Bonding & Structure Flashcards
What are the 3 main types of chemical bonds?
- Ionic
- Covalent
- Metallic
Define ionic bonding
The electrostatic attraction between positive & negative ions
Give an example of a iconically bonded substance
NaCl ( Sodium Chloride - salt)
Define covalent bonding
Electrostatic attraction between a shared pair of electrons and the nuclei
Define metallic bonding
Electrostatic attraction between the positive metal ions and the sea of delocalised electrons
Electrons in which shell are represented in a dot & cross diagram
The outer shell
Why do giant ionic lattices conduct electricity when liquid but not when solid?
In solid state the ions are in fixed positions and therefore cannot move. When they are in liquid state the ions are mobile and can freely carry the charge.
Do giant ionic lattices have a high or low melting & boiling point?
They have a high melting and boiling point because a large amount of energy is required to overcome the electrostatic bonds.
In what type of solvents do ionic lattices dissolve?
Polar solvents
E.g water
Why are ionic compounds soluble in water?
Water has a polar bond. Hydrogen atoms have a positive charge (1+) and oxygen atoms and a negative charge (2-). These charges are able to attract charged ions
What is it called when atoms are bonded by a single pair of shared electrons?
A single bond
How many covalent bonds does carbon form?
4
How many covalent bonds does oxygen form?
2
What is a lone pair?
Electrons in the outer shell that are not involved in the bonding
What is formed when atoms share 2 pairs of electrons?
A double bond
E.g CO2 O = C = O
What is formed when atoms share 3 pairs of electrons?
A triple bond
What is the average bond enthalpy
Measure of average energy needed to break the bond
What is a dative covalent bond?
A bond where both of the shared electrons are suppplied by 1 atom
How are Oxonium ions formed?
Formed when acid is added to water,
H3O+
What does expansion of the octet mean?
When a bonded atom has more than 8 electrons in the outer shell
What are the types of covalent structure?
- Simple molecular lattice
- Giant covalent lattice
Describe the bonding in simple molecular structures
Atoms within the same molecule are held by strong covalent bonds and different molecules are held by weak intermolecular forces
Why do simple molecular structures have low melting & boiling points?
A small amount of energy is enough to overcome the weak intermolecular forces
Can simple molecular structures conduct electricity?
No, they are not conductors
Why don’t simple molecular structures conduct electricity?
They have no free charged particles to move around
Simple molecular structures dissolve in what type of solvent?
Non polar solvents
Give examples of giant covalent structures
Diamond
Graphite
Silicon dioxide, SiO2
List some properties of giant covalent structures
High melting & boiling point
Non conductors of electricity, (except graphite)
Insoluble in polar & non polar solvents
How does graphite conduct electricity
Delocalised electrons present between the layers are able to move freely carrying the charge
Why do giant covalent structures have high melting & boiling point?
Strong covalent bonds within the molecules need to be broken which requires a lot of energy
Draw & describe the structure of a diamond
3D tetrahedral structures of C atoms, with each C atom bonded to 4 others
What does the shape of a molecule depend on?
Number of electron pairs in the outer shell
Number of these electrons which are bonded and lone pairs
What is the shape, diagram and bond angle in a shape with 2 bonded pairs and 0 lone pairs?
E.g?
Linear
180 degreees
BeCl2
What is the shape, diagram and bond angle in a shape with 3 bonding pairs and 0 lone pairs?
Trigonal planar
120 degrees
What is the shape, diagram and bond angle in a shape with 4 bonded pairs and 0 lone pairs?
Tetrahedral
109.5 degrees
What is the shape, diagram and bond angle in a shape with 5 bonded pairs and 0 lone pairs?
Trigonal bipyramid
90 degrees and 120 degrees
What is the shape, diagram and bond angle in a shape with 6 bonded pairs and 0 line pairs?
Octahedral
90 degrees
What is the shape, diagram and bond angle in a shape with 3 bonded pairs and 1 lone pairs?
Pyramidal
107 degrees
What is the shape, diagram and bond angle in a shape with 2 bonded pairs and 2 lone pairs?
Non linear
104.5 degrees
By how many degrees does each lone pair reduce the bond angle?
2.5 degrees
Define electronegativity
The ability of an atom to attract the pair of electrons (the electron density) in a covalent bond
In which direction of the periodic table does electronegativity increase?
Top right, towards fluorine
What does it mean when the bond is non-polar?
The electrons in the bond are evenly distributed
What is the most electronegative element?
Fluorine
How is a polar bond formed?
Bonding atoms have different electronegativities
Why is H2O polar, whereas CO2 is non polar?
CO2 is a symmetrical molecule, so there is no overall dipole
What is meant by intermolecular force?
The attractive force between neighbouring molecules
What are the 2 types of intermolecular forces?
Hydrogen bonding
Van der Waals’ forces
What is the strongest type of intermolecular force?
Hydrogen bonding
What are the 2 interactions that can be referred as Van der Waals’ forces?
Permanent dipole - induced dipole interaction
Permanent dipole - permanent dipole interaction
Describe permanent dipole-induced dipole interactions
When a molecule with a permanent dipole is close to other non polar molecules it causes the non polar molecule to become slightly polar leading to attraction
Describe permanent dipole-permanent dipole interactions
Some molecules with polar bonds have permanent dipoles — forces of attraction between those dipoles and those of neighbouring molecules
Describe London forces
London forces are caused by random movements of electrons
Thus leads to instantaneous dipoles
Instantaneous dipole induces a dipole in nearby molecules
Induced dipoles attract one another
Are London forces greater in smaller or larger molecules?
Larger due to more electrons
Are London forces greater in smaller or larger molecules?
Larger due to more electrons
Does boiling point increase or decrease down the noble gas group?
Boiling point increases because the number of electrons increases and hence the strength of London forces also increases
What condition are needed for hydrogen bond in to occur?
O-H, N-H or F-H bond, lone pair of electrons on O, F, N
Because O, N and F are highly electronegative, H nucleus is left exposed
Strong forces of attraction between H nucleus and lone pair of electrons on O, N, F
Why is ice less dense than liquid water?
In ice, the water molecules are arranged in an orderly pattern. It has an open lattice with hydrogen bonds
In water, the lattice is collapsed and the molecules are closer together
Why does water have a melting/ boiling point higher than expected?
Hydrogen bonds are stronger than other intermolecular forces so extra strength is required to overcome the forces
