periodic variation in physical properties of the elements h to ar 38.1the periodic table...
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Periodic Variation in PPeriodic Variation in Physical Properties of thhysical Properties of th
e Elements H to Are Elements H to Ar
38.138.1 The Periodic TableThe Periodic Table
38.238.2 Periodic Variation in Physical Properties Periodic Variation in Physical Properties
of Elementsof Elements
3838
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.2)
• With more and more elements being discovered
needed a way to organize them effectively
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.2)
• The modern Periodic Table
the basis of the atomic numbers and electronic configurations of eleme
nt
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.3)
• The earliest version of the Periodic Table
introduced in 1869
by a Russian chemist called Dimitri Mendeleev
38.1 The Periodic Table (SB p.3)
A portion of one of Dimitri Mendeleev’s handwritten drafts of the Periodic Table
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.3)
• Mendeleev created the first Periodic Table based on atomic masses
• Many elements had similar properties
occurred periodically
the name Periodic Table was used
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.3)
• The periodic law stated
the chemical and physical properties of the elements vary in a periodic
way with their atomic masses
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.3)
• Example:
Lithium, sodium, potassium, rubidium and caesium
have similar chemical properties
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.3)
• Example:
Beryllium, magnesium, calcium, strontium and barium
also have similar chemical properties
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.3)
• According to Mendeleev’s theory
they could be perfectly arranged by increasing atomic masses
• Some elements did not match perfectly
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.3)
• Tellurium is heavier than iodine
but the chemical properties of tellurium did not match with th
ose of chlorine and bromine
the chemical properties of iodine did not match with those of sulphur a
nd selenium
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.3)
• Tellurium should be placed before iodine
even though tellurium was heavier than iodine
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.3)
• The modern Periodic Table
arranged according to atomic numbers instead of atomic ma
sses
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.4)
• The modern Periodic Table is divided into
7 horizontal rows called periods
18 vertical columns called groups
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.4)
• Elements with atoms having the same number of electron shells
put in the same period
• Elements having the same number of outermost shell electrons
put in the same group
The Periodic Table The Periodic Table
38.1 The Periodic Table (SB p.4)
• Elements can be classified as
s-block elements
p-block elements
d-block elements
f-block elements
38.1 The Periodic Table (SB p.4)
• Group IA and Group IIA elements constitute the s-block
• They are elements with outermost shell electrons occupying the s orbital
1. 1. s s -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• Group IA elements have only one outermost shell electron occupying the s orbital
• Examples:
Lithium, sodium, potassium, rubidium, caesium and francium
1. 1. s s -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• They are highly reactive metals
• They are known as the alkali metals
1. 1. s s -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• Group IIA elements have two outermost shell electrons in the s orbital
• Example:
Beryllium, magnesium, calcium, strontium, barium and radium
1. 1. s s -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• They are also chemically reactive
• They are known as the alkaline earth metals
1. 1. s s -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• Elements having electronic configurations from [ ] ns2np1 to [ ] ns2np6
• They include Group IIIA, IVA, VA, VIA, VIIA and 0
2. 2. p p -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• Group VIIA elements are all non-metals
• They are known as the halogens
2. 2. p p -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• Group 0 elements are called noble gases
• They have a fully-filled outermost electron shell
gives rise to extra stability
the very stable electronic configuration
2. 2. p p -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• s-Block and p-block elements together are also known as representative elements
2. 2. p p -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• Elements with electronic configurations from [ ] (n – 1)d1ns2 (Group IIIB) to[ ] (n – 1)d10ns2 (Group IIB)
• They are also called transition elements
3. 3. d d -Block Elements-Block Elements
38.1 The Periodic Table (SB p.4)
• Two series of f-block elements in which the 4f and 5f orbitals being filled up with 1 to 14 electrons respectively
• They are the lanthanide series and the actinide series
• They are sometimes called inner-transition elements
4. 4. f f -Block Elements-Block Elements
38.1 The Periodic Table (SB p.5)
Elements can be classified as s-block elements, p-block elements, d-block elements and f-block elements in the Periodic Table
First ionization enthalpy First ionization enthalpy
38.2 Periodic Variation in Physical Properties of Elements (SB p.6)
The first ionization enthalpy of an atom is the energy required to remove one mole of electrons from one mole of its gaseous atoms to form one mole of gaseous ions with one positive charge.
First ionization enthalpy First ionization enthalpy
38.2 Periodic Variation in Physical Properties of Elements (SB p.6)
• Energy is required
overcome the attractive forces between the nucleus and the electr
on to be removed
the ionization enthalpy always has a positive value
First ionization enthalpy First ionization enthalpy
38.2 Periodic Variation in Physical Properties of Elements (SB p.6)
• The ionization enthalpy of an element
reflects the relative force of attraction between the nucleus and the electron being removed
First ionization enthalpy First ionization enthalpy
38.2 Periodic Variation in Physical Properties of Elements (SB p.6)
• Four main factors affecting the magnitude of the ionization enthalpy of an atom:
1. the electronic configuration of an atom;
2. the nuclear charge;
3. the screening effect; and
4. the atomic radius
38.2 Periodic Variation in Physical Properties of Elements (SB p.6)
The first ionization enthalpies of the first 20 elements
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
Variation in the first ionization enthalpy of the first 20 elements
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• The consequence of the increase in nuclear charge with atomic numbers
1.1. General increase in the first ionizatiGeneral increase in the first ionization enthalpy across both Periods 2 aon enthalpy across both Periods 2 and 3nd 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• At the same time
additional electrons are entering the same electron shell
they have poor screening effect
1.1. General increase in the first ionizatiGeneral increase in the first ionization enthalpy across both Periods 2 aon enthalpy across both Periods 2 and 3nd 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• In other words
an increase in effective nuclear charge across the periods
1.1. General increase in the first ionizatiGeneral increase in the first ionization enthalpy across both Periods 2 aon enthalpy across both Periods 2 and 3nd 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• Going across a period
the electrons are drawn closer to the nucleus
more energy is required to remove an electron from the atom
the first ionization enthalpy generally increases across both Periods 2 a
nd 3
1.1. General increase in the first ionizatiGeneral increase in the first ionization enthalpy across both Periods 2 aon enthalpy across both Periods 2 and 3nd 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• In Period 2
the first ionization enthalpy of boron is lower than that of beryllium
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• In Period 3
the first ionization enthalpy of aluminium is lower than that of magnesium
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• Boron and aluminium have [ ] ns2np1 electronic configurations
easier to remove the outermost p electron
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
the electron is shielded from the attraction of the nucleus by the completely filled s orbitals (ns2)
The first ionization enthalpies of Group III elements are not very high
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• Beryllium and magnesium have a relatively stable electronic configuration
the s orbital is completely filled
a relatively large amount of energy is needed to ionize their atoms
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• In Period 2
the first ionization enthalpy of oxygen is lower than that of nitrogen
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• In Period 3
the first ionization enthalpy of sulphur is lower than that of phosphorus
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• The atoms of oxygen and sulphur have one electron more than the half-filled p sub-shell
when the electronic configuration of half-filled p sub-shell (np3) is attai
ned
extra stability is gained
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• A relatively small amount of energy is required to remove the first electron from the atoms of oxygen and sulphur
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.7)
• The electronic configurations of nitrogen and phosphorus are [ ] ns2np3 (i.e. half-filled p sub-shell)
a relatively stable electronic configuration
more energy is required to remove an electron from their atoms
2.2. Irregularities with general increase iIrregularities with general increase in the first ionization enthalpy acrosn the first ionization enthalpy across both Periods 2 and 3s both Periods 2 and 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• The element at the end of each period (i.e. the noble gas)
has a completely filled octet (except helium which has a duplet)
this electronic configuration is very stable
3.3. A sharp drop in the first ionization entA sharp drop in the first ionization enthalpy from one period to the nexthalpy from one period to the next
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
A large amount of energy is required to remove an electron from their
atoms
3.3. A sharp drop in the first ionization entA sharp drop in the first ionization enthalpy from one period to the nexthalpy from one period to the next
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• The element at the beginning of the next period (i.e. the Group I element)
has an electron entering a new electron shell
further away from the nucleus
3.3. A sharp drop in the first ionization entA sharp drop in the first ionization enthalpy from one period to the nexthalpy from one period to the next
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
The attractive force between the nucleus and the electron is relatively weak
3.3. A sharp drop in the first ionization entA sharp drop in the first ionization enthalpy from one period to the nexthalpy from one period to the next
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• This s electron is shielded from the attraction of the nucleus effectively by the inner electron shells
once this electron is removed, a stable electronic configuration is
attained
3.3. A sharp drop in the first ionization entA sharp drop in the first ionization enthalpy from one period to the nexthalpy from one period to the next
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
The first ionization enthalpies of Group I elements are relatively low
3.3. A sharp drop in the first ionization entA sharp drop in the first ionization enthalpy from one period to the nexthalpy from one period to the next
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• When going down a group
increase in atomic radius
the outermost shell electrons will experience less attraction from the
nucleus
4.4. The first ionization enthalpy decreases The first ionization enthalpy decreases down any group in the Periodic Tabledown any group in the Periodic Table
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• There is an increase in the nuclear charge down a group
the outermost shell electrons would experience less attraction from t
he positively charged nucleus
the first ionization enthalpy decreases down a group
4.4. The first ionization enthalpy decreases The first ionization enthalpy decreases down any group in the Periodic Tabledown any group in the Periodic Table
Atomic radius Atomic radius
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
Atomic radius is used to describe the size of an atom.
Atomic radius Atomic radius
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• For non-metals
the atomic radii commonly used are the covalent radii
Atomic radius Atomic radius
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• For metals
the metallic radii are used
Atomic radius Atomic radius
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
Covalent radius is defined as half the internuclear distance between two covalently bonded atoms in a molecule of the element.
Atomic radius Atomic radius
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
Metallic radius is defined as half the internuclear distance between two atoms in a metallic crystal.
Atomic radius Atomic radius
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• The atomic radius of an atom is governed by two factors:
1. Attraction between the nucleus and the electrons
2. Screening of the outermost shell electrons from the nucleus by inne
r electron shells
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• The greater the number of protons in the nucleus
the higher the nuclear charge
1. 1. Attraction between the nuclAttraction between the nucleus and the electronseus and the electrons
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• This results in greater attraction between the nucleus and the electrons
the electrons are drawn closer to the nucleus
the atomic radius becomes smaller
1. 1. Attraction between the nuclAttraction between the nucleus and the electronseus and the electrons
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• As electrons are negatively charged
repulsion between the outermost shell electrons and the electrons on the inner shells of an atom
the outermost shell electrons are screened from the attraction of t
he nucleus
2. 2. Screening of the outermost shell Screening of the outermost shell electrons from the nucleus by inner elelectrons from the nucleus by inner electron shellsectron shells
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• The greater the number of electron shells in the atom
the greater the screening effect
2. 2. Screening of the outermost shell Screening of the outermost shell electrons from the nucleus by inner elelectrons from the nucleus by inner electron shellsectron shells
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
• The outermost shell electrons are less strongly held by the nucleus
the atomic radius becomes larger
2. 2. Screening of the outermost shell Screening of the outermost shell electrons from the nucleus by inner elelectrons from the nucleus by inner electron shellsectron shells
38.2 Periodic Variation in Physical Properties of Elements (SB p.9)
The atomic radii of the first 20 elements
38.2 Periodic Variation in Physical Properties of Elements (SB p.9)
Variation in atomic radius of the first 20 elements
Atomic radius Atomic radius
• Within a given period
the atomic radii decrease progressively with increasing atomic numbers
an increase in atomic number by one means that one more electron and one more proton are added in the atom
38.2 Periodic Variation in Physical Properties of Elements (SB p.9)
Atomic radius Atomic radius
• The additional electron
cause an increase in repulsion between the electrons in the
outermost shell
results in an increase in atomic radius
38.2 Periodic Variation in Physical Properties of Elements (SB p.9)
Atomic radius Atomic radius
• The additional proton in the nucleus
cause the electrons to experience greater attractive forces from the
nucleus
38.2 Periodic Variation in Physical Properties of Elements (SB p.9)
Atomic radius Atomic radius
• The newly added electron
goes to the outermost shell
is at approximately the same distance from the nucleus
the repulsion between the electrons is relatively ineffective to cause an
increase in atomic radius
38.2 Periodic Variation in Physical Properties of Elements (SB p.9)
Atomic radius Atomic radius
• The effect of increasing nuclear charge outweighs the effect of repulsion between the electrons
an increase in effective nuclear charge
the atomic radii of elements decrease across a period
38.2 Periodic Variation in Physical Properties of Elements (SB p.9)
Atomic radius Atomic radius
• If we look closer
sharp decrease in atomic radius from the first element to the third eleme
nt of each period
followed by a gradual decrease along subsequent elements
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
Atomic radius Atomic radius
• At the beginning of each period
increasing effective nuclear charge with atomic numbers predomin
ates
greater contraction of the electron cloud
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
Atomic radius Atomic radius
• When more electrons are added to the same electron shell
the effect of repulsion between electrons becomes more significa
nt
the effective nuclear charge increases only slowly towards the
end of the period
the decrease in atomic radius is thus smaller
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
Atomic radius Atomic radius
• Going down a group in the Periodic Table
the atoms have more electron shells occupied
the outermost electron shells become further away from the nucleus
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
Atomic radius Atomic radius
• The outermost shell electrons
more effectively shielded by the inner electron shells from the nuclear charge
decrease in the attractive force between the nucleus and the
outermost shell electrons
the atomic radii of elements increase down a group
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
Electronegativity Electronegativity
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
Electronegativity is the relative tendency of an atom to attract bonding electrons towards itself in a covalent bond.
Electronegativity Electronegativity
• Pauling assigned electronegativity values to the elements on an arbitrary scale from 0 to 4
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
Electronegativity Electronegativity
• The higher the electronegativity value of an atom
the higher the ability of the atom to attract bonding electrons towa
rds itself in a covalent bond
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
Electronegativity Electronegativity
• Fluorine
the most electronegative element
assigned an electronegativity value of 4.0 in Pauling’s scale
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
38.2 Periodic Variation in Physical Properties of Elements (SB p.10)
Electronegativity values of the first 20 elements
38.2 Periodic Variation in Physical Properties of Elements (SB p.11)
Variation in electronegativity values of the first 20 elements
Electronegativity Electronegativity
• Going across Periods 2 and 3 in the Periodic Table
electronegativity of the elements increases from left to right
the decrease in atomic size
38.2 Periodic Variation in Physical Properties of Elements (SB p.11)
Electronegativity Electronegativity
• As the effect of increasing nuclear charge outweighs the screening effect of the electrons in the same electron shell
the bonding electrons are attracted more strongly
38.2 Periodic Variation in Physical Properties of Elements (SB p.11)
Electronegativity Electronegativity
• Moving down a group in the Periodic Table
electronegativity of the elements decreases
the increase in atomic size
38.2 Periodic Variation in Physical Properties of Elements (SB p.11)
Electronegativity Electronegativity
• With the increase in number of electron shells and greater screening effect
the bonding electrons are attracted less strongly
38.2 Periodic Variation in Physical Properties of Elements (SB p.11)
Melting point Melting point
38.2 Periodic Variation in Physical Properties of Elements (SB p.11)
The melting point of a substance is the temperature at which the substance changes from its solid phase to liquid phase.
Melting point Melting point
• A solid does not melt
unless there is sufficient energy to overcome the forces holding t
he particles together in the solid state
38.2 Periodic Variation in Physical Properties of Elements (SB p.11)
Melting point Melting point
• The amount of energy depends on
1. the magnitude of the attractive forces between the particles
2. how the particles are arranged in the solid
38.2 Periodic Variation in Physical Properties of Elements (SB p.11)
38.2 Periodic Variation in Physical Properties of Elements (SB p.11)
The melting points of the first 20 elements
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
Variation in melting point of the first 20 elements
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
• Both lithium and beryllium have a giant metallic structure
• The metallic bond strength increases with the number of outermost shell electrons
1.1. A steady increase in melting point from litA steady increase in melting point from lithium to boron and from sodium to alumihium to boron and from sodium to aluminiumnium
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
• As lithium has only one outermost shell electron while beryllium has two
the metallic bond strength in beryllium is stronger than that in lithium
beryllium has a higher melting point than lithium
1.1. A steady increase in melting point from litA steady increase in melting point from lithium to boron and from sodium to alumihium to boron and from sodium to aluminiumnium
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
• Boron has a giant covalent structure
• The bonding that holds the boron atoms together is stronger than those of lithium and beryllium
the melting point of boron is higher than those of lithium and berylli
um
1.1. A steady increase in melting point from litA steady increase in melting point from lithium to boron and from sodium to alumihium to boron and from sodium to aluminiumnium
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
• For Period 3 elements
sodium, magnesium and aluminium all have a giant metallic structure
1.1. A steady increase in melting point from litA steady increase in melting point from lithium to boron and from sodium to alumihium to boron and from sodium to aluminiumnium
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
• There is an increase in number of electrons involved in the metallic bond
the strength of metallic bond increases from sodium to aluminium
the melting point increases from sodium to aluminium
1.1. A steady increase in melting point from litA steady increase in melting point from lithium to boron and from sodium to alumihium to boron and from sodium to aluminiumnium
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
• Both carbon and silicon have a giant covalent structure
the atoms are held together by strong covalent bonds
2.2. Carbon and silicon correspond to the maxCarbon and silicon correspond to the maxima in Periods 2 and 3 respectivelyima in Periods 2 and 3 respectively
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
• A large amount of energy is needed to overcome the strong covalent bonds
the melting points of carbon and silicon are extremely high
2.2. Carbon and silicon correspond to the maxCarbon and silicon correspond to the maxima in Periods 2 and 3 respectivelyima in Periods 2 and 3 respectively
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
• They all exist as discrete molecules
held together by weak van der Waals’ forces
3.3. The melting points of the elements from The melting points of the elements from nitrogen to neon and from phosphorus tnitrogen to neon and from phosphorus to argon are relatively lowo argon are relatively low
38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
• Only a little amount of energy is needed to overcome the weak van der Waals’ forces
their melting points are relatively low
3.3. The melting points of the elements from The melting points of the elements from nitrogen to neon and from phosphorus tnitrogen to neon and from phosphorus to argon are relatively lowo argon are relatively low
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
Melting point Melting point
• In Period 3
sulphur exists as S8 molecules in its molecular crystal
phosphorus exists as P4 molecules in its solid molecular crystal
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
Melting point Melting point
• S8 molecule
a higher molecular mass
a greater surface area for contact with neighbouring molecules
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
Melting point Melting point
• The van der Waals’ forces between S8 molecules are stronger than those between P4 molecules
the melting point of sulphur is higher than that of phosphorus
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
Melting point Melting point
• Sulphur
higher melting point than chlorine
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
Melting point Melting point
• Chlorine
only exists as diatomic molecules
the van der Waals’ forces between S8 molecules are stronger th
an those between Cl2 molecules
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
Example 38-1Example 38-1 Check Point 38-2Check Point 38-2
38.2 Periodic Variation in Physical Properties of Elements (SB p.14)
Structure and Structure and BondingBonding
A summary of the variations in structure and bonding of elements across both Periods 2
38.2 Periodic Variation in Physical Properties of Elements (SB p.14)
Structure and Structure and BondingBonding
A summary of the variations in structure and bonding of elements across both Periods 3
38.2 Periodic Variation in Physical Properties of Elements (SB p.14)
Structure and BondingStructure and Bonding
• In each of the periods, the structures of the elements changes from
giant metallic structures
followed by giant covalent structures
finally to simple molecular structures
38.2 Periodic Variation in Physical Properties of Elements (SB p.14)
Structure and BondingStructure and Bonding
• Going across the periods from left to right
the bonding of the elements also varies in a repeating pattern
from metallic bonding to covalentbonding
The atomic numbers of tellurium and iodine are 52 and 53 respectively. Why is tellurium heavier than iodine?
AnswerAtomic number of an element is not related to the mass of an atom
of the element. The atomic number of an element is the number of p
rotons in an atom of the element. It is unique for each element. The
mass of an atom of the element is mainly determined by the number
of protons and neutrons in the nucleus. Therefore, tellurium is heavi
er than iodine though the atomic number of tellurium is smaller than
that of iodine.Back
38.1 The Periodic Table (SB p.3)
To which block (s-, p-, d- or f-) in the Periodic Table do rubidium, gold, astatine and uranium belong respectively? AnswerRubidium: s-block
Gold: d-block
Astatine: p-block
Uranium: f-block
Back
38.1 The Periodic Table (SB p.5)
Which element would have the highest first ionization enthalpy?
AnswerHelium
Back
38.2 Periodic Variation in Physical Properties of Elements (SB p.6)
Which element would have the smallest atomic radius?
AnswerHelium
Back
38.2 Periodic Variation in Physical Properties of Elements (SB p.8)
Why is the melting point of chlorine higher than argon?
AnswerChlorine atom has a higher effective nuclear charge than argon atom,
so the atomic radius of chlorine is smaller than that of argon. Therefore,
the van der Waals’ forces between chlorine molecules are stronger th
an those between argon molecules. Since a higher amount of energy i
s needed to overcome the stronger van der Waals’ forces, the melting
point of chlorine is higher than that of argon.
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38.2 Periodic Variation in Physical Properties of Elements (SB p.12)
Considering the trend of atomic radius in the Periodic Table, arrange the elements Si, N and P in the order of increasing atomic radius. Explain your answer briefly.
AnswerIn the Periodic Table, N is above P in Group VA. As the atomic radius increases down a group, the atomic radius of N is smaller than that of P.
Si and P belong to the same period. Since the atomic radius decreases across a period, the atomic radius of P is smaller than that of Si.
Therefore, the atomic radius increases in the order: N < P < Si.
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38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
(a) With the help of the Periodic Table only, arrange the elements selenium, sulphur and argon in the order of increasing first ionization enthalpies.Answer
(a) The first ionization enthalpy increases in the order: Se < S < Ar.
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
(b) Describe and explain the general periodic trend of atomic radius of elements in the Periodic Table.
Answer
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
(b) Within a given period, the atomic radii decrease progressively with incr
easing atomic numbers. This is because an increase in atomic number
by one means that one more electron and one more proton are added i
n the atom. The additional electron would cause an increase in repulsi
on between the electrons in the outermost shell and results in an incre
ase in atomic radius. The additional proton in the nucleus would cause
the electrons to experience greater attractive forces from the nucleus.
Due to the fact that the newly added electron goes to the outermost sh
ell and is at approximately the same distance from the nucleus, the rep
ulsion between the electrons is relatively ineffective to cause an increa
se in atomic radius. Therefore, the effect of increasing nuclear charge
outweighs the effect of repulsion between the electrons. That means, t
here is an increase in effective nuclear charge. As a result, the atomic r
adii of elements decrease across a period.
(c) With reference to Fig. 38-9 on p.11 (variation in electronegativity value of the first 20 elements), explain why the alkali metals are almost at the bottom of the troughs, whereas the halogens are at the peaks of the plot.
Answer
38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
(c) The alkali metals are almost at the bottom of troughs, indicating that
they have low electronegativity values. It is because their nuclear c
harge is effectively shielded by the fully-filled inner electron shells o
f electrons, and the bonding electrons are attracted less strongly. O
n the other hand, the halogens appear at the peaks. This indicates t
hat they have high electronegativity values. It is because they have
one electron less than the octet electronic configuration. They tend t
o attract an electron to complete the octet, and the bonding electron
s are attracted strongly.
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38.2 Periodic Variation in Physical Properties of Elements (SB p.13)
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