Bonding physical chemistry Flashcards
What forces hold the positive ions and negative ions together in ionic compounds
Electrostatic forces
What is a molecule
A group of atoms held together by covalent
Within a molecule how are covalent bond within atoms held together
By electrostatic attraction that occurs between the nuclei and the shared electrons
What are the 3 types of bonding
Ionic
Covalent
Metallic
What is a double bone
When four electrons are shared
Why do substances composed of molecules (solids,liquid, gas) have low melting points
This is due to the weak attraction between molecules so not a lot of energy is needed to separate them
Why do substances composed of molecules (solids,liquid, gas) have low melting points
This is due to the weak attraction between molecules so not a lot of energy is needed to separate them
Why are molecules poor conductors of electricity
As they are neutral due to them not having any charged particles
What is dative covalent bonding
It’s when in covalent bond one atom will supply both electrons
What must happen for dative covalent bonding to occur
The atom supplying the electrons has a lone pair of electrons and has a full outer shell
The atom receiving the electrons is electron efficient and dosent have a filled outer shell
What is a lone pair of electrons
Electrons that aren’t involved in the covalent bond
On a diagram how are dative covalent bonds represented
By an arrow
What is the structure of metals
It’s positive ions which form a lattice and they exist in a sea of delocalised electrons
In metals what do the outer layers of atoms do
The outer layers of atoms merge
What is the amount of deloclasied electrons dependant on
The amount of deloclasied electrons is dependant on the amount of electrons lost by each metal atom
Why do metals contain such large structures
As the metallic bonding spreads throught the metal
Name the properties of metals
Strong
High melting points
Malleable
Good conductors of heat and electricity
Why are metals such good conductors of heat
The sea of electrons have high thermal conductivites
The ions are closely packed together so when heated they vibrate vigrously and enegry spreads throughout the metal as a result
What does the strength of the metallic bond dependant on
The size of the ion and it’s charge
How does the charge of the ion make metallic bond strong
As it means that there are more deloclasied electrons and so a stronger electrostatic attraction occurs between the ions and electrons
How does ion size make a strong metallic bond
If the ion size is smaller the electrons become closer to the positive nucleus and this makes the bond stronger
What two things within a metal gives it a high boiling point and melting point
It’s has a large structure and the
strong attraction between the metal ions and the electrons
What does ductile mean
Layers slide over each other
What is Electro negativity
The power of an atom to attract electron density in a covalent bond to it’s self
What factors effect electron negativity
Nuclear charge
The shielding of nuclear charge by electron in it’s inner shell
The distance between the nucleus and the outer shell of electrons
Why does electron negativity increase across a period
This is because the nuclear charge increases so the attraction of the nucleus to the outer shells is strong
Going up a group why does electron negativity increase
This is due to there being less shielding From the inner electrons as the atoms gets smaller
What is polarity of a covalent bond
It’s when atoms that are bonded covalently have unequal distributed number of electrons
What are polar covalent bonds
When atoms are bond covalently have an uneven distribution of electrons
What can Increase the polarity of covalent bonds
The greater the difference in electro negativity
When two different atoms are bonded covalently how are the electrons spread
They spread to the atom that is most electronegative
What are the 3 types of intermolecular bonds
Van der vaals
Dipole-dipole
Hydrogen bond
Name in order of strength of each bond
Hydrogen bond
Dipole - dipole
Van der waals
What is polarity
The unequal distribution of electron density within a covalent bond between atoms
When do dipole dipole forces occur
They occur between molecules that contain permeant dipoles
What are van der waals forces
They are small very weak electrostatic attractions that occur between molecules and atoms
What causes van der waals forces to occur
Positive and negative charges that make up all atoms and molecules
Although neutral why may a dipole occur in a atom
As a result of electrons constantly moving around it causes the distribution of charge to change
How is the dipole a temporary one
As the electrons are always changing direction the dipole does as well and so when a dipole occurs it’s only instant and temporary
What affect does a dipole occurring in one atom have on surrounding atoms
It has an effect on electron distribution of the nearby surrounding atoms and so they become attracted to the original atom
What has the original atom caused in the nearby atoms
It had induced dipoles
When electron disturbution in the original atom has changed what effect does it have on the other atoms
It will induce new dipoles in the surrounding atoms and these new dipoles become attracted to the original atom
What is the attraction of the new dipoles to the original atom
Van der waals
What happens to van der waals when more electrons are present
They increase in size
What conditions are needed for hydrogen bond to take place
Lone pair of electrons
Highly electronegative atoms
A positively charged hydrogen atom so it attracts the lone pair of electrons
What are the 3 electronegative atoms that can bond with hydrogen
Oxygen
Fluorine
Nitrogen
Why do solids expand when heated
This is because when heated the particles in the solid move apart slightly causing the solid to expand
What is enthalpy change of melting
The amount of enegry needed to weaken the forces in a solid so it can become a liquid
Why does temperature not change when a solid melts
As the heat enegry is being absorbed by the forces in a solid causing it to weaken and then melt
What is enthalpy
A measure of the change In Heat under pressure
What it’s the enthalpy change of vaporisation
The amount of energy needed to break the intermolecular forces between liquid particles so a gas forms
What are crystals
They are solids in which there particles are in a regular arrangement and are held by forces of attraction
What are the 4 types if crystals
Ionic
Metallic
Molecular
Metallic
Describe the structure of ionic crystals
They have strong electrostatic attraction forces as they have oppositely charged ions
By having a structure comprised of strong electrostatic forces what property does it give ionic crystals
They have high melting points as a result
Describe the structure of metallic crystals
They contain a lattice of positive ions that are surrounded by a sea of deloclasied electrons and they have a strong attraction
Describe the structure of molecular crystals
It’s a regular arrangement of molecules held together by intermolecular forces
How are atoms within the molecules held
They are held by covalent bond
Why do molecular crystals have low melting points
As the intermolecular forces between the molecules are very weak
What is the structure of macromolecules
The covalent bonds between atoms extends throughout the structure making the molecular larger
What two macromolecules are made from carbon
Diamond and graphite
Describe the structure of carbon
Each carbon atom forms four covalent bonds throughout the structure of diamond
What properties does diamond have a result of it’s large structure
It’s a hard material
High melting point
What two bonds are present in graphite
Covalent and van der waals
How is the structure of graphite different to that of diamond
Unlike in diamond graphite froms 3 covalent bonds for each carbon atom
Why is graphite able to conduct electricity unlike
It contains an extra electron in each carbon atom so it because deloclasied when carries the charge through
Why is graphite so soft
It contains van der waals forces between it’s layers so the layers slide over one another
What is electron pair reply soon theory
That pairs is electrons around atoms will repel one another
Give the order in which repulsion increases between bonding pairs
Bonding pair -bonding pair
Lone pair bond pair
Lone pair lone pair
When a molecule contains two pairs of electrons what is it’s shape and bond angle
Linear and 180 because it contains to bond pairs that repel as much as possible
When a molecules contains 3 bond pairs and no lone pairs what’s it’s shape and angle
Trigonal plannar bond angle 120
When a molecule has 2 bond pairs and 1 lone pair what’s the bond angle
118 and bent line molecule
When a molecule contains 4 bonding pairs what’s it’s shape and bond angle
109.5 and it’s a tetrahedral
When a molecule has 3 bonding pairs and one lone pair what’s it’s shape and bond angle
It’s a trigonal pyramid and the angle is 107
When a molecule contains two bond pairs and two electron pairs what’s it’s angle and shape
Bent line molecule and the angle is 104.5
When a molecule has 5 bond pairs what’s it’s shape and bond angle
Trigonal bipyramid 120 and 90
What is a molecule contains 3 bond pairs and two lone pair what’s the angle and shape
The shape is trigonal planar and the bond angle is 120
When a molecule contains 6 bond pairs what’s the shape and angle
The shape is octahedral and angle is 90
When the molecule has 5 bond pairs and 1 lone pair
The shape is square pyramid and the angle is 89
When the molecule has two lone Pairs and 4 bond pairs what’s the shape and angle
It’s a square planar and the angle is 90
