Topic 2 - Bonding Flashcards
Definition if ionic bonding
A strong electrostatic force of attraction between oppositely charged ions in a lattice
Why do chemical bonds form?
When atoms share or transfer electrons to achieve a more stable electron arrangement, often a full outer main level of electrons.
Formula of sulfate
SO4 (2-)
Formula of nitrate
NO3 (-)
Formula of Hydroxide
OH (-)
Formula of carbonate
CO3 (2-)
Formula of Ammonium
NH4 (+)
Properties of ionically bonded compounds …
Always solid at room temp
Giant structures = high melting points
Only conducts when molten or in aqueous solution as ions are not free when solid
Definition of metallic bonding
Strong electrostatic force of attraction between positive metal ions and sea of delocalised electrons
Structure in metallic bonding
Giant metallic lattice
Properties of metals x4
Good conductors of electricity as delocalised electrons can move throughout the structure.
High thermal conductivity due to delocalised electrons and the closely packed ions allowing vigorous vibrations.
Malleable and Ductile - arranged in layers which can slide and each metal ion will still be in the same environment.
High melting points
What does the strength of a metal depend on?
Charge on the ion - bigger charge = more delocalised electrons and the strong the force of attraction between electrons and metal ions.
Size of the ion - Smaller ion means the closer the electrons are to the positive nucleus = stronger bond
What is a covalent bond?
A strong electrostatic force of attraction between positive nuclei of the atoms involved and the shared pair of electrons
What’s the difference between a single covalent bond and multiple covalent bonds?
A single covalent bond contains one pair of shared electrons
Multiple covalent bonds contain multiple shared pairs
What is a dative covalent bond?
A co-ordinate (dative covalent) bond contains a shared pair of electrons with both electrons supplied by one atom.
Melting and boiling of ionic structure
High as lots of energy is required to overcome the strong electrostatic forces of attraction between oppositely charged ions.
Other word for giant covalent
Macromolecular
Diamond structure and properties x4
Each carbon strongly, covalently bonded to 4 other carbons in a giant lattice of atoms which are arranged tetrahedrally.
High melting and boiling
Does not conduct electricity as there are no freely moving charged particles
Very hard as strong covalent bonds hold atoms in fixed positions
Graphite structure and properties?
Each carbon atom strongly, covalently bonded to 3 others forming a giant lattice of atoms in a trigonal planar arrangement.
High melting and boiling point
Does conduct electricity as between layers there are delocalised electrons that can move freely and conduct
Soft and slippery as there are weak forces of attraction between the layers which are easily overcome to allow the layers to slide relative to one another
Temperature of any substance is ….
Directly proportional to the mean kinetic energy of the particles
Why do liquids cool as they evaporate?
As some of the KE is used to overcome the forces of attraction between particles to allow them to escape.
The leads to a lower mean KE and therefore a lower T
What happens when a solid is heated?
Particles vibrate faster
KE + T increase
What happens during melting?
Heat energy is used to overcome or partially overcome the forces of attraction between particles **instead of ** increasing the KE. Therefore T is constant through melting.
As KE remains constant
What happens during boiling.
Heat energy is used to overcome the forces or bonds between the particles rather than increase the KE.
Liquid boils but KE remains constant so T remains constant
Ice and Iodine are examples of?
Molecular crystals
Describe Ice
Each water molecule comprises of one oxygen atom and two hydrogens.
Each hydrogen atom is covalently bonded to the oxygen.
Although the covalent bonds within molecules are very strong, there are weak intermolecular forces of attraction between molecules leading to a low melting and boiling point.
Does not conduct as there are no freely moving charged particles
Describe Iodine.
Each molecule of iodine comprises two Iodine atoms which are joined by one covalent bond
Although the covalent bond within the molecule is very strong, weak intermolecular forces of attraction occur between molecules
Low sublimation point as IMFs require little energy to break
Does not conduct electricity as there are no freely moving charged particle.
Define electronegativity.
The power of an atom to withdraw electron density towards itself in a covalent bond
What 3 factors affect electron negativity
No. of protons in the nucleus - more protons = stronger attraction
Size of atom - Smaller atom means the e- in the covalent bond is closer to the nucleus = stronger attraction
Shielding - more electron shells between the nucleus and the shared e- = weaker attraction
What is a polar bond?
A covalent bond existing between atoms with different electronegativity.
This leads to unsymmetrical electron distribution and a partial positive charge on the less electronegative and partial negative charge on the more electronegative atom involved.
Why do dipoles form?
Due to uneven distributions of electrons due to different electronegativities of the atoms in a molecule.
Why do some molecules with polar bonds not have permanent dipoles?
When a molecule is symmetrical - dipoles cancel each other out leading to no overall permanent dipole
When molecules have similar electronegativities
When are weak IMFs broken?
When molecular substances are vapourised
List the IMFs strongest to weakest
Hydrogen bonds
Permanent dipole dipole forces
Van der Waals forces
How do van der Waals forces work?
The electron cloud is in constant motion
This leads to a temporary electron imbalance
Leading to a temporary dipole in the molecule which induces a temporary dipole in another molecule.
Leading to a temporary attraction between the temporary dipoles, this is the Van der Waals force
What are Intermolecular forces?
Weak electrostatic forces of attraction acting between molecules
What makes the Van der Waals force stronger how does it correlate to its melting point?
As a molecule gets larger so does the boiling point
There are more electrons leading to a stronger VDW force.
This then requires more energy to overcome the forces between molecules
Where are VDW forces present?
In all molecular substances at all times
How do dipoles form?
Due to uneven distribution of electrons in a molecule. This is due to differences in electronegativity of the atoms in a molecule.
When do permanent dipole - dipole forces form?
Dipole - dipole attractions in polar molecules
When do permanent dipole - dipole forces not form?
In non polar molecules
Sometimes individual bonds are polar but if the shape is symmetrical then the polar bonds cancel each other out.
What 2 conditions are needed for a hydrogen bond to form?
A very electronegative atom (N, O, F) with an available lone pair of electrons
And a Hydrogen atom directly bonded to a very electronegative atom
What atoms are sufficiently electronegative for a Hydrogen bond to form?
N, O and F
When do the H bonds break in solid, liquid and gas?
Solid - Bonds are permanent
Liquid - Continously breaking and reforming
Gas - Permanently broken
Why does ice have a lower density than water?
As the molecules are held apart in a tetrahedral structure of hydrogen and covalent bonds. This is different to liquid water where the bonds are constantly breaking and reforming.
Much empty space between molecules.
Larger volume with the same mass of water
= lower density
How and why do pairs electrons in the outer shell of an atom arrange themselves?
As far apart as possible as to minimise repulsion
