2.2.2 Bonding And Structure Flashcards
What is ionic bonding?
The strong electrostatic attraction between positive and negative ions
What is a giant ionic lattice?
A three-dimensional structure of positive and negative ions that are strongly attracted in all directions.
What are the properties of ionic bonding?
- between metals and non-metals
-electrons transferred from metal to non-metal - metal forms +ve ion and non-metal forms -ve ion
- oppositely charged ions have strong electrostatic attraction
What is the structure of ionic compounds?
Giant ionic lattice
3D structure of oppositely charged ions. Ions attract each other in all directions
What are the mpt and bpt of ionic compounds?
High mpt + bpt
Strong electrostatic attraction between +ve and -ve ions - requires a large amount of energy to overcome and break bonds
More highly charged ions = greater electrostatic attraction between ions
What is the conductivity of ionic compounds?
Don’t conduct electricity in solid state - fixed position in lattice
When molten or dissolved ions are free to move and current can flow
What is the solubility of ionic compounds?
Many compounds soluble in water
As dissolves, lattice breaks down and ions are released into solution and ions are stabilised by coordination to water molecules.
Ionic compounds are soluble in polar substances
What is a covalent bond?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Why do atoms expand their octet?
Usually atoms can form enough covalent bonds to obtain noble gas configuration- not always possible
- elements in period 3 or above can expand their octet using d-orbitals
- they do this as unpaired electrons pair up and the no that can pair up is equivalent to no of electrons in outer shell
What is a dative bond?
A covalent bond where the shared pair of electrons is provided by one of the bond atoms only.
When does covalent bonding take place?
Between non-metals
Electrons are shared between atoms
Can form simple molecular
Or giant structures e.g. diamond
What is average bond enthalpy?
Measurement of covalent bond strength
What is electron pair repulsion theory?
- the shape of a molecule is determined by the number of electron pairs in the outer shell of the central atom
# the electron pairs repel each other and arrange themselves as far apart as possible
What is a linear shape?
2 bp
180° bond angle
What is a trigonal planar shape?
3bp
120° bond angle
What is a tetrahedral shape?
4 bp
109.5° bond angle
What is a trigonal bipyramid shape?
5bp
90 and 120° bond angle
(see notes)
What is an octahedral shape?
6bp
90° bond angle
What happens when molecules have lone pairs?
Lone pairs repel more than bond pairs
Lp-lp > lp-bp > bp-bp
Each lone pair reduces the bond angle by 2.5
What is a non-linear shape?
2bp 2lp
Tetrahedral without 2 bonds
104.5° bond angle
What is a pyramidal shape?
3bp 1lp
Tetrahedral without 1 bond
107° bond angle
M3 to cm3
X 1,000,000
Describe simple molecular covalent
Atoms in molecule held together by strong covalent bonds
The molecules are held together with weak intermolecular forces
These could be:
London forces
Permanent dipole-dipole
Hydrogen bonds
Why are melting points of simple molecular substances low?
Not a large amount of energy needed to break the weak intermolecular forces. Covalent bonds aren’t broken bc they are strong
What is the electrical conductivity of covalent compounds?
Don’t conduct electricity because there are no free electrons or charged particles to move.
What is the solubility of covalent simple molecular structures?
Dissolve in organic (non-polar) solvents
But not in polar solvents such as water
Bc bonds need to be broken in the molecular structure and new bonds formed with solvent molecules (weak London forces are able to form between covalent molecules and these solvents, helping…)
Describe the structure of graphite
Each C is bonded to 3 other C atoms by STRONG COVALENT bonds. Each C atom has one further electron that contributes to the sea of delocalised electrons between LAYERS OF HEXAGONAL RINGS. Electron between layers = attractive force (albeit weak) that holds the layers together.
Describe the structure of diamond
Each C atom is bonded to 4 other C atoms with strong covalent bonds in a tetrahedral shape around each C.
What is the mpt and bpt of giant covalent structures?
Very high
Covalent bonds need to be broken and this takes up a large amount of energy
What is the electrical conductivity of giant covalent structures?
Diamond doesn’t conduct electricity - no free electrons, they are used in covalent bonds
Graphite can conduct electricity - electrons between layers are able to move parallel to layers when voltage is applied
What is the solubility of giant covalent structures?
To dissolve them would need huge amounts of energy as covalent bonds would need to be broken
What is metallic bonding?
Atoms in solid metal are held together by metallic bonding
Atoms are ionised
+ve ions (cations) occupy fixed positions in the lattice
outer shell electrons are delocalised and shared between all atoms in metallic structure
Metal is held together by attractions between all positive ions and negative electrons (especially delocalised electrons)
Describe metallic bonding structure
Delocalised electrons spread throughout the structure
Electrons can move within the structure
Charges are balanced over whole structure
Lattice of positive ions in fixed positions surrounded by sea of delocalised electrons that can move
What are the mpt and bpt of metals?
High
Electrons free to move through structure but ions fixed
Strong attraction between +ve ions and -ve electrons
High temperature needed to overcome metallic bonds and dislodge from rigid positions in lattice
What is the conductivity of metals?
Delocalised electrons can move freely and so metals can conduct electricity even when solid
What is the malleability and ductility of metals?
Ductile - can be drawn out and stretched, can be drawn into wires
Malleable - can be hammered to different shapes
Due to movement of delocalised electrons, atoms or layers can slide past each other
