S Block Elements Flashcards
Lithium and beryllium
-The lightest element lithium and beryllium of these groups are unique in many ways because their small sizes result in a high charge density on the ions which produce strong polarizing effects and high heels of hydration.
-Lithium and beryllium differ market live from their heavier congeners.
- lithium has many similarities to its diagonal neighbour magnesium in beryllium group.
-beryllium shows resemblance to aluminium which is its diagonal neighbour in boron group.
Group trends:
- From top to bottom decreases
- From left to right increases
- Electronegativity (given by pauling)
- Ionization potential
- Electron affinity
- Hydration energy of ions
- Boiling and melting point
Electronegativity of alkali metals group
- Li -> 1.0
- Na -> 0.9
- K -> 0.8
- Rb -> 0.8
- Cs -> 0.7
(The elements have very small electronegativity values and are generally called electropositive elements)
Ionization potential
-1st ionization is low mostly than 2nd ionization b\c outer e- are is sheilded effectively from the nucleus by the inner e-
-the first ionization enthalpy of each the alkali metal is lower than corresponding alkaline earth metal in the same period because the latter has an extra nuclear proton which causes an increase in the electrostatic attractive force between the nucleus and the outermost electrons.
-there is a progressive decrease in ionization enthalpies in each series as the outermost electron is less firmly held as the group is descended
- atomic size increases ionization enthalpies decreases
Group trends:
- Top to bottom increase
- left to right decreases
- Radii sizes of atoms and cations
- Radii of cations
- Reactivity (chemical property)
Radii sizes of atoms and cations
- the alkali metals have the largest covalent retire of all elements in their respective periods because the possess the smallest nuclear charge which exerts the weakest electrostatic attractive forces on the outermost electrons
- the elements of beryllium family have the next largest atoms because of the same reasons.
Electrode potential (trend)
The electrode potential is a major of the total enthalpy change when a solid metal ‘M’ is brought into aqueous medium in the form of ‘M+’ (aq)
Density is melting and boiling points of s block
- the IA and IIA group elements have relatively large volumes and smaller nuclear masses than the other elements in their respective period.
- the trend to be less thans and have lower melting and boiling points
- all the alkali metals have body centred cubic structure.
- the IIA group metals are appreciably harder than alkali metals because the presence of divalent cations in their metallic structure produced greater binding forces.
Elements of group IA & IIA
•Associated with => IA = ns1 (principle oxidation state # 1+)
•Associated with => IIA = ns2 (principle oxidation state# 2+)
•Elements francium (87) and radium (88) are radioactive
•The elements of both these groups with the exception of beryllium which gives many distinctly covalent compounds from colourless ionic compounds.
•The compounds of IA group and IIA group elements differ markedly in their solubility and thermal stability these differences in properties arise mainly from difference in anic size and charge density.
Alkali metals and alkaline earth metal
•The IA group elements are called alkali metals because they form soluble hydroxide which are alkaline.
•The IIA group elements are known as alkaline earth metals their hydroxides are also alkaline but they are sparingly soluble in water and these metals exists as their oxides in the earth.
Radii (sizes) of cations
•since the elements IA and IIA groups have large sizes. Low ionization enthalpy, low electron affinity values these elements readily loss there Valence electrons to form cations with the positive charge of oneplus and 2 + respectively.
