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
Given an example of an ionically bonded substance
NaCl (Sodium Chloride - salt)
Define covalent bonding
Electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
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 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 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 + charge and oxygen atoms have a - 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 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 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?
The 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 marks)
● High melting and boiling point
● Non conductors of electricity, except graphite
● Insoluble in polar and 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 and boiling points?
Strong covalent bonds within the molecules need to be broken which requires a lot of energy
Draw and describe the structure of a diamond
3D tetrahedral structure of C atoms, with each C atom
bonded to four 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?
Linear
180°
What is the shape, diagram and bond angle in a shape with 3
bonding pairs and 0 lone pairs?
Trigonal planar
120°
What is the shape, diagram and bond angle in a shape with 4
bonded pairs and 0 lone pairs?
Tetrahedral
109.5°
What is the shape, diagram and bond angle in a shape with 5
bonded pairs and 0 lone pairs?
Trigonal bipyramidal
90° and 120°
What is the shape, diagram and bond angle in a shape with 6
bonded pairs and 0 lone pairs?
Octahedral
90°
What is the shape, diagram and bond angle in a shape with 3
bonded pairs and 1 lone pairs?
Pyramidal
107°
What is the shape, diagram 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 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?
Attractive force between neighbouring
molecules
What are the 3 types of intermolecular forces?
in order of strength
hydrogen bonding
permanent dipole-dipole forces
induced dipole-dipole interactions (london dispersion forces)
What is the strongest type of intermolecular force?
hydrogen bonding
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 dispersion 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 dispersion 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 force 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 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
