2.2 Electrons, Bonding And Structure Flashcards
How many electrons are in the 1st energy level?
2
How many electrons are in the 2nd energy level?
8
How many electrons are in the 3rd energy level?
18
How many electrons are in the 4th energy level?
32
How many orbitals and electrons are in: S P D F
S-1 orbital, 2 electrons
P-3 orbitals, 6 electrons
D-5 orbitals, 10 electrons
F-7 orbitals, 14 electrons
What is the shape of an s orbital and a p orbital?
S orbital - spherical
P orbital - dumbbell (3 p orbitals at right angle to each other)
Define an oribital
A region around the nucleus that can hold up to two electrons, with opposite spins
What is the filling order to work out electron configuration?
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, (8s, 5g, 6f, 7d, 8p, and 9s)
How can we explain the electron configuration for chromium and copper
Sub-shells like to be full or half full. As 4s and 3d are so close in energy, electrons can move between them easily, and rearrange to make full and half full sub shells
What’s an ionic bond?
Electrostatic forces of attraction between two oppositley charged ions
Describe sodium chloride
NaCl has a giant ionic lattice
Each ion is electrostatically attracted in ALL directions to ions of the opposite charged
NaCl is cube shaped
Lots of energy needed to break up lattice
High melting point (801℃)
Explain the 3 behaviours of ionic compounds
- Conduct electricity when molten or dissolved
- high mp and bp
- tend to dissolve in water as water molecules are polar (parts of molecule have negative and others have positive charge pulling apart lattice)
What’s a covalent bond?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What is Dative covalent bonding?
How is it shown in diagrams?
Its when both electrons come from one atom
It is shown in diagrams by an arrow pointing away from the donor atom
OR when only dots are in the dative covalent bond part In a dot and cross diagram
ie NH4+ where the nitrogen atom donates 2 electrons to a H+ proton.
What does the phrase ‘expand the octet’ mean?
When some compounds can use the d orbital to ‘expand the octet’. So can have more then 8 electrons in the outer shell.
ie sulfur hexafluoride where sulfur Has 12 electrons in its outer shell.
What is average bond ?
- Measures how much energy is required to break a covalent bond
- The higher the bond enthalpy the stronger the bond
Are lone pairs or bonding pairs more electron dense?
Lone pairs are more electron dense so repel more
Aufbau principle
Electrons enter the lowest possible energy level
Hund’s rule of maximum multiplicity
When in orbitals of equal energy electrons will try and remain unpaired
Raul’s exclusion principle
2 electrons can go in each orbital provided they are of opposite spin
Lone pair/lone pair
bonding pair/bonding pair
Lone pair/Bonding pair
Which angle is the biggest?
Which angle is the smallest?
Biggest angle: Lone pair/lone pair
Smallest angle: Bonding pair/ bonding pair
What’s the shape and bond angles of a molecule with 2 bonded pairs?
180˚
Linear molecule
BeCl2
What’s the shape and bond angles of a molecule with 3 bonded pairs?
120˚
Trigonal planar
BF3
What’s the shape and bond angles of a molecule with 4 bonded pairs, no lone pairs?
109.5˚
tetrahedral
NH4+
What’s the shape and bond angles of a molecule with 3 bonded pairs, 1 lone pairs?
107˚
Trigonal pyramidal
PF3
What’s the shape and bond angles of a molecule with 2 bonded pairs, 2 lone pairs?
104.5˚
Nonlinear or ‘bent’
H20
What’s the shape and bond angles of a molecule with 5 bonded pairs, 0 lone pairs?
90˚, 120˚
Triogonal bipyramidal
PCl5
What’s the shape and bond angles of a molecule with 6 bonded pairs, 0 lone pairs?
90˚
Octahedral
SF6
How do you work out the shape and bond angle of a molecule?
- Dot and cross diagram
- Count total number of electron pairs (bonding and lone)
- Based on the number of electron pairs, decide the overall shape and starting bond angle
- Subtract 2.5 from the starting bond angle for each lone pair to find the angle of the molecule
Whats the electronegativity (measured using a Pauling scale) of H, C, N, CL, O, F
H is 2.1 C is 2.5 N is 3.0 Cl is 3.0 O is 3.5 F is 4.0
What is electronegativtiy?
An atoms ability to attract the electron pair in a covalent bond.
What makes a bond polar?
In a covalent bond when there are 2 atoms of different electronegaitvities, the bonding electrons are pulled towards the more electronegative atom.
What’s a dipole?
The difference in charge between 2 atoms caused by a shift in electron density in the bond
What causes a permanent dipole?
Difference in electronegativity between 2 atoms in a polar bond
Why are the covalent bonds in diatomic elements non-polar? (Pure covalent)
The bonded atoms come from the same element so have equal electronegativites and so electrons are equally attracted to both nuclei
What determines wether or not a molecule has an overall (molecular) dipole?
The arrangement of the polar bonds
When does a molecule have an overall dipole and is polar?
When the polar bonds are arranged so that they don’t cancel each other out
so charge is arranged unevenly across the whole molecule
When does a molecule have no overall dipole so is non-polar?
When the polar bonds are arranged symmetrically so that the dipoles cancel each other out
Why can only bonds between atoms of a single element, like diatomic gases, be purely covalent?
Because the electronegativity difference between the atoms is 0
So the bonding electrons are arranged completely evenly within the bond
What are the three types of intermolecular forces?
Induced dipole-dipole interactions (London forces)
permanent dipole-dipole interactions
hydrogen bonds
What are van der waals forces?
Induced dipole-dipole (london dispersion forces) and permanent dipole-dipole
whats a Permanent dipole-induced dipole?
Permanent dipole-induced dipole is where a molecule with a permanent dipole causes a dipole in a non-polar molecule, the two molecules then attract
Whats a Permanent dipole-permanent dipole?
Permanent dipole-permanent dipole is where opposite charges on two molecules with permanent dipoles attract
What’s responsible for holding iodine molcules together in a lattice?
induced dipole-dipole forces
if a molecule is large or has a greater surface area how will it effect boiling points?
it will have stronger induced dipole-dipole forces meaning higher boiling points. As larger molecules have larger electron clouds and greater surace areas have a bigger exposed electron cloud.
What is the strongest intermolecular force?
Hydrogen bonding
What is london dispersion forces?
4 points
London (dispersion) is where electrons in atoms constantly moving
They become unevenly spread which gives atoms a temporary dipole
This induces a temporary dipole moment in the neighboring atom, repelling or attracting its cloud
Attraction is relatively weak, increases with increasing number of electrons
H-Cl — H-Cl
What is hydrogen bonding?
Occur when H is bonded to N, O or F
The bond is the attraction between a lone pair on one N, O or F to a δ+ H attached to N, O or F on a nearby molecule
F, N and O are all very electronegative
Bond is polarized
Bond drawn as dashed line
water is common hydrogen bonding molecule
What makes ice less dense then water?
• Hydrogen bonding gives water unusual properties
• Low density
○ Form a fixed lattice of hydrogen bonded molecules
○ Hydrogen bonds hold molecules apart, they are long
○ In liquid water molecules move past each other often
○ Form hydrogen bonds less often so less held apart and move closer together
○ So ice is less dense than water
What gives water a realtively high melting and boilling point?
• High melting and boiling point
○ Hydrogen bonds are stronger than van der Waals’ forces
○ Extra strength has to be overcome to melt or boil water
○ So the melting and boiling points are much higher than other compounds like it
What are the 3 main properties of water?
- Ice is less dense then water
- high surface tension that allows insects to walk on water
- Relatively high melting and boiling point compared to van der waals forces
Physical properties of simple covalent lattices?
• Low melting and boiling points due to weak intermolecular forces
• Non-conductors as there are no free ions
• Mostly soluble in non-polar solvents
○ Molecules that form simple covalent lattices are often non-polar
○ So they’re soluble in non-polar solvents
○ Things like ice that are polar will dissolve in polar solvents
What is meant by a lattice?
A regular arrangment of ions repeated many times
What is a lone pair?
A pair of electrons not used in bonding
on the outer shell
What is meant by bond enthalpy?
Enthalpy change when one mole of a bond
in the gas phase is brocken
How do vanderwaals forces arise?
Creating the dipole
(Uneven distribution of electrons)
causes an instantaneous dipole OR temporary
dipole (in a molecule)
Induction of a second dipole
Causes induced dipoles in neighbouring molecules
what condtion is required to turn aqeuos sodium hydroxide to form bleach?
Cold, dilute NaOH
