Chemical Bonding

Chemical bonds _____________________ that hold atoms together in compounds. The electrons involved in bonding are usually those in the _____________________ (valence) shell. Most elements in compounds want to gain _____________________ configuration. They will do so by either _________________or _________________ electrons (_____________________ compounds) or by __________________ electrons (_____________________ compounds)

Ionic and Covalent bonding Chemical bonds are classified into two types: _____________________results from electrostatic attractions among ions; which are formed by the transfer of one or more electrons from one atom to another. (metals low χ with nonmetals high χ) (χ = electronegativity) _____________________ results from sharing one or more electron pairs between two atoms. (nonmetals only similar χ )

Comparison of Ionic & Covalent Compounds Melting Pt Solubility (polar solvents) (nonpolar solvents) Conductivity (molten & aqueous solutions) High Low Soluble Insoluble Insoluble Soluble High Low

Ionic vs. Covalent bonding 2 extremes in bonding _________________ covalent bonds electrons equally shared by the atoms _________________ ionic bonds electrons are completely lost or gained by one of the atoms most compounds fall somewhere _________________ these two extremes

Terminology # of atoms in the molecule _____________________ = 1 atom Ex. He _____________________ = 2 atoms Ex. O2 _____________________ = 3 atoms Ex. O3 _____________________ = many Ex. H2SO4 or S8 _____________________ : the mlcl is composed of only 1 kind of atom: O2, H2, P4 _____________________ : the mlcl is made up of more than 1 kind of atom: H2O

Lewis Dot Representations of Atoms or Lewis dot formulas, a convenient bookkeeping method for ____________________ (electrons that are transferred or involved in chemical bonding) Only the electrons in the outermost s and p orbitals are shown as dots.

elements in the same group have same Lewis dot structures For groups _____________________, the group number equals the # of _____________________ electrons Valence electrons determine the chemical and physical properties of the elements as well as the kinds of __________________ they form.

Ionic Bonding metals react with nonmetals to form ionic compounds _____________________ or positive (+) ions (metals) atoms have lost 1 or more electrons _____________________ or negative (-) ions (nonmetals) atoms have gained 1 or more electrons

We can use Lewis formulas to represent the neutral atoms and the ions they form.

underlying reasons for LiF formation 1s 2s 2p Li ­¯ ­ F ­¯ ­¯ ­ ¯ ­¯­ becomes Li+ ­¯ [He] F- ­¯ ­¯ ­¯ ­¯ ­¯ [Ne]

Li+ ions contain two electrons F- ions contain ten electrons same number as helium F- ions contain ten electrons same number as neon Li+ ions are isoelectronic with _____________________ F- ions are isoelectronic with _____________________ *Isoelectronic species contain the _____________________ number of electrons. cations become isoelectronic with _____________________ noble gas anions become isoelectronic with _____________________ noble gas

similarly for all of the IIA & VIIA M(s) + X2 ® M2+ X2- IIA metals with VIIA nonmetals, mostly ionic compounds ~ exceptions - BeCl2, BeBr2, BeI2 these are covalent compounds Be(s) + F2(g) ® BeF2(s) electronically this is happening similarly for all of the IIA & VIIA M(s) + X2 ® M2+ X2-

SUMMARIZING TABLE Groups Gen. Form. Example IA + VIIA MX IIA + VIIA MX2 IIIA + VIIA MX3 IA + VIA M2X IIA + VIA MX IIIA + VIA M2X3 NaF BaCl2 AlF3 Na2O BaO Al2S3

SUMMARIZING TABLE Groups Gen. Form. Example IA + VA M3X IIA + VA M3X2 IIIA + VA MX Na3N Mg3P2 AlN H forms ionic compounds with IA and IIA metals (metal hydrides) LiH, KH, CaH2, BaH2,, etc. other H compounds are covalent

lattice energy _____________________ - the energy needed to separate oppositely charged ions. It is the energy that converts an ionic solid into widely separated gas ions The _____________________ the lattice energy, the _____________________ the ionic bond. The stronger the ionic bond the _____________________ in water at a given temperature, since the ions must _____________________ _____________________ from one another and attach to water in order to dissolve.

Coulomb’s Law _____________________ Law: for electrostatic attraction and/or repulsion. Applies to charged particles, magnets, gravitation, ionization energy, lattice energy ~ ions with high (big)charges = F is large ~ ions with small (little) charges = F is small

if opposite charges - The greater (bigger) the charges the greater the _____________________ if like charges - The _____________________ (bigger) the charges the greater the repulsion. Also the closer the particles are the ________________ the attraction or repulsion will be.

When Applying Coulomb’s Law to Ionic Compounds E = k Energy = lattice energy, Q1 = charge of positive ion Q2 = charge of negative ion r = bond length, the distance between the nuclei of the 2 ions – can also be _____________________ by the Period.

For r (Use the Period of the element that is _____________________ with the ion! Na is in Period 3 and has 3 occupied energy levels. Na+ has lost an electron. It has 10 electrons and is isoelectronic with Ne in Period 2. Na+ has only 2 occupied energy levels.)

arrange these compounds in order of increasing attractions among ions KCl, Al2O3, CaO

1. Which has a stronger ionic bond, NaCl or KCl. Explain why 1. Which has a stronger ionic bond, NaCl or KCl? Explain why. The lattice energy of ________ is stronger, so this is the stronger ionic bond. Both have an electron charge of -1 and an effective nuclear charge of 1. But the valence electrons of _____ are in the 3rd energy level, leading to a shorter bond length (measured as distance between ionic nuclei) and a stronger ionic bond than ________.

2. Which has a stronger ionic bond, NaCl or AlCl3. Explain why 2. Which has a stronger ionic bond, NaCl or AlCl3? Explain why. The ________ has a stronger ionic bond. Both have the same -1 charge for the chloride ion, and both Na+ and Al+3 are isoelectronic with Ne and therefore have 2 occupied energy levels. But the higher positive charge of the ________ ion leads to a stronger lattice energy and a stronger ionic bond.

3. Which is more soluble in 80° C water, NaCl or KCl 3. Which is more soluble in 80° C water, NaCl or KCl? Explain why You can dissolve more grams of ________ in 100 grams of 80° C water since it has a weaker ionic bond/lattice energy which requires less energy to separate/dissociate the ions from one another and allow them to attach to the polar water molecules.

4. Which is more soluble in 80° C water, NaCl or AlCl3 4. Which is more soluble in 80° C water, NaCl or AlCl3? Explain why ________ is more soluble in 80° C water since it has a weaker ionic bond/lattice energy which requires less energy to separate/dissociate the ions from one another and allow them to attach to the polar water molecules.

5. Why is Na2O considered soluble in water while Al2O3 is not Q2 for oxygen is the same for both compounds, a -2. Radius of oxygen is the same for both, and Na+ and Al+3 are isoelectronic. So the larger Q1 charge of Al+3 makes the lattice energy of the ________ greater, and since the ions stay bonded to one another it will not dissociate and dissolve.

Structures of Ionic Compounds extended three dimensional arrays of oppositely charged ions _____________________ points because coulomb force is strong

Covalent Bonding covalent bonds formed when atoms share electrons share 2 electrons - ___________________covalent bond share 4 electrons - ___________________covalent bond share 6 electrons - ___________________covalent bond attraction is electrostatic in nature lower potential energy when bonded

Covalent bonding may be explained by 2 different theories (more on this coming soon) ___________________ ___________________(VB) theory: each atom has electrons in atomic orbitals which overlap to form bonds ___________________ ___________________(MO) theory: the electrons belong to the molecule as a whole and are in molecular orbitals instead of belonging to each atom

General rules for Lewis Dot Diagrams for Covalent bonds The element needing the most electrons to fill its octet is usually the central atom The most symmetrical skeleton is usually correct Halogens and H always share one electron to complete outer shell In ternary acids, H are bonded to O (ternary acids are oxy-acids: they contain H, O, and another nonmetal)

Carbon always obeys the octet rule Carbon rarely has lone pairs of electrons. Exception: If it’s at the end of a molecule or ion. Ex. CN- , CO, CNO When forming multiple bonds between atoms, both atoms donate the same number of electrons

Oxygen atoms normally bond to other nonmetals, not to each other Oxygen can do several things depending on the mlcl. Single bond by sharing an electron Single bond by accepting 2 electrons from another atom and not sharing at all Double bonds by sharing 2 of its electrons

Pure covalent bonds - Nonpolar Covalent Bonds ___________________ : diatomic molecules hydrogen, H2 fluorine, F2 nitrogen, N2 ___________________ covalent bonds - electrons are shared equally symmetrical charge distribution - must be the ___________________ ______________to share exactly equally

Lewis dot representation H2 molecule formation

Polar Covalent bonds - Unequal sharing of electrons ______________________________: diatomic molecules hydrogen halides hydrogen fluoride, HF hydrogen chloride, HCl hydrogen bromide, HBr

___________________ bonds - unequally shared electrons ___________________ charge distribution different ___________________ ___________________ Some bonds are ___________________, Ex. HF

Polar Covalent Bonds Electron density map of HF H-F blue areas low electron density red areas high electron density polar molecules have separation of centers of negative and positive charge

Some bonds are only slightly polar, ex. HI

Polar Covalent Bonds Electron density map of HI H-I blue areas low electron density red areas high electron density notice that the charge separation is not as ______ as for HF HI is only slightly polar

The Octet Rule ___________________ ___________________ elements achieve noble gas configurations in most of their compounds. Lewis dot formulas are based on the ___________________. H needs two electrons to have Helium's noble gas configuration, everything else wants 8

Lewis Dot Formulas for Molecules and Polyatomic Ions water, H2O

Lewis Dot Formulas for Molecules and Polyatomic Ions ammonia molecule , NH3

Lewis Dot Formulas for Molecules and Polyatomic Ions ammonium ion , NH4+

Lewis Dot Formulas for Molecules and Polyatomic Ions hydrogen cyanide, HCN

Lewis Dot Formulas for Molecules and Polyatomic Ions sulfite ion, SO32-

Resonance Two or more Lewis dot diagrams are needed to describe the bonding in a molecule or ion. LDD for sulfur trioxide, SO3

Resonance three possible structures for SO3 invoke resonance Double-headed arrows are used to indicate resonance formulas.

Resonance flaw in our representations of molecules no single or double bonds in SO3 all bonds are the same length best picture

More Resonance structures Carbonate, CO3 -2

More Resonance structures Nitrate, NO3 -1

More Resonance structures Nitrite, NO2 -1

List of common Resonance structures Sulfite ion, SO32- Sulfur trioxide, SO3 Carbonate ion, CO32- Nitrate ion, NO31- Nitrite ion, NO21- *Sulfate ion, SO42- *Sulfur dioxide, SO2 *Ozone, O3 *Benzene, C6H6

Formal Charges The concept of formal charges helps us choose the correct Lewis structure for a molecule. If a ___________________ ___________________ has a high formal charge it’s not a very good one. A formal charge is assigned to each element in a compound Formal charge = group # - (e- you can assign to that atom) Or F.C. = (valence e- ) – (# of bonds + # of unshared e- )

Let’s assign formal charges for the elements in the L. D. D Let’s assign formal charges for the elements in the L.D.D. from water, H2O to sulfite ion, SO32-

Sigma and Pi bonds ___________________ ___________________(σ) : result of head- on (end to end overlap, there is a free rotation around σ bonds. ___________________ ___________________(π) : result of side- on overlap of p orbitals. There is no free rotation around a π bond. The side –on overlap locks the molecule into place. All ________________ bonds are sigma bonds: 1σ bond All ________________ bonds: 1 σ bond, 1 π bond All ________________ bonds: 1 σ bond, 2 π bonds

Limitations of the Octet Rule for Lewis Formulas species in which the central element must have a share of more or less than 8 valence electrons to accommodate all substituents compounds of the d- and f-transition metals In cases where the octet rule does not apply, the elements attached to the central atom nearly always attain noble gas configurations. The central atom does not

Limitations of the Octet Rule for Lewis Formulas Write LDD for BBr3

Limitations of the Octet Rule for Lewis Formulas Write LDD for AsF5

Limitations of the Octet Rule for Lewis Formulas Write LDD for XeF4