Foundations of Chemistry(Bonding)

electron shell

electron shell

group of atomic orbitals with the same principal quantum number (n)

what is n?

principal quantum number. The number that represents the overall energy level of the orbital. The bigger n is, the further the distance between the energy level and the atomic nucleus

atomic orbital

a region in an atom that can hold up to 2 electrons with opposite spins

How many electrons can the 1st shell hold?

2

How many electrons can the 2nd shell hold?

8

How many electrons can the 3rd shell hold?

18

How many electrons can the 4th shell hold?

32

Why can orbitals only hold 2 electrons spinning in opposite directions?

• electrons carry negative charge

• as the spin on an axis they generate a magnetic field

• They spin either clockwise or anticlockwise which is represented by arrows

• Electrons in the same orbital spin in different directions

How do you show the electron arrangements?

Show as n then orbital type then number of electrons in that orbital

What is an electrons density map?

shows where the probability of finding an electron is highest

What is an s orbital?

spherical

1 in every energy level

What is an p orbital?

dumb-bell shaped

Px is on x axis, Py on y axis and Pz on z axis

3 in every energy level from n=2 upwards

How many d orbitals and from which energy shell?

5 d orbitals from n=3 upward

How many f orbitals and from which energy shell?

7 f orbitals from n = 4 upwards

What is an electron energy shell made up of?

atomic orbitals with the same principle quantum number

What does each sub-shell contain?

orbitals of the same type

How many s orbitals in an s orbital sub-shell?

1

How many p orbitals in an p orbital sub-shell?

3

How many d orbitals in an d orbital sub-shell?

5

How many f orbitals in an f orbital sub-shell?

7

Where are the highest energy electrons?

furthest from the nucleus

What are the rules for filling sub-shells?

• electrons are added 1 at a time

• the lowest available energy level is filled first

• Each energy level must be filled before the next, higher energy level starts to fill

  • 4s is filled before 3d as lower energy

• Each orbital is built singly before pairing starts

What does a single arrow show in an orbital?

1 electron spinning

What does a double arrow show in an orbital?

2 electrons spinning in opposite directions

How is noble gas notation used?

• Go back to the most recent noble gas and put it in square brackets

• Write the remaining sub-shells

Do you take from 4s or 3d first when electrons are removed?

4s

What is ionic bonding?

the electrostatic attraction between positive and negative ions

How do we represent ionic bonding?

dot and cross diagram

What is an ionic lattice and why do they form?

a regular repeated 3D arrangement of atoms, ions or molecules in a metal or other crystalline structure that forms because attraction between oppositely charged particles happens equally in all directions

Covalent bonding

the strong electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms

Caused by the overlap of atomic orbitals, each containing 1 electron to give a shared pair

How do we measure the strength of Covalent bonds?

average bond enthalpy

What is a lone pair?

an outer shell pair of electrons that’s not involved in chemical bonding

What is an example of an electron deficient outer shell?

BF3, the boron only has 6 electrons in its outer shell

What is an example of an expanded outer shell?

SF6 has 12 electrons in its outer shell as it has expanded its octet

What is a dative covalent bond?

formed when the shared pair of electrons of the covalent bond is provided by only one of the atoms

shown by an arrow showing the direction that the electrons have been donated

What is a pure covalent bond?

no difference in electronegativity

What is a polar bond?

has a permanent dipole and so a slight charge

What is electronegativity?

the measure of an atoms ability to attract a shared pair of electrons

What is a permanent dipole?

small, permanent, charge difference across the bond that results from a difference in electronegativities of the bonded atoms

Where is the elements with the highest electronegativity and why?

top right because the 7th group has a high nuclear charge and the top has less electron shielding and a smaller atomic radius

Why do lone pairs repel more than bonded pairs and what does this result in?

They are slightly closer to the atom and take up more space than bonded pairs

since they repel more lone pairs repel bonded pairs closer together and reduce their bond angle

2.5 degrees per lone pair

What do multiple bonds make?

bonding region

How do you find the bond angle?

divide 360 by the number of electron pairs/bond regions

How do you know if a molecule is polar?

If its individual dipoles won’t cancel out

Intramolecular vs intermolecular interactions

intra-molecular interactions (ionic and covalent bonds) are very strong

intermolecular forces are much weaker interactions

What are permanent dipole-dipole interactions?

electrostatic attraction between molecules with permanent dipoles

comparatively strong

What are induced dipole-dipole interactions?

• London Forces

• electrons are constantly moving

• this can cause temporary a dipole across the molecule at any moment

• this then induces dipoles in neighbouring molecules

• these small induced molecules attract each other causing weak intermolecular forces

Why does boiling point increase with molecular size?

As molecular size increases so does the number of electrons meaning that there is a higher chance of a temporary dipole being made. This means that there are more London forces and so more energy is needed to overcome them resulting in an increase in boiling point

What is a hydrogen bond?

a strong dipole-dipole interaction between an electron deficient hydrogen atom on 1 molecule and a lone pair of electrons on a very electronegative atom (NOF)

What do you need for Hydrogen bonds to form?

a hydrogen atom, and an atom with a very high electronegativity and lone pairs

• Electrons are so far away from hydrogen that almost ready to be donated as a proton to a base

What are waters anomalous properties?

• If a molecule has hydrogen bonds that its boiling point is higher than expected as Hydrogen bonds are comparatively strong

• When ice forms an open lattice structure forms and water expands due to the Hydrogen bonds being longer than the covalent bonds (177pm vs 99pm). This makes ice less dense that water

• When ice melts the lattice collapses as the H-bonds are broken and the molecules move closer together

What bond angles do you need to know?

• 2 bonded pairs = linear = 180

• 3 bonded pairs = trigonal planar = 120

• 4 bonded pairs = tetrahedral = 109.5

• 6 bonded pairs = octahedral = 90

• 3 bonded pairs and 1 lone pair = trigonal pyramidal = 107

• 2 bonded pairs and 2 lone pairs = non-linear = 104.5