Periods
Characteristics of periods (horizontal rows) including the number of elements and electron shell filling.
What is Periods?
A horizontal row in the periodic table of chemical elements, characterized by the filling of a specific principal energy level (shell).
Key points
- Define what a period is in the context of the periodic table.
- Relate periods to principal energy levels.
- Determine the number of elements in each period based on electronic configuration.
- Describe the general trends of atomic properties across a period.
Common exam trap
Confusing periods with groups.
Definitions
- Term
Period
- Meaning
A horizontal row in the periodic table of chemical elements, characterized by the filling of a specific principal energy level (shell).
- Term
Principal Energy Level (Shell)
- Meaning
An energy level in an atom, designated by the principal quantum number (n), which describes the size and energy of the electron's orbit.
Learning objectives
Define what a period is in the context of the periodic table.
Relate periods to principal energy levels.
Determine the number of elements in each period based on electronic configuration.
Describe the general trends of atomic properties across a period.
Prerequisites
Atomic structure (protons, neutrons, electrons)
Electronic configuration
Quantum numbers
Shells and subshells (s, p, d, f orbitals)
Common mistakes
Confusing periods with groups.
Incorrectly assuming the number of elements in each period without considering subshell filling.
Misinterpreting the trends of properties across a period.
Forgetting the inclusion of lanthanoids and actinoids in periods 6 and 7.
Keywords
Period
Horizontal row
Principal energy level
Shell
Electronic configuration
Atomic radius
Ionization energy
Electronegativity
Periodic trends
Practice preview
The first period contains only two elements, Hydrogen (H) and Helium (He). This is because:…
medium
The second period of the periodic table contains elements from Lithium (Li) to Neon (Ne). How many elements are present in the second period?…
easy
Which of the following elements belongs to the third period and has the highest ionization enthalpy among the elements of that period?…
medium