eLFH - Chemical Bonds and Reactions Flashcards
Why do bonds occur
Atoms tend to their lowest energy by giving, receiving or sharing electrons to get filled and stable orbitals when possible
Forms of bonds created b electrons holding atoms in association
Sharing electrons - covalent bonds
Transferring electrons - ionic bonds
Covalent bonds definition
Shared electrons in outer orbitals form strong covalent bonds
E.g. Carbon has 4 electrons in outer orbital with maximum possible 8
Hydrogen has 1 electron in outer orbital with maximum possible 2
Therefore CH4 forms with covalent bonds to fully occupy all outer orbitals
Ionic bonds definition
Transfer of electron from one outer orbital to another
Electrostatic forces then hold atoms together
E.g. Chloride atom will attract the single electron from outer orbital of Sodium thus giving both stable outer orbitals
Leaves Cl- and Na+ charges and ionic attraction keeps atoms together
Which bond is stronger - covalent or ionic
Covalent bonds are stronger
What happens to strength of bond and shape of molecule as number of shared electrons increases
Strength of bond increases with increased number of shared electrons
Free rotation also decreases and therefore molecules become more rigid, and isomerism results
Atoms in molecules bond in different ways depending on conditions in which they are joined, and exert differing properties
Types of forces that give molecules specific 3D shapes
Hydrogen bonding
Hydrophobic bonding
Van der Waals forces
Hydrogen bond definition
Hydrogen atom covalently bound to another atom
Hydrogen atom becomes positive and other atom negative charged
Creates dipolar attractive force
Therefore positive hydrogen atom in molecule attracts to negatively charged atom on another of the same molecule within the substance
Hydrophobic bond definition
Non polar molecules interact to exclude water molecules from between them
E.g. phospholipid bilayer
Molecules behave in this way to achieve lower energy state
Van der Waals forces definition
Weak intermolecular forces of attraction between electron clouds of neighbouring atoms
Weak but numerous so become more important
Types of repulsive forces that act on molecules to prevent aggregation
Electrostatic repulsion
Steric hindrance
Electrostatic repulsion definition and example
Similarly charged molecules with repel
E.g. RBCs have net negative electrical charge, therefore do not aggregate
Steric hindrance definition
Certain parts of molecules will be larger or smaller than others, and may have rigid shapes
Therefore certain molecule combinations will be impossible
E.g. jigsaw pieces that don’t fit
Organic chemistry definition
Study of carbon molecules
Examples of groups that can be attached to chains of carbon molecules
Hydroxyl
Amino
Carboxyl
Methyl ether
