1 - Atomic structure and the periodic table
●
Atomic particle Location Relative mass Relative charge
Proton Nucleus 1 +1
Neutron Nucleus 1
1( 1840 ) 0
Electron Orbiting shells 1 -1
1840
Atomic number and mass number
● ***Atomic number (𝑍): number of protons in nucleus (of atom)
● ***Mass number: number of protons PLUS neutrons in nucleus (of atom, of
particular isotope)
𝐴 (𝑚𝑎𝑠𝑠 𝑛𝑢𝑚𝑏𝑒𝑟) (𝑐ℎ𝑎𝑟𝑔𝑒) 62 −
● 𝑍 (𝑎𝑡𝑜𝑚𝑖𝑐 𝑛𝑢𝑚𝑏𝑒𝑟)
𝑋 (𝑒𝑙𝑒𝑚𝑒𝑛𝑡\𝑠)(𝑠𝑢𝑏𝑠𝑐𝑟𝑖𝑝𝑡), eg 31
𝑁𝑂3 (31 protons, 31 neutrons, 32
electrons)
Isotopes and relative isotopic masses
● ***Isotopes: atoms of same element (with same number of protons) but different
number of neutrons
1
● ***Relative isotopic mass: mass of an atom of a particular isotope compared to 12
of the mass of a carbon-12 atom
● ***Relative atomic mass (Ar): weighted average mass of an atom of an element
1
compared to 12
of the mass of a carbon-12 atom
● ***Relative formula/molecular (if simple molecules) mass (Mr): average mass of
1
compound divided by 12
of the mass of a carbon-12 atom
Electron configuration and energy levels
● Elements usually form ions with a noble gas configuration (ie full outer electron shell)
○ ***Exceptions: Cu2+
● Each quantum electron shell can only hold a limited number of electrons (n is energy
level):
○ n = 1: 2 (1s2)
○ n = 2: 8 (2s2 2p6)
○ n = 3: 18 (3s2 3p6 3d10)
○ n = 4: 32 (4s2 4p6 4d10 4f14)
1
, (n: no. of electron shells/energy levels, vacuum limit when E ≡ 0.00, increasing
energy from ground state, visible light when 2 ≤ n ≤ 3)
● ***Evidence for existence of quantum shells - atomic emission spectra
○ Only light of very precise energies is absorbed (electrons will NOT keep this
energy, ∴ emitted - of very precise energies)
○ Energy of light given out is difference in energy between the initial
(ground-promoted) shell and the final (relaxed) shell
○ ∴ Energies of the electrons possess themselves must be very precise, ie
electrons exist in shells
● Main shells divide into sub-shells: sharp, principal, diffuse, fundamental
2
●
Atomic particle Location Relative mass Relative charge
Proton Nucleus 1 +1
Neutron Nucleus 1
1( 1840 ) 0
Electron Orbiting shells 1 -1
1840
Atomic number and mass number
● ***Atomic number (𝑍): number of protons in nucleus (of atom)
● ***Mass number: number of protons PLUS neutrons in nucleus (of atom, of
particular isotope)
𝐴 (𝑚𝑎𝑠𝑠 𝑛𝑢𝑚𝑏𝑒𝑟) (𝑐ℎ𝑎𝑟𝑔𝑒) 62 −
● 𝑍 (𝑎𝑡𝑜𝑚𝑖𝑐 𝑛𝑢𝑚𝑏𝑒𝑟)
𝑋 (𝑒𝑙𝑒𝑚𝑒𝑛𝑡\𝑠)(𝑠𝑢𝑏𝑠𝑐𝑟𝑖𝑝𝑡), eg 31
𝑁𝑂3 (31 protons, 31 neutrons, 32
electrons)
Isotopes and relative isotopic masses
● ***Isotopes: atoms of same element (with same number of protons) but different
number of neutrons
1
● ***Relative isotopic mass: mass of an atom of a particular isotope compared to 12
of the mass of a carbon-12 atom
● ***Relative atomic mass (Ar): weighted average mass of an atom of an element
1
compared to 12
of the mass of a carbon-12 atom
● ***Relative formula/molecular (if simple molecules) mass (Mr): average mass of
1
compound divided by 12
of the mass of a carbon-12 atom
Electron configuration and energy levels
● Elements usually form ions with a noble gas configuration (ie full outer electron shell)
○ ***Exceptions: Cu2+
● Each quantum electron shell can only hold a limited number of electrons (n is energy
level):
○ n = 1: 2 (1s2)
○ n = 2: 8 (2s2 2p6)
○ n = 3: 18 (3s2 3p6 3d10)
○ n = 4: 32 (4s2 4p6 4d10 4f14)
1
, (n: no. of electron shells/energy levels, vacuum limit when E ≡ 0.00, increasing
energy from ground state, visible light when 2 ≤ n ≤ 3)
● ***Evidence for existence of quantum shells - atomic emission spectra
○ Only light of very precise energies is absorbed (electrons will NOT keep this
energy, ∴ emitted - of very precise energies)
○ Energy of light given out is difference in energy between the initial
(ground-promoted) shell and the final (relaxed) shell
○ ∴ Energies of the electrons possess themselves must be very precise, ie
electrons exist in shells
● Main shells divide into sub-shells: sharp, principal, diffuse, fundamental
2
