CHEMISTRY AS LEVEL OCR
SUMMARY NOTES (Periodic
Table and Energy) ABBEY
COLLEGE CAMBRIDGE.
, Module 3: Periodic table and energy
Periodicity
7.1 The periodic table
The periodic table - then
• Over 60 elements arranged by Mendeleev in order of atomic mass
• Lined up elements in groups with similar properties
• If properties did not fit, Mendeleev swapped elements and left gap
o Assuming atomic mass measurements were incorrect / elements yet to
discovered
• Even predicted properties of the missing elements from group trends
The periodic table - now
• As of 2014 PT has 114 elements arranged in 7 horizontal periods and 8 vertical groups
• Most important organisation tool
• First point of reference for chemists
• Helpful to remember where common elements are positioned, their atomic number and
relative atomic masses
Arranging the elements
• Position of elements linked to physical and chemical properties
• Atomic number
o From left to right, elements are arranged in order of increasing atomic number
• Groups
o Elements are arranged in vertical columns called groups
o Each element in a group has atoms with same no. of outer shell electrons and
similar properties
• Periods and periodicity
o Elements are arranged in horizontal rows called periods
o No. of period gives the no. of the highest energy electron shell in an element's
atoms.
o Across periods, there is a repeating trend in properties - periodicity
o Most obvious periodicity in properties - trend from metals to nonmetals
o Periodicity of several properties:
▪ Electron configuration
▪ Ionisation energy
▪ Structure
▪ Melting point
Period trend in electron configurations
• Chemistry of each element is determined by its electron configuration, particularly outer,
highest energy electron shell
Trend across a period
• Each period starts with an electron in a new highest energy shell
o Across period 2, 2s subshell fills with 2 electrons, followed by the 2p subshell
with 6 electrons
o Across period 3, the same pattern of filling is repeated for the 3s and 3p subshell
o Across period 4, although the 3d subshell is involved, the highest shell number is
n = 4. From the n = 4, only the 4s and 4p subshell are occupied
o For each period, s- and p-subshells are filled in the same way
Trend down a group
• Elements in each group have atoms with the same no. of electrons in their outer shell
, • Elements in each group also have atoms with the same no. of electron in each subshells
o Element in the same group will have similar chemistry
Blocks
• Elements can be divided into blockers corresponding to their hughes energy subshell
• 4 distinct blocks, s, p, d and f
• Old numbers are the number used in IGCSE, group 1-7 and then 0
o This system is based on s- and p-blocks
SUMMARY NOTES (Periodic
Table and Energy) ABBEY
COLLEGE CAMBRIDGE.
, Module 3: Periodic table and energy
Periodicity
7.1 The periodic table
The periodic table - then
• Over 60 elements arranged by Mendeleev in order of atomic mass
• Lined up elements in groups with similar properties
• If properties did not fit, Mendeleev swapped elements and left gap
o Assuming atomic mass measurements were incorrect / elements yet to
discovered
• Even predicted properties of the missing elements from group trends
The periodic table - now
• As of 2014 PT has 114 elements arranged in 7 horizontal periods and 8 vertical groups
• Most important organisation tool
• First point of reference for chemists
• Helpful to remember where common elements are positioned, their atomic number and
relative atomic masses
Arranging the elements
• Position of elements linked to physical and chemical properties
• Atomic number
o From left to right, elements are arranged in order of increasing atomic number
• Groups
o Elements are arranged in vertical columns called groups
o Each element in a group has atoms with same no. of outer shell electrons and
similar properties
• Periods and periodicity
o Elements are arranged in horizontal rows called periods
o No. of period gives the no. of the highest energy electron shell in an element's
atoms.
o Across periods, there is a repeating trend in properties - periodicity
o Most obvious periodicity in properties - trend from metals to nonmetals
o Periodicity of several properties:
▪ Electron configuration
▪ Ionisation energy
▪ Structure
▪ Melting point
Period trend in electron configurations
• Chemistry of each element is determined by its electron configuration, particularly outer,
highest energy electron shell
Trend across a period
• Each period starts with an electron in a new highest energy shell
o Across period 2, 2s subshell fills with 2 electrons, followed by the 2p subshell
with 6 electrons
o Across period 3, the same pattern of filling is repeated for the 3s and 3p subshell
o Across period 4, although the 3d subshell is involved, the highest shell number is
n = 4. From the n = 4, only the 4s and 4p subshell are occupied
o For each period, s- and p-subshells are filled in the same way
Trend down a group
• Elements in each group have atoms with the same no. of electrons in their outer shell
, • Elements in each group also have atoms with the same no. of electron in each subshells
o Element in the same group will have similar chemistry
Blocks
• Elements can be divided into blockers corresponding to their hughes energy subshell
• 4 distinct blocks, s, p, d and f
• Old numbers are the number used in IGCSE, group 1-7 and then 0
o This system is based on s- and p-blocks
