Biochemistry
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How do electrons exist?
In a probability density - they belong in a certain possibility within
How are shells and sub shells arranged?
By energy level
Why are electrons added to 4s before 3d?
4s is at a lower energy level than 3d
What causes electron shielding and what does electron shielding cause?
Filled up shells and sub shells - it weakens the nuclear charge to outer electrons
Definition of a mole?
Amount of any substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12
What does periodicity refer to?
Patterns of physical and chemical properties within the periodic table
What happens to the atomic radius as you go down a group?
Down a group - atomic radius increases
What happens to the atomic radius when you go across a period and why?
Atomic radius decreases. This is because as you go across a period, more electrons are being added to the sub shells but they’re not increasing in energy levels so theres no extra shielding. However, you’re adding more protons which increases the nuclear charge and draws more electrons closer to the nucleus
Definition of ionisation energy?
The energy required to remove one mole of electrons from one mole of gaseous atoms
Why do noble gases have a high ionisation energy?
Have a full outer shell of electrons
Why do group one elements have a low ionisation energy?
Theres only one electron in their outermost shell so theres low level of nuclear charge
What gives a higher level of stability in an atom?
When a sub shell if filled or half filled
Across a period, what is the general pattern of ionisation energy?
Increases
Down a group, what is the general pattern of ionisation energy?
Decreases
What is electronegativity?
A measure of the tendency of an atom to attract a pair of bonding electrons via Pauling scale. Fluorine is most electronegative (4.0) and Cs and Fr are least electronegative (0.7)
Across a period, what is the general patter of electronegativity and why?
Electronegativity increases across a period as there is a lower atomic radius so the nuclear charge exerts a higher level of control over outer shells of electrons
Down a group, what is the general patter of electronegativity and why?
Electronegativity decreases down a group as theres increased levels of shielding due to more filled shells so less attractive forces from the nucleus to pull outer electrons closer
What is orbital hybridisation?
A theory/model that explains how elements form bonds when their electron structure is unfavourable - carbon is the biggest example of this
Why is carbon a good example of orbital hybridisation?
There are only 2 electrons in carbons outer shell but it needs 4 to share - it hybridises the outer electrons (making one large sub shell out of two) so 2p becomes 2sp^3. Each become half filled. The structure changes too and electrons spread as far as possible (trigonal pyramidal - 109.47º)
What is an ionic bond?
A chemical link between two oppositely charged ions, caused by the electrostatic force between oppositely charged ions in an ionic compound - always between metals and non-metals
Properties of ionic compounds
• High melting and boiling points - Water soluble
What is a covalent bond?
A chemical link formed when two atoms share electron pairs - always between non-metals
How are carbon-carbon sigma bonds formed?
Through sp^3 hybridisation
How are carbon-carbon double bonds (pi bonds) formed?
Formed through sp^2 hybridisation using a sigma and pi bond. There’s an electron dense area surround the bonds