5) Electrons and bonding Flashcards
Energy increases as shell number _?
increases
Define principal quantum number n
a number representing the relative overall energy of each orbital, which increases with distance from the nucleus
What are the sets of orbitals with the same n-value referred to as?
electron shells or energy levels
Define atomic orbital
a region around the nucleus that can hold up to 2 e-, with opposite spins
Describe a s-orbital
spherical shape
as n increases, radius increases
Describe a p-orbital
dumb-bell shape
as n increases, reaches further away from the nucleus
Define sub-shell
a group of orbitals of the same type within a shell
Describe 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 (bus-seating rule)
What is special about the 3d sub-shell?
it is at a higher energy level than the 4s sub-shell so it is filled after and emptied after the 4s sub-shell
What does electron pairing with opposite spins help to do?
counteract the repulsion between the negative charges of the 2 electrons
When orbitals with the same energy are occupied singly first (bus-seating rule), what does it prevent?
any repulsion between paired electrons until there is no further orbital available at the same energy level
Define electron configuration
a shorthand representation that shows how electrons occupy sub-shells in an atom
In an electron configuration, how are shells listed?
in shell order rather than in order of filing
How can electron configurations be expressed more simply?
in terms of previous noble gas plus outer electron sub shells
When are positive ions / cations formed?
when atoms lose electrons
When are negative ions / anions formed?
when atoms gain electrons
Define ionic bonding
the electrostatic attraction between positive and negative ions
In ionic bonding electrons are _ whereas, in covalent bonding electrons are _?
transferred
shared
Define giant ionic lattice
3D structure of oppositely charged ions, bonded together by strong ionic bonds
Give 3 features of giant ionic lattices
high melting and boiling points
many dissolve in polar solvents e.g. water
conducts electricity as a liquid or aqueous solution
Why do ionic lattices containing ions with greater ionic charges have higher melting points?
there is stronger attraction between ions
What two conditions must be met for a giant ionic lattice to dissolve in a polar solvent?
the ionic lattice is broken down
solvent molecules e.g. water attract and surround the ions in solution
How are giant ionic lattices able to conduct electricity as a liquid or aqueous solution?
the ions are free to move as mobile charge carriers
Define covalent bonding
the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Where can covalent bonding occur?
between atoms in non-metallic elements
compounds of non-metallic elements
polyatomic ions
Define covalent bond
the overlap of atomic orbitals, each containing 1 electron to give a shared pair of electrons
Give 3 common features of a covalent bond
- the shared pair of electrons is attracted to the nuclei of both of the bonding atoms
- the bonded atoms often have outer shells with the same electron structure as the nearest noble gas
- the attraction is localised, acting solely between the shared pair of electrons and the nuclei of the two bonded atoms (forming a molecule)
Define molecule
the smallest part of a covalent compound that can exist while retaining its chemical identity, consisted of two or more atoms covalently bonded together
Define displayed formula
a formula showing the relative positioning of all the atoms in a molecule and the bonds between them
Define lone pair
an outer shell pair of electrons that is not involved in chemical bonding
How many covalent bonds can carbon form?
4
How many covalent bonds can nitrogen form?
3
How many covalent bonds can oxygen form?
2
How many covalent bonds can hydrogen form?
1
What is special about Boron?
has only 3 outer shell electrons which can be paired - showing predictions for bonding cannot be based solely on noble gas electron structure
For elements in period 2, the n=2 outer shell can hold just 8 electrons. But what is special about phosphorous, sulfur and chlorine?
the n=3 outer shell can hold 18 electrons, so more electrons are available for bonding
Give the formula for different fluorides containing phosphorous
PF3
PF5
Give the formula for different fluorides containing sulfur
SF2
SF4
SF6
Give the formula for different fluorides containing chlorine
ClF
ClF3
ClF5
ClF7
What is significant about SF6
expansion of the octet where sulfur’s outer shell contains more electrons than the nearest noble gas
only possible from the n=3 shell when a d-sub-shell becomes available for expansion
In a double covalent bond, the electrostatic attraction is between _ and the nuclei of the bonding atoms
two shared pairs of electrons
In a triple covalent bond, the electrostatic attraction is between _ and the nuclei of the bonding atoms
three shared pairs of electrons
Define dative covalent / coordinate bond
a shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only
In a dative covalent bond, what would the shared electron pair have been originally?
a lone pair of electrons on one of the bonded atoms
What does average bond enthalpy serve as a measurement of?
covalent bond strength
The larger the value of average bond enthalpy, the _ the covalent bond.
stronger
