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Atomic Bonding and Structure : (Ionic Bonding (Physical Properties (Low…
Atomic Bonding and Structure :
Ionic Bonding
Physical Properties
Low
Volatility
Volatility
: The tendency of a substance to vaporize
Soluble in Water (electrostatic forces of the polar water molecules are stronger than the electrostatic forces keeping the ions together)
Electronegativity
: a measure of the tendency of an atom to attract a bonding pair of electrons
Conduct Electricity in Water or as a Liquid (due to high movement of molecules in liquid form)
Solid with High Melting and Boiling Points (due to strong attraction between molecules)
Ionic Bonding caused by
electrostatic attraction
between these ions
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Loss and gain in electrons determined by:
Electron Configuration
Metals lose valence electrons to form
Cations
Nonmetals gain valence electrons to form
Anions
Anions
: Negative Ions
Cations
: Positive Ions
Solids with Lattice Structures
Common Examples:
Polyatomic Ions
NH4+
NO3-
HCO3-
CO32-
Covalent Bonding
Lewis Structures
: Dot diagrams drawn to show the sharing of electrons and all valence electrons in a covalently bonded molecule
Lewis Structure of Carbon Dioxide
The Octet Rule
: tendency of atoms to gain a valence shell with a total of 8 electrons
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Exception to the rule: Be and B can form a stable compound without an octet
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Lewis Structure of Boron Trifluoride
Bond Polarity
: caused by a difference in electronegativity between two bonded atoms
How to Tell if a Molecule is Polar?
if there are no polar bonds, it's not polar
if there are polar bonds, but the shape is symmetrical, it's not polar
if there are polar bonds and the molecule is not symmetrical, it's polar
Water is a Polar Molecule
It's based on a molecule's
Electronegativity
: High electronegativity means a strong polarity (if there is no symmetry)
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Types of Bonds
Double
: Medium Length and Height, Two pairs of shared electrons (C, N, O, S)
Triple
: Shortest and Strongest Bond, Three pairs of shared electrons (C)
Single
: Longest and Weakest Bond, One pair of shared electrons (All elements)
The electrostatic attraction between a
shared pair of electrons
and the
positively charged nuclei
Resonance
: used to explain why molecular shapes and bond lengths didn't conform to classical ideas of bonding
when there is more than one possible position for a double bond in a molecule
Benzene
Due to delocalized electrons that make the bond length between 1 and 2
VSEPR Theory
: Helps identify the shape and structure of molecules based on lone and bond pairs
Link to VSEPR Shape Video
Intermolecular Bonds
London Dispersion Forces
: Weakest bond, present in all molecules, formation of a temporary dipole, depends on molecular mass and surface area
Dipole-Dipole Forces
: Medium strength bond, polar molecules that attract each other
Hydrogen Bonding:
Strongest of the three bonds, when hydrogen is bonded to nitrogen, oxygen or fluorine, the hydrogen becomes positive, still weaker than a covalent bond
Metallic Bonding
It's the electrostatic attraction between a lattice of positive ions and delocalized electrons.
The strength of a metallic bond depends on the charge of the ions and the radius of the metal ion.
Alloys usually contain more than one metal and have enhanced properties.
Common Examples: Brass, Bronze, Iron and Steel
Nature of Science
Use theories to explain phenomenon
Looking for trends
Using models
Obtain evidence through prediction and testing
TOK
All theories (like the octet rule) have exceptions
There is indirect and direct evidence for the existence of ions
Resonance structures either decrease or increase the validity of Lewis Structures
