2.2.2 Bonding and structure Flashcards
What are the 3 main types of chemical bonds?
Ionic
Covalent
Metallic
Define ionic bonding
The electrostatic attraction between positive and negative ions
Give an example of an ionically bonded substances
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 delocalized electrons
Electrons in which shell are represented in a dot and cross diagram
The outer shell
Why does giant ionic lattices conduct electricity when liquid but not when solid?
In solid state, the ions are in fixed positions and thus cannot move. When they are in liquid state, the ions are mobile and thus can freely carry the charge
Giant ionic lattices have high or low melting and boiling point? Explain your answer
They have high melting and boiling point because a large amount of energy is require 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 delta positive charge and oxygen atoms have a delta negative charge
These charges are able to attract charged ions
What is it called when atoms are bonded by a single pair of shared electrons?
Single bond
How many covalent bonds does carbon form?
4
How many covalent bond 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 two pairs of electrons
Double bond
What is formed when atoms share three pairs of electrons?
Triple bond
What is 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 supplied by one 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 and boiling point?
Small amount of energy is enough to overcome the intermolecular forces
Can simple molecular structures conduct electricity?
No, they are non conductors
Why do simple molecular structures not 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? (3)
High melting and boiling point
Non conductors of electricity, except graphite
Insoluble in polar and non-polar solvents
How does graphite conduct electricity?
Delocalized electrons present between the layers are able to move freely carrying the charge
Why do giant covalent structures have high melting and boiling point?
Strong covalent bonds within the molecules need to be broken which requires a lot of energy
Draw and describe the structure of diamond
3D tetrahedral structure 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 and bond angle in a shape with 2 bonded pairs and 0 lone pairs?
Linear
180
What is the shape and bond angle in a shape with 3 bonding pairs and 0 lone pairs?
Trigonal planar
120
What is the shape and bond angle in a shape with 4 bonded pairs and 0 lone pairs?
Tetrahedral
109.5
What is the shape and bond angle in a shape with 5 bonded pairs and 0 lone pairs?
Trigonal bipyramid
90 and 120
What is the shape and bond angle in a shape with 6 bonded pairs and 0 lone pairs?
Octahedral
90
What is the shape and bond angle in a shape with 3 bonded pairs and 1 lone pair?
Pyramidal
107
What is the shape and bond angle in a shape with 2 bonded pairs and 2 lone pairs?
Non linear
104.5
By how many degrees does each lone pair reduce the bond angle?
2.5
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?
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
This 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
Does boiling point increase or decrease down the noble gas group? Why?
Boiling point increases because the number of electrons increases and hence the strength of london forces also increases
What conditions are needed for hydrogen bonding 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
Draw a diagram of hydrogen bonding
hydorgen bondin
Why is ice less dense than liquid water?
In ice, the water molecules are arranged in a 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
