Topic 2 Flashcards
what is an ionic bond
Bond where oppositely charged ions are held together by strong electrostatic force of attraction in a lattice structure
What happens in ionic lattice
Oppositely charged ions are held together
What are the 3 conditions for an ion to be formed easily
- The charge of the ions is small
- The size of parent atoms from which the ions are formed is ; small for anion ( negative ion ) , large for cation ( positive )
- The electronic structure of the ion is stable
why does ionic bond have High Melting point
Ionic solids contain a lattice structure which contains many ions held by strong electrostatic forces of attraction. This requires higher energy to overcome
why does ionic compounds conduct electricity
Conducts electricity in molten or dissolved in a solution due to the charged ions being free to move and carry the charge
why is an ionic compound soluble
They are soluble because water is polar. These polar molecules can attract positive and negative ions which causes them to break up the structure and seperate them
Why are ionic compound brittle
If stress/forced is applied he layers of ions slide over each other meaning the charged ions and alligned with the same charge causing them to repel and break apart
What does the strength of ionic bond depend on
- Size of charge: The larger charge on an ion the stronger the force of attraction and therefore more energy is required to break it apart
- Radii: The smaller ion has stronger electrostatic force of attraction between ions as they are packed closer together
What happens to ionic radii as you go down group
The radii increases as there are more shells
what are isoelectronic ions
different ions with same number of electrons
what happens to ionic radii as you go down group for isoelectronic ions
The radii decreases as there is increase positive charge while shielding and repulsion stay the same.
Evidence for charged particles
Electrolysis of copper chromate on wet filter paper shows that when electricity is passed though green c.c on wt filter paper the ions seperate. The positive copper ions move towards the negative cathode ( you can see blue solution ) while the negative chromate ions move towards positive anode ( you can see yellow solution )
what is a covalent bond
a bond where electrons are shared which creates a strong force of attraction between the shared electrons and the positive nucleus
Why do atoms form covalent bonds
to reach the nearest noble gas electronic configuration
What is the orbital theory
Theory which suggests that covalent bonds are formed when orbitals each containing 1 electron overlap to form a region of space where an electron pair can be found.
what is an octet
a situation where some atoms don’t achieve the 8 electron arrangement in the outer shell
why does an octet occur
- not having enough electrons
- They have too many electrons which could cause them to go over the octet
what are the 2 rules to an octet
- unpaired electrons always pair up
- The max number of electrons that can pair up is equivalent to the number of electrons in outer shell
what is a diative covalent bond
Formed when an empty orbital overlaps with an orbital that contains 2 and donates both electrons in the bond
what correlation does bond length have with bond strength
the shorter the bond length the stronger the bond
why is this
this is due to an increase in the force of attraction between the 2 nuclei and the shared electrons because of the nuclei and bonding electrons being closer together
How can you decrease bond length
By increasing the number of electron shells
simple covalent molecule:
bonding
electrical
solubility
BP
1.Bonding: Atoms are joined together within the molecule by covalent bond
2. Electrical: Don’t conduct electricity as they have no ions or free electrons
3. Solubility: Tend to be more soluble in organic solvents than in water
4. BP: weak intermolecular forces lead to low BP
Graphite Characteristics
- Found in pencil, soot, charcoal
- Giant Covalent Molecule
- Carbon atoms are bonded to 4 others
- The delocalised electrons between layers allow it to conduct electricity
- High MP due to strong covalent bonds holding it in place
- Layers can slide over each other as there are weak forces between layers
- insoluble as covalent bonds are too strong to break
Diamond Characteristics
- Each carbon atom is bonded to 4 others
- Doesn’t conduct electricity due to no delocalised electrons
- High MP due to strong covalent bonds
- Insoluble as covalent bonds are too strong to break up
Graphene Characteristics
- Used in smart phone screens and air craft shells
- Each carbon atom is bonded to 3 others
- one atom thick
- delocalised electrons conduct electricity
What are Dipoles
A bond or molecule who have opposite charges
what are London Forces
Forces that exist between atoms + molecule due to an induced dipole
How is a London force formed
Since electrons can move around in their orbitals one side could have more electrons than the other which creates temporary dipoles. This dipole then induces another molecule / atom to form a bond with it
what makes the London Forces stronger
If there is higher number of electrons it creates and stronger force of attraction withe the positive nucleus which requires greater energy to seperate them
What are dipole - dipole forces
Forces that exist due to interactions between polar molecules
what is a hydrogen bond
A strong intermolecular force that occurs when you have a very electronegative element that’s bonded with hydrogen. The electronegative element ( N, F, O ) bonds with the lone pair of hydrogen
Order of strongest bonds from weakest to strongest
London
Dipole-Dipole
Hydrogen Forces
What is electronegativity
The ability for an atom to attract electrons towards itself in a covalent bond
What are the trends in electronegativity
Decreases down a group
Increases along a period
Pauling scale
A scale which quantifies how electronegative an element i
What happens if there is high electronegativity difference
Ionic bond is formed
What happens when there is low electronegtivity difference
Covalent bond is formed
What happens to symetrical polar bonds
there is no overall polarity
what is a metallic bond
Bonding where the positive metal ions are surrounded by delocalised electrons
How is this formed
When metal atoms donate electrons to form a sea of delocalised electrons
Why does it have High MP/BP
There is strong force of attraction between positive metal on and negative delocalised electron.
what makes a metallic bond stronger
If the metal atoms give up more electrons as there will higher force of attraction
why can metals conduct electricity
The delocalised electrons are free to move
How can metals conduct heat
The delocalised electrons can transfer the kinetic energy
why are metals insoluble
the metallic bonds are too strong to break apart
Why are metals malleable and ductile
Are malleable and ductile due to layers of ions being able to slide over each other.When they slide over each other the electrons allign themselves to retain attraction between ions and delocalised electrons
