2.2.2 bonding and structure Flashcards
What is ionic bonding?
Ionic bonding is the electrostatic attraction between positive and negative ions.
What is the structure like in a giant ionic lattice?
Each ion is surrounded by oppositely charged ions, forming a giant ionic lattice.
Why are ionic compounds usually solids at room temperature?
There is insufficient energy to overcome the strong electrostatic forces of attraction between the oppositely charged ions in a giant ionic lattice. Due to this they have high melting and boiling points.
Why do many ionic compounds dissolve in polar solvents?
Polar molecules break down the lattice and surround each ion in solution.
What are the two main processes for solubility?
-ionic lattice must be broken down
-water molecules attract and surround the the ions
Why do not all ionic compounds dissolve in polar solvents?
Ionic compounds made of ions with large charges, the ionic attraction may be too strong for water to be able to break down the lattice structure.
Why do ionic compounds in their solid state not conduct electricity?
The ions are in a fixed position and there are no mobile charge carriers making it a non-conductor.
Why do ionic compounds conduct electricity when liquid or dissolved?
The solid state of the ionic lattice breaks down and the ions are now free to move as mobile charge carriers making it a conductor.
What is covalent bonding?
Covalent bonding is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
What is a dative covalent bond?
A dative bond is a covalent bond in which the shared pair of electrons has been supplied by one of the atoms only.
What is average bond enthalpy?
Average bond enthalpy serves as a measurement of covalent bond strength.
What is the electron-pair repulsion theory?
-electron pairs repel as far as possible
-lone pairs will repel more strongly than bonding pairs
-lone pairs will push bonding pairs closer together
What is the bond angle and pairs of a linear molecule?
A linear molecule has:
2 bonding pairs
0 lone pairs
180 degrees
What is the bond angle and pairs of a non-linear molecule?
A non-linear molecule has:
2 bonding pairs
2 lone pairs
104.5 degrees
What is the bond angle and pairs of a trigonal planar molecule?
A trigonal planar molecule has:
3 bonding pairs
0 lone pairs
120 degrees
What is the bond angle and pairs of a pyramidal molecule?
A pyramidal molecule has:
3 bonding pairs
1 lone pair
107 degrees
What is the bond angle and pairs of a tetrahedral molecule?
A tetrahedral molecule has:
4 bonding pairs
0 lone pairs
109.5 degrees
What is the bond angle and pairs of an octahedral molecule?
An octahedral molecule has:
6 bonding pairs
0 lone pairs
90 degrees
What is electronegativity?
Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond.
How is electronegativity measured?
The Pauling scale is used to compare the electronegativity of the atoms of different elements.
What is the trend of the Pauling scale?
Across the periodic table the electronegativity increases and increase up the table.
What is a non-polar bond?
The bonded electron pair is shared equally between the bonded atoms.
When will a bond be non-polar?
A bond will be non-polar when the bonded atoms are the same or the bonded atoms have similar or the same electronegativity.
What is a polar bond?
The bonded electron pair is shared unequally between the bonded atoms.
What is an intermolecular force?
Intermolecular forces are weak interactions between dipoles of different molecules.
What are the three main categories of intermolecular forces?
Induced dipole-dipole interactions (LDF)
Permanent dipole-dipole interactions
Hydrogen bonding
What is an induced dipole-dipole interaction?
-movement of electrons produces a changing dipole in a molecule
-an instantaneous dipole exists
-instantaneous dipole induces a dipole on a neighbouring molecule
-induced dipole induces further dipoles on neighbouring molecules
What effects the strength of an LDF?
The number of electrons:
-more electrons=larger instantaneous and induced dipoles
-more electrons=the greater the induced dipole-dipole interactions
-more electrons=the stronger the attractive forces between molecules
What is the structure of a simple molecular lattice?
In a simple molecular lattice the molecules are held in place by weak intermolecular forces and the atoms within each molecule are bonded together strongly by covalent bonds.
Why do simple molecular substances have low and melting points?
In a simple molecular lattice, the weak intermolecular forces can be broken by little energy (room temperature).
What happens when a simple molecular lattice is broken apart during melting?
Only the weak intermolecular forces break, and the covalent bonds are strong and do not break.
What happens when a simple molecular compound is added to a non-polar solvent?
Intermolecular forces form between the molecules and the solvent.
The interactions weaken the intermolecular forces in the lattice, and the intermolecular forces break and the compound dissolves.
Why are simple molecular substances insoluble in polar solvents?
There is little interaction between the molecules in the lattice and the solvent molecules.
The intermolecular bonding within the polar solvent is too strong to be broken.
Why are simple molecular compounds non-conductors of electricity?
There are no mobile charge carriers that can move within the structure, and with no charged particles that can move, there is nothing to complete an electrical circuit.
What atoms bond with hydrogen to create a hydrogen bond?
Oxygen
Florine
Nitrogen
What is the order of intermolecular forces by strength?
strongest-
Hydrogen bonding
Permanent dipole-dipole
Induced dipole-dipole (LDF)
weakest-
What are two anomalous properties of water and explain?
-The solid is less dense than the liquid.
Hydrogen bonds hold water molecules apart in an open lattice structure. The water molecules in ice are further apart than in water and so solid ice is less dense than liquid water and floats.
-Relatively high melting and boiling point.
An appreciable quantity of energy is needed to break hydrogen bonds in water.
