Chem 20: Exam 2 Chapters 6

Positive Ions: Loss of Electrons

-Magnesium atoms in Group 2A(2) are neutral. They have 12 electrons and 12 protons, and they -will lose two electrons to have the same number of valence electrons as neon and a filled energy level. -form an ion with 10 electrons and 12 protons, and an ionic charge of 2+, Mg2+

Positive Ions: Metals lose Electrons

-Metals-Group 1A(1), group 2A(2), and Group 3A(13)- -have low ionization energies -readily lose one or more electrons to form ions with a positive charge. -Lose electrons until they have the same number of valence electrons as the nearest noble gas, usually eight valence electrons.

Naming Ionic Compounds: K2O

-Name the ionic compound K2O STEP 1: CATION: K+, from Group 1A(1) ANION: O2-, from Group 6A(16) STEP 2: The cation K+, is potassium STEP 3: The name of the anion is oxide. STEP 4: K2O is POTASSIUM OXIDE

Negative Ions: Nonmetals gain electrons

-Nonmetals-Group 5A(15), Group 6A(16), and Group 7A(17)- -have high ionization energies -readily gain one or more valence electrons to form ions with a negative charge in ionic compounds. -gain electrons until they have the same number of valence electrons as the nearest noble gas, usually eight valence electrons. -Chlorine atoms in Group 7A(17) are neutral. They have 17 electrons and 17 protons, and they -will gain one electron to have the same number of valence electrons as argon and a filled energy level. -form an ion with 18 electrons and 17 protons, and an ionic charge of 1-, Cl-

Rules of Resonance Structures

-Resonance structures must have the same connectivity -only electron positions can change -Resonance structures must have the same number of electrons. -Second row elements have a maximum of 8 electrons -bonding and nonbonding -third row can have expanded octet

6.4: Polyatomic Ions

-Sodium Chlorite, NaClO2, is used in the processing and bleaching of pulp from wood fibers and recycled cardboard. -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. -have a negative charge except for NH4+, ammonium, which has a positive charge.

Positive Ions: Loss of Electrons

-Sodium atoms in Group 1A(1) are neutral, with 11 electrons and 11 protons. They -lose one electron to have the same number of valence electrons as neon and a filled energy level. -will form an ion with 10 electrons, and 11 protons, and an ionic charge of 1+, Na+.

NaCl, an Ionic Compound

-Sodium chloride, is more commonly known as table salt. The magnification of NaCl crystals shows the arrangement of Na+ and Cl- ions in a NaCl crystal.

Formulas of Ionic Compounds

-The CHEMICAL FORMULA -represents the symbols and subscripts in the lowest whole-number ratio of atoms or ions -of ionic compounds is such that the sum of ion charges equals zero. -has charge balance -total positive charge=total negative charge

Electronegativity

-The ELECTRONEGATIVITY value of an element indicates the attraction of an atom for the shared electrons in a bond. ELECTRONEGATIVITY: -increases from left to right going across a period on the periodic table. -increases from the bottom to the top of the periodic table. -is high for the nonmetals, with fluorine as the highest. -is low for the metals.

VSEPR Theory

-The 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 the specific shape of a molecule is determined by the number of atoms attached to the central atom.

Variations in Bonding

-The difference in ELECTRONEGATIVITY values for two atoms can be used to predict the type of chemical bond. -If the electronegativity difference is between 0 and 0.4, the bond is nonpolar covalent. -If the electronegativity difference is between 0.5 and 1.8, the bond is polar covalent. -If the electronegativity difference is greater than 1.8, the bond is ionic.

6.6: Electronegativity and Bond Polarity

-The electronegativity values of representative elements in Group 1A(1) to Group 7A(17).

Writing Formulas from the name of an Ionic Compound

-The formula for an ionic compound is written from -The first part of the name that describes the metal ion. -the second part of the name that specifies the nonmetal ion. -Subscripts are added, to balance the charge.

6.5: Molecular Compounds: Sharing Electrons

-The number of covalent bonds that a nonmetal atom forms is usually equal to the number of electrons it needs to achieve a stable electron arrangement.

Sharing Electrons between Atoms of Different Elements

-The number of electrons a nonmetal atom shares and the number of covalent bonds it forms are usually equal to the number of electrons it needs to achieve a noble gas arrangement. Table 6.10 Typical Bonding Patterns of some Nonmetals

6.8 Attractive Forces in Compounds

-The protein shape is stabilized by attractive forces between functional groups of side chains (R groups) on the amino acids, causing it to twist and bend into a specific 3-D shape.

Writing Ionic Formulas from Ion Charges

-To balance ionic charges in an ionic compound, TOTAL POSITIVE CHARGE= TOTAL NEGATIVE CHARGE

Electron-Dot Formulas: Molecular Compounds

-To draw the electron-dot formula for a fluorine molecule, F2, -we start with the electron-dot symbols for each fluorine atom -each fluorine atom shares one electron to form a covalent bond, giving each fluorine an octet.

Metals with Variable Charge

-Transition metals except for Zn2+, Cd2+, and Ag+ form two or more positive ions (cations). -A ROMAN NUMERAL equal to the ion charge is placed in parentheses immediately after the metal name. Cu2+ Copper(II) Cu+ Copper(I) Fe2+ Iron(II) Fe3+ Iron(III) Pb2+ Lead(II) Pb4+ Lead(IV) Cr3+ Chromium(III) Cr6+ Chromium(VI)

Determination of Variable Charge

-Use the charge on the anion and charge balance to calculate the charge on the metal ion. MnF2 Mn charge +2 F- charge= 0 ? + 2(-1)=0 2+ + 2-=0 Manganese(II) fluoride

Ionic Charges from Group Numbers

-We can use the group numbers in the periodic table to determine the charges for the ions of the representative elements. Table 6.2 Examples:

Central Atoms with Four Electron Groups

In a molecule of NH3, -three electron groups include three bonds to H atoms and one is a lone pair around the central atom, N. -the repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109 degrees. -the shape with three bonds and a lone pair on the central atom is called TRIGONAL PYRAMIDAL.

Naming Compounds with Polyatomic Ions

-When naming ionic compounds containing polyatomic ions, -first write the positive ion, usually a metal -write the name of the polyatomic ion second -Recognizing polyatomic ions in a chemical formula helps to name the compound correctly. As with other ionic compounds, no prefixes are used. Na2SO4 FePO4 Al2(CO3)3 Sodium sulfate Iron(III) phosphate Aluminum- carbonate

Names and Formulas of Molecular Compounds

-When naming molecular 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.

Writing Formulas for 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: Magnesium ion Nitrate ion Mg2+ + NO3- NO3- ____________________________________________________________ (2+) + 2(1-) = 0 Mg2+ + 2NO3- = Mg(NO3)2

Exception to the Octet Rule

-While the octet rule is useful, there are exceptions. -Hydrogen requires just two electrons to form a noble gas arrangement. -Nonmetals P, S, Cl, Br, and I can form compounds with 10 or 12 valence electrons. -The S atom has an octet in many compounds, but in SF6, there are 12 valence electrons or six bonds to the sulfur atom.

Writing Formulas with Polyatomic Ions: Aluminum Bicarbonate

-Write the formula for aluminum bicarbonate. SOLUTION: STEP 1: Identify the cation and polyatomic ion(anion) CATION: Al3+ ANION: HCO3- STEP 2: Balance the charges Al3+ HCO3- HCO3- HCO3- _________________________________________________________ 1(3+) + 3(1-)= 0 STEP 3: Write the formula, cation first, using the subscripts from charge balance. Al(HCO3)3

Writing Formulas from the Name of an Ionic Compound: Iron(III) Chloride

-Write the formula for iron(III) chloride. SOLUTION: STEP 1: identify the cation and anion Type of Ion CATION ANION Name iron(III) chloride Group transition element Group 7A(17) Symbol of Ion Fe3+ Cl- STEP 2: Balance the Charges. Fe3+ Cl- Cl- Cl- __________________________________________________________ 1(3+) + 3(1-)= 0 STEP 3: Write the formula, cation first, using subscripts from the charge balance. FeCl3

Study Check: Select the correct formula for each compound. A) Aluminum nitrate B) Copper(III) nitrate C) Iron(III) hydroxide D) tin(IV) hydroxide

A) Al(NO3)3 B) Cu(NO3)2 C) Fe(OH)3 D) Sn(OH)4

Properties of Ionic Compounds

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.

6.2: Writing Formulas for Ionic Compounds

IONIC COMPOUNDS: consist of positive and negative charges held together by the strong electrical attractions between oppositely charged ions.

Central Atoms with Four Electron Groups

In a molecule of CH4, -four electron groups are attached to H atoms around the central atom, carbon. -the repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109 degrees. -the shape with four bonds on the central atom is called TETRAHEDRAL.

Central Groups with Two Electron Groups

In a molecule of CO2, -two electron groups are placed around the central atom, carbon. -the repulsion is minimized by placing the two groups on opposite sides of the carbon atom, giving the molecule a LINEAR arrangement with bond angles of 180 degrees. -the shape with two electron groups around the central atom is called LINEAR.

Central Atoms with Four Electron Groups

In a molecule of H2O, -two electron groups are attached to H atoms and two lone pairs are around the central atom, O. -the repulsion is minimized by placing the four groups at corners of a tetrahedron with bond angles of 109 degrees. -the shape with two bonds and two lone pairs on the central atom is called BENT.

Nonpolar Covalent Bonds

-A NONPOLAR COVALENT BOND: -occurs between nonmetals -is an equal or almost equal sharing of electrons by two bonding atoms. -has a very small electronegativity difference. EXAMPLES:

Polar Covalent Bonds

-A POLAR COVALENT BOND: -occurs between nonmetal atoms. -is an unequal sharing of electrons. -has a moderate electronegativity difference. EXAMPLES:

Dipoles and Bond Polarity

-A POLAR COVALENT BOND: becomes more polar as the difference in electronegativity increases. The separation of charges in a polar bond is called a DIPOLE. -The positive and negative ends of the dipole are located by using -the lowercase Greek letter delta with a positive or negative charge. -an arrow that points from the positive to the negative end of the dipole. EXAMPLES of DIPOLES IN POLAR COVALENT BONDS:

Compounds: Ionic or Covalent?

-A compound is usually -IONIC: if the first element in the formula or the name is a METAL or the polyatomic ion NH4+ -In K2O, K is a METAL. The compound is ionic: potassium oxide. -COVALENT: if the first element in the formula is a NONMETAL -In N2O, N is a NONMETAL. The compound is covalent: dinitrogen oxide.

Formation of a Hydrogen Molecule

-A hydrogen molecule, H2, -forms as the atoms move close and the positive charge of the nucleus attracts the electron of the other atom -has a shared pair of electrons that form a covalent bond to give each atom a noble gas arrangement of He to each H atom. -is more stable than individual H atoms.

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:

Ions: Transfer of Electrons

-Atoms form positively charged ions when they lose electrons and negatively charged ions when they gain electrons. -Ionic bonds are formed by the strong attractive forces between positive and negative ions.

Ionic and Covalent Bonds

-Chemical bonds are formed when atoms lose, gain, or share valence electrons to acquire an octet of eight valence electrons (octet rule). -Ionic Bonds: occur when the 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.

Diatomic Molecules

-Elements hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine exist as diatomic molecules. -THERE ARE SEVEN DIATOMIC MOLECULES: H2, N2, O2, F2, Cl2, Br2, and I2.

6.7: Shapes and Polarity of Molecules

-In a molecule of methane, CH4, the central C atom is bonded to four H atoms. The best geometry for minimal repulsion is tetrahedral, with bond angles of 109 degrees.

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.

Resonance

-In truth, the electrons that form the second C-O bond in the double bonds below do not always sit between that C and that O, but rather can move among the two oxygens and the carbon. -They are not localized; they are delocalized.

6.3: Naming Ionic Compounds

-Iodized salt contains KI, potassium iodide, to prevent iodine deficiency. -When naming an ionic compound, -the name of the metal is written first and is the same as the name of the element. -the name of the nonmetal is the -first syllable of the nonmetal name and ide ending and is written second. -a space is placed between the names of the metal and nonmetal ion.

Covalent Bonds

-MOLECULAR COMPOUNDS: Form when -atoms of two or more nonmetals share electrons and form a COVALENT BOND -valence electrons are shared by nonmetal atoms to achieve stability. -A molecule forms when two or more atoms share electrons.

Central Atoms with three Electron Groups: SO2 molecule

In a molecule of SO2, -three electron groups are placed around the central atom, S: 1. a single-bonded O atom 2. a double-bonded O atom 3. a lone pair of electrons -the repulsion is minimized by placing the three groups as far apart as possible. -the shape with two bonds and a lone pair on the central atom is called BENT.

Central Atoms with Three Electron Groups

In a molecule of formaldehyde, H2CO3, -three electron groups are placed around the central atom, carbon. -the repulsion is minimized by placing the three groups as far apart as possible, at bond angles of 120 degrees. -the shape with three electron groups around the central atom is called TRIGONAL PLANAR.

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 F, O, or N and a lone pair on F, O, or N. -Hydrogen bonds are the strongest force between molecules and play a major role in the shape of DNA.

Dipoles: Polar Molecules- H2O

In polar molecules such as H2O, -there are two lone pairs and two bonds around the central atom. -there are dipoles that do not cancel, making the molecule positive at one end and negative at the other end. -there is a partial negative charge on the central atom.

Dipoles: Polar Molecules-NH3

In polar molecules such as NH3, -there is one lone pair and three bonds around the central atom. -there are dipoles that do not cancel, making the molecule positive at one end and negative at the other end. -there is a partial negative charge on the central atom.

Naming Ionic Compounds with Variable Charge Metals: FeCl2

de-Name the ionic compound FeCl2 STEP 1: Determine the charge of the cation from the anion. STEP 2: Name the cation by its element name and use a Roman numeral in parentheses for the charge. -iron(II) STEP 3: Name the anion by using the first syllable of its element name followed by ide. -Chloride STEP 4: Write the name for the cation first and the anion second. -iron(II) chloride

Writing Lewis Structures

1. Find the sum of valence electrons of all atoms in the polyatomic ion or molecule. -If it is an anion, add one electron for each negative charge. -If it is a cation, subtract one electron for each positive charge. 2. The central atom is the least electronegative element that isn't hydrogen. Connect the outer atoms to it by single bonds 3. Fill the octets of the outer atoms. 4. Fill the octet of the central atom. 5. If you run out of electrons before the central atom has an octet..... ...form multiple bonds until it does.

Names of Polyatomic Ions

1. Names of most common polyatomic ions end in ate. SO4^2- sulfate PO4^3- phosphate NO3- nitrate 2. When a related ion has one fewer oxygen, its name ends in ite. SO3^2- sulfite PO3^3- phosphite NO2- nitrite 3. Exceptions to these rules are the following: CN- cyanide OH- hydroxide 4. Add an H+ to the polyatomic ion; add +1 to its charge. CO3^2- +H^+= HCO3- carbonate +H^+= bicarbonate or hydrogen carbonate SO4^2- +H^+= HSO4- sulfate +H^+= bisulfate or hydrogen sulfate 5. Halogens form four polyatomic ions with oxygen, each with a -1 charge. ClO4- perchlorate ClO3- chlorate ClO2- chlorite ClO- hypochlorite

Hints on Lewis Dot Structures

1. Octet rule is the most useful guideline. 2. Carbon forms 4 bonds. 3. Hydrogen typically forms ONE bond to other atoms. 4. When multiple bonds are forming, they are usually between C, N, P, O, or S. 5. Nonmetals can form single, double, and triple bonds, but not quadruple bonds. 6. ALWAYS ACCOUNT FOR SINGLE BONDS AND LONE PAIRS BEFORE FORMING MULTIPLE BONDS. 7. Look for resonance structures.

Guide to Naming Molecular Compounds

1. name the first nonmetal by its element name. 2. name the second nonmetal by using the first syllable of its element name followed by ide. 3. Add prefixes to indicate the number of atoms (subscripts).

Dispersion Forces

DISPERSION FORCES: -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.

Determination of Polarity

Determine if the molecule OF2 is polar or nonpolar. SOLUTION: 1. O-F: Oxygen is 3.5 and fluorine is 4.0, so the difference in electronegativity is 0.5, and the bonds are polar covalent. 2. If the bonds are polar covalent, draw the electron-dot formula and determine if the dipoles cancel.

Melting Points and Attractive Forces

Melting points of compounds -are related to the strength of attractive forces between molecules or compounds. -are lower as a result of weak forces such as dispersion forces. -are higher as a result of stronger attractive forces such as hydrogen bonding. -are highest in ionic compounds as a result of the strong attractive forces between ions in the compound.

Dipoles: Nonpolar Molecules

NONPOLAR MOLECULES: -such as H2, Cl2, and O2 are nonpolar because they contain nonpolar bonds. -with polar bonds can be nonpolar if the dipoles in the polar bonds cancel each other in a symmetrical arrangement such as in CO2 and CCl4.

Dipoles: Polar Molecules

POLAR MOLECULES: such as HCl are polar because -one end of the molecule is more negatively charged than the other. -the polar bonds in the molecule do not cancel each other. -the electrons are shared unequally in the polar covalent bond.

Resonance Structures and Isomers

RESONANCE STRUCTURES: Two or more equivalent Lewis structures for a molecule or ion that are created by changing only the positions of the electrons, in which the actual species is an average of the resonance structures. RESONANCE HYBRID: A species that has an actual structure that is the average of two or more Lewis structures. ISOMERS: Two compounds having the same molecular formulas but have different structural formulas and different physical and chemical properties.

Study Check: Write the ionic formula of the compound formed with Ba2+ and Cl- ions.

SOLUTION: 1. Write the symbols of the ions: Ba2+ Cl- 2. Balance the charges: 1(2+) + 2(1-) = 0 3. Writing the cation first and the anion second gives the formula BaCl2

Active Exercise: Draw the Lewis diagram for the hydrogen carbonate ion, HCO-3

SOLUTION: -1(H)+4(C) +3 x 6(O) + 1(charge)= 24 -Carbon is the central atom, since carbon is less electronegative than oxygen and hydrogen is always a terminal atom. -All atoms check -Hydrogen has one electron pair, and all other atoms have four. -Enclosing Lewis diagram in square brackets indicating the charge.

Active Exercise: Draw the Lewis diagram for ammonia, NH3.

SOLUTION: -5(N) +3 x 1(H) = 8 -Since a hydrogen atom is never central, the nitrogen atom must be central. -Eight electrons in the tentative diagram match the number available. The diagram is complete.

Predict the Molecular Shape of H2S

SOLUTION: STEP 1: Draw the electron-dot formula. STEP 2: arrange electron groups around the central atom to minimize repulsion. -To minimize repulsion, electron groups have a tetrahedral arrangement. STEP 3: use atoms bonded to central atom to determine the shape. -With two bonds and two lone pairs, the shape is bent.

Writing Formulas for Molecular Compounds: Diboron Trioxide Write the formula for the covalent compound diboron trioxide.

SOLUTION: STEP 1: Write the symbols in order of the elements in the name. -The first nonmetal is boron (B) and the second nonmetal is oxygen (O). -BO STEP 2: Write any prefixes as subscripts. -The prefix di in diboron indicates there are two boron atoms and is shown as a subscript after B. The prefix tri in trioxide indicates there are three oxygen atoms and is shown as a subscript after O. -B2O3

Naming Molecular Compounds: NCl3 Name the covalent compound NCl3

SOLUTION: Symbol of element: N Cl Name: nitrogen chlorine (Cl) Subscript: 1 3 Prefix: none tri STEP 1: Name the first nonmetal by its element name. -The first nonmetal (N) is nitrogen. STEP 2: Name the second element by using the first syllable of its name followed by ide. -The second nonmetal (Cl) is chloride. STEP 3: Add prefixes to indicate number of atoms. -Because there is one nitrogen atom, no prefix is needed. The subscript 3 for the Cl atom is shown as the prefix tri. NCl3, nitrogen trichloride

Drawing a Lewis Diagram

STEP 1: Count the total number of valence electrons -Adjust for charge on ions STEP 2: Place the least electronegative atom(s) in the center of the molecule STEP 3: Draw the tentative diagram -join atoms by single bonds -add unshared pairs to complete octet around all atoms except hydrogen. STEP 4: Calculate number of valence electrons in tentative diagram and compare with actual. -If diagram has more, remove lone pair from central and terminal atoms and replace with additional bonding pair. -Repeat process till the number matches. STEP 5: Check the Lewis Diagram -Hydrogen atom must have only one bond and all other atoms should have total four electron pairs.

Guide to Determination of Polarity

STEP 1: Determine if the bonds are polar covalent or nonpolar covalent. STEP 2: If the bonds are polar covalent, draw the electron-dot formula and determine if the dipoles cancel.

Guide to Naming Compounds with Polyatomic Ions

STEP 1: Identify cation and polyatomic ion(anion) STEP 2: Name cation, using a Roman numeral, if needed STEP 3: Name polyatomic ion STEP 4: Write name for compound, cation first, and polyatomic ion second

Guide to Writing Formulas from the Name of an Ionic Compound

STEP 1: Identify the cation and anion. STEP 2: Balance the charges. STEP 3: Write the formula, cation first, using subscripts from the charge balance.

Writing Formulas from Names of Molecular Compounds

STEP 1: Write the symbols in the order of the elements in the name. STEP 2: Write any prefixes as subscripts.

Guide to Predicting Molecular Shape

STEP 1: draw the electron-dot formula STEP 2: arrange the electron groups around the central atom to minimize repulsion. STEP 3: use the atoms bonded to the central atom to determine the molecular shape.

Guide to Naming Ionic Compounds

STEP 1: identify the cation and anion. STEP 2: name the cation by its element name. STEP 3: name the anion by using the first syllable of its element name followed by ide. STEP 4: write the name for the cation first and the name of the anion second.

Guide to Writing Formulas with Polyatomic Ions

STEP 1: identify the cation and polyatomic ion (anion) STEP 2: Balance the charges STEP 3: Write the formula, cation first, using the subscripts from charge balance.