Atomic theory 10 Flashcards
What is intermolecular bonding?
An attractions between atoms of different molecules
Define hydrogen bonding
A hydrogen bond is a force of attraction that occurs between molecules when hydrogen is bonded to a smaller more electronegative element such as O, F or N.
When does hydrogen bonding occur?
When hydrogen is bonded, in a molecule to a smaller more electronegative element like F, O or N
When does the most effective H-bonds occur?
When H is bonded to F, O or N.
Can hydrogen bonding only occur within or between a molecule
ONLY BETWEEN!!
Is a lot of energy needed to break hydrogen bonds?
Yes more energy is needed to break them
Why is more energy needed to break hydrogen bonds?
Due to their presence
Why does water have a high boiling point?
Due to the presence of hydrogen bonds, more energy is needed to break them down
Why is water a liquid at r.t and H2S a gas?
Because the intermolecular forces of attraction between H₂S molecules are considerably weaker than the hydrogen bonding between water molecules, hence the molecules in hydrogen sulfide are freer to move apart making H₂S a gas.
What are polar molecules attracted to?
Other polar molecules
Polar molecules are attracted to other polar molecules. What kind of attraction is this and what is it known as?
- An attraction between atoms of different molecules
- known as intermolecular bonding / dipole-dipole attractions.
Are attractions between ions strong or weak?
Extremely strong
Attractions between ions are extremely strong. What does this give rise to?
Gives rise to ionic compounds being crystalline solids.
Do the attractions between ions have high or low boiling points and melting points?
High
Are dipole-dipole attractions between covalent molecules stronger or weaker in comparison to the attractions between ions?
Weaker
Hydrogen bonding is a special type of ……..
Intermolecular force of attraction (dipole-dipole interaction)
What are hydrogen bonds stronger than?
Other types of dipole-dipole interactions.
Give an example of hydrogen bonding
Hydrogen bonding between H₂O molecules
Are hydrogen bonds strong or weak?
Relatively weak, but exert a large influence on the physical and chemical properties on the molecules that form them.
Does water have a relatively high or low boiling point compared to molecules of similar molecular mass
High
What does hydrogen bonding account for in water?
The high solubility’s of polar compounds in water.
Give two examples of common molecules that have hydrogen bonding between the molecules.
HF
NH₃
What are Van der Waal’s forces?
Weak intermolecular forces of attraction that exist between all states of matter.
What are Van der Waal’s forces caused by?
Caused by the internal shifts in the electrons in the molecule.
Why is there a temporary dipole set up in the molecule of Van der Waal’s forces of attraction?
As at any given time the electrons being shared may be closer to one end of the molecule than the other.
Does it require a lot of energy to break Van der Waal’s forces?
No
What attract each other using Van der Waal’s forces of attraction?
Non-polar molecules
What are the only intermolecular forces of attraction between gaseous molecules?
Van der Waal’s forces.
What are dipole-dipole interactions?
Weak intermolecular forces of attraction between polar molecules.
What are dipole-dipole interactions described as being?
Permanent dipoles
Why are dipole-dipole interactions described as being permanent dipoles?
As the molecules are constantly polar.
Is the energy needed to break dipole-dipole attractions constant or does it vary?
Varies
How much energy is need to break dipole-dipole interactions, in comparison to Van der Waal’s and hydrogen bonding?
More energy than that needed to break Van der Waals and less than needed to break Hydrogne bonding.
What are the boiling point of a substance and its state of matter determined by?
(a) the strength of the intermolecular forces of attractions
(b) the size of the molecule
The stronger the intermolecular forces and the larger/heavier the molecule …………………………
the more energy will be required to break the molecules up from each other.
How polar are ionic compounds?
Extremely polar
Which compounds have the strongest forces of attractions?
Ionic compounds
Which compounds have high boiling points and are usually crystalline solids?
Ionic compounds
What compounds have relatively lower boiling points and may be liquids?
Polar covalent compounds that have hydrogen bonding between the molecules.
What compounds have high boiling points, may be gases and are slightly weaker than polar compounds that have hydrogen bonding between the molecules?
Polar covalent compounds that have dipole-dipole interactions.
What compounds have extremely low boiling points and generally tend to be gases (but exceptions occur)
Compounds with the very weak Van der Waal’s forces.
Checklist for questions on states of matter or boiling points.
1, Get electronegativity difference to determine the type of intramolecular bonding.
- ↳ This will then determine the strength of the inter bonding i.e. intra = ionic, inter = extremely strong etc.
- ↳ reason for the state of matter or the high or low boiling point and the size of the molecule.
Use electronegativity values to predict the type of bond expected between hydrogen and sulfur. (L.C)
Weakly polar / almost non-polar
Write the chemical equation for hydrogen sulphide. (L.C)
H₂S
Would you expect the hydrogen sulphide molecule to be linear or non-linear in shape? Justify your answer.(L.C)
- Non-linear
- There are lone(non-bonding) pairs
Hydrogen sulphide has a boiling point of 212.3 K and water has a boiling point of 373 K. Account for the difference in the boiling points of these substances. (L.C)
- Water has hydrogen bonds
- Weak dipole-dipole forces in H₂S /
- Weaker intermolecular forces in H₂S
Would you expect hydrogen sulphide to be soluble in water? Explain your answer. (L.C)
- No / only slightly soluble
- Does not form hydrogen with water
Explain the term intermolecular forces (L.C)
Attractive (repulsive) forces between molecules.
Use your knowledge of intermolecular forces to explain why methane has a very low boiling point (164°C) (L.C)
- Very weak intermolecular forces
- Weak Van der Waal’s forces of attraction
The relative molecular mass of methane is only slightly lower than that of water but the boiling point of water is much higher (100°C). Suggest a reason for this. (L.C)
- Much stronger hydrogen bonds between water molecules
Why do ionic substances conduct electricity when molten or dissolved in water but not in the solid state? (L.C)
Molten/dissolved : ions free to move
Solid : ions not free to move / ions locked in position
Show that the ammonia molecule (NH₃) has polar covalent bonding. Describe the processes involved when ammonia dissolves in water. (L.C)
- There is an electronegativity difference between N and H
- Showing unequal sharing
- N with greater attraction
Define electronegativity (L.C)
The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.
Account for the difference in bond angle between the two molecules, 107.3 degrees in ammonia and 109.5 degrees in silane. (L.C)
- Lone pair of electrons has greater repelling power than a bond pair of electrons.
- Bonds in NH₃ pushed closer together than in SiH₄
- Ammonia has three bond pairs where silane has four bond pairs
Use electronegativity values to determine which bond, the N-H bond in ammonia or the Si-H bond in silane, is the more polar. (L.C)
N - H = 0.84
Si - H = 0.3
⇒
N - H is more polar
Define electronegativity (L.C)
The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.
Use electronegativity values to determine which bond, the N-H bond in ammonia or the Si-H bond in silane, is the more polar. (L.C)
N - H = 0.84
Si - H = 0.3
⇒ N - H is more polar
Which of the two substances ammonia (NH₃) or silane (SiH₄) has hydrogen bonding between its molecules? Justify your answer. (L.C)
- Ammonia
- In ammonia hydrogen bonded to a small highly electronegative element
Give the reason why a molecule with polar bonds can be non-polar. (L.C)
- Centres of positive and negative charge coincides
- Dipole moments cancel
Why is there an increase in electronegativity value moving from gallium to germanium in the periodic table? (L.C)
- Nuclear charge increasing
- Atomic radius increasing
Define electronegativity (L.C)
The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond..
Write the molecular formula for the simplest compound formed between germanium (IV) and hydrogen. (L.C)
GeH₄
Would you expect the compound GeH₄ to be water soluble? Explain your answer. (L.C)
- No
- GeH₄ is a non-polar solute
Suggest a reason why ammonia has the highest boiling point of ammonia, phosphine and arsine. (L.C)
Hydrogen bonding in ammonia (azane) is stronger than the other intermolecular forces in phosphane or arsane.
Suggest a reason why phosphine’s boiling point is lower than that of arsine. (L.C)
- Phosphine molecules are smaller
- Phosphine has a smaller degree of intermolecular forces
Define electronegativity (L.C)
The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.
Use electronegativity values to predict the type of bonding in chlorine monofluoride. (L.C)
Polar covalent
Define electronegativity (L.C)
The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.,
