Atomic Theory 9

What is a covalent bond

A bond formed when atoms share pairs of electrons

Why do atoms share electrons

To attain eight electrons in the outer shell

What type of bond is covalent bonding

Intramolecular bonding

What is a sigma bond

A covalent bond formed by end on overlap of orbitals

What orbitals can form sigma bonds

s with s or s with p or p with p

What is a pi bond

A covalent bond formed by sideways overlap of p orbitals

What orbitals form pi bonds

p orbitals only

Which bond forms first in multiple bonding

Sigma bond

Why does a sigma bond form first

Greater overlap gives greater stability

Which is stronger sigma or pi

Sigma is stronger

Why is sigma stronger than pi

Sigma has more orbital overlap

How many sigma bonds are in a single bond

One sigma bond

How many sigma and pi bonds are in a double bond

One sigma and one pi

How many sigma and pi bonds are in a triple bond

One sigma and two pi

What is a pure covalent bond

A bond where electrons are shared equally

What is a polar covalent bond

A bond where electrons are shared unequally

What charge does the more electronegative atom get

Slight negative δ minus

What charge does the less electronegative atom get

Slight positive δ plus

What is a dative covalent bond

A covalent bond where both shared electrons come from one atom

What is a polar molecule

A molecule where centres of negativity and the centres of positivity do not coincide

What is a dipole

A molecule or bond with separated positive and negative charge

What is a permanent dipole

A permanent separation of charge

Why is water polar

It is V shaped so dipoles do not cancel

Can a molecule have polar bonds and be non polar

Yes if the molecule is symmetrical

What happens when a charged rod is brought near water stream

The water stream is deflected

Why is cyclohexane not deflected

It is non polar

Do pure covalent substances conduct electricity

No because there are no free ions

Why do covalent compounds have low boiling points

Weak intermolecular forces need little energy to overcome

What state are many covalent compounds at room temperature

Gases or liquids

Are covalent compounds generally soluble in water

Usually no

What intermolecular force acts in pure covalent substances

Van der Waals forces

What intermolecular force acts in polar covalent substances

Dipole dipole attractions

Which molecules have hydrogen bonding

Ones that contain H bonded to O, F, N