Topic 2 - Bonding and Structure Flashcards
What is the definition of an Orbital?
The area around an atom where there is a high probability of finding an electron
What is the definition of Bonding?
How atoms or ions form attractive forces
What is the definition of Structure?
How atoms or ions are arranged
What is the definition of Isolelectronic?
When two atoms, ions or molecules have the same electronic configuration and same number of valence electrons e.g Na(+), Mg(2+) and Al(3+)
Why do atoms form bonds?
In order to become more stable (they do not have to have a full outer shell of this to be the case)
Definition of Ionic Bonding
The electrostatic forces of attraction between oppositely charged ions
Definition of Covalent bonding
The electrostatic forces of attraction between the negative shared pair of electrons and their adjacent, positively charged nuclei
Definition of Metallic Bonding
The electrostatic forces of attraction between the delocalised (sea of) electrons and the positively charged ions
What factors affect the strength of the ionic bond
- The charge of the ions involved
- the radius of the ions (ionic radius)
What is the trend in ionic radius down a group?
The ionic radius increases due to more filled shells of electrons meaning shielding increases so there is less attraction between the electrons and the nucleus
Ionic Charge density formula
= charge/ionic radius
Which two atoms form ions that are electron deficient?
Be is in group 2 and only has 4 electrons in its outer shell when it forms BeCl2
B is in group 3 and only has 6 electrons in its outer shell when it forms BF3
Which two atoms from ions that are expanded octets and break the octet rule?
P has 5 electrons in its outer shell and forms PCl5 and therefore has 10 electrons in its outer shell
S has 6 electrons in its outer shell and forms SF6 and therefore has 12 electrons in its outer shell
What is a dative covalent bond (coordinate bond)
Like a normal covalent bond it involves a shared pair of electrons, however, in a dative covalent bond, both of the electrons originate from one atom.
Give an example of an ion that has a dative covalent
NH4 (+) when NH3 and H+ are bonded together
Why do dative covalent bonds occur?
When an atom, such as nitrogen in NH3, has a non-bonded pair of electrons
How do you show a dative covalent bond?
- In a dot and cross diagram they are from the same species so are drawn as the same, dots or crosses
- In a stick diagram you draw an arrow from the species with the pair of electrons to the atoms that is accepting them
What two factors does bond length depend on?
- The size of the atoms
- The number of shared electron pairs (As this increases the strength of the covalent/ionic bond gets greater)
As bond strength decreases, bond length…
Increases
What is pure ionic bonding?
Pure ionic bonding is when there is only a very little polarising effect of the negative ion by the positive ion so the ions are perfectly spherical. The electrons are shared equally between the two atoms (however, this rarely happens)
What does pure ionic bonding require?
- A large positive ion with a low charge
- A small negative ion
What is polarisation?
When a cation distorts the electron cloud of an anion
Why do certain ions have a higher polarising effect?
As they have a high charge density e.g Al (3+), which will attract an anion with a large ionic radius
Why are larger negative ions more easily polarised than smaller negative ions?
As their outer electrons are less attracted to their nucleus and so more easily distorted