Bonding Flashcards
Describe the structure of ionic compounds?
Giant ionic lattice
Electrostatic forces of attraction between oppositely charged ions
What are the properties of ionic compounds and why?
Electrical Conductivity:
Ionic compounds do not conduct electricity when solid as the ions are not free to move and carry charge but they can when molten or aqueous as the ions are free to move.
Strength:
Ionic compounds shatter easily as they are brittle
Any disruption to the structure causes negative ions to align and repel
Melting point:
Ionic compounds have a high melting point as there is strong electrostatic forces of attraction between oppositely charged ions, and forces act in all directions
What is the rule with high melting points?
The larger the charge of the ion the stronger the attraction and the smaller the ion the stronger the attraction therefore higher melting points
What are the properties of metals (metallic bonding)
Electrical Conductivity:
Metals can conduct electricity due to the movement of the sea of delocalised electrons through the structure
Heat Conductivity:
Metals can conduct heat due to the energy of the sea of delocalised electrons increasing which makes them move faster
Metals are malleable as they can be shaped without breaking
Metals are ductile which means they can be drawn into wires
Strength:
Metals are strong as they have a strong electrostatic force between the positive ions and the negative sea of delocalised electrons
What does strength depend on?
The charge on the ion and the size (high charge but small)
Why do smaller ions attract electrons more strongly?
The electrons are closer to the nucleus
What does covalent bonding consist of?
A shared pair of electrons
When do covalent bonds form?
When orbitals, each containing one electron overlap, this forms a region in space where an electron pair can be found; new molecular orbitals are formed. (The greater the overlap the stronger the bond)
Describe the Octet Rule.
The tendency of atoms to prefer to have 8 electrons in the outer shell and when atoms have fewer than 8 they tend to react and form more stable compounds. With this rule we do not consider d or f electrons instead we consider s and p electrons.
What is co-ordinate bonding?
A shared pair of electrons but both electrons come from the same atom - represented by an arrow —->
What are the properties of simple covalent molecules?
- Low melting and boiling point (weak intermolecular forces)
- Poor conductors of electricity - If they dissolve in water and remain as molecules, the solutions do not conduct electricity.
What is electronegativity?
It is the power of an atom to attract the electron density in a covalent bond towards itself.
State and explain the factors affecting electronegativity?
Large nuclear charge- More protons, so stronger attraction between nucleus and bonding pair of electrons
Small atomic radius- Electrons closer to the nucleus so there is a stronger attraction between nucleus and bonding pair of electrons
Less shielding- Less shells of electrons between the nucleus and electrons therefore less shielding (repulsion) so stronger attraction between nucleus and bonding pair of electrons.
What is the trend in electronegativity down a group?
There is a decrease in electronegativity down a group as nuclear charge increases but atomic radius increases therefore there is less attraction between the positive nucleus and bonding pair of electrons
What is the trend in electronegativity across a period?
There is an increase in electronegativity across a period as nuclear charge increases and atomic radius decreases and shielding stays the same. Therefore there is a stronger attraction between the nucleus and bonding pair of electrons
What is polarity?
The unequal sharing of electrons between the atoms that are bonded covalently
Is there bond polarity when two atoms are identical?
No because the electrons are equally distributed so there is no difference in electronegativity
How is a dipole formed?
One atom will pull the electrons closer to its end, it will have a slight negative charge and the other will have a slight positive charge therefore there is a difference in electronegativity which leads to a charge difference (dipole)
What is the difference between intramolecular bonds and intermolecular forces?
Intramolecular bonds affect chemical properties eg. reactivity
whereas intermolecular forces affect physical properties eg. boiling point (applies to simple covalent molecules)
What are the 3 types of forces?
Van der Waals which acts between all atoms and molecules , Dipole-dipole which only act between certain types of atoms and hydrogen bonding which also only acts between certain atoms
What does the Van der Waals force consist of?
An instantaneous dipole and an induced dipole are bonded together and there is a repulsion of electrons
Give an example of Dipole-dipole forces.
2 H-Cl peramanent dipoles have an attraction so positive and negative part bond together. The extra attraction between dipoles means more energy is required to seperate molecules so higher BP
What is hydrogen bonding?
It is when hydrogen is covalently bonded to F, N and O, the bond is highly polarised that the H of one molecule forms a weak bond with F , N , O of another molecule, often attracted to lone pairs.
