Atoms and Properties of Subatomic particles Atom
- Smallest component of an element having the chemical properties of the element
- Made up of electron, proton and neutron
Subatomic Particles
Property
Proton
Electron
Neutron
Relative Charge
+1
-1
0
Relative Mass
1
1/1836
1
- Angle of Deflection = k ( Charge / Mass)
Atomic Number, Mass Number and Isotopes
-
Atomic number, Z
- Number of protons
- Determines Chemical identity
Mass number, A
- Total number of protons and neutrons
Isotopes
- atoms with same number of electrons but different number of neutrons
Arrangement of Electrons
- The Principal Quantum Number, n, describes the minimum energy level of an electron and the size of an atomic orbital
- Maximum number of electrons that can occupy the orbitals = 2n2
- Each principal quantum shell can be subdivided into subshells
Principal Quantum Shell
Number of Subshell
Type of Subshell
Notation for Subshell
1
1
s
1s
2
2
s,p
2s,2p
3
3
s,p,d
3s,3p,3d
4
4
s,p,d,f
4s,4p,4d,4f
Atomic Orbitals
- Defined as region of space with a 90% probability of finding an electron
(ii) Rule 2 : Hund's Rule of Multiplicity - Each orbital must be singly occupied before electrons are paired
(iii) Rule 3 : Pauli's Expulsion Principle
- Electrons within the same orbital has to have opposite direction, to reduce inter-electronic repulsion
Physical Periodicity Effective Nuclear Charge, Zeff
- Net Nuclear Charge experienced by an outer electron
- Zeff = Z - S , where Z is nuclear charge and S is shielding effect
Changes in Zeff
(i) Down the group
- Nuclear charge increase as no. of protons increase
- Shielding effect increase as no. of orbitals increase
- Zeff relatively the same
(ii) Across period
- Nuclear charge increase as no. of protons increase
- Shielding effect constant as it is the same orbital
- Zeff increase
Trend in Atomic Radius
(i) Across the period
- As Zeff increase, EOFA increase and Ar decrease
(ii) Down the group
- No. of Quantum Shells increase, Ar increase
Trend in Ionic Radius
(i) Special:
- As Anion has one more quantum shell than cations, Ar of Cations < Ar of Anions
Ionization Energy
- nth Ionization energy is the energy required to remove 1 mole of electrons from 1 moles of gaseous (n-1) positive ions to form1 moles of gaseous ions with n+ charge
Factors that affect IE
(i) Nuclear Charge, Z
- Increase in nuclear charge = Increase in EOFA = Increase in IE
(ii) Size of atoms
- Ar decrease = Increase in EOFA = Increase in IE
IE graph
- IE1 < IE2 < IE3
- As more electrons are removed, there are more and more protons compared to electrons. Therefore EOFA increase and IE has to increase
- Jumps in IE represents change in quantum shell
Trends of IE
(i) Down the group
- No. of Quantum Shell Increase = Ar increase = EOFA decrease = IE decrease
(ii) Across the period
- Increase in no. of protons = increase in nuclear charge = Increase in EOFA = Increase in IE
(iii) Anomalies
a) Group 2 and 3
- Different subshell; Group 2 is S subshell and Group 3 is P subshell
b) Group 5 and 6
- Electrons in Grp 5 all unpaired while there is a paired electron in Grp 6, causing interelectronic repulsion, lowering IE for Group 6
Atom
- Smallest component of an element having the chemical properties of the element
- Made up of electron, proton and neutron
Subatomic Particles
Atomic Number, Mass Number and Isotopes
-
Atomic number, Z
- Number of protons
- Determines Chemical identity
Mass number, A
- Total number of protons and neutrons
Isotopes
- atoms with same number of electrons but different number of neutrons
Arrangement of Electrons
- The Principal Quantum Number, n, describes the minimum energy level of an electron and the size of an atomic orbital
- Maximum number of electrons that can occupy the orbitals = 2n2
- Each principal quantum shell can be subdivided into subshells
Atomic Orbitals
- Defined as region of space with a 90% probability of finding an electron
- Each S subshell only has one s orbital
- Each P subshell has 3 p orbital
Electronic Configuration
(i) Rule 1 : ' Building-Up' Principle
(ii) Rule 2 : Hund's Rule of Multiplicity
- Each orbital must be singly occupied before electrons are paired
(iii) Rule 3 : Pauli's Expulsion Principle
- Electrons within the same orbital has to have opposite direction, to reduce inter-electronic repulsion
Physical Periodicity
Effective Nuclear Charge, Zeff
- Net Nuclear Charge experienced by an outer electron
- Zeff = Z - S , where Z is nuclear charge and S is shielding effect
Changes in Zeff
(i) Down the group
- Nuclear charge increase as no. of protons increase
- Shielding effect increase as no. of orbitals increase
- Zeff relatively the same
(ii) Across period
- Nuclear charge increase as no. of protons increase
- Shielding effect constant as it is the same orbital
- Zeff increase
- Zeff increase = Electrostatic Forces of Attraction Increase = Ionization Energy Increase / Atomic Radius Decrease
- Higher nuclear charge = smaller atomic radius
- Higher shielding effect = larger atomic radius
Trend in Atomic Radius
(i) Across the period
- As Zeff increase, EOFA increase and Ar decrease
(ii) Down the group
- No. of Quantum Shells increase, Ar increase
Trend in Ionic Radius
(i) Special:
- As Anion has one more quantum shell than cations, Ar of Cations < Ar of Anions
Ionization Energy
- nth Ionization energy is the energy required to remove 1 mole of electrons from 1 moles of gaseous (n-1) positive ions to form1 moles of gaseous ions with n+ charge
Factors that affect IE
(i) Nuclear Charge, Z
- Increase in nuclear charge = Increase in EOFA = Increase in IE
(ii) Size of atoms
- Ar decrease = Increase in EOFA = Increase in IE
IE graph
- IE1 < IE2 < IE3
- As more electrons are removed, there are more and more protons compared to electrons. Therefore EOFA increase and IE has to increase
- Jumps in IE represents change in quantum shell
Trends of IE
(i) Down the group
- No. of Quantum Shell Increase = Ar increase = EOFA decrease = IE decrease
(ii) Across the period
- Increase in no. of protons = increase in nuclear charge = Increase in EOFA = Increase in IE
(iii) Anomalies
a) Group 2 and 3
- Different subshell; Group 2 is S subshell and Group 3 is P subshell
b) Group 5 and 6
- Electrons in Grp 5 all unpaired while there is a paired electron in Grp 6, causing interelectronic repulsion, lowering IE for Group 6