Studied by 12 people
What are polyatomic ions
Ions made up of more than one atom which together have experiences a loss/gain of electrons so carry a charge
What are the charges of polyatomic ions
Nitrate = 1-
Hydroxide = 1-
Hydrogencarbonate = 1-
Carbonate = 2-
Sulfate = 2-
Phosphate = 3-
Ammonium = 1+
What is the co-ordination number in a lattice structure
expresses the number of ions that surround a given ion in a lattice structure
What are the properties of ionic lattice structures
High melting and boiling points due to the strong electrostatic forces.
Solids at room temperature
Non volatile (does not tend to vapourize)
Soluble in polar solvents
Conducts electricity when molten or dissolved as the ions are free to move
Brittle due to the movements in the ions places similar charges next to each other, causing repulsion
How does the electronegativity determine if a substance will bond ionically
if the electronegativity difference between the 2 atoms is greater than 1.8
What makes up a double bond
one sigma bond and one pi bond
What makes up a triple bond
one sigma bond and two pi bonds
How does bond length affect bond enthalpy
A longer bond is weaker due to the electron pair being further from the pull of the nuclei in larger molecules. A larger atomic radius means a longer bond.
How does the bond length and enthalpy change between single, double and triple bonds.
The longest bond is single, and the shortest is triple
Meaning the triple bond is the strongest
What is a coordinate (dative) bond
Both electrons in the shared pair are from one atom. This bond is shown by an arrow
What are the exceptions to the octet rule.
Boron and beryllium
They form stable molecules where the central atom has fewer than 8 electrons in the valence shell. These are said to be electron deficient and have the tendency to form a coordinate bond to complete the octet.
How do London Dispersion forces occur
When at a random moment, the electron cloud can be stronger in a certain area causing an instantaneous dipole. This can induce a dipole of another molecule causing attraction called London dispersion forces.
What is a sigma bond
When 2 s, 2 p or and s and a p orbitals overlap
This occurs along the bond axis
This always forms in a single covalent bond
What is a pi bond
When 2 p orbitals overlap sideways
They are weaker than sigma bonds.
They occur in double and triple bonds
What occurs in sp2 hybridisation
One s orbital and 2 p orbitals hybridise to produce 3 equal sp2 orbitals.
How does the number of electron domains show us the hybridisation
2 electron domains = sp
3 electron domains = sp2
4 electron domains = sp3
What are the properties of London dispersion forces
The weakest type of intermolecular bonds
Increases with a greater number of electrons as this increases the change of an instantaneous dipole
Only forces which exist between non polar molecules
What are dipole-dipole attractive forces
Occurs when there is a difference in electronegativities causing a permanent dipole. These dipoles will attract neighbouring molecules
What are the properties of dipole-dipole forces
Stronger than London Dispersion
Occurs between polar molecules
What are Van der Waals forces
An umbrella term which includes
Dipole-dipole
Induced dipole-dipole
Induced dipole-Induced dipole
What is hydrogen bonding
When the hydrogen electron pair is pulled away by nitrogen, oxygen or flourine due to high electronegativity differences
What are the properties of hydrogen bonds
The strongest type of intermolecular forces
Most prominent in water, causes many of waters distinguishable features
What is the strength of a metallic bond determined by
The number of delocalised electrons (more = stronger)
The charge of the cation (more = stronger)
The radius of the cation (smaller = stronger)
When does a net dipole occur
When there are different elements (with different electronegativities) bonded to the same central ion, and it is non symmetrical
The presence of lone pairs, and it is non symmetrical
What is the equation for formal charge
FC = number of valence electrons - (1/2 electrons in bonded pairs + number of electrons in lone pairs)
What is formal charge used for
to determine the most stable structure from a variety of possible structures
The formal charge closest to zero means a more stable structure
Note
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