C7| PERIODIC PROPERTIES

Question 1

Development of periodic table

Answer 1

Developed by Mendeleev and Meyer on basis of similarity in chemical and physical properties exhibited by certain elements.

Question 2

Effect of valence electrons

Answer 2

Elements with same no. of valence electrons share a group where they exhibit similar characteristics as a result of electrons. Differences are due to them being in different shells

Question 3

Effective nuclear charge (Zeff)

Answer 3

Nuclear charge outer electron experiences after accounting for repulsions by other electrons in the atom.

Question 4

How Zeff works

Answer 4

Core electrons are effective in screening the the outer electrons from full charge of nucleas.
But electrons in same shell do not screen each other effective.

Question 5

Zeff trend

Answer 5

Increase across period

Question 6

Atomic radi trend

Answer 6

Increase down grouo
Decrease left to right

Question 7

Cations and anions atomic radius difference

Answer 7

Cations are smaller, anions are larger.

Question 8

Isoelectronic series + atomic radius

Answer 8

A series of ions that have the same no. of electrons. Therefore determine atomic radius : size decreases with increasing atomic number as electrons are attached more strongly to nucleas as it’s positive charge increases.

Question 9

Ionization energy

Answer 9

Minimum energy required to remove an electron from ground state of isolated gaseous atom/ion

Question 10

Ionization Energy trend

Answer 10

I1<12<I3 etc. As you get closer to core, attractive forces increase and Zeff increases.
Ionization energy decrease down group and increase across period

Question 11

IE +atomic radi+ Zeff

Answer 11

Increase Zeff & Avg distance of electron from nucleas= More difficult to remove electron =Increased IE

Across period =Increased Zeff, decrease atomic radius = Increased IE

Question 12

Electron Affinity

Answer 12

Energy change upon adding electron to an atom in gas phase forming as ion.

Negative EA= anion is stable
Positive EA= Anion is not stable relative to separated atom /electron.

Question 13

EA trend

Answer 13

More negative across period
Halogens have most EA
EA increase up group and across period
Noble gases EA are positive therefore electron added would occupy a new n

Question 14

Metallic Character

Answer 14

Tendency of element to exhibit properties of metals.
Increases down group and decreased across period

Question 15

Metal properties

Answer 15

Strong
Malleable
Shiny/luster
Good conductors of heat and electricity

Question 16

Metal +non metal

Answer 16

Metal atoms are oxidized to cations and ionic substances are formed.

Question 17

Nonmetals

Answer 17

Luster
Poor Conductors
Gases at RT
Molecular if composed of entirely gases
React with bases to form salts and water
Nonmetal oxides are acidic

Question 18

Alkali metal

Answer 18

Low densities
Low MP
Low IE therefore very reactive towards nonmetals.

Question 19

Alkaline Earth Metals

Answer 19

Harder
Denser
Higher MP
Very reactive towards non metals
Readily lose 2+ ions of our electrons
React with hydrogen to form hydride ion (H-) so does alkaline metal

Question 20

Distinct elements

Answer 20

Hydrogen : forms Molecular compounds with nonmetals like oxygen and hydrogen

Oxygen : O2 (ozone). O3. Strong tendency to gain e from other elements thus oxidizing them.
Combine with metals to form oxides, peroxide, superoxides

Sulphur : S8, With metals it is the sulfide ion of S2-

Question 21

Halogen

Answer 21

Exist as diatomic molecules
Most negative EA
Form 1- ions especially in rxns with metals

Question 22

Noble gases

Answer 22

Exist as monatomic gases.
Un reactive
Only heaviest gases are known to form compounds with active nonmetals