Ionic and Molecular Compounds Chemistry 100 What are

Ionic and Molecular Compounds Chemistry 100

What are Ions? An ion is an atom that has gained or lost one or more electrons. Ions always have a charge. • Metal atoms: lose electrons → positive ion • Nonmetal atoms: gain electrons → negative ion

Positive Ions: Loss of Electrons • Metals • The ionization energies are low • By a loss of their valence electrons • With the electron configuration of the nearest noble gas • That have fewer electrons than protons Group 1 A metals ion 1+ Group 2 A metals ion 2+ Group 3 A metals ion 3+ Mg Group 2 A lose of 2 e-

Negative Ions: Gain of Electrons Nonmetals The ionization energy is high By a gain of valence electrons With the electron configuration of the nearest noble gas • with fewer protons than electrons Group 5 A nonmetals ion Group 6 A nonmetals ion Group 7 A nonmetals ion • • Cl: Group 7 A gain e- to form octet -1 3− 2− 1−

Octet Rule An octet • is 8 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. loss e- (oxidized) +1 +2 gain e- (reduced) + 3 -4 -3 -2 -1 0

Ionic Charges from Group Numbers Group Charge Group 1 A 1+ Group 2 A 2+ Positive Charges Group 3 A 3+ Group 5 A Group 6 A Group 7 A 3− 2− 1− Negative Charges

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 • Total positive charge = Total negative charge o sum of the ionic charges is always zero - neutral • The symbol of the metal is written first, followed by the symbol of the nonmetal o metal symbol, nonmetal symbol

Ionic Compounds Na. Cl Is an Ionic Compound Formula for Mg. Cl 2

Study Check 1 Write the ionic formula of the compound formed with: A. Na+ and O 2− 1) Na. O 2) Na 2 O 3) Na. O 2 B. Al 3+ and Cl− 1) Al. Cl 3 2) Al. Cl 3) Al 3 Cl C. Mg 2+ and N 3− 1) Mg. N 2) Mg 2 N 3 3) Mg 3 N 2

Study Check 1 Answer A. Na+ and O 2− 2) Na 2 O check: 2 Na+ + O 2 - = 2(1+) + 1(2 -) = 0 B. Al 3+ and Cl− 1) Al. Cl 3 check: Al 3+ + 3 Cl- = 1(3+) + 3(1 -) = 0 C. Mg 2+ and N 3− 3) Mg 3 N 2 check: 3 Mg 2+ + 2 N 3 - = 3(2+) + 2(3 -) = 0

Naming and Writing Ionic Formulas • First name: Metal ion (cation) its element name • Second name: Nonmetal ion (anion) is first syllable of its element name + ide • Space separates the metal ion from the nonmetal

Study Check 2 Name the following ionic compound. A. Ca. O B. Li 2 S C. Mg. Cl 2

Study Check 2 Answers Write the name of the metal first and the name of the nonmetal second with the ending -ide. A. The name of Ca. O is calcium oxide. B. The name of Li 2 S is lithium sulfide. C. The name of Mg. Cl 2 is magnesium chloride.

Study Check 3 Write the formula and names for the compounds the following ions: Br− Na+ Al 3+ S 2 - N 3 -

Study Check 3 Answers Write the formula and names for the compounds the following ions: Br− S 2 - N 3 - Na+ Na. Br sodium bromide Na 2 S sodium sulfide Na 3 N sodium nitride Al 3+ Al. Br 3 aluminum bromide Al 2 S 3 aluminum sulfide Al. N aluminum nitride

Transition Metals With Variable Charge Transition metals form two or more positive ions (cations), except for Zn 2+, Cd 2+, and Ag+ Roman numeral is Cu 2+ copper(II) Cu+ copper(I) Fe 2+ iron(II) Fe 3+ iron(III) equal Pb 2+ Pb 4+ Cr 3+ Cr 6+ to ionic charge lead(II) lead(IV) chromium(III) chromium(VI)

Determination of Variable Charge Name: Sn. O 2 Name: Cu. O • The cation charge must balance the anion charge • Two O 2− ions are found, so 2 x (2−) = 4− • The Sn ion must have a 4+ charge • Correct name: tin(IV) oxide • The cation charge must balance the anion charge • One O 2− ions is found, so 1 x (2−) = 2− • The Cu ion must have a 2+ charge • Correct name: copper(II) oxide

Study Check 4 Name the following ionic compounds: A. B. C. D. Fe. S Zn. O Cu 3 N Ba. Br 2

Study Check 4 Answers Name the following ionic compounds: A. B. C. D. Fe. S Zn. O Cu 3 N Ba. Br 2 iron(II) sulfide zinc oxide copper(I) nitride barium bromide

Study Check 5 Write Chemical Formulas for the following compounds: A. Nickel(II) sulfide B. Zinc chloride C. Iron(III) oxide

Study Check 5 Answers A. Nickel(II) Sulfide Ni 2+ S 2− 1(2+) + 1(2−) = 0 B. Zinc Chloride Zn. Cl 2 Zn 2+ Cl− 1(2+) + 2(1−) = 0 Ni. S C. Iron(III) oxide Fe 2 O 3 The Roman numeral (III) indicates that the charge on the iron is 3+, Fe 3+ O 2− 2(3+) + 3(2−) = 0

Polyatomic Ions • Are a group of atoms that always stick together with a specific ionic charge • Often consist of a nonmetal such as phosphorus, sulfur, carbon, or nitrogen bonded to oxygen • Usually have a 1−, 2−, or 3− charge • Gained 1, 2, or 3 e- to complete octets • NH 4+ only positive charge • Names of most common polyatomic ions end in ate SO 42− sulfate PO 43− phosphate NO 3− nitrate

Naming Polyatomic Ions • The cation (usually a metal ion) is named first • Followed by the name of the polyatomic ion

Study Check 6 Name each of the following compounds containing polyatomic ions: A. Mg. SO 3 B. Mg. SO 4 C. Ca(Cl. O 3)2

Study Check 6 Answers Step 1 cation/anion Step 2 Name cation Step 3 Name anion Step 4 Name compound A. Mg. SO 3 Mg 2+ SO 32− magnesium sulfite B. Mg. SO 4 Mg 2+ SO 42− magnesium sulfate C. Ca(Cl. O 3)2 Ca 2+ Cl. O 3− calcium chlorate

Molecular Compounds: Sharing Electrons • When atoms share electrons to complete octets • Between nonmetal atoms from Groups 4 A, 5 A, 6 A, and 7 A • Covalent bonds result when two nonmetal atoms share a pair of electrons • Carbon atoms have 4 valence electrons, but want an octet

Names and Formulas of Molecular Compounds • Name the first nonmetal by its element name • Name the second nonmetal by changing the last part of its element name to -ide • Add prefixes to indicate the number of atoms (subscripts) • When vowels o and o or a and o appear together, the first vowel is omitted Example: CO 2 carbon dioxide NCl 3 nitrogen trichloride B 2 O 3 diboron trioxide

Lewis Structures for Molecules • The shared electrons are shown as two dots or a single line between atoms • Draw the electron-dot formula for methane, CH 4 • Electron-dot symbols for C and H • We need four hydrogen atoms to complete carbon’s octet

Double and Triple Covalent Bonds Atoms of carbon, oxygen, nitrogen, and sulfur A double bond: o occurs when atoms share two pairs of electrons o forms when there are not enough electrons to complete octets A triple bond: o occurs when atoms share three pairs of electrons o forms when there are not enough electrons to complete octets

Study Check 7 Determine if each compound is ionic (I) or covalent (C ), and write the formula. A. sulfur trioxide B. aluminum carbonate C. dinitrogen tetroxide D. copper(I) sulfate

Study Check 7 Answers Determine if each compound is ionic (I) or covalent (C ), and write the formula. A. sulfur trioxide (C) S, 3 O SO 3 B. aluminum carbonate (I) Al 3+, CO 32− Al 2(CO 3) 3 C. dinitrogen tetroxide (C) 2 N, 4 O N 2 O 4 D. copper(I) sulfate Cu+, SO 42− Cu 2 SO 4 (I)

Electronegativity • Indicates the attraction of an atom for the shared electrons in a chemical bond • Range from 0. 7 (low) to 4. 0 (high) • Elements with high electronegativity pull valance electrons strongly toward themselves • Increases from left to right going across a period on the periodic table • Nonmetals is high, with fluorine as the highest • Metals is low

Predicting Bond Types F O Cl N Br H C P S Se I highest electronegativity high electronegativity more electronegativity moderate level • Allows for predictions of polar vs nonpolar covalent bonds • Ionic bonds = metal and nonmetal atoms

Electronegativity and Bond Types

Study Check 8 Electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following: A. B. C. D. K-N N-O Cl-Cl H-Cl

Study Check 8 Answers A. B. C. D. K-N N-O Cl-Cl H-Cl Difference 2. 2 0. 5 0. 0 0. 9 Type of bond ionic (I) polar covalent (P) nonpolar covalent (NP) polar covalent (P)

Shapes of Molecules To 1. 2. 3. determine molecular shape: draw the electron-dot structure count the electron pairs around the central atom count the bonded atoms to determine shape 4 bonded atoms and 0 lone pairs = tetrahedral 3 bonded atoms and 1 lone pairs = pyramidal 2 bonded atoms and 2 lone pairs = bent

Attractive Forces and Melting Points • 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