CHAPTER 7 Chemical Bonding Chemical bonds that hold

CHAPTER 7 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) ¬ ___________ results from sharing one or more electron pairs between two atoms. (nonmetals only similar χ )

Comparison of Ionic & Covalent Compounds Ionic � Melting Pt � Solubility ◦ (polar solvents) � Solubility ◦ (nonpolar solvents) � Conductivity ◦ (molten & aqueous solutions) Covalent

Ionic vs. Covalent bonding 2 extremes in bonding ______________________ ◦ electrons equally shared by the atoms ______________________ ◦ 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 2 atoms 3 atoms many Ex. Ex. He O 2 O 3 H 2 SO 4 or S 8 : the mlcl is composed of only 1 kind of atom: O 2, H 2, P 4 � ___________ : the mlcl is made up of more than 1 kind of atom: H 2 O � ___________

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 ___________ react with ___________ to form ___________ 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 ___________ atoms and the _______ they form.

underlying reasons for Li. F formation 1 s Li ¯ F ¯ 2 s 2 p ¯ ¯ ¯ becomes Li+ ¯ [___] F- ¯ ¯ [___] ¯

Li+ ions contain two 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

IIA metals with VIIA nonmetals, mostly _________compounds ~ exceptions - Be. Cl 2, Be. Br 2, Be. I 2 these are covalent compounds Be(s) + F 2(g) ® Be. F 2(s) electronically this is happening similarly for all of the IIA & VIIA M(s) + X 2 ® M 2+ X 2 -

SUMMARIZING TABLE Groups Gen. Form. IA + VIIA MX IIA + VIIA MX 2 IIIA + VIIA MX 3 IA + VIA M 2 X IIA + VIA MX IIIA + VIA M 2 X 3 Example

SUMMARIZING TABLE Groups Gen. Form. IA + VA M 3 X IIA + VA M 3 X 2 IIIA + VA MX Example H forms ionic compounds with IA and IIA metals Li. H, KH, Ca. H 2, Ba. H 2, , etc. other H compounds are covalent

lattice energy ___________ - the energy needed to separate oppositely charged 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 ~ ions with high (big)charges = ___________ ~ ions with small (large) charges = ___________

When Applying Coulomb’s Law to Ionic Compounds (From Ch. 6) E=k Energy = lattice energy, Q 1 = charge of positive ion Q 2 = charge of negative ion r = bond length, the distance between the nuclei of the 2 ions – can also be ___________ by the Period.

r (Use the Period of the element that is ___________ with the ion! � For � 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, Al 2 O 3, Ca. O

1. Which has a stronger ionic bond, Na. Cl or KCl? Explain why. The lattice energy of _________________, 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 ___ 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, Na. Cl or Al. Cl 3? 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 ___________ leads to a stronger lattice energy and a stronger ionic bond.

3. Which is more soluble in 80° C water, Na. Cl or KCl? Explain why You can dissolve more grams of ____ in 100 grams of 80° C water since it has a ______________________ 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, Na. Cl or Al. Cl 3? Explain why _____is more soluble in 80° C water since it has a ______________________ which requires less energy to ___________ the ions from one another and allow them to attach to the polar water molecules.

5. Why is Na 2 O considered soluble in water while Al 2 O 3 is not Q 2 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 Q 1 charge makes the ___________ 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 ___________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 ◦ ________________________: each atom has electrons in atomic orbitals which overlap to form bonds (Ch. 8) ◦ ________________________: the electrons belong to the molecule as a whole and are in molecular orbitals instead of belonging to each atom (Ch. 9)

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, H 2 ◦ fluorine, F 2 ◦ nitrogen, N 2 ________covalent bonds - electrons are shared equally symmetrical charge distribution must be the ____________to share exactly equally

Lewis dot representation H 2 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 ◦ blue areas - low electron density ◦ red areas - high electron density polar molecules have ________of centers of negative and positive charge

Some bonds are only _____________, ex. HI

Polar Covalent Bonds Electron density map of HI ◦ 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, H 2 O ammonia molecule , NH 3 ammonium ion , NH 4+ sulfite ion, SO 32 - hydrogen cyanide, HCN

Resonance � Two or more Lewis dot diagrams are needed to describe the bonding in a molecule or ion. � LDD for sulfur trioxide, SO 3

Resonance three possible structures for SO 3 invoke resonance ◦ Double-headed arrows are used to indicate resonance formulas.

Resonance flaw in our representations of molecules no single or double bonds in SO 3 all bonds are the same length best picture

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. � Formal Or charge = group # - e- you can assign to that atom F. C. = (valence e- ) – (# of bonds + # of unshared e- ) pg 289

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 ¹ º 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. ◦ ________________________

Limitations of the Octet Rule for Lewis Formulas � Write LDD for BBr 3 � Write LDD for As. F 5 � Write LDD for Xe. F 4

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