2:Bonding and Structure Flashcards
What is ionic bonding?
The electrostatic attraction between oppositely charged ions
What is the formula for hydroxide ion?
OH−
What is the formula for nitrate ion?
NO3^-
What is the formula for ammonium ion?
NH4 ^+
What is the formula for sulphate ion?
SO4^2-
What is the formula for carbonate ion?
CO3^2-
What are the features of giant ionic structures?
- regular structure
- cubic shape
- giant repeating patterns
Give an example of a giant ionic structure?
NaCl
Why can ionic compounds dissolve in water?
Water molecules are polar, so they attract the anions and cation which break up the structure
Why can ionic structures conduct electricity when molten or dissolved in a solution?
The ions are free to move around.
Why do ionic compounds have high melting points?
There are many strong electrostatic forces between oppositely charged ions
- therefore more energy is needed to overcome these forces
Why are ionic compounds brittle?
When struck with a hammer the layers slide - so the cations align with cations and anions align with anions. They repel each other and the structure breaks apart
Why does the size of the charge increase the strength of the ionic bond?
The bigger the charge of the ion the stronger the electrostatic attraction between ions.
- Therefore more energy is required to overcome these forces
Why does the size of the ion (ionic radius) affect the strength of the ionic bond?
The smaller the ion the stronger the electrostatic attraction between the ions
-> smaller ions can pack together more closely so more energy is required to overcome these strong forces
Which ions have the highest charge density?
Ions with smaller radius and higher charge
Why does ionic radius increase as you go down a group?
Number of electrons shell increases
Why does the ionic radius in isoelectric ions decrease as atomic number increases?
More protons for the same number of electrons so attractive force from nucleus increases
Describe the experiment to show evidence for charged particles?
Electrolysis of copper(II)chromate(VI) on wet filter paper
- add a drop of green copper(II)chromate(VI) is placed on wet filter paper and electricity is passed through (to separate the ions)
- Positive Blue Cu2+ ions move to cathode
- Negative Yellow CrO4^2- ions move to anode
What is covalent bonding?
The electrostatic attraction between a shared pair of electrons of two non-metal atoms and their nuclei
What are dative bonds (co-ordinate bonds)?
Covalent bond where the shared pair of electrons comes from one atom
What happens to bond enthalpy the shorter the bond?
The bond enthalpy will be higher
What two forces are acting in a covalent bond?
- attraction - between shared pair of electrons and positive nuclei
- repulsion - between like charged electrons and like charged nuclei
What is bond length a result of?
The balance between the attraction and repulsion force in a covalent bond.
How does a greater electron density cause high bond enthalpy?
There is a stronger attraction force so atoms are pulled closer towards each other. This leads to shorter bond length which results in higher bond enthalpy.
Why does the C-C triple bond have a higher bond enthalpy than a C-C single bond?
C-C triple bond has a higher electron density shared, so there is a shorter bond
* - so there is a higher bond enthalpy*
Why do molecules have specific shapes?
- Bonds repel each other equally as they contain electrons so they will want to be as far apart as possible
What is the shape of a molecule with 2 bond pairs and 0 lone pairs?
Linear
What is the shape of a molecule with 3 bond pairs and 0 lone pairs?
Trigonal planar
What is the shape of a molecule with 4 bond pairs and 0 lone pairs?
Tetrahedral
What is the shape of a molecule with 5 bond pairs and 0 lone pairs?
Trigonal Bipyramidal
What is the shape of a molecule with 6 bond pairs and 0 lone pairs?
Octahedral
What is the shape of a molecule with 3 bond pairs and 1 lone pairs?
Trigonal pyramidal
What is the shape of a molecule with 2 bond pairs and 2 lone pairs?
V-shaped
What are the properties of graphite?
1) each carbon has 3 bonds with one delocalised electron
2) conduct electricity and thermal energy
3) layers slide over each other
4) lightweight
5) insoluble
Why can graphite transfer thermal energy and conduct electricity?
Delocalised electrons
Why can the layers of graphite slide over each other?
There are weak forces between the layers
Why is graphite lightweight?
Layers are far apart compared to its covalent bond length. This means it has a low density and therefore lightweight
Why is graphite insoluble?
Covalent bonds are too strong to break
What are the properties of diamond?
1) each carbon atoms has 4 bonds
2) can conduct heat well
3) very high melting point
4) doesn’t conduct electricity
5) insoluble
6) same structure as SiO2
Why can diamond conduct heat well?
It’s tightly packed, in a rigid arrangement
Why can’t diamond conduct electricity but graphite and grapheme can?
Diamond doesn’t have any delocalised electrons to conduct or transfer energy
Why is diamond insoluble?
Covalent bonds are too strong to break
What are the properties of graphene?
1) it is a single layer of graphite (so it’s 1 atom thick)
2) made up of hexagonal carbon rings
3) lightweight and transparent
4) contains delocalised electrons which strengthen the covalent bonds
Why is graphene lightweight and transparent?
Because it’s one atom thick
What is metallic bonding?
The strong electrostatic attraction between the nuclei of metal cations and delocalised electrons
What increases the melting point in metallic bonding?
More electrons being donated to the sea of delocalised electrons
Why do metal compounds have a high melting point?
Due to strong electrostatic attraction between cations and delocalised electrons which require a high amount of energy to overcome
Why are metal compounds insoluble?
Due to strong metallic bonds
Why are metal compounds malleable and ductile?
Ion layers can slide across each other and still retain an attraction between cations and delocalised electrons
What is electronegativity?
The ability for an atom to attract a pair of electrons towards itself in a covalent bond
What is the most electronegative element, according to the Pauling Scale?
Fluorine
What scale do we use to determine electronegativity?
The Pauling Scale
What does a bigger difference in electronegativity between atoms mean?
The more ionic the compound will be
What does it mean if a bond is polar?
There is a significant difference in electronegativity between atoms
- the bigger the difference in electronegativity the more polar the bond will be
What makes a covalent bond non-polar?
When atoms have the same/similar levels of electronegativity.
- e.g. hydrocarbons are non-polar
Order the intermolecular forces from strongest to weakest (1 being the strongest).
1) Hydrogen bonds
2) Permanent dipole - dipole
3) London forces
When does hydrogen bonding occur?
When hydrogen on one molecule forms a bond with the lone pair of either oxygen,fluorine or nitrogen
What is permanent dipole-dipole ?
The δ- of one permanent dipole molecule is attracted to the δ+ of another
What are London forces?
Forces that occur when the δ+ of a temporary dipole molecule is attracted to the δ- of another
What is the difference between bonds and forces?
Forces occur between molecules
Bonds occur between atoms
