Week 5: Bonding Flashcards
(28 cards)
Why do atoms react?
To gain a full outer shell.
What do ionic compounds often exist (as in the solid state)?
Giant crystalline lattices with alternating cations and anions, held together by the attraction of their opposite charges.
What are the properties of Ionic Compounds?
- High melting points
- Often water soluble
- Conduct electricity when liquid or in the aqueous solution.
- Crystals shatter easily
Why do ionic compounds have high melting/boiling points?
Held together by strong electrostatic forces.
What causes electrical conductivity?
The movement of charged particles, such as ions.
Why can ionic compounds conduct electricity when melted?
The ions are fused are free to move about.
How can ionic compounds conduct electricity in an aqueous solution?
The layers of water molecules reduce the attractions of positive and negative ions, meaning that the kinetic energy of the ions is enough for them to move freely.
- Ions will then move towards charged electrodes.
What does it mean if ions are hydrated?
Soluble ionic lattices dissolve when placed into water.
The ions become surrounded by water molecules and are said to be hydrated.
Why are ions and water attracted to eachother?
As water is a polar molecule
Why is water a polar molecule?
H and O2 are share electrons but the oxygen has a greater attraction for the shared electrons.
This makes the oxygen slightly more negative.
What is electronegativity?
A value which shows how much an element holds onto its electrons.
Which factor influences electronegativity?
Nuclear charge
(Shown by electronegativity increasing along rows)
What is a Covalent bond?
A bond involving shared electrons.
Involves non-metals.
How does electronegativity influence covalent bonds?
Occurs with elements that have almost identical electronegativities.
What is a dipole?
Bond/Molecule with ends that have opposite charges.
Are polar covalent molecules soluble in water?
Yes
Are non-polar molecules soluble in water?
No
What are Van-der-Waals forces?
- As an atom moves its electrons are moving meaning there will be points when the nucleus of the atom is not directly at the centre.
- This means that the side furthest away from the nucleus will be more negative due to the electron cloud being more on one side than the other.
- This forms a temporary dipole.
- This may induce a dipole in another atom, making it an induced dipole.
- Induced-dipole-Induced-dipole interactions are called Van der Waals forces.
What increases Van der Waals forces?
Molecular size due to larger electron clouds
Is a a water-insoluble molecule hydrophilic or hydrophobic?
Hydrophobic
How does as a water-insoluble molecule interact when places in water?
Hydrophobic - So they will clump together in order to minimise disruption to the H-bonding network in water.
How does Hydrogen bonding occur?
Interaction between a hydrogen attached to an electronegative element and an atom with a lone pair of electrons.
How do hydrogen bonds hold other elements together?
- When a hydrogen atom is covalently bonded to a very electronegative element (such as fluorine or oxygen), the polarity enables different molecules to attract each other.
- These forces are in addition to the van der Waals forces already present.
- The hydrogen atoms act as a bridge between atoms of the other element.
- The links between the hydrogen atoms and the electro negative atoms are called hydrogen bonds.
Order the three bonds in terms of strength?
Covalent
Van der Waals
Hydrogen
