ATOMIC ORBITAL DIAGRAMS AND ELECTRON CONFIGURATION.

ATOMIC ORBITAL DIAGRAMS AND ELECTRON CONFIGURATION

CHEMICAL BONDS, MOLECULES, AND COMPOUNDS

Lewis Dot Symbols Show Valence Electrons - Nobel Gas Electron Configuration – Octet Rule

The Octet Rule for Some Diatomic Gases (H 2, N 2, O 2, F 2 ) Example of F 2 Single covalent bond consisting of 2 shared electrons By sharing, each F gets a stable octet of 8 electrons Same as neon, the noble gasimmediately following F (4.2.1)

The Octet Rule for Chemical Compounds Atoms attempt to attain a noble gas electron configuration in compounds Figure 4.3. Stable EC of noble gas in the ionic compound NaCl acquired when the Na atom loses an electron and the Cl atom gains an electron

Carbon tends to share electrons to form covalent bonds with almost all other elements as shown for methane gas in Figure 4.4

IONIC BONDING An ion is an atom or group of atoms having an unequal number of electrons and protons, therefore, a net electrical charge Cation has a positive charge Anion has a negative charge The most stable cations and anions have the same number of electrons as a noble gas – They are isoelectronic to a noble gas. An ionic compound contains both cations and anions Held together by ionic bonds

Table 4.1. Ions with Neon and Argon Electron Configurations ElectronElectronsIon electron Elementconfigurationgained/lostIonconfiguration Isoelectronic with noble gas EC

Figure 4.5. Representation of the Structure of Ionic NaCl Nearest ions to each Cl - ion (arrow) are 6 Na + ions and nearest ions to each Na + ion are 6 Cl - ions

Lattice Energy Lattice energy is the energy required to separate all the ions in a crystalline lattice The lattice energy of NaCl is +785 kJ/mol

Ion Size Smaller ions get closer increasing lattice energy Cations smaller than corresponding neutral atoms Anions are larger than corresponding neutral atoms Cations decrease in size across a period with increasing + charge Anions increase in size across a period with increasing - charge See trends in ion size in Figure 4.7

Relative Diameters of Some Ions from Single Atoms Diameters in picometers, pm

Formation of Some Example Ionic Compounds Al 2 O 3

CHEMICAL FORMULAS OF COMPOUNDS Figure 4.16. Example of Calcium Phosphate

CHEMICAL FORMULAS OF IONIC COMPOUNDS

Naming Cations Elements of Groups 1A, 2A, and Al form only one type of cation; the name of the cation is the name of the metal followed by the word “ion” “Always ions”

Naming Cations For cations derived from other metals, –use Roman numerals to show charge Example: Iron(II) is Fe 2+ Iron (III) is Fe 3+

Naming Cations Do Not Use

Naming Anions For monatomic (containing only one atom) anions, add “ide” to the end –here are the monatomic anions we deal with most often

Polyatomic Ions –common names, where still widely used, are given in parentheses

Forming Chemical Bonds According to the Lewis model ionic bond –an atom may lose or gain enough electrons to acquire a filled valence shell and become an ion. An ionic bond is the result of the force of attraction between a cation and an anion. covalentbond –an atom may share electrons with one or more other atoms to acquire a filled valence shell. A covalent bond is the result of the force of attraction between two atoms that share one or more pairs of electrons.

Forming an Ionic Bond In forming sodium chloride, NaCl –we use a single-headed curved arrow to show this transfer of one electron

Formulas of Ionic Compounds The total number of positive charges must equal the total number of negative charges –lithium ion and bromide ion form LiBr –barium ion and iodide ion form BaI 2 –aluminum ion and sulfide ion form Al 2 S 3 –sodium ion and bicarbonate ion form NaHCO 3 –potassium ion and phosphate ion form K 3 PO 4

Naming Ionic Compounds Binary ionic compounds –the name of metal from which the positive ion is formed followed by the name of the negative ion; subscripts are ignored –AlCl 3 is aluminum chloride –LiBr is lithium bromide –Ag 2 S is silver sulfide –MgO is magnesium oxide –KCl is potassium chloride

Naming Ionic Compounds Binary ionic compounds of metals that form two different cations –for systematic names, use Roman numerals to show charge on the metal ion; for common names (not used in this class), use the -ous, -ic suffixes –CuO is copper(II) oxide; cupric oxide –Cu 2 O is copper(I) oxide; cuprous oxide –FeO is iron(II) oxide; ferrous oxide –Fe 2 O 3 is iron(III) oxide; ferric oxide

Naming Ionic Compounds Ionic compounds that contain polyatomic ions –name the positive ion first followed by the name of the negative ion –NaNO 3 is sodium nitrate –CaCO 3 is calcium carbonate –NaH 2 PO 4 is sodium dihydrogen phosphate –NH 4 OH is ammonium hydroxide –FeCO 3 is iron(II) carbonate; ferrous carbonate –Fe 2 (CO 3 ) 3 is iron(III) carbonate; ferric carbonate –CuSO 4 is copper(II) sulfate; cupric sulfate

FUNDAMENTALS OF COVALENT BONDING

Forming a Covalent Bond A covalent bond is formed by sharing one or more pairs of electrons –the pair of electrons is shared by both atoms and, at the same time, fills the valence shell of each atom –example: –example: in forming H 2, each hydrogen contributes one electron to the single bond

COVALENT BONDING Figure 4.9. Energy Relationships in Covalent Bonds, H-H

COVALENT BONDS IN COMPOUNDS Covalent bonding of H Atoms to C and N Atoms

Lewis Structures

Covalent Bonds in H 2 O and HF

Compounds of Si, P, S, and Cl with H

Compounds of air pollution CO, NO 2, O 3, SO 2

Compounds that do not Conform to the Octet Rule

SOME OTHER ASPECTS OF COVALENT BONDING Single covalent bonds consist of 2 shared electrons Double covalent bonds consist of 4 shared electrons Triple covalent bonds consist of 6 shared electrons

Lengths and Strengths of Covalent Bonds Bond type:SingleDoubleTriple in C 2 H 6 in C 2 H 4 in C 2 H 2 Bond length:154 pm134 pm120 pm (pm stands for picometers) Bond strength:348 kJ/mol614 kJ/mol839 kJ/mol Stronger, shorter bonds Chemical bonds may absorb infrared radiation Higher frequencies for shorter, stronger bonds Representation of a bond as a spring, Figure 4.14.

Electronegativity and Covalent Bonding Electronegativity refers to the ability of a bonded atom to attract electrons to itself

Sharing Electrons — Unequally For the HCl molecule, the large Cl nucleus has a relatively much stronger attraction for the electrons in the bond Cl end of the molecule has more of a negative charge Polar covalent bond Nonpolar covalent bonds are formed between atoms of the same element or atoms with similar electronegativies H:H Nonpolar bond

Molecular Compounds Molecular compound:Molecular compound: a compound in which all bonds are covalent Naming binary molecular compounds –the less electronegative element is named first –prefixes “di-”, tri-”, etc. are used to show the number of atoms of each element; the prefix “mono-” is omitted when it refers to the first atom, and is rarely used with the second atom. Exception: carbon monoxide –NO is nitrogen oxide (nitric oxide) –SF 2 is sulfur difluoride –N 2 O is dinitrogen oxide (laughing gas)