Only noble gases exist naturally as single, uncombined atoms.
All other atoms: combined. CHEMICAL BONDS: Electrostatic forces
that hold atoms together in compounds. - In nature, systems of
lower energy (more stable) tend to be favoured over system of
higher energy (less stable). - Bonded atoms tend to have lower
energies (ie. more favourable!)
Slide 3
Chemical bonding involves the interaction of valence electrons
(outermost electrons) - Lets you see exactly how many electrons are
involved in the bond helps you keep track of the number of valence
electrons. - Two ways to show bonding pairs of electrons: (Dots
represent a lone pair (non-bonding pair) of electrons.)
Slide 4
Force of attraction between oppositely charged ions. Occurs
between atoms with large differences in electronegativity (why is
this? Periodic Table!) Ionic solid: arranged in a specific sequence
of repeating units minimum possible energy. Atoms of ionic
compounds usually come from s and p blocks.
Slide 5
PPs, pg. 165 #1-4
Slide 6
- Crystalline with smooth, shiny surfaces - Hard but brittle -
Non-conductors of electricity and heat - High melting points - Many
are soluble in water
Slide 7
Lattice energy: the amount of energy given off when ionic
crystal forms from the gaseous ions of its elements. Example: MgF 2
has lattice energy= 2957 kJ/mol Same amount of energy needed to
break up the ionic crystal. Compounds with larger lattice energies
have higher melting points.
Slide 8
Balance between forces of attraction and repulsion that act
between the nuclei and electrons of two or more atoms. Optimum
separation for atoms at which nucleus-electron attractions,
nucleus-nucleus repulsions, and electron-electron repulsions
achieve a balance. Results in the sharing of pairs of electrons.
Formation of new Orbital: overlapping of atomic orbitals. Lower
energy levels than original atomic orbitals.
Slide 9
In most cases, covalent bonding allows atoms to acquire noble
gas configurations. Hydrogen must fill its s orbital. Carbon must
fill its 2s and three 2p orbitals.
Slide 10
Energy required to break the force of attraction between two
atoms in a bond and to separate them. Measures the strength of a
bond. Increase in bond energy due to increase of (-) charge in
between the two nuclei. Therefore, nuclei are more attracted to the
overlap orbital.
Slide 11
Using Physical Properties Covalent (molecular) compounds: Exist
as a soft solid, liquid, or a gas at RT. Low melting and boiling
points Poor conductors of electricity May not be soluble in water.
Using Formula of the Compound Two atoms with identical
electronegativities share electrons equally. Therefore, the bond is
_______________________. Very different electronegativities one
atom attracts electrons more. For example, sodium chloride sodiums
valence electron has a very high probability of being found near
sodium. This bond is ________________. Electron is not actually not
lost, gained, or transferred. bonding contiuum
Slide 12
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PPs 5-8
Slide 14
Properties: Conduct electricity and heat in both solid and
liquid states. Malleable and ductile. Bonding Difference in
electronegativities not large enough to form ionic bonds. Do not
have a sufficient number of valence electrons to form covalent
bonds with one another. Electrons are shared but different than
covalent.
Slide 15
Metals composed of densely packed core of cations. Electrons
are shared and mobile can move throughout metal. Force of
attraction between the positively charged cations and the pool of
valence electrons that move among them metallic bond.
Slide 16
Conductivity (heat and electricity): electrons can move freely
throughout the metallic structure. Malleability and Ductility:
metallic bonds are non-directional. Cations can slide over one
another. Melting and Boiling Points: Group 1 metals have lower
melting and boiling points of Group 2 greater number of valence
electrons and larger positive charge = stronger metallic bonding
forces. Transition metals: generally high melting and boiling
points.
Slide 17
SR, page. 171 #1, 2-7.
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Slide 22
When one atom contributes both of the electrons to the shared
pair. Occurs when a filled atomic orbital overlaps with an empty
atomic orbital. Behaves in the same way as any other single
covalent bond.
Slide 23
Slide 24
Bonds between S and O are identical: two one-and-a-half bonds.
Resonance structures are combinations hybrids if its two resonance
structures. Does NOT shift back and forth between bonds. Resonance
structures: models that give the same relative position of atoms as
in Lewis structures, but show different places for their bonding
and lone pairs.
Slide 25
PPs, page 177 #9-12.
Slide 26
Expanded valence energy level: bonding in some molecules is
best explained by a model that shows more than eight electrons in
the valence energy level of the central atom. Experimental evidence
suggests that larger atoms can accommodate additional valence
electrons because of their size. Sometimes, must violate the octet
rule to allow for more than four bonds around a central atom.
Slide 27
PPs, pg. 178 #14-17
Slide 28
Lewis structures do not communicate any information about a
molecules shape. VSEPR (Valence-Shell Electron-Pair Repulsion)
Theory: Bonding pairs and lone pairs of electrons repel one
another. Lone pair (LP) will spread out more than a bond pair
repulsion is greatest between lone pairs (LP LP) Bonding pairs (BP)
are more localized between nuclei, so spread out less. BP-BP
repulsions are smaller than LP- LP repulsions. Repulsion between BP
and LP is intermediate.
Slide 29
When all electron groups are bonding pairs, a molecule will
have one of these shapes. If there are lone pairs, variations of
these result.
Slide 30
Shape of molecule depends on electron pairs.
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Predicting Molecular Shape
Slide 35
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PPs, 185 #18-22
Slide 37
Recall: For diatomic molecules: bond polarity is also the
molecules polarity. Dipole: term used to describe the charge
separation for an entire molecule. Molecular Polarity/Molecular
Shape Table: A: central atom X: more electronegative than A. Y:
more electronegative than X.
Slide 38
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Slide 40
PPs, page 188 # 23-26 SR, page 189. # 1-3, 5, 6
Slide 41
Intramolecular Forces: forces exerted within a molecule or
polyatomic ion. Intermolecular Forces: forces of attraction and
repulsion that act between molecules or ions. also called van der
Waals forces. 1) Dipole-dipole forces 2) Ion-dipole forces 3)
Induced dipole forces 4) Dispersion forces 5) Hydrogen bonding
Slide 42
Polar molecules (dipoles) in liquid form orient themselves so
that oppositely charged ends are near to one another. -Polar
molecules will tend to attract one another more at room temperature
than similarly sized non- polar molecules would. -More energy
required to separate polar molecules than non-polar of similar
molar mass. -Higher melting and boiling points.
Slide 43
Force of attraction between an ion and a dipole. Reason why
most ionic solids are soluble.
Slide 44
Induced by charge 1) Ion-induced dipole force: - When an ion in
close proximity to a non-polar molecule distorts the electron
density of the non-polar molecule. - Molecule becomes temporarily
polarized two species are attracted to each other 2) Dipole-induced
dipole force: - Charge on polar molecule induces the charge on a
non-polar molecule.
Slide 45
Shared pairs of electrons in covalent bonds are constantly
vibrating. Bond vibrations cause momentary, uneven distributions of
charge. Act between any particles. Factors of Magnitude: Number of
electrons: larger molecules, more uneven distribution of charge.
Raise boiling point. Shape of molecule: sphere has less surface
area than linear molecule. More linear molecules have higher
boiling points than spherical.
Slide 46
Strong form of dipole-dipole attraction that exists between a
hydrogen atom in a polar- bonded molecule that contains bonds such
as H-O, H-N, H-F, and an unshared pair of electrons on another
small, electronegative atom such as O, N, or F. Small,
electronegative atom can be on its own, but is usually bonded in a
molecule. H-bond is about 5% as strong as a single covalent bond
strength in numbers. Ex// DNA
Slide 47
Why is water less dense in a solid state than in a liquid
state? Water molecules align in a specific pattern so that hydrogen
atoms of one molecule are oriented toward the oxygen atom of
another molecule. If water molecules behave as most molecules do,
lake water would freeze from the bottom up floating ice insulates
the water beneath it. Polar covalent compounds are soluble in water
Ex// alcohols (O-H bonds), ammonia (N-H bonds), small mass amines
(N-H), etc.
Slide 48
Slide 49
Crystalling solids: organized particle arrangements with
distinct shapes: gemstones, etc. Amorphous solids: indistinct
shapes: particle arrangements lack order: glass and rubber.
Made up of individual atoms held together by ONLY by dispersion
forces noble gases. Very low melting and boiling points.
Slide 52
Made up of molecules. Mainly dispersion forces. Low melting and
boiling points. Can be made up of polar molecules, with higher
melting and boiling points.
Slide 53
Carbon-Based Network Solids Allotrope: different crystalline or
molecular forms of the same element that differ in physical and
chemical properties. Read more about network solids on page
192.
Slide 54
Array of ions, arranged at regular positions in a crystal
lattice. Different and distinct arrangement depending on ions
involved: charge and size. Anion is usually larger than the cation,
and so it determines the arrangement of ions in the crystal lattice
(oranges and kiwis).
Slide 55
Slide 56
Molecules that are not arranged in an orderly, crystalline
structure. Glass: heat silica sand to melting point (1700 degrees
C), add limestone and soda ash, and allow to cool 4000 years
ago!
Slide 57
KEVLAR: Thin, lightweight fabric that can withstand startling
impacts and piercing forces. Interlaced strands of fibre to make a
net. Capable of absorbing large amounts of energy (heat, kinetic,
etc.) Bulletproof vests, protective gloves. Strands of KEVLAR are
twisted to make increase density and thickness and strands are
woven very tightly. http://www.youtube.com/watch?v=L-
ZbBIhLDUw&feature=related
Slide 58
Polymers containing aromatic and amide groups. Strength comes
from: intramolecular forces in the aromatic groups that limit bond
rotation in the strait chains amide linkage - intermolecular
hydrogen bonding between strait chains.
Slide 59
a material with no resistance to electrical current none of the
energy is given off as heat. Even good conductors, such as copper,
give off wasted heat as electric current passes through them
resistance. Superconductors are perfect electrical conductors.
Future of superconductors: once a current is induced in a circuit,
the current continues to flow indefinitely without diminishing.
Ability to completely repel magnetic field lines magnet over a
superconductor will hover in mid-air.
Slide 60
SR, page 208 # 1-3, 7-9. (If you can not answer these
questions, look through the section!)