Trends in the Periodic Table
Nuclear Charge: more protons that are in the nucleus, the stronger the attraction between the nucleus and the outer electrons
Screening Effect: electrons in the inner shells help to weaken the force of attraction between the nucleus and the electrons in the outer shell
Screening Effect: electrons in the inner shells help to weaken the force of attraction between the nucleus and the electrons in the outer shell
Atomic Radius
ATOMIC RADIUS: of an atom is defined as half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond
Atomic radius decreases across a period because of:
Atomic radius increases down a group because of:
Atomic radius decreases across a period because of:
- Increasing nuclear charge
- No increase in screening effect
Atomic radius increases down a group because of:
- New shells
- Screening effect increases
Ionisation Energy
FIRST IONISATION ENERGY: is the energy required to remove the most loosely bound electron from a neutral, gaseous atom in its ground state
Ionisation energy increases across a period because of:
Ionisation energy decreases down a group because of:
Exceptions:
- Increasing nuclear charge
- Decreasing Atomic Radius
Ionisation energy decreases down a group because of:
- Increasing atomic radius
- Screening effect increases
Exceptions:
- Requires more energy to remove beryllium or magnesium than one might expect because the outer-most sub-level in these elements is full which gives extra stability to this sub-level. Hence it is more difficult to remove and electron from it. Be = 1s2 , 2s2 Mg = 1s2, 2s2, 2p6, 3s2
- Likewise, it requires more energy than expected to remove electrons from nitrogen and phosphorous as both of their outermost sub-levels are half-filled which has extra stability. Hence it requires more energy to remove the outermost electons N = 1s2, 2s2, 2p3 P = 1s2, 2s2, 2p6, 3s2, 3p3
Ionisation energy provide evidence for existence of energy levels. For example there is a large increase in energy required to remove the second electron from an atom of pottassium because the second electron is coming from an ion with a full outer shell (i.e. 8 electrons)
Electronegativity
ElLECTRONEGATIVITY: is the relative attraction that am atom in a molecule has for the shared pair of electrons in a covalent bond
Electronegativity increases across a period because of:
Electronegativity decreases down a group because of:
- Increasing nuclear charge
- Decreasing atomic radius
Electronegativity decreases down a group because of:
- Increasing atomic radius
- Screening effect increases
Trends Within Groups
GROUP 1: ALKALI METALS
These react by losing their outermost electron which means they become more reactive down the group
These react by losing their outermost electron which means they become more reactive down the group
Reactions with oxygen (speed of reaction increases down the group):
Reactions with water (speed of reaction increases down the group):
- 2Li + 1/2O2 -> Li2O
- 2Na + 1/2O2 -> Na2O
- 2K + 1/2O2 -> K2O
Reactions with water (speed of reaction increases down the group):
- Li + H2O -> LiOH + 1/2H2
- Na + H2O -> NaOH + 1/2H2
- K + H2O -> KOH + 1/2H2
GROUP 7: THE HALOGENS
Being non-metals, the elements react by gaining an electrons so they become less reactive down the group.
This is because the size of the atom increases down the group and therefore the number of electrons increases. This makes the van der Waals forces between the molecules stronger, therefore more energy is required to separate them
Being non-metals, the elements react by gaining an electrons so they become less reactive down the group.
- Halogens boiling points increase going down the group.
- At room temperature fluorine, and chlorine are gases, bromine is a liquid and iodine is a solid
This is because the size of the atom increases down the group and therefore the number of electrons increases. This makes the van der Waals forces between the molecules stronger, therefore more energy is required to separate them