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Periodicity (Electronegativity (As we go down a group, electronegativity…
Periodicity
Electronegativity
As we go down a group, electronegativity decereases this is because the covalent radius increases and therefore the force acting over the longer distance decreases. There are also more electron shells and therefore meaning that as we continue down there is a more present shielding effect. This
As we go across a period, electronegativity increases, as there are fewer spaces left on the outer shells of these atoms and they have large positive charges in the nucleus this creates a smaller atom as well as less shells for a shielding effect creating a higher affinity for these electrons as if they get one they will be far more stable
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Ionisation Energy
As we go down a Group the ionisation energy decreases, this is because the covalent radius also gets larger and therefore the distance between the charges increases and so the pull of both charges is lessened. There are also more electron shells moving down a group allowing for a shielding effect and therefore the pull on the outermost electrons is weakened. Both these factors mean that removing an electron is far easier.
As we go across the period the ionisation energy increases as yes, there are new electrons added but to already existing shells and therefore there is non shielding effect and due to an increase in atomic number the increase in the nucleic charge pulls the electrons closer meaning more energy is needed to remove an electron
Ionisation energy is the amount of energy needed to delocalise one mole of electrons from an element in a gaseous state
Covalent Radius
When going down a group, there is an increase in atomic number and so the greater nucleus positive charge but this also means there is a greater number of electrons and so the lower shells shield the higher shells allowing them to be further from the nucleus without feeling the positive attraction as severely.
When going across a period there is an decrease in atomic number and therefore there is one extra electron in the present shell but there isn't any new shells and so this lacks shielding effect and the opposite charges pull each-other far stronger with greater charges creating a smaller atom
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Monatomic elements
Monatomic elements are elements which only exist in molecules of their own atom as they occur in group 8/0 and therefore have full outer valence electron shells meaning they cannot bond to other atoms. Therefore these elements are incredibly stable.
Monatomic elements experience forces of attraction between each molecule we call this force LDF (London Dispersion Force). This force is created by the uneven distribution of electron in the shells surrounding the atom and so certain areas of the atom can become charged. This charge difference can then induce a unbalance within other atoms and so an induced dipole is in effect and LDFs are prominent through the substance.
Diatomic elements
Diatomic elements exist as discrete double molecule couples they tend to be in group 7 (H,O,N,F,Cl,Br,I) and these elements.
There is again a trend in boiling points as larger molecules such as Bromine have far more electrons than hydrogen such that this unbalance for a larger molecule can cause stronger LDFs between molecules
Phosphorus P4, Sulphur S8 and the Fullerenes
Phosphorus and sulphur exist in discrete molecules themselves as the tetrahedral P4 and the puckered ring of S8 these molecules have low melting and boling points as they are still discrete molecules but their LDFs are strong enough to keep them solid at room temperature
Carbon comes in four forms graphite, graphene, diamond and fullerenes, Fullerenes are unique as compared to the other types of carbon it exists as a discrete molecule and so has intermoleular bonds with itself such as LDFs compared to the covalent network striuctures of graphite and diamond.