S3.1: The Periodic Table: Classification Of Elements

Question 1

How is the periodic table arranged?

Answer 1

Order of increasing atomic number 1-118

18 vertical columns -> groups:
Similar valence electrons

Row -> period:
Period number n is the outer energy level that is occupied by electrons

Exceptions: H and He
-> allocated in a group based on similarities in physical/chemical properties

Question 2

What are the different blocks of the periodic table?

Answer 2

S block:
Elements that have only s-electrons in the outer shell

P block:
Elements that have at least 1 p-electron in the outer shell

D block:
Elements that have at least 1 d-electron and at least 1 s-electron but no f/p electrons in the outer shell

Question 3

What is periodicity?

Answer 3

The study of periodic trends
Repeating patterns in the chemical properties of the elements

Physical and chemical properties -> pattern
Same group -> similar features
Same period -> properties gradually change

Question 4

What are some common group names?

Answer 4

1 - alkali metal
2 - alkali earth metal

3-10 - transition metals

17 - halogens
18 - noble gases

Question 5

Periodic trends: atomic radius

Answer 5

Measure of the size of an atom
Distance between nucleus of an atom and the outermost electron shell

Decrease across a period:
Increased nuclear charge -> greater pull of the nuclei on electrons

Increase down a group:
Increased number of shells
Electrons in inner shell repel outer shell

Question 6

Periodic trends: ionic radius

Answer 6

Measure of the size of an ion

Increase down a group:
Shell number increases

Complicated across period:
—> depends on charge of ion
-> increase with negative charge
-> decrease with positive charge

Anions -> gain electrons, but nuclear charge same -> increased repulsion -> increased radius

Cations -> lose electrons, same nuclear charge -> more attraction -> decreased radius

Question 7

Periodic trends: ionization energy

Answer 7

The amount of energy required to remove one mole of electrons from one mole of atoms of an element in a gaseous state to form one mole of gaseous ions
-> unit: kJ/mole

Trend caused by four factors:
Size of nuclear charge
Distance of outer electrons from the nucleus
Shielding effect of inner electrons
Spin-pair repulsion (paired electron in same orbital repel more than electrons in different orbitals -> easier to remove)

Increase across a period:
Nuclear charge increase
Distance decrease
Shielding constant
-> rapid decrease from one period to next -> increased distance and shielding

Decreases down a group:
Nuclear charge increases BUT
Distance increases
Shielding increases
-> effective nuclear charge decrease as shielding increase

Question 8

Periodic trend: electron affinity

Answer 8

The amount of energy released when one mole of electrons is gained by one mole of atoms of an element in the gaseous state to form one mole of gaseous ions
-> kJ/mol

Same patterns as ionization but reversed and shifted one element right

Strongest pull on electrons -> greater amount of energy released when anions form
-> why group 17 has highest electron affinities

first always exo, second can be endo -> overcome repulsion between electrons+negative ion -> require energy

Generally increase across period

Generally decrease down a group:
-> less exothermic
Larger radius -> less attraction
More shielding -> less nuclear charge

Exception: fluorine -> smaller than excepted
-> small atom
-> additional atoms in 2p -> considerable repulsion

Question 9

Periodic trend: electronegativity

Answer 9

The ability of an atom to attract a pair of electrons toward itself in a covalent bond
-> result of nucleus ability to attract outer shell electrons

Increases across a period:
Nuclear charge increases
Shielding same
Atomic radius decreases

Decreases down a group:
Nuclear charge increases BUT
Shielding increases
Atomic radius increases

Question 10

What are the rules for oxidation states?

Answer 10

Ionic compound:
Oxidation state of each element = charge on ion

Covalent compound:
Assume it is ionic
More electronegative atom -> negative ion

Algebraic sum of all oxidation states = 0

For ion: algebraic sum of all oxidation states = charge of ion

Elements + other elements = 0

Oxygen + other element = -2
-> unless peroxide

Hydrogen + other element = +1
-> unless certain metal hydrides

Translation metals -> variable oxidation states
-> used when naming element

Question 11

Naming oxyanion + nature of oxides

Answer 11

Oxidation number of non-metallic element (roman numerals)
Bonded to oxygen -> -ate suffix

Metal oxides - basic or amphoteric
Non-metal oxides - acidic

Question 12

Properties of alkali metals

Answer 12

From Li -> Cs

Physical properties:
atomic radius increases
ionic radius increases
melting and boiling point decreases
1st ionisation energy decreases
electronegativity decreases
electron affinity decreases

Chemical properties:
Increasing reactivity with water and halogens

Question 13

Properties of halogens

Answer 13

From F -> I

Physical properties:
atomic radius increases
ionic radius increases
melting and boiling point increases
1st ionisation energy decreases
electronegativity decreases
electron affinity decreases (generally)

Chemical properties:
Oxidizing ability decreases
-> chlorine will displace bromine