Chemical Bonding. Types of Chemical Bonds Ionic Bonding – bonding as a result of atoms giving away...
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Transcript of Chemical Bonding. Types of Chemical Bonds Ionic Bonding – bonding as a result of atoms giving away...
Chemical Bonding
Types of Chemical Bonds
Ionic Bonding – bonding as a result of atoms giving away or receiving e-; attraction between cations and anions
Covalent Bonding – bonding as a result of atoms sharing e-
Q: How do we know whether ionic or covalent?
A: Compare electronegativities of the atoms.
In general:
Small difference = covalent bondMedium difference = polar covalentLarge difference = ionic bond
Covalent Bonding & Molecular Compounds
Covalent Bonding & Molecular Compounds
Molecule – a neutral group of atoms held together by covalent bonds
Molecular Compound – a compound whose simplest units are molecules
Molecular Formula – shows the type and number of atoms present
Diatomic molecule – molecule with two atoms
Forming Covalent Bonds
• Atoms almost always favor an arrangement with lower potential energy
• As atoms get closer, the positively charged nucleus is attracted to the negatively charged electron cloud
Covalent Bond Characteristics
Bond length – the average distance between two bonded atoms at minimum potential energy
Bond energy – the amount of energy needed to break a chemical bond; measured in kJ/mol
Overlapping orbitals
The Octet Rule
Chemical compounds tend to form so that each atom has an octet of electrons in its highest energy level
Exceptions to the rule to exist; called expanded octets
Electron Dot Notation & Lewis Structures
Electron configuration showing only the valence electrons around the chemical symbol
Unshared pair (lone pair) – a pair of electrons NOT involved in bonding and belong only to one atom
Drawing Lewis Structures
1. Determine type and number of atoms
2. Find total number of valence electrons
3. Arrange atoms with carbon in the middle; if no carbon present, least electronegative element in the middle; hydrogen is never the central atom
4. Add unshared pairs of electrons forming octets
Ex – NH3, H2S, CO2, HCN
Resonance Structures
Bonding in molecules or ions that cannot be correctly represented by a single Lewis structure
Ex – ozone
Ionic Bonding & Ionic Compounds
Ionic Compounds
Ionic compounds – made of positive and negative ions combined so the charges are equal (zero)
Formula unit – simplest collection of atoms wich form an ionic compound’s formula
Ex – sodium chloride (NaCl)
Ionic Bonding
Involve a transfer of electrons making one atom positively charged and the other negatively charged (cations and anions)
Form a crystal lattice structure which balances the charges of the ions
Lattice energy – amount of energy released when 1 mole of an ionic compound is formed from gaseous ions
Ionic Bonding
Electrostatic forces hold ionic compounds together
Makes ionic compound very hard but brittle
Strong attractions raise boiling and melting points
Polyatomic Ions
• Charged group of covalently bonded atoms
• Charge is on the collective group; not any particular atom
• Caused by an excess or shortage of electrons
• Lewis structures are written in brackets
Metallic Bonding
The chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons
Outer-most electrons are free to move between overlapping orbitals
This accounts for metals ability to conduct heat and electricity
Metallic Bonding
Can absorb a wide range of light wavelengths
Immediately lose energy and fall to lower level
Accounts for metals shiny appearance
Bonding is the same in all directions
Accounts for properties of malleability and ductility
Intermolecular Forces(Dipole-Dipole)
• Created by equal but opposite charges separated by short distances
• Strongest intermolecular force
• Represented by an arrow in the negative direction
• Polar molecules have dipole moments
Intermolecular Forces (Hydrogen Bonding)
• The intermolecular force in which a hydrogen atom is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule
• Creates a fairly strong dipole-dipole force
Intermolecular Forces(London Dispersion Forces)
• Slight attraction between molecules caused by instantaneous dipole moments
• Weakest intermolecular force
• Only force acting between noble gases and non-polar molecules