C5- Electrons And Bonding Flashcards
What are shells and their capacity?
- Shells = energy levels.
- As shell number increases, energy increases.
- Shell 1 = 2 electrons
- Shell 2 = 8 electrons
- Shell 3 = 18 electrons
- shell 4= 32 electrons
What is an atomic orbital?
A region around the nucleus that can hold up to two electrons, with opposite spins.
- the opposite spins is what allows the electrons to exist together as they would usually repel one another.
- 4 types of orbitals: s- , p- , d- , f-
Each has a different shape.
s-orbitals.
- electron cloud in shape of a sphere.
- each shell from n=1 contains one s-orbital.
- can hold one or two electrons.
- radius of the orbital increases with shell number.
p-orbitals.
- electron cloud in shape of an 8.
- one orbital can hold one/two electrons.
- there are 3 separate p-orbitals at right angles to each other:
Px - horizontal 8 shape.
Py - diagonal 8 shape.
Pz - vertical 8 shape. - each shell from n=2 contains three p-orbitals.
- distance from p-orbital to nucleus increases with shell number.
d-orbitals and f-orbitals.
d-orbitals:
each shell from n=3 contains five d-orbitals.
f-orbitals:
each shell from n=4 contains seven f-orbitals.
What is principal quantum number?
shell number
What is a sub-shell?
A group of orbitals of the same type within a shell.
Explain the filling of orbitals in terms of energy.
Orbitals fill in order of increasing energy:
- n=2 shell ; 2s, 2p
- n=3 shell; 3s, 3p, 3d
- n=4 shell; 4s, 4p, 4d, 4f
The new sub-shell added always has higher energy.
The 4s sub-shell is at a lower energy level than the 3d sub-shell, therefore it fills first. (Order = 3p, 4s, 3d)
What are the rules of the filling of orbitals?
- Orbitals fill in order of increasing energy.
- Electrons pair with opposite spins.
- Orbitals with the same energy are occupied singly first.
Why do electrons pair with opposite spins?
-electrons are negatively charged so repel one another.
- electrons have a property called spin; either up or down.
An electron is shown as an arrow indicating its spin.
- the 2 electrons in an orbital must have opposite spins in order to counteract the repulsion between the negative charges.
Why are orbitals with the same energy occupied singly first?
To prevent any repulsions between paired electrons until no further orbital is available at the same energy level.
What is electron configuration?
Shows how sub-shells are occupied by electrons in an atom.
Can be expressed simply in terms of the previous noble gas plus the outer electron sub-shells. This is useful for emphasising similarities in the outer shell configuration.
What blocks is the periodic table divided into?
S-block:
- highest energy electrons in s-sub-shells. (Left block of 2 groups)
P-block:
-highest energy electrons in p-sub-shells. (right block of 6 groups)
D-block:
- highest energy electrons in d-sub-shell. (centre block of 10 groups)
Explain the electron configuration of ions.
When forming ions (s and p-block) the highest energy sub-shells lose or gain electrons.
For ions in the d-block, the 4s sub-shell fills and empties before the 3d sub-shell.
What is ionic bonding?
The electrostatic attraction between positive and negative ions. It holds together cations and anions in ionic compounds.
What are the common cations and anions?
Cations:
- metal ions; Na+ , Ca^2+, Al^3+
- ammonium ions; NH4^+
Anions:
- non-metal ions; Cl- , O^2-
- polyatomic ions; NO3^- , SO4^2-
What is a dot and cross diagram?
In dot and cross diagrams, outer shell electrons from a metal atom and transferred to the outer shell of a non-metal atom.
Explain the structure of ionic compounds.
- each ion attracts oppositely charged ions in all directions.
This results in a giant ionic lattice.
Explain the melting and boiling point of ionic compounds.
- almost all ionic compounds are solid at room temp.
- most have a high mp and bp.
High temperatures provide the large quantity of energy needed to overcome the strong electrostatic attraction between the ions. - melting points are higher for lattices containing ions with greater charges as there is stronger attraction.
- ionic attraction also depends on the size of ions.
Explain the solubility of ionic lattices.
- many ionic compounds dissolve in polar solvents (eg. Water)
Polar water molecules break down the lattice and surround each ion in solution.
-compounds with ions of large charges may not be very soluble, as ionic attraction is too strong to break. - depends on the relative strengths of the attractions in the lattice and attractions between ions and water molecules.
Explain the electrical conductivity of ionic lattices.
- in solid state = ionic compound does not conduct electricity as there are no delocalised electrons.
- can conduct when melted or dissolved in water as solid lattice breaks down and ions are now free to move.
Explain covalent bonding.
It is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atom.
Occurs between:
- non-metallic elements.
- compounds of non-metallic elements.
- polyatomic ions.
The atoms are bonded together in a single small unit- a small molecule, a giant covalent structure or a charged polyatomic ion.
Explain a covalent bond in terms of orbitals.
A covalent bond is the overlap of atomic orbitals (each with 1 electron) to give a shared pair of electrons.
- shared pair is attracted to the nuclei of both atoms.
- bonded atoms often have the same outer electron structure as the nearest noble gas.
What is meant by: a covalent bond is localised?
The attraction is localised, acting solely between the shared pair of electrons and the nuclei of the two bonded atoms.
The result can be a small unit called a molecule (consisting of two or more atoms)
A molecule is the smallest part of a covalent compound that can exist whilst retaining the chemical properties of the compound.
How can covalent bonds be shown?
Dot and cross diagrams:
-in covalent bonding electrons are shared unlike ionic bonding where they are transferred.
- atoms are drawn as overlapping circles.
- can also be shown as displayed formula which shows the relative positioning of atoms and the bonds between them (as lines).
Both ways also show any lone pairs.
What is meant by expansion of the octet?
When the outer shell contains far more than the nearest noble gas, it is called expansion of the octet.
This is only possible from the n=3 shell, when a d-sub-shell becomes available for expansion.
What is a multiple covalent bond?
Exists when two atoms share more than one pair of electrons.
Double covalent bond?
- the electrostatic attraction between 2 shared pair of electrons and nuclei of the bonded atoms.
- all atoms have 8 electrons in their outer shell and structure is of the nearest noble gas.
Triple covalent bond?
- electrostatic attraction between 3 shared pairs of electrons and nuclei of the bonded atoms.
- all atoms have electron structure of the nearest noble gas.
What are dative covalent bonds?
A dative bond (aka coordinate bond) is a covalent bond in which the shared pair of electrons has been supplied by one of the bonded atoms only.
- shared pair of electrons was originally a lone pair of electrons on one of the atoms.
What is average bond enthalpy?
Serves as a measurement of covalent bond strength.
The larger the value of average bond enthalpy, the stronger the covalent bond.
