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 lattice
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 positve metal ions and the sea of delocalised electrons
Electrons in which shell are represented in a dot and cross diagram?
The outer shell
Why do giant ionic lattices conduct electricity when liquid but not when solid?
In solid state the ions are held 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 points? 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
Why are ionic compounds soluble in water?
Water has a polar bond. Hydrogen atoms have a δ⁺ charge and oxygen atoms have a δ⁻ 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 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 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 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 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 particle to mave around
Simple molecular structures dissolve in what type of solvent?
Non polar solvents
Give an example of a giant covalent structure
- Diamond
- Graphite
- Silicon dioxide
What are some properties of giant covalent structures?
- High melting and boiling points
- Non conductors of electricity except graphite
- Insoluble in polar and non polar solvents
How does graphite conduct electricty?
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 lots of energy
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 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 bonded 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 bipyramidal
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 pairs
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 abilty 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 is meant 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 symetrical molecule so there is no overall dipole
What is meant by intermolecular force
Attractive forces between neighbouring molecules
What are the two types of intermolecular forces?
- Hydrogen bonding
- Van der Waals’ forces
What is the strongest type of intermolecular force?
Hydrogen bonding
Describe London forces?
- Londone 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 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
Why is ice less dense than liquid water?
- In ice the water molecules are arranged in orderly patterns. It has an open lattice with hydrogen bonds
- In water the lattice is collapsed and the molecules are closer toegether
Why does water have a higher melting/ boiling point than expected?
Hydrogen bonds are stronger than other intermolecular forces so extra strength is required to overcome the forces
