpolar bonds with polar bonds such as CO2 can be nonpolar if the polar bonds cancel each other in a symmetrical arrangement dipoles cancel out, which makes the molecule nonpolar Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Polar Molecules Polar molecules such as HCl are polar
because one end of the molecule is more negatively charged than the other when polar bonds in the molecule do not cancel each other because the electrons are shared unequally in the polar covalent bond Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Polar Molecules In polar molecules
with three or more atoms, the shape of the molecule determines whether the dipoles cancel or not there are often lone pairs around the central atom such as H2O, the dipoles do not cancel, making the molecule positive at one end and negative at the other end such as H2O, there is a dipole on the central atom Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Dipole-Dipole Attractions and Hydrogen Bonds
In covalent compounds, polar molecules exert attractive forces called dipole-dipole attractions form strong dipole attractions called hydrogen bonds between hydrogen atoms bonded to very electronegative atoms of F, O, or N Hydrogen bonds are the strongest force between molecules and play a major role in the shape of DNA. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Dispersion Forces Dispersion forces are
weak attractions between nonpolar molecules caused by temporary dipoles that develop when molecules bump into each other weak, but make it possible for nonpolar molecules to form liquids and solids Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Melting Points and Attractive Forces
of compounds are related to the strength of attractive forces between molecules or compounds are lower due to weak forces such as dispersion forces are higher due to stronger attractive forces such as hydrogen bonding are highest in ionic compounds due to the strong attractive forces between ions in the compound Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Melting Points of Selected Substances

Chapter 4 Compounds and Their Bonds

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