Slo# 13.1 Elements and periodicity

Question 1

what is periodicity

Answer 1

the tendency to recur at intervals

Question 2

hhow are elements classified into groups and periods

Answer 2

elements with similar properties are grouped together
periods are in order of increasing atomic number
blocks: valence orbital (s,p,d,f)
families
metals, non metals and metalloids
normal elements (A block) transition elements ( B block)

Question 3

which families are in the periodic table and what is the reason for their respected classification

Answer 3

alkali metals (group 1): react with water to form strong alkalis
alkaline earth metals (group 2): found in the earth’s crust, have alkaline properties
halogens (group 7): react to form salts
noble gasses (group 8): do not react

Question 4

rare earth metals

Answer 4

lanthanides (lanthanum 57) and actinides (actinium 89) series are also called r are earth metals due to their scarcity.
they are radioactive (i.e uranium), silver or grey metals with high luster, tarnish readily in air, have high electrical conductivity

Question 5

atomic radius

Answer 5

increases down a group (addition of shells)
decreases along a period (increase in positive charge)

Question 6

ionization energy

Answer 6

the amount of energy required to remove the outermost electron from a gaseous atom at ground state
down group: decreases (more shielding effect)
along period: increases (more effective nuclear charge)

Question 7

which group has highest ionization energy

Answer 7

highest ionization energy is of inert gases

Question 8

electron affinity

Answer 8

energy released or absorbed by a gaseous atom as an electron is added to it
decreases down a group
increases along a period

Question 9

in which cases is the value of Ea written with positive and negative values

Answer 9

if energy is released the value is negative i.e in the case of electronegative elements (i.e halogens) as they absorb their first electron
if energy is absorbed the value is positive i.e when an electron is added to a uninegative electron it is repelled by the electron already present

Question 10

melting and boiling points

Answer 10

determined by the force of attraction

Question 11

melting and boiling points trend in periods
explanation?

Answer 11

=>increase along short periods till 4A as bonding gets stronger as the atom has more electrons to share in a bond
i.e highest in carbon (4 valence electrons) lowest in sodium (1 bonding electron)
=>decreases after that as the atoms instead of existing in the form of a covalent lattice exist as small molecules(usually gasses) i.e Cl2, N2

Question 12

melting and boiling points trend in groups
explanation

Answer 12

=>decreases down group 1A and 2A
because of increased shielding effect
=> increases down group 7A
because the bigger atoms form stronger molecules with each other because of higher polarizability

Question 13

electrical conductance

Answer 13

metals of group 1A and 2A are good conductors becuase of their free valence electrons
varies abruptly in transition elements
6A and 7A are insulators
tin and lead of 4A are conductors

Question 14

what are coinage metals

Answer 14

metals of group 1B due to their excellent electrical conductivity
specifically gold, silver and copper