Periodic trends Flashcards
Change of effective nuclear charge down the group
Each of the Group 1 metal has an increase of 1 core electron shell, hence the shielding effect increases down the group.
However, as the increase in shielding effect increases more than the nuclear charge, effective nuclear charge decreases, resulting in the nucleus exerting a weaker hold/pull on its valence electrons.
Change of density down the group
The density of the alkali metals generally increases down the group. Atomic mass increases faster than the atomic volume.
Physical properties of alkali metals
They are relatively soft and can be cut easily with a knife.
They have low melting and boiling points compared with other metals.
They are good conductors of heat and electricity.
change of melting and boiling points down the group
The melting and boiling points decrease down the group. The size of the metal cation increases down the group. As the size of the cations increases down the group, the electrostatic forces of attraction between the sea of delocalised electrons and the metal cations decreases. So metallic bonding weakens down the group. Less energy is required to break the weaker metallic bonds.
Chemical properties of alkali metals
Group 1 elements are the most reactive metals in the Periodic Table.
They have similar chemical properties because all the elements have similar electronic configuration, that is, one electron in their outermost shell.
The Group I metals are very reactive. They react rapidly with air and vigorously with water.
They are kept under oil to prevent them from coming into contact with air and water.
They are called alkali metals as they react readily with water to form alkalis.
Change of reactivity down the group
the metals become more reactive on going down the Group i.e. reducing power increases (tendency to be oxidised increases) down the group.
reaction of alkali metals with water
All the alkali metals react with cold water to form alkalis (soluble metal hydroxides) and hydrogen gas.
Physical properties of halogens
All halogens have low melting and boiling points.
All the halogens are coloured and are non-conductors of electricity.
On going down the group, the colour intensity increases, and the melting and boiling points increase.
Change of properties of halogens down the group
the size of the electron cloud and hence, the polarizability of the halogen molecule increases. Stronger dispersion forces exist between the molecules and more energy is needed to overcome the intermolecular forces of attraction. Hence, the volatility of the halogens decreases down Group 17, and the melting and boiling points increases down the group as well.
The increase in strength of dispersion forces down the group explains the change in physical state of the elements down Group 17.
displacement of halogens
a more reactive halogen (top of the group) displaces a halogen (lower of the group)
change of boiling and melting points of noble gas down a group
their boiling and melting points increase, the electrostatic forces of attraction increases and more energy is required to overcome the stronger forces of attraction. (They have dispersion forces. The atomic size increases, and the number of electrons also increases)
definition of transition metals
A transition element is a d-block element that forms some compounds containing its ion with an incomplete d-subshell
Trends in melting and boiling point
S-block metals (alkali metals) have lower boiling point than transition metals.
S-block metals: Only 1 or 2 valence electrons are involved in metallic bonding, less energy is required.
Transition metals: Both 4s and 3d electrons are involved in metallic bonding due to their proximity in energies. More energy is required
Trend in densities
S- block metals: Low, Low in atomic masses. Large atomic radius, less efficient packing, resulting in less no. of atoms per unit volume
Transition metals: Very high, Higher atomic masses. Small atomic radius, close packing of
atoms resulting in more no. of atoms per unit volume
Trend in melting and boiling points across the period (question)
From Sc to V, the melting points and boiling points increases due to the increase in the number of
unpaired electrons that are involved in metallic bonding.
Mn has a relatively low melting points and boiling points. The electronic configuration of Mn is
[Ar]3d 4s. Due to the apparent stability of the d^5 configuration (half-filled d-subshell), the 3d electrons are less available for delocalization. This results in weaker metallic bonding. The same effect is expected for Cr, but that occurs to a lesser degree because the nuclear charge of Cr is lower.
From Fe to Zn, the melting points and boiling points generally decreases as electrons begin to pair up in the 3d orbitals. The paired electrons do not participate fully in metallic bonding, and this decreases the strength of the metallic bond.
