Chapter 5 - Structure and Bonding Flashcards
What can an electron be thought of as ?
A negatively charged cloud with the shape of an orbital, called an electron cloud
Shells are regarded as what ?
Energy levels
What happens to energy as the shell number increases ?
Energy increases
What is the shell number referred to as ?
Principal quantum number (n)
What are shells made up of ?
Atomic orbitals
What is an orbital ?
- An orbital is an area around the nucleus where electrons with opposite spin are likely to be found
What are the different orbitals ?
- S orbitals
- P orbitals
- D orbitals
- F orbitals
How many electrons can be held in an orbital ?
One or two, no more
How many orbitals does each type contain ?
- S - one
- P - three
- D - five
- F - seven
How many electrons can be held in each type of orbital ?
- S - two
- P - six
- D - ten
- F - fourteen
What is the shape of an s orbital ?
Spherical
What is the shape of a p orbital ?
- Dumbbell
- Theres three types, one in each plane (x,y and z)
What are the rules of orbital fillings ?
- Orbitals fill in order of increasing energy
- Electrons pair with opposite spins
- Orbitals with the same energy are occupied singly first
Explain the rule of orbitals filling in order of increasing energy
- 1s is filled first
- Then 2s and 2p
- Then 3s, 3p, 4s and then 3d
Where does this rule cause confusion ?
- The 3d sub-shell has higher energy than the 4s.
- So the 4s fills before the 3d
State the orbital filling until the 4th shell
- 1s
- 2s, 2p
- 3s, 3p, 4s, 3d
- 4p, 4d, 4f
Explain the rule of electrons pair with opposite spins
- Electrons are negatively charged and repel one another
- Electrons can have spin up or spin down
- If electrons have opposite spin, the charge repulsion is counteracted enough for both to be in the orbital, they cancel out
Explain the rule of orbital filling when the same energy subshells are occupied singly first
- Within a sub shell, the orbitals have the same energy
- One electron occupies each orbital before pairing begins.
- This prevents repulsion until no unoccupied orbitals remain
How can electron configuration be shortened ?
- 1s2 can be expressed as [He]
- 1s2 2s2 2p6 can be expressed as [Ne]
- 1s2 2s2 2p6 3s2 3p6 can be expressed as [Ar]
What is this format called ?
Shorthand notation
What happens in terms of energy sub-shells when forming ions ?
The highest energy sub shells lose or gain electrons
What is ionic bonding ?
The electrostatic attraction between oppositely charged ions
In what directions are ions attracted to other ions ?
In all directions
What is the result of ions attracting oppositely charged ions in all directions ?
Giant ionic lattice
How are the melting and boiling points of ionic compounds explained ?
High temperatures are required to provide the energy to overcome the strong electrostatic attraction between the ions
What happens to the melting points for giant ionic lattices, when ionic charge increases ?
Melting point increases as there is a stronger attraction between ions
When are ionic compounds soluble ?
They dissolve in polar solvents such as water
What does solubility require ?
- The ionic lattice must be broken down
- Water molecules must attract and surround the ions
What does solubility (of ionic compounds) depend on ?
The strength of the attraction within the giant ionic lattice and the attractions between ions and water molecules
When can ionic compounds conduct electricity ?
- When molten or dissolved in water
Why can’t ionic compounds conduct electricity when solid ?
- The ions are in a fixed position
- This means that they can not carry charge
Why can ionic compounds conduct electricity when molten or dissolved in water ?
- The solid ionic lattice breaks down
- The ions are now free to move and carry charge
Summarise the properties of most ionic compounds
- High melting and boiling points
- Tend to dissolve in polar solvents such as water
- Conduct electricity only in the liquid state or in aqueous solution
What is covalent bonding ?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What actually is a covalent bond ?
The overlap of two atomic orbitals, each containing one electron, to give a shared pair of electrons.
How does covalent bonding differ to ionic bonding ?
- The attraction in covalent bonding is localised
- This means it only acts on the shared pair of electrons and the nuclei of the two bonded atoms
How can covalent bonding be displayed ?
With dot and cross diagrams
What is a multiple covalent bond ?
Two atoms share more than one pair of electrons
What is a double bond ?
A double bond occurs when the electrostatic attraction is between two shared pairs of electrons, and the nuclei of the bonding atoms
What is a triple bond ?
A triple bond occurs when the electrostatic attraction is between three shared pairs of electrons, and the nuclei of the bonding atoms
What is a dative covalent bond ?
- A dative covalent bond occurs when the shared pair of electrons has been supplied by one of the bonding atoms only
- Originally a lone pair
Give an example of a dative covalent bond
- An ammonia molecule donates its lone pair of electrons to an H+ ion.
- Forming an ammonium ion
What is average bond enthalpy ?
- A measure of covalent bond strength.
- Larger value = stronger bond
