Chemical bonds connect atoms to each other within a compound◦ Also known as Intramolecular forces of attraction
It requires energy (ie: the addition of heat) to break a bond
Chemical bonds store potential energy
Atoms will gain, lose, or share electrons in order to achieve a full valence shell
Electronegativity differences between atoms help determine what type of bond with form between them:◦ Electrons are always attracted to the atom with the
higher electronegativity
Bonds that involve a transfer of an electron from one atom to another
Bonding due to electromagnetic forces
Formed between a metal and a nonmetal
Electronegativity difference between the atoms is 1.7 and higher
Formed between two nonmetals
Electronegativity difference is less than 1.7
Involve the sharing of electrons
Since “like charges” repel, pairs of electrons will repel other pairs of electrons
Each pair will take a position that will be as far away as possible from other pairs of electrons
Shapes of molecules are influenced by this phenomenon
Polar Covalent bonds
◦ Bonds between atoms that do not share electrons equally, caused by elements having different electronegativities
◦ Electrons are pulled harder by atoms with the higher electronegativity. This creates a “dipole moment”
Polar molecules
◦ Are asymmetrical because there is a “dominant” directional pull of electrons (quasi + & quasi -), although the molecule itself, is neutral
◦ Polar molecules generally have higher boiling and melting points their non-polar counterparts
Non-polar covalent bonds
◦ Bonds between atoms that equally share electrons, (they have the same electronegativity that results in an END of zero)
Non-polar covalent molecules
◦ Are symmetrical without any “dominate” directional pulling of electrons
◦ Can have polar bonds, non-polar bonds, or a combination of both
Coordinate covalent bonds
◦ A bond between atoms in which one of the atoms provides all the shared bonds
◦ Otherwise, not different than any other covalent bond
Metallic bonds
◦ Bonding between metals
◦ “Sea of electrons”: metals are arranged in fixed patterns, but the electrons are free to move. (this often polarizes the metal and makes it magnetic)
◦ Metals are good conductors of heat and electricity because of the mobile electrons
Ionic solids
◦ High melting points
◦ Are crystalline in structure
◦ Do not conduct electricity, except in aqueous solutions (because it dissociates into freely moving ions)(the more ions it breaks into – the more conductive it is)
Molecular substances
◦ May exist as solids, liquids, or gases (depending on the strength of attraction between molecules)
◦ Examples: water, ammonia, sugar, oxygen
Molecular substances
◦ Formed by covalent bonding
◦ Relatively soft (compared to ionic solids)
◦ Poor conductors of heat and electricity (no ions) Sugar dissolves, but does not dissociate
◦ Relatively low melting points
Network solids
◦ Solids that are covalently bonded into “giant networks”
◦ Usually one element bonded to itself many times
◦ Examples: diamonds, graphite, asbestos, plastics
Attraction between molecules
◦ Dipole-dipole interactions
◦ Hydrogen Bonding
◦ Van der Waals Forces
◦ Molecule-Ion Attraction
Dipole-dipole interaction
◦ Attraction between polar molecules (dipoles)
◦ Molecules arrange themselves so that a positively charged “end” (δ+) lines up with a negatively charged “end” (δ–).
Hydrogen “bonding”
◦ Attractive force between H and F, O, N in separate molecules
◦ Causes substances to have higher boiling points because of this additional attractive force
◦ Much stronger than dipole-dipole forces
◦ Usually represented by a dotted line ( - - - - - - )
van der Waal’s forces
◦ The major force of attraction between non-polar molecules
◦ Act similarly to gravitational forces; VDW forces increase with increasing mass and increasing proximity of the molecule to another molecule
◦ Makes it possible for non-polar substances to exist as solids and liquids