Electronic Structure Flashcards
What is the number given to each shell called?
Principal quantum number
What can be said about the energy and principal quantum number when a shell gets further away from the nucleus?
The higher it’s energy and the larger it’s principal quantum number is
What are shells divided into?
Sub-shells
What are the 4 types of sub-shell?
S
P
D
F
What is an orbital?
A region of a sub-shell that contains a maximum of 2 electrons with opposite spins
What is spin?
A type of momentum possessed by an electron which can either be up or down
How many electrons can s sub-shells hold?
2
How many electrons can p sub-shells hold?
6
How many electrons can d sub-shells hold?
10
How many electrons can f sub-shells hold?
14
What can be said about the energy of orbitals in the same sub-shell?
They have the same energy
What is spin-pairing?
When there are 2 electrons in an orbital which spin in opposite directions
What shape are s-orbitals?
Spherical
What shape are p-orbitals?
Dumbbell shape
What is the formula for the number of electrons a shell can hold?
2n^2 (n being shell number)
What is electron configuration?
The number of electrons and how they’re arranged
Why do 4s sub-shells fill first before 3d sub-shells?
4s sub-shells have a lower energy level
What did Werner Heisenberg came up with?
The theory that you cannot know the speed of an electron or it’s exact position
What was Heisenberg’s theory called?
Uncertainty principle
How do ions form?
When atoms lose or gain electrons to become positively or negatively charged
What is electrostatic attraction?
A strong force between positive and negative ions
What is an ionic bond?
An electrostatic attraction between 2 oppositely charged ions
What is an ionic compound?
When oppositely charged ions form an ionic bond
What are ionic crystals?
Giant lattice (regular structure) of ions
How does a lattice form?
When each ion is electrostatically attracted in all directions to ions of the opposite charge
Describe the electrical conductivity of ionic compounds
Conduct electricity when molten or dissolved, but not when solid
Why do ionic compounds not conduct electricity when solid?
There are no mobile ions as they’re fixed in position by strong metallic bonds
Why do ionic compounds conduct electricity when molten or dissolved?
They have ions that are free to move (mobile ions) so can carry charge
Describe the melting and boiling points of ionic compounds?
Have high melting and boiling points
Why do ionic compounds have high melting and boiling points?
The giant ionic lattices are held together by strong electrostatic forces (which takes lots of energy to overcome)
Describe the solubility of ionic compounds
Tend to dissolve in water
Why do ionic compounds tend to dissolve in water?
Water molecules are polar, so the water molecules pull the ions away from the lattice and cause it to dissolve
What does polar molecule mean?
Part of the molecule has a negative charge, the other bits have a positive charge
How are molecules formed?
When 2 or more atoms bond together
What are molecules held together by?
Strong covalent bonds
What is a covalent bond?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Give an example of a molecule with triple bonds
Nitrogen (N2)
Give an example of a molecule with double bonds
Oxygen (O2)
What is different between a single covalent bond and a dative covalent bond?
In a single covalent bond, atoms share electrons with the electrons coming from each atom. Dative covalent bonds shares electrons but both electrons come from the same atom
How can you show a dative bond on a diagram?
By an arrow, pointing away from the donor atom
What is different about boron trifluoride?
The boron only has 6 electrons on its outer shell
What does expanding the octet mean?
Having an outer shell with more than 8 electrons
Give an example of a molecule that expands the octet
Sulfur Hexafluoride, has 12 electrons in it’s outer shell
What does enthalpy mean?
Another word for energy
What does the average bond enthalpy tell you?
The strength of a covalent bond
What does average bond enthalpy measure?
The average energy needed to break a bond
What does the shape of a molecule depend on?
The number of pairs of electrons in the outer shell of the central atom
What are shared electrons called?
Bonding pairs
What are unshared electrons called?
Lone pairs
What do pairs of electrons do?
Repel each other (as they’re both negatively charged)
Which repels more, lone pairs or bonding pairs?
Lone pairs
Why do lone pairs repel more?
Being closer to the central atom causes lone-pairs to take up more of the available ‘bonding space’
What is electron pair repulsion theory?
That the greatest bond angles are between lone pairs of electrons, and bond angles between bonding pairs are reduced because they’re pushed together by lone pair repulsion
When drawing shapes of molecules, what does a broken line (e.g. |||||) show?
A bond pointing away from you
When drawing shapes of molecules, what does a wedge line show?
A bond pointing towards you
When drawing shapes of molecules, what does a line show?
A bond that isn’t pointing towards or away from you
What is the bond angle of a linear shape?
180°
What electron pairs does a linear shape have?
2 bonding pairs, 0 lone pairs
Why do linear molecules have a bond angle of 180°?
The pairs of bonding electrons repel each other, so are positioned as far away as possible from each other
What electron pairs does a trigonal planar have?
3 bonding pairs, 0 lone pairs
What is the bond angle of a trigonal planar?
120°
What electron pairs does a non-linear molecule (with 3 electron pairs) have?
2 bonding pairs, 1 lone pair
What is the bond angle of a non-linear with 3 electron pairs?
A bit less than 120°
What electron pairs does a tetrahedral have?
4 bonding pairs, 0 lone pairs
What is the bond angle of a tetrahedral?
109.5°
What electron pairs does a trigonal pyramidal have?
3 bonding pairs, 1 lone pair
What is the bond angle of a trigonal pyramidal?
107°
What electron pairs does a non-linear (with 4 electron pairs) have?
2 bonding pairs, 2 lone pairs
What is the bond angle of a non-linear with 4 electron pairs?
104.5
What is a molecule with 5 bonding pairs called?
Trigonal bipyramidal
What are the bond angles in a trigonal bipyramidal?
90° and 120°
Why do trigonal bipyramidal molecules have 2 bond angles?
Because 3 of the atoms will form a trigonal planar shape (120°) and the other 2 atoms will be at 90°
What is a molecule with 6 bonding pairs called?
Octahedral
What are all the bond angles in an octahedral?
90°
What types of bonds can only be purely covalent?
Only bonds between atoms of a single element (e.g. diatonic gases)
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond
What is the general trend in electronegativity?
Increases as you move towards Fluorine
What is the trend of electronegativity down a group?
It decreases
What is the trend of electronegativity across a period?
It increases
What does a higher electronegativity number mean?
Means that element is better able to attract the bonding electrons
What are the covalent bonds in diatonic gases?
Non-polar
What does non-polar mean?
Where the atoms have equal electronegativities and so the electrons are equally attracted to both nuclei
What is a polar bond?
A covalent bond where a difference in electronegativity has caused a shift in electron density in the bond
In a covalent bond between 2 atoms with different electronegativities, where are the bonding electrons pulled to?
The most electronegative atom
In a polar bond, what does the difference in electronegativity between the atoms cause?
A permanent dipole
What is a dipole?
A difference in charge between the 2 atoms caused by a shift in electron density in the bond
Between 2 atoms, the greater the difference in electronegativity…
… The more polar the bond
What do polar molecules have?
An overall dipole
What determines whether a polar molecule has an overall dipole?
The arrangement of polar bonds
Why does CO2 have no overall dipole?
Because it is a linear molecule, the shape of the molecule is symmetrical. This causes the dipoles to cancel each other out, so it will be non-polar and have no overall dipole
For a greater difference in electronegativity, what will the difference in type of bond be?
The less covalent and the more ionic it will be
In general, what will the bonds be if the difference in electronegativity is less than 0.4?
Non-polar covalent bonds
In general, what will the bonds be if the difference in electronegativity is between 0.4 and 2.0?
Polar covalent bonds
In general, what will the bonds be if the difference in electronegativity is greater than 2.0?
Ionic
What are intermolecular forces?
Forces between molecules
How strong are intermolecular forces compared to covalent, ionic or metallic bonds?
Much weaker
What are the 3 types of intermolecular bonding?
Permanent dipole-dipole interactions
Induced dipole-dipole interactions
Hydrogen bonding
Which is the strongest of the 3 types of intermolecular bonding?
Hydrogen bonding
What does induced dipole-dipole interactions cause?
All atoms and molecules to be attracted to each other
What cause a temporary dipole?
When the electrons in an atom are to more side than the other (increasing the charge on that side)
What does a temporary dipole cause?
Another temporary induced dipole in the opposite direction of a neighbouring atom (which causes them to attract)
What trend in strength of induced dipole-dipole interactions occurs the larger the molecule?
Larger the molecule, the larger the electron clouds meaning stronger induced dipole-dipole interactions
Why do molecules with a greater surface area have stronger induced dipole-dipole interactions?
The have more of the electron cloud exposed
What can induced dipole-dipole interactions also be called?
London forces
What are permanent dipole-dipole interactions?
Where the ẟ+ and the ẟ- charges on polar molecules cause weak electrostatic forces of attraction between molecules
What is Hydrogen bonding?
A bond that only occurs when Hydrogen is covalently bonded to fluorine, nitrogen or oxygen
What is charge density?
A measure of how much positive or negative charge there are in a certain volume
What is the charge density of Hydrogen like?
Very high as it is small
What do molecules with Hydrogen bonding normally contain?
-OH or -NH groups
What are the properties of molecules with Hydrogen bonding?
Soluble in water
High melting and boiling points
Why do water and ammonia have very high melting points compared to the other hydrides in their group?
Because more energy is needed to break the Hydrogen bonds
Why do icebergs float on water?
Ice is less dense than water
How are water molecules in ice held together?
By Hydrogen bonds
Why is ice less dense than water?
Ice has Hydrogen bonds. Since Hydrogen bonds are long, the molecules in ice will be further apart than in liquid (making it less dense)
When drawing Hydrogen bonds, where does the ẟ+ go?
Goes on the H atom
When drawing Hydrogen bonds, where does the ẟ- go?
On the electronegative atom
What are the bonds and forces like in simple covalent compounds?
Strong bonds within compounds, but weak forces between the molecules
What is the electrical conductivity of simple covalent compounds?
They don’t conduct electricity (as they’re overall uncharged)
What is the melting and boiling points of simple covalent compounds like?
Melting and boiling points are low, as the intermolecular forces that hold together the molecules are weak, so don’t need much energy to break
When melting or boiling and simple covalent compounds, what bonds/forces do you have to break?
Have to break the intermolecular forces that hold together the molecules in a compound (But not the covalent bonds that hold the atoms together in a molecule)
What is the trend in melting and boiling points as intermolecular forces get stronger?
Melting and boiling points increase
What is the solubility of simple covalent compounds with Hydrogen bonds?
Compounds with Hydrogen bonds can form Hydrogen bonds with water molecules, so will be soluble
What is the solubility of simple covalent compounds that are non-polar?
Insoluble
What are the 2 factors, as you go down the Group 7 Hydrides, that affect the strength of the intermolecular forces?
The polarity of the molecules decrease, so the strength of the permanent dipole-dipole interactions decreases
The number of electrons in the molecule increases, so the strength of the permanent dipole-dipole interactions increase
