Chapter 5 (2.2.1/2) Flashcards
Describe shells
- shells are regarded as energy levels
- energy increases as shell no. increases
- shell number or energy level number is called the principal quantum number, n
What are atomic orbitals?
An atomic orbital is a region around the nucleus that can hold up-to 2 electrons, with opposite spins. Shells are made up of atomic orbitals.
Describe s-orbitals
- electron cloud is within the shape of a sphere
- each shell from n=1 has 1 s-orbital
- the greater the shell number, n, the greater the radius of its s-orbital
Describe p-orbitals
- electron shape within the shape of a dumb-bell
- 3 separate p-orbitals at right angles to one another: px, py, pz
- each shell from n=2 has 3 p-orbitals
- the greater the shell number, the further the p-orbital is from the nucleus
Describe d-orbitals
- each shell from n=3 has 5 d-orbitals
What happens to orbitals within each shell?
within each shell, orbitals of the same type are grouped together as sub-shells
How do orbitals fill?
Within each shell, the new type of sub-shell added has a higher energy + orbitals fill in order of increasing energy.
Describe how electrons pair with opposite spins
- electrons repel one another since they are negative
- they have a spin - either up or down
- electron is shown as an arrow indicating spin
- 2 electrons in an orbital must have opposite spins. This helps counteract the repulsion between the negative charges
How are electrons occupied in orbitals?
-Within a sub-shell, 1 electron occupies each orbital before pairing starts, preventing any repulsion between paired electrons until there is no further orbital available at the same energy level
How is Periodic table divided into blocks
Highest energy sub shell in…..
S-block - s sub shell (left 2 block groups)
P-block - p sub shell (right 6 block groups)
D-block - d sub shell (centre 10 groups)
How are ions formed for s / p block elements?
Highest energy sub shell (eg.3s) will be lost first
How are ions formed for d block elements?
- 4s fills first but also empties compared to 3d
- 4s at a lower energy level when filling, but higher when emptying
Ionic bonding
Electrostatic attraction between positive + negative ions. Holds together cations + anions in ionic compounds.
Structure of ionic compounds
- Each ion attracts oppositely charged ions in ALL directions.
- Results in a giant ionic lattice structure containing billions of ions (actual number only determined by crystal size)
Effect of structure on melt/boil points (ionic)
- At RTP, Insufficient energy to overcome forces in the lattice so High temperatures needed.
- melting points are higher for ions w/ higher charges- stronger attraction between ions
- also depends on size of the ions (bigger= higher)
How Ionic compounds dissolve?
- They dissolve in polar solvents (water)
- Polar solvent molecules form IM bonds with the solute surrounding the ions from the solute causing it to dissolve.
Solubility requires…
- Ionic lattice must be broken down
- Polar solvent molecules must attract/ surround the ions
When an ionic compounds have large charges….
The attraction may be too strong for water to be able to break down the lattice structure, so a stronger polar solvent may be needed.
Solubility dependent on…
Relative strengths of attractions within the giant ionic lattice + attraction between ions and water (solvent) molecules
Pattern for solubility
Solubility decreases as ionic charge increases
Electrical conductivity of ionic compounds in the solid state
- ions are in fixed positions in the giant ionic lattice
- there are no mobile charge carriers
Non conductors of electricity in the solid state
Electrical conductivity of ionic compounds in the liquid state
- the solid ionic lattice breaks down
- the ions are now free to move as mobile charge carriers
conductors of electricity in liquid and aqueous states
What is a covalent bond?
The strong electrostatic forces of attraction between a shared pair of electrons + the nuclei of the bonded atoms
Where do covalent bonds occur?
- a small molecule e.g. H2
- a giant covalent structure e.g. SiO2
- a charged polyatomic ion e.g. NH4+
What is a covalent bond in terms of orbitals?
- a covalent bond is the overlap of atomic orbitals, each containing 1e-, to give a shared pair of electrons
- shared pair = attracted to the nuclei of both the bonding atoms
Describe a localised covalent bond
- in a covalent bond, the attraction is localised, acting solely between the shared pair of electrons+ the nuclei of 2 bonded atoms
- the result is a molecule
What are lone pairs?
Lone pairs are pairs of electrons that are not shared
How can SF6 have 12 outer shell electrons?
- the 6 unpaired electrons from sulfur become paired
- outer shell now has 12 electrons - more than the nearest noble gas
- expansion of the octet - only possible from n=3 shell, when a d-sub-shell become available for the expansion
When do multiple covalent bonds exist?
Multiple covalent bonds exists when 2 atoms share more than one pair of electrons
What is a double/triple covalent bond?
In a double/triple covalent bond, the electrostatic forces of attraction are between 2/3 shared pairs of electrons + the nuclei of the bonding atoms
What is a dative covalent bond?
- a covalent bond in which the shared pair of electrons has been supplied by one of the bonding pairs only
- shared pair was originally a lone pair from one of the bonded atoms
What is average bond enthalpy?
- serves as a measurement of covalent bond strength
- kJ/mol
- the larger the value of the average bond enthalpy, the stronger the covalent bond
