Periodicity, Structure and Bonding Flashcards
Atomic Size
Distance from the centre of the atom to its edge
Atomic Size Trend Along A Period
atomic size decreases due to the increased nuclear charge/more protons pulling the electrons within the same shell closer.
Atomic Size Trend Down A Group
atomic size increases due to addition energy levels and electron shielding effect, the inner electrons shield the outer electrons from the pull of of the positive nucleus, therefore the outer electrons are further away
Ionisation energy
energy required to remove one mole of electrons from one mole of atoms in the gaseous state.
I.E along a period
ionisation energy becomes greater due to the increase in nuclear charge/more protons attracting the electrons within the same energy level. The energy therefore increase
I.E down a group
ionisation energy decreases due to the electron energy levels and shielding effect. The outer electrons therefore experience less of the positive pull of the nucleus.
Electronegativity
attraction an atom has for the shared pair of electrons in a covalent bond
Electronegativity along a period
Electronegativity increases along a period, due to the the greater nuclear positive charge, due to an increase in protons, increases the pull on the outer electrons. The outer electrons are therefore more difficult to remove.
Electronegativity down a group
Electronegativity decreases down a group as there are more energy levels and the outer electrons are further away form the nuclear positive charge. The pull on the outer electrons is less,hence Electronegativity decreasing.
3 inter molecular forces
Permanent dipole-Permanent Dipole attraction, Hydrogen Bonding and London dispersion forces.
Permanent dipole-Permanent Dipole
the electrostatic attraction between the oppositely charged dipole ends of two or more polar molecules.
Permanent dipole-Permanent Dipole Molecule
will have higher mp and bp due to the greater inter molecular attraction, more energy is required to separate the molecule
Spatial Arrangement Symmetrical
when the polar bond’s spatial arrangement is symmetrical then the molecules is non polar
Spatial Arrangement Unsymmetrical
when the polar bond’s spatial arrangement is unsymmetrical then the molecule is polar
To define Polarity or Non-Polarity
- Check the difference in electronegativity
- Determine if bonds are weak/strong covalent/ionic bonds
- Check the shape
- State polarity
Hydrogen Bonding
Electronegativity difference between hydrogen and nitrogen or oxygen or fluorine is very large, which results in strong polar bonds that cause strong inter molecular attractions than simple PD-PD,
How is London Dispersion Forces Caused
An uneven distribution of electrons can lead to a dipole which induce dipole on a nearby atom. The attraction of these 2 dipoles London Dispersion Forces
How is London Dispersion Forces Affected?
the bigger the atom due to an increase in total number of electrons, the greater the London forces due to larger dipoles formed. Therefore increasing the energy required to desperate these molecules, hence increase in mp and bp
Elements that have London Dispersion Forces
diatomic elements, noble gases, sulphur, phosphorous and fullerene.
Non-polar London Dispersion Forces
Non-polar molecules will only have ldf’s
hydrocarbons such as alkanes and alkenes have only ldfs due to their symmetrical arrangement
Noble Gases
insoluble and do not conduct
have low mp and bp due to weak London forces that exists between atoms, which are easily broken at low temperatures, hence the, are gases
Diatomic Elements
Have non-polar covalent bonds within the molecules
These strong bonds don’t break during melting and boiling. They have LDF, which are weak, easily broken at low temps
Molecular Solids
P4,S8,C60,I2
don’t conduct
Iodine has bigger atoms due to more electrons that lead to stronger LDF.
Phosphorous, Suplhur and Fullerene have more atoms hence stronger LDF’s
Covalent Networks
solid at room but insoluble in water
graphite conducts due to only 3 out of 4 electrons bonding
Strong covalent bonds inside and outside
Metallic Elements
Contain metallic bonding.
As the number of delocalized outer electrons increase, the hardness, mp and bp also increase. The strenght of the metallic bond increases with the increases attraction between the positive core and increasing number of delocalised electrons
Covalent Radius
is half the length of the covalent bond, the distance between both nuclei in a covalent bond
