4.2 Covalent bonding Flashcards
When does covalent bonding occur?
When elements have difference in electronegativity less than 1.8. Usually between non-metal elements
Covalent bond
Electrostatic attraction between positively charged nuclei and shared pair of bonding electrons
Why are covalent bonds often required?
To achieve full outer shell of electrons
Bond strength
Amount of energy needed to break bonds between atoms
Bond length
Distance between nuclei of bonded atoms
How does bond length change down a group?
Bond length increases down a group as atomic radius increases which means less effective nuclear charge. Number of energy levels also increases
Relationship between bond length and bond strength
As bond length decreases, bond strength increases and vice versa. More distance means less attraction
Are multiple bonds shorter or longer than single bonds? Are they stronger or weaker?
They are shorter and stronger as attraction is greater with more bonds
How does bond strength affect reactivity?
As bond strength increases, reactivity decreases. eg. N2 has triple bond which means it’s unreactive as it requires too much energy to overcome attraction. It is less reactive than O2
What is a coordinate covalent bond?
A bond where both bonding electrons come from one atom
Which molecule is an exception to electron deficiency?
AlCl3 has a polar covalent bond and it needs 2 more electrons for an octet. At high temp, it exists as a normal molecule but at lower temp it combines with another AlCl3 to form a DIMER
What is the bond if difference in electronegativity is 0.1 to 0.5?
Non-polar covalent bond
What is the bond with electronegativity difference of 0?
Pure covalent as electrons are shared equally
What happens when bond is polar and what is formed?
There is unequal sharing of electrons which forms a bond dipole (one element is more attractive)
What is the bond with greatest polarity?
H-F bond
