1.3 Structure and Bonding Flashcards
Order of strength of bonds:
Covalent/dative covalent
Ionic
Metallic
H-Bonds
Dipole-dipole attractions
Van der waal’s forces
Define an ionic bond.
Strong electrostatic attractions between ions of opposite charge (be specific in questions) made by electron transfer. The metal gives up electrons whilst the non-metals accept electrons.
Define a covalent bond.
The sharing of a pair of electrons between 2 atoms of similar electronegativities.
Define dative covalent bonding.
The sharing of a pair of electrons but both shared electrons come from 1 atom only.
What are the 2 rules of the VSEPR?
-Covalent bonds are made of electron pairs. They repel each other as far apart as possible.
-Order of repulsion:
2 lone pairs > lone pair-bonding pair> 2 bonding pairs
(lone pairs repel more than bonding pairs of electrons)
What is the effect of each addition of a lone pair on the bond angle?
The bond angle decreases by 2.5 degrees each time.
Define metallic bonds.
Regularly arranged positive metal ions in a sea of delocalised electrons.
Why are metals malleable and ductile?
Layers of atoms/ ions move over each other, new metallic bonds form in new positions (just as strong as the original)
Diff between intramolecular and intermolecular forces.
Intramolecular- between atoms in one molecule
Intermolecular- between 2 separate molecules
Define electronegativity.
The power of an atom to attract electrons towards itself from a covalent bond.
What are the most electronegative elements and why?
N, O, F
-few shells and shielding
-nucleus is close to the bonding electrons
-therefore best at pulling electrons towards themselves
What factors affect electronegativity and how?
Atomic radius- the smaller the atomic radius the higher electronegativity
Shells and shielding- the fewer shells the higher the electronegativity
Nuclear charge- the higher the number of protons the higher the electronegativity
Electronegativity trend down a group:
Decreases
-more shells and more shielding
-the nucleus is further away from the electrons in the covalent bond
Electronegativity trend across a period:
Increases
-same shells and same shielding
-but the number of protons increases
Diff between non-polar bonds and polar bonds.
Non-polar bonds:
2 atoms with same/very similar electronegativities. Equal sharing of electrons
Polar bonds:
2 atoms that are both electronegative BUT one is more electronegative than the other
(so electrons are more attracted towards the more electronegative atom (delta +ve to delta -ve))
Polar molecules
Just because a molecule has polar bonds it does not meant that it will be a polar molecule (a DIPOLE)
There has to be an uneven distribution of delta negative areas resulting in an overall movement of electrons.
Describe van der waal’s and how they are formed.
Occurs between 2 non-polar molecules
TEMPORARY electron fluctuations cause an induced dipole which will induce a dipole in a neighbouring molecule so they temporarily stick together.
Describe dipole-dipole attractions
Occurs between 2 polar molecules (permanent dipoles)
Describe Hydrogen bonds and how they are formed.
Must have one of the 3 most electronegative elements (N,O,F) and a lone pair of electrons ON ONE MOLECULE and a partially positive hydrogen ion bonded to N,O,F ON THE OTHER
MOLECULE
The hydrogen bond is an attraction between hydrogen and lone pair of electrons.
Criteria for drawing H-Bonds:
-Show all lone pairs
-H-bond is LINEAR
-Put all partial charges on both molecules
Describe structure and bonding in a giant ionic lattice.
Very strong ionic bonds
Very high melting point as there are many ionic bonds that need to be broken, requiring a lot of energy
Does not conduct as a solid- no free moving electrons or ions but does conduct when molten or aqueous because the ions are free to move.
Giant covalent/macromolecular: describe the structure and bonding in diamond.
4 covalent bonds per carbon atom
V high melting point- lots of strong covalent bonds requiring a lot of energy to break
V hard
Insoluble in any solvent
Does not conduct- no free moving electrons or ions
Giant covalent/macromolecular: describe the structure and bonding in graphite.
3 covalent bonds per carbon atom, 4th outer electron of each atom is delocalised
Layer structure made of hexagonal rings
High melting point- van der waals forces have t o break (between layers) and then the strong covalent bonds
Insoluble in any solvent
Slippery, used as a dry lubricant- sheets can slide over each other
Does conduct- delocalised electrons free to move along layers (not between) allowing a current to flow
Giant covalent/macromolecular: structure and bonding in Silicon dioxide (sand)
Each O shared between 2 Si atoms, similar to diamond
High melting point- lots of strong covalent bonds require lots energy to break
Hard- strong covalent bonds
Does not conduct- no free moving ions or electrons
Insoluble in water and organic solvents
Describe structure and bonding in simple molecular- VAN DER WAALS
Molecules bonded by van der waals or H-bonds BETWEEN THEM
e.g Iodine
V low melting point- only van der waals need to be broken so little energy required, it sublimes all at same time
Does not conduct- no free moving electrons or ions
Insoluble in water as it is non-polar
Non-polar molecules cannot
dissolve in polar molecules
Describe properties in simple molecular- H-BONDS
Higher boiling point than expected
Surface tension
-reason for meniscus
-allows transport of water in xylem
Water (liquid) has a greater density than ice because the H-Bonds hold the water molecules apart
Evidence for hydrogen bonds from boiling points of compounds:
H2X
H2O
H2O
Higher boiling point than expected because there are 2 hydrogen bonds per H2O molecule
Evidence for hydrogen bonds from boiling points of compounds: XH3
NH3
Has a higher boiling point than expected
has hydrogen bonds between the molecules
Evidence for hydrogen bonds from boiling points of compounds: XH3
PH3 to AsH3 to SbH3
Boiling points increase:
Van der waals forces between the molecules
Increase in the number of electrons in the molecules therefore and increase in electron fluctuations therefore stronger van der waals between the molecules
