BONDING – Chapters 8 & 9

There are 3 basic types of chemical bonding:

  1. Ionic-the electrostatic bond that holds oppositely charged particles together
  2. Metallic-the attraction of a metallic cation for delocalized electrons
  3. Covalent-the chemical bond that results from the sharing of valence electrons

CHAPTER 8

I IONIC BONDING (8.1-8.2)

Chemical bond –the force that holds two atoms together

Cation –

Cations are formed when atoms _____lose_ electrons therefore giving the ion a __positive charge

Anion –

Anions are formed when atoms _____gain___ electrons therefore giving the ion a __negative___charge

Ionic bond –

Properties of Ionic Compounds

Formed from M/NM (metal/nonmetal)

M are the ____metals___ and NM are the nonmetals____

Stability results from (in order):

1. FILLED E level 2. FILLED sublevel 3. HALF-FILLED sublevel

Form crystal lattice –

 __high___ melting points (high or low?)

_high______boiling points (high or low?)

High electrical conductivity (means its solutions conduct ____electricity______)

Brittle, Hard compounds

Generally have ____high_____ lattice energies

HONORS:

Lattice energy –

The more negative the lattice energy, the ______the bond (force of attraction)

Smaller ions have a more negative lattice E value, b/c valence e- are ______to the nucleus and held more tightly.

Which do you expect to have a stronger bond:

lithium chloride or potassium chloride? ______why?______

lithium chloride or lithium bromide?______why? ______

calcium sulfide or magnesium sulfide?______why? ______

Lattice E is also affected by the charge of the ion. The larger the positive or negative ion, the more ______the lattice energy and the ______the bond.

Which do you expect to have a stronger bond:

Strontium chloride or silver chloride? ______Why?______

Calcium nitrate or lithium nitrate? ______why? ______

II METALLIC BONDS (8.4)

Metallic bonds are M/M alloys and affect the properties of metals.

Metallic bond –the attraction of metallic cation for delocalized electrons

Delocalized electrons –the electrons present in outer energy levels of the bonding metallic atoms are not held by any specific atom and can move easily from one atom to the next.

Delocalized electrons can ___easily____ move from one atom to the next. This gives metals unique properties. In other words, they are “metal ions plus a sea of mobile electrons”.

Electron sea model – proposes that all the metal atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons.

Properties of Metals:

__moderately high_____ melting points

high______boiling points

high_____ electrical conductivity

malleable – can be hammered into sheets

ductile –can be drawn into wires

luster –shines

durable –generally

alloy- a mixture of elements that that has metallic properties

COMPLETE CHART:

3 common alloys:elements in alloyuses

BrassCu, Znplumbing, hardware, lightning

BronzeCu, Zn, SnBearings, Bells, Medals

CastironFe, Ccasting

CHAPTER 9

III COVALENT BOND

Why do atoms bond?Sometimes two atoms that both need to gain valence electrons to become stable have a similar attraction for electrons.

Covalent bonds are normally NM/NM molecules

Covalent bond – The chemical bond that results from the sharing of valence electrons

Molecule – formed when two or more atoms bond covalently

Diatomic molecule –the molecules formed are more stable than the individual atoms

Made up of two of the same atoms

Lone pair – An unshared pair of electrons

Single covalent bond –when one electron pair is shared

Sigma bond – When the electron pair is shared in an area centered between the two atoms.

σ

Double covalent bond – a total of two electronpairs are shared consists of one sigma bond and one pi bond

Triple covalent bond –when three pairs of electrons are shared consists of one sigma bond and 2 pi bonds

Bond length – the distance between the two bonding nuclei at the position of maximum attraction

Bond dissociation energy – indicates the strength of a chemical bond because a direct relationship exists between bond energy and bond length

Because bond breaking always requires the addition of__ energy, bond dissociation energy is always ____positive______. Single bonds ______double bonds ______triple bonds

Endothermic –when a greater amount of energy is required to break the existing bonds in the reaction than is released when the new bonds form

Exothermic – when more energy is released forming new bonds than is required to break bonds in the initial reaction.

Naming Binary Molecular Cmpds (9.2)

  1. name 1st element first, second is named second
  1. second name ends with suffix: -ide
  1. use prefixes to indicate number of each atom type

Prefixes: 1 - _mono____6 - hexa

2 - _di______7 - __hepta______

3 - __tri______8 - __octa______

4 - __tetra_____9 - ___nona______

5 - __penta______10 - _deca______

p. 249 copy and answer 13-17 on the back (use examples at bottom of page to see how molecular cmpd name is found)

Molecular Shape (geometry) (9.4)

VSEPR is acronym for: valence shell electron pair repulsion

VSEPR Modelstates that the arrangement of atoms _____minimizes______the repulsion of shared and unshared ___pairs___ of electrons around the central atom. To minimize repulsion is to maximize separation.

Bond angles:

unshared – unshared unshared – shared > shared – shared

NOTE: As the number of shared pairs increases, the bond length decreases

Therefore, shorter the length, the stronger the bond!!

So triple bonds are the strongest (most bond E) & single bonds are weakest (least bond E)

NOTE: Lone pair electrons will distort the bond angle

Diatomic atoms will have single, double, or triple bonds.

Ex: H2 singleO2double N2tripleF2single

Ex: C atoms will usually form single bonds

Ex: water molecule:

Using the chart on p. 260, complete the following information.

Molecular Shape / Bond angle / 3D pic / example
Linear / 180 / / Sp
Trigonal planar / 120 / / Sp2
Tetrahedral / 109.5 / / Sp3
Trigonal pyramidal / 107.3 / / Sp3
Bent / 104.5 / / Sp3

Predicting Shapes:

Electronegativity -(EN)

When electronegative differences are > 1.70, the bond is more ___ionic______.

When electronegative differences are < 1.70, the bond is more covalent_____.

Therefore, the F2 (F-F) bond is __covalent_____ b/c the diff. in electronegativity (EN) values is ___zero____.

Likewise the Br2 bond is ___covalent______, the H2 bond is ___covalent____, etc. for ALL diatomic atoms.

List the 7 diatomic atoms here: O2 F2 H2 N2 Cl2 Br2 I2

Polar covalent bond – a measure of the tendency to accept an electron

(p. 265) A polar molecule has a partial __positive___ charge on one side, while the other side of the molecule has a partial _negative_ charge. Thus: two separate charges on opposite sides, thus the term: POLAR

Ex: H2O

“Like dissolves like” therefore polar molecules will dissolve ___polar___ molecules and nonpolar molecules will dissolve nonpolar molecules. Based on this, it can be concluded that since oil and butter will not dissolve in water, they must be nonpolar molecules. (will or will not) (Polar or nonpolar)

Properties of Covalent Cmpds

all properties “opposite” of ionic cmpds

between atoms in molecules – strong

between individual molecules – weak

* intermolecular force –(electrostatic) the weak forces of attraction between individual molecules

van der Waals force – vary in strength but are weaker then ionic bonds

low MP (therefore sugar melts, salt does not); low BP

many molecules exist as gases

if solid, relatively soft (Ex: wax or paraffin)

* INTERMOLECULAR FORCES

1. Dispersion forces – attraction between the molecules

  • London forces – A weak and temporary dispersion force

2. dipole – dipole forces – the end of one dipoles attraction to the end of an oppositely charged end of another dipole

3. hydrogen bonding – formed between the hydrogen end of on dipole and the F, O,N, atom on another dipole

One unique type of intermolecular force, is the Hydrogen Bonding (sec. 13.2)

Hydrogen bonding occurs often when H is bonded to O, N, and F. Ex: water (H2O)

Unique properties of H bonding are:

water is liquid at room temp. [similar comparable molecular masses are gases – ammonia (NH3) carbon dioxide (CO2), etc.]

strong bonds (high surface tension for H2O so H2O “overflows” a container, bugs can “walk” on water, and H2O “beads up” on surfaces)

strong H bonding in the DNA molecule

high BP for H2O(l) although it is NOT an ionic cmpd

Bond strength: H bond > dipole> London/van der Waals