Covalent bonding: When two atoms share pairs of electrons
A dative covalent bond forms when the shared pair of electrons in the covalent bond comes from only one of the bonding atoms.
Metallic bonding: the electrostatic force of attraction between positive metal ions and delocalised electrons
What are the 3 main factors affecting the strength of metallic bonding?
NuclearCharge
Number of Delocalised Electrons per atom
Size of Ion
What structure do ionic structures take? Giant Ionic Lattice
What are the properties of ionic compounds?
They are usually crystalline solids.
They have high melting points and boiling points.
They are usually soluble in water
They conduct electricity when dissolved in water or when melted
Explain 3 key properties of metals
High melting points due to strong metallic bonds in giant metallic structures, these are hard to break
Good conductors of electricity because delocalised electrons can move through the structure and carry a charge
Malleable because layers of ions can slide over each other, held together by electrostatic forces
Describe properties of simple molecules
Low boiling / melting points - due to weak intermolecular forces between molecules
Poor conductivity because there aren't any ions + electrons are localised
Linear:
b.p = 2
l.p = 0
bond angle = 180
example = CO2BeF2
Trigonal Planar
b.p = 3
l.p = 0
bond angle = 120
example = BF3 , AlCl3
Tetrahedrall:
b.p = 0
b.p = 4
bond angle = 109.5
Trigonal Bipyramidal:
b.p = 5
l.p = 0
b.a = 90 and 120
Trigonal Pyramida:
b.p = 3
l.p = 1
b.a = 107
Bent
b.p = 2
l.p = 2
b.a = 104.5
examples = H20, SCl2
What shape is formed from 4 bp and 1 lp? see-saw
What shape is formed from 3 b.p and 2 l.p? T shape
What shape is formed from 3 l.p and 2 b.p? Linear
What shape is made from 4 bond pairs and 2 lone pairs? Square Planar
Electronegativity: the power of an atom to attract bonded electrons in a covalent bond towards itself
FONCI are the most electronegative atoms
Electronegativity is measured on the Pauling scale, ranging from 0 to 4
Electronegativity will increase across a period as the number of protons increases but there is similar shielding.
Electronegativity will decrease down a group because the distance between the nucleus and bonded electrons increase and the shielding of the inner shell electrons increases.
Dipole moment: The overall effect of polarity of the bonds in a molecule
Describe van der Waals’ forces of attraction:
Temporary dipoles are created by the random movement of electrons
→ induces dipole in neighbouring molecule
→ temporary induced dipole-dipole attraction aka van der Waals forces of attraction
What factors lead to stronger Van Der Waals forces?
More electrons
Bigger surface area
The boiling point of halogens down group 7 increases because there are more electrons in bigger molecules .
Long chain alkanes have a higher b.p than spherical shaped alkanes because ...
There is a larger surface area of contact between chained molecules than there is spherical molecules.
Describe permanent dipole-dipole forces:
Electrostatic forces between polar molecules
Stronger than Van der Waals so compounds have higher boiling point
What is hydrogen bonding? The strongest type of intermolecularforce that forms between Hydrogen and F, O, N. The lone pair on these atoms attract a hydrogen atom on another molecule.
3 types of intermolecular forces:
Van Der Waals
Dipole-Dipole
Hydrogen Bonds
What are the 4 types of crystal structures?
Ionic
Metallic
Simple Molecular
Giant Covalent
Describe the properties of simple molecular compounds
low melting point because of weak intermolecular forces
poor solubility in water
poor conducitivity of electricity in solid/when molten as there are no ions / electrons are localised
generally mostly gases and liquids
State 5 properties of metals
high mp/bp due to strong attraction between +ve ions and sea of delocalised electrons
insoluble
good conductors of electricity
shiny
malleable, as layers of ions can slide over each other
Solid:
Arrangement: Tightly packed in a regular arrangement
Movement: Vibrate in fixed positions
Liquid:
Arrangement: Tightly packed in a random arrangement
Movement: Particles move freely and have more energy than in a solid
Gases:
Arrangement: Spaced out and in a random arrangement
Movement: Particles move freely and have lots of energy
Graphite is soft because the structure is in planes/layers and weak bonds between planes mean they can slide
Electronegativity: The power of an atom or nucleus to withdraw or attract a pair of electrons in a covalent bond