Simple Covalent Molecules & Intermolecular Forces - Structure & Properties (2.2) Flashcards
Give an example of a specific type of dipole-dipole interaction
Hydrogen bonding (an extreme example of dipole-dipole interaction)
What elements can H bond to in hydrogen bonding?
F, O or N
How does hydrogen bond donor bond?
H bonded directly to F, O or N
How does hydrogen bond acceptor bond?
Lone pair of electrons on F, O or N
What happens if two atoms have the same electronegativity values?
The electrons lie directly in the middle of the bond & it is non-polar
Describe London forces briefly
Random fluctuations in electrons can produce temporary dipoles
Give the 3 other names for London forces
Dispersion forces
Induced dipole-induced dipole interactions
Temporary dipole-dipole
Explain how London forces occur between molecules
- The temporary dipole induces a dipole in a neighbouring molecule
- A dipole-dipole interaction is formed momentarily & then disappears
Give two factors that affect the strength of London forces and how they affect London forces
- The size of the molecule
- The number of electrons
Both increase the chance of an uneven distribution of electrons & stronger London forces
What type of molecules do London forces occur between?
All molecules
What type of molecules do dipole-dipole interactions occur between?
Molecules that have a permanent dipole
What type of molecules do hydrogen bonds occur between?
Molecules with a H bond donor and a H bond acceptor
Do giant covalent lattices have high/low melting points? Explain why
- Giant covalent lattices have v. high melting points
- Covalent bonds are v. strong & require a lot of energy to be broken
What happens to the forces & bonds when simple covalent molecules melt/boil?
The covalent bonds do NOT break and the molecule remains intact BUT the weak intermolecular forces between the molecules break
Explain what intermolecular forces are (in terms of interaction between molecules)
Intermolecular forces are the attractive or repulsive forces between slightly positive & slightly negative ends of a molecule
Give the 3 main types of intermolecular force
- Permanent dipole-dipole interactions
- Hydrogen bonds
- London forces
How is an electron cloud created?
Electrons can move all around the surface of the molecule
What makes a molecule non-polar?
When electrons are evenly spread within the molecule
What makes a molecule polar?
- When electrons are unevenly spread to give a dipole
- One side is slightly more positive (less electrons)
- The other side is slightly more negative (more electrons)
What is electronegativity?
The power of an atom to attract electron density from inside a covalent bond
(if an atom is more electronegative than the other, it is more negative, therefore it attracts more electrons)
Why do permanent dipoles occur?
Due to differences in electronegativity
What factors affect electronegativity?
- Atomic radius
- Nuclear charge
- Shielding
What is the trend in electronegativity across periods in the periodic table?
Electronegativity increases across periods
What is the trend in electronegativity down groups in the periodic table?
Electronegativity decreases down groups
Why is a BOND polar?
When there is a significant difference in electronegativity values
Give 3 examples of polar bonds
C-N C-O C-F C-Cl C-Br O-H N-H X-H (X is any halogen)
Give an example of a bond that is not polar
C-H
Explain how dipole-dipole forces occur between molecules
The molecules align so that the δ+ ends are attracted to the δ- ends of a neighbouring molecule
How does size of the dipole affect the interaction?
The larger the dipole, the stronger the dipole-dipole interaction
