bonding and structure Flashcards
Why do simple molecular structures have low melting and boiling point
Small amount of energy is enough to overcome the intermolecular forces
Describe how metals are malleable and ductile
Layers of positive ions can easily slide over one another and take up different positions
In which direction of the periodic table does electronegativity increase
Top right, towards flourine
What is the strongest type of intermolecular force
Hydrogen bonding
What is meant by intermolecular force
Attractive forces between neighbouring molecules
Why is ice less dense than water
- In ice, the water molecules are arranged in an open lattice with hydrogen bonds
- In water, the lattice is collapsed and the molecules are closer together
Does boiling point increase or decrease going down the noble gas group, why?
- Boiling point increases
- Because the number of electrons increases
- And the strength of london forces also increases
How many covalent bonds does oxygen form?
2
What are the 3 main types of chemical bonds
- Ionic
- Covalent
- Metallic
Why do simple molecular structures not conduct electricity
They have no free charged particles to move around
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
Simple molecular structures dissolve in what type of solvent?
Non polar solvents
Describe pernament dipole-dipole interactions
- Some molecules with polar bonds have permanent dipoles
- Leading to forces of attraction between those dipoles and those of neighbouring molecules
In what type of solvents do ionic lattices dissolve?
Polar solvents
Define electronegativity
The ability of an atom to attract the pair of electrons (the electron density) in a covalent bond
How many covalent bonds does carbon form?
4
What is formed when atoms share two pairs of electrons
Double bond
Why do giant ionic lattices conduct electricity when liquid, but not when solid?
- In a solid state the ions are in a fixed position and cannot move and carry charge
- When they are in a liquid state the ions are mobile and can freely carry the charge
How is a polar bond formed
Bonding atoms have different electronegativities
What is the most electronegative element
Flourine
Define ionic bonding
The electrostatic attraction between positive and negative ions
Can simple molecular structures conduct electricity?
No they are non-conductors
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
Why is H2O polar, whereas CO2 is non polar
CO2 is a symmetrical molecule so there is no overall dipole
What is avarage bond enthalpy?
Measure of average energy needed to break the covalent bond
Define metallic bonding
Electrostatic attraction between the positive metal ions and the sea of delocalised electrons
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
How does graphite conduct electricity
- Delocalised electrons present between the layers are able to move freely carrying the charge
Give examples of giant covalent structures
- Diamond
- Graphite
- Silicon dioxide
What does expansion of the octet mean?
When a bonded atom has more than 8 electrons in the outer shell
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
List properties of giant covalent structures
- High melting and boiling point
- Non conductors of electricity, except graphite
- Insoluble in polar and non-polar solvents
Why are ionic compounds soluble in water?
- Water has a polar bond
- Hydrogen atoms have a 1+ charge and oxygen atoms have a 2- charge
- These charges are able to attract charged ions
What does it mean when the bond is non-polar
The electrons in the bond are evenly distributed
Describe how metals have high melting and boiling point
Many strong metallic bonds in giant metallic structures so large amounts of heat energy are required to overcome forces and break these bonds
By how many degrees does each lone pair reduce the bond angle
2.5
Describe how metals are good conductors of electricity and heat
There are free electrons that are available to move and carry charge
What conditions are needed for hydrogen bonding to occur
- O-H, N-H, F-H bond, lone pair of electrons on O, F, N
- O, N, F are highly elecronegative so the H nucleus is exposed
- Strong force of attraction between H nucleus and lone pair of electrons on O, N, F
What is a lone pair?
Electrons in the outer shell that are not involved in bonding
What is a dative covalent bond
A bond where both of the shared electrons are supplied by one atom
What is formed when atoms share three pairs of electrons?
Triple bond
What is it called when atoms are bonded by a single pair of shared electrons?
Single bond
What are the 2 interactions that can be referred as Van Der Waals’ forces
- Pernament dipole interaction
- Induced dipole interaction
Describe London forces
- London forces are caused by random movements of electrons
- Leading to instantaneous dipoles
- Instantenous 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
What are the types of intermolecular forces
- Hydrogen bonds
- Pernament dipole-dipole
- Induced dipole-dipole (London)
Do giant ionic lattices have high or low melting and boiling points? Explain your answer
- They have high melting and boiling points
- Because a large amount of energy is required to overcome the electrostatic bonds
How are oxonium ions formed?
When acid is added to water, H3O+
Explain induced dipole-dipole interactions
- When a molecule with a pernament dipole is close to another non-polar molecule it causes the non-polar molecule to become slightly polar leading to attraction
Define covalent bonding
The electrostatic attraction between a shared pair of electrons and the nuclei
List the types of structures that covalent molecules form
- Simple molecular lattice
- Giant covalent lattice
Describe the tetrahedral shape
- Angle: 109.5
- Bond pairs: 4
- Lone pairs: 0
Describe the linear shape
- Angle: 180
- Bond pairs: 2
- Lone pairs: 0
Describe the trigonal bipyramid shape
- Angle: 90
- Bond pairs: 5
- Lone pairs: 0
Describe the pyramidal shape
- Angle: 107
- Bond pairs: 3
- Lone pairs: 1
Describe the trigonal planar shape
- Angle: 120
- Bond pairs: 3
- Lone pairs: 0
Describe the non-linear shape shape
- Angle: 103.4
- Bond pairs: 2
- Lone pairs: 2
Describe the octahedral shape
- Angle: 90
- Bond pairs: 6
- Lone pairs: 0
