s and p Flashcards
why are they called s block elements
valence electrons present in s block
why they called p block elements
group 3a to 8a elements except helium.
valence electrons in p block
f block elements
lanthanides and actinides. valence e in f block
Classification of elements in blocks is based on the:
A.Ease of removal of electron
B.Ease of gain electron
C.Number of electrons present in the valence shell
D.Valence orbital of the element involved in chemical bonding
D.
Classification of elements in blocks is based on the valence orbitals of the elements involved in chemical bonding. Elements are classified into four blocks: i. s-block ii. P-block iii. d-block iv. f-block
assumptiions for measuring atomic size.
- atoms assumed as spherical
2.size of atoms expressed in terms of atomic,ionic and covalent radii
Methods of measuring atomic radius
distance bw centres of adjacent atoms by
. xrays
.spectroscopy
.electron diffraction
why cant atomic radius be determined precisely
- no sharp boundary of an tom.
2.electronic probability distribution is affected by neighbouring atoms.
atomic radii trend
1.decreases from left to right in a period.
due to;
increase in nuclear charge
sheilding remains same from left to right
2.increases from top to bottom
due tp;
increase in shells
increased shielding
ionic radii (cationic and anionic)
- catonic radius smaller than parent atom.
.shell may be removed
.eff nuclear charge increases
2.anionic radii larger than parent (cl to cl-)
.atom expands its valence shell
isoelectronic species
cations of any period have similar number of electrons(are isoelectronic to each other)
similarly anions do this too(also isolelectronic to noble gases)
covalent radii trend
left to right decreaase
top to bottom increase
(almost same as atomic radi)
ionisation energy
min energy req to remove an electron from its gaseous atom to form ion
ionisation energy trends
along the group
.decreases top to bottom
along the period
increases from left to right
factors affecting ionisation energies(4)
- I.E inersely propotional to atomic radius
- I.E directly propotional to nuclear charge
- I.E inverse with sheilding
- penetration effect direct relation with I.E
sheilding effect across the period?
remains constant.
(down the group becomes stronger. along the period has same shell)
reverse of ionisation energy process is called
electron affinity
which group of elements have the highest I.E
group VIIIA or noble gases
electron affinity
energy released when an electron adds to empty or half filled orbital of a gas atom to form an anion 1- ion.
first ea always exo -
second always endo +
trends of e.a
decreases down the group
increases left to right
why fluorine’s E.A is less than that of chlorines
F2 is small and have 7 electrons in 2s and 2p subshells which have a thick electron cloud(which repels incoming electrons.)
which groups have abnormal trend of E.A(low ea) in every peroid
group 2a, 5a and 8a.(hence, halogens have highest ea)
(2a)metals love to lose e- not gain
(5a) have half filled p shell
(8a) have filled valence shell.[doesnt need.]
bond formed bw elements of low i.e and high e.a.
ionic.
low i.e=metals
high ea=non metals.
electronegativity
tendency of an atom to ATTRACT A SHARED ELECTRON PAIR to itself.
electron affinity trends with reasons
- decreases down the group
(increase in atomic size and sheilding efect)
2.increases from left to right
(decrease in atomic size and sheilding constant)
E.N difference= nature
if EN diff> 1.7 = BOND IS IONIC
if EN diff<1.7 and >0.5= POLAR COVALENT
EN<0.5 =NON POLAR COVALENT
EN=1.7 = BOTH IONIC AND COVALENT CHARACTER
element having i.e_____ and E.A_______would be most electronegative
high and high.
left to right both increase.
m.p and boiling point trends group 1a and 2a
decreases from top to bottom
due to increase in atomic size
and metallic bond weakens.
M.P trends group (3a-4a)
decreases top to bottom
M.p and B.p trends (group 5a-7a)
increase from top to bottom due to;
molecules being small
increase in size
polarizability increases
attractive forces increase
variation of m.p and b.p left to right
both increase up to group 4a then decreases going to 6a
group 2 elements reaction with oxygen
berellium at 800 degree
Magnesium burns with dazzling white light
Calcium brick red flame
strontium bright red
barium apple green
group 2 elements reaction with water
berillium inreactive
magnesium with hot water to give H2
calcium sinks in cold water to give H2
strontium and barium vigourous reaction forming soluble hydroxides
G2 reaction with nitrogen
form nitrides “M3N2”.
hydrolysis produce ammonia
Group 3 elements with water
Boron only with steam gives B2O
Aluminium doesnt due to protective oxide layer (corrosion free)
Thalium [Tl] forms thalium hydroxide
Group 3 with oxygen
all reactive at high temp to produce trioxides. {M2O3}
Boron reacts in amorphous form
Al forms a stable layer of Al2O3 acts as protective layer at 800 degree.{used for flashlight photgraphy}
group 3a with Chlorine
high temperature required to form Trihalides MX3
Boron forms covalent liq boron trichloride on heating
Al burns when heated strongly in chlorine gas
thalliumonly forms TlF3 and TlCl3
ionisation energyy is the index of metallic character meaning
atoms with low ie are metals, intermediate are metalloid and high I.E are Non-metals
i.e and e.a main differnce
e.a is the ADDITION OF e-
i.e is the REOMVAL of e-
