Foundations In Chemistry 2 Flashcards
What is an atomic orbital
Electrons inhibit regions of space known as orbitals
What is the heinsenburg uncertainty principle
You cannot know with certainty both where an electron is and where its going next
It is impossible to define with absolute precision, at the same time, both the position and the momentum of an electron
What orbitals are available at the first energy level
1s orbital
What orbitals are available at the second energy level
2p , 2s
How many electrons are in each orbital
2
What is the aufbau principle
Electrons fill low energy orbitals before they fill higher energy ones
What is a shell
A group of atomic orbitals with the same principle quantum number , n
What is ionic bonding
The electrostatic attraction between positive and negative ions
What is electronegativity?
The ability of an atom to attract the pair of electrons in a covalent bond
What happens when two atoms have the same electronegativity
The pair of electrons in the covalent bond are equally attracted to the nuclei
What happens when one atom is more electronegative than the other ?
the electron pair in the covalent bond are close to the more electronegative atoms nucleus
What is the most electronegative element?
FLUORINE
What 3 factors does electronegativity depend on?
- Size of the positive charge on the nucleus
- Atomic radius
- Shielding of the nucleus by electrons in inner shells
How does electronegativity depend on the size of the positive charge on the nucleus?
moving left to right across the period, the number of protons in the nucleus increases
increased positive charge increases the attraction between the nucleus and the pair of electrons in the covalent bond
How does electronegativity depend on atomic radius?
Smaller the atomic radius, the closer the bonding electrons will be to the nucleus of the atom
As we move from down to up across periods the atomic radius increases
As we move across groups the atomic radius decreases
How does the shielding of the nucleus by electrons in inner shells effect electronegativity?
electrons in inner shells screen electrons in the outer shell from the positive charge of the nucleus
Greater number of electrons= lower in electronegativity
What is a dipole?
When an electron pairs much closer to one atom than the other, the separation of charge is called a dipole .
The separation of charge is then called a polar covalent bond.
What are intermolecular forces
Weak forces that act between molecules
What are the three types of intermolecular forces?
Induced dipole- dipole interactions
Permanent dipole- dipole interactions
Hydrogen bonds
What are induced dipole dipole interactions?
Dipoles that are induced from an instantaneous dipole where their is random movements of electrons, causing there to be a slight negative charge on one side compared to the other
What does the strength of London forces depend on?
Number of electrons
What is a permant dipole?
Where two atoms that are bonded have different electronegativities, a polar bond forms. The more electronegative atom draws more of the negative that he towards itself and away the other atom .
Examples of giant covalent structures
Diamond
Graphene
Graphite
Diamond structure and properties
-atoms arranged in a tetrahedral structure
- bond angle of 109.5
-large melting and boiling points due to the large amount of energy required to break the covalent bonds
-does not conduct electricity, every electron is in a covalent bond
-insoluble, solvents cannot disrupt the large number of strong covalent bonds
Graphite structure and properties
-carbon atoms form only 3 bonds, delocalised electrons
-bond angle of 120
-delocalised electrons act as mobile charge carriers
-good conductor of electricity
Graphene structure and properties
-single layer of graphite
-slippery
-also delocalised electrons
-thin sheets
-good conductor of electricity
What is hydrogen bonding
When the lone electrons are attracted to the slightly positive atom
What is the strongest type of intermolecular force.
Hydrogen bonds
What are 2 conditions of hydrogen bonding
- hydrogen atom bonded to a strongly electronegative element
- the electronegative atom must have at least one lone pair of electrons
What is hydrogen bonding in water?
- water molecules undergo hydrogen bonding
- when we boil water, it takes a great deal of energy to break the hydrogen bonds
- relatively high melting snd boiling points
- solid ice is less dense than water
Why is ice less dense than water
As we reach freezing point the water molecule arranges themselves into an ordered structure which is stabilised by the network of hydrogen bonds. In ice, the water molecules are further apart then in liquid water, making it less dense
What happens to the atomic radius as you move across a period
It increases top to bottom, moving down a group
Number of electrons increases as you move down a group
Outer electron shell is further from the nucleus
Each element has one more full outer shell
Increases amount of shielding between the nucleus and outer electron
Less attraction between outer electron and nucleus
How does atomic radius differ from across the periods (left to right)
Decreases
Each element has one more proton in its nucleus than the element before.
Positive charge increases across the period, increased attraction between the nucleus and electrons
- draws the electrons closer to the nucleus, causes the atomic radius to decrease across the group
Why does first ionisation energy increases across the as we move across a period?
The positive charge in the nucleus increases, as the number of protons increases
The increases the attraction between the nucleus and the electrons
Atomic radius decreases across a period
Both the increased nuclear charge and the decreases atomic radius mean the outer electrons are more attracted to the nucleus
Why does ionisation energy decrease as we go down a group?
Atomic radius decreases
-outer electrons shell are further away from the nucleus
Number of internal electron shells increases
- there is more shielding between the nucleus and the outer electrons
What is metallic bonding
Negative delocalised electrons ate strongly attracted to the positive cations by electrostatic attraction
What are the key features of giant metallic lattice
Cations are fixed in place
Delocalised electrons are free to move, can conduct electricity in solids and liquids
Relatively high melting and boiling points
Delocalised electrons have a strong attraction to cations, requires a lot of energy to overcome
Do not dissolve
Brittle
What is the principle quantum number
The number each shell is given
Example, first shell has a principe quantum number of 1
How to work out maximum number of electrons
2n2
What are atomic orbitals
A region around the nucleus that can hold up to 2 electrons with opposite spins
What is an electron
A cloud of negative charge
What are the different types if atomic orbitals
S
P
D
F
What shape is the s orbital
Spherical
What shape is the p orbital
Dumb bell
What are the rules of electron configuration
Orbitals with the lowest energies are filled first
Can have up to 2 electrons in the same orbital but must have opposite spins
Orbitals with the same orbital, individually fill first with electrons then pair . Electrons in the same orbital repel
When is the 3d sub shell more stable
When it is half full or completely full
What is electron repulsion theory
Pairs of electrons repel all the outer shells
Electron pairs now move as far apart as possible to minimise repulsion
How are shapes of molecules determined
Electrons pairs surrounding central atom
Liner molecule
Bond angle of 180
0 lone pairs
2 bonding pairs
Tetrahedral molecule
Bond angle of 109.5
0 lone pairs
4 bonding pairs
Trigonal planar
Bond angle of 120
0 lone pairs
3 bonding pairs
Trigonal bipyramidal
Bond angle of 120 / 90
0 lone pairs
5 bonding pairs
Octahedral
Bond angle of 90
0 lone pairs
6 bonding pairs
How much do you decrease a bond angle by with each lone pair
2.5 degrees, lone pairs repel more strongly than bonding pairs
Name all the shapes of molecules that have 0 lone pairs
Linear molecule
Octahedral
Trigonal planar
Trigonal bipyramidal
Tetrahedral
Pyramidal
Bond angle of 107
1 lone pair
3 bonding pairs
Non linear
Bond angle of 104.5
2 lone pairs
2 bonding pairs
Name the only 2 shapes of molecules that have lone pairs
Pyramidal
Non linear
What is covalent bonding
When a non metal reacts with a metal creating a shared pair of electrons
What are lone pairs
Any electrons that are not user to form a covalent bond
What is a dative bond
When an ion no longer has electrons to share so teh atom it is attempting to share with uses its lone pair of electrons to form a covalent bond
What are the two main points about dative bonds
In order for dative bonds to form, the acceptor atom must be electron deficient, must be available orbitals for the electron to occupy
Dative bonds are exactly the same as normal covalent bonds
What are the properties of ionic bonding
Giant ionic lattice=
Every ion is attracted to every oppositely charged ion causing the electrostatic forces of attraction
Very high melting and boiling points
Tend to be soluble in polar solvents
Do not conduct electricity ehen solid
If charges on ion increase, solubility often decreases as the water molecules cannot overcome the electrostatic forces of attraction
What is an ionic bond
Transfer of electrons from one metal to the non metal
what is electronegativity
the relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself
when does a polar covalent bond form
when the elements in the bond have different electronegativities
