s block (I group elements ) Flashcards
Nature of oxysalts: Alkali metals readily react with oxyacids forming corresponding salts with evolution of hydrogenThe members of Group IA or 1, except hydrogen are called
alkali metals
s block element react with water to form ______solutions
alkanline
All the group 1A elements are _____metals(colour and hardness)
soft and slivery grey
Their valence electron configurations are ____
ns1
The group IA of the periodic table consists of six elements—
lithium, sodium, potassium, rubidium, caesium and francium besides hydrogen
the hydroxides of these metals are soluble in____ and these solutions are ________ in nature.
the hydroxides of these metals are soluble in water highly alkaline in nature.
The alkali metals are so reactive that, they must be stored under _____
oil or kerosene
The silvery lustre of alkali metals is due to the presence of ______
highly mobile electrons of the metallic lattice.
these metals are soft in nature because
the metallic bonding is not so strong.
the softness increases with increase of atomic number because
because there is continuous decrease of metallic bond strength on account of an increase in atomic size
Bigger is the size of metal kernel weaker is the ___
metallic bonding
Group IA atoms are the _____ (compared size) acc to the periodic table
Group IA atoms are the largest in their horizontal periods in the periodic table
When the outermost electron is removed to give a positive ion, the size decreases considerably. There are two reasons for this
: (i) The outermost shell of electron has been completely removed.
(ii) The positive charge on the nucleus is now acting on lesser number of electrons, i.e., attraction increases which brings contraction in size
Atomic as well as ionic size increases from Li to Fr
due to the presence of one extra shell of electrons
how is atomic volume and atomic no related
Atomic volume also increases as the atomic number increases
density of s block
Density gradually increases in moving down from Li to Cs. Potassium is, however, lighter than sodium.
The reason for the low values in density?
is that these metals have high atomic volumes. The abnormal value of potassium is due to unusual increase in atomic size, i.e., atomic volume.
the metals have low melting and boiling points. These decrease in moving down from Li to Cs… why?
as the metallic bond strength decreases or cohesive force decreases.
reasons for low Ionisation energies and electropositive character of s block
Due to their large size, the outermost electron is far from the nucleus and can easily be removed. Their ionisation energies or ionisation enthalpies are relatively low…. the metals have a great tendency to lose the ns' electron to change into M+ ions explains electro+ character
As the ionisation enthalpy decreases from
li to cs
from Li to Cs, the electropositive character (increases or decreases)
, the electropositive character increases, i.e., metallic character increases
The reactivity of these metals increasesfrom
li to cs
The ns1; electron is so loosely held that even the low energy photons (light) can eject this electron from the metal surface. This property is termed as
photoelectric effect
___ and ___are used in photoelectric cells which are sensitive to blue light
K and Cs
The alkali metals can lose their ns1; electron quite easily to form univalent positive ion, M+
its just facts to remember ;)
the radii of the hydrated ion decreases from
li+ to cs+
he ionic conductance of these hydrated ions increases from .
[Li(aq.)] to [Cs(aq.)]*
Hydration of ions is an process
exothermic
explain hydration energy.
The energy released when one gram mole of an ion is dissolved in water to get it hydrated is called hydration energy.
reasons why alkali metals have high reactivity
(i)they have low ionization energies and are readily lose thier electrons to form M+
(ii)They have low heat of atomisation and easily come into vaporised form.
(iii) They have high heats of hydration
explain their Reactivity towards air
On exposure to moist air, all alkali metals except lithium tarnish quickly. The effect of atmosphere increases from Li to Cs. These are, therefore, always kept under kerosene to protect them from air.
Lithium when heated in air combines with _______ to form _________
Lithium when heated in air combines with nitrogen to form nitride
explain their Reactivity towards water:
Alkali metals decompose water with the evolution of hydrogen.Lithium decomposes water slowly. Sodium reacts with water quickly, K, Rb and Cs react with water vigorously. The decomposition is highly exothermic and the evolved hydrogen sometimes inflames. Thus, the reactivity towards water increases from Li to Cs. This is due to increase of electropositive character in the same order
The alkali metals also react with alcohols forming ______ with the evolution of hydrogen.
The alkali metals also react with alcohols forming alkoxides with the evolution of hydrogen. This reaction is used in preliminary test of alcoholic group
explain their Affinity for non-metals
Affinity for non-metals: Alkali metals have great affinity for non-metals
explain their Reactivity towards hydrogen:
The alkali metals combine directly with hydrogen to form crystalline hydrides of the formula MH. These hydrides are ionic and contain the hydride
The electrolysis of the fused hydride (LiH) yields hydrogen at anode [other hydrides decompose before melting.]
facts
The hydrides react with water liberating hydrogen
facts
The ionic character of the bonds in these hydrides increases from _____to_____ and their stability decreases in the same order. They are powerful reducing agents especially at high temperatures.
The ionic character of the bonds in these hydrides increases from LiH to CSH and their stability decreases in the same order. They are powerful reducing agents especially at high temperatures.
explain Reactivity towards oxygen (oxides and hydroxides):
Affinity towards oxygen increases. When heated in atmosphere of oxygen, the alkali metals ignite and form oxides. On combustion Li forms Li2O; sodium gives the peroxide, Na2O2 and potassium, rubidium and caesium give superoxides
The peroxides and superoxides become more stable with increase ________
The peroxides and superoxides become more stable with increase in atomic number of the alkali meta
explain The formation and stability of these oxides of s bolck
The formation and stability of these oxides can be explained on the basis of lattice energy effects. Li* ion being a small ion has a strong positive field around it and can stabilise only a small anion, O2 whereas Na* being a large cation can stabilise a large ion and so on.
The normal oxides react with water to form
hydroxides
The basic nature of the oxides (M2O) increases gradually on________in the group
The basic nature of the oxides (M2O) increases gradually on moving down in the group
explain hydroxides (MOH)
The hydroxides (MOH) are colourless, strong alkaline and corrosive compounds. These are soluble in water and dissolve with the evolution of heat. The hydroxides are thermally stable except LiOH!
The relative strength of the hydroxides increases from
LiOH to CSOH (CsOH >RbOH >KOH >NaOH LiOH)