IB Chemistry: Periodicity Notes
What is Periodicity?
Periodicity refers to the recurring trends/repeating patterns in the
properties of elements as you move across periods (rows) and down
groups (columns) in the Periodic Table.
These trends are linked to electron configuration and how
the electrons interact with each other and the nucleus.
The Periodic Table Structure
Periods: Horizontal rows of the Periodic Table. As you move from
left to right across a period:
o The atomic number increases.
o Elements have more protons, more electrons, and
a larger nuclear charge.
Groups: Vertical columns. Elements in the same group have the
same valence electrons, leading to similar chemical properties.
Key Periodic Trends
a) Atomic Radius
Definition: The distance from the nucleus to the outermost
electron.
Trend Across a Period:
o Decreases from left to right.
o The electrons are pulled closer to the nucleus as the nuclear
charge increases.
Trend Down a Group:
o Increases as you go down a group.
o New electron shells are added, increasing the distance from
the nucleus.
b) Ionization Energy
, Definition: The energy required to remove one mole of electrons
from one mole of gaseous atoms.
Trend Across a Period:
o Increases from left to right.
o More protons = stronger nuclear attraction, making it harder
to remove electrons.
Trend Down a Group:
o Decreases as you go down a group.
o Outer electrons are further from the nucleus and experience
more shielding, so it’s easier to remove them.
c) Electronegativity
Definition: A measure of the ability of an atom to attract bonding
electrons.
Trend Across a Period:
o Increases from left to right.
o As the nuclear charge increases, atoms pull electrons more
strongly.
Trend Down a Group:
o Decreases as you go down a group.
o Larger atoms have a weaker pull on bonding electrons.
d) Electron Affinity
Definition: It is the amount of energy released when an electron is
added to a gaseous atom to form a negative ion (anion). i.e. X +e-
X-
Trend across the period:
o Increases from left to right
o As the nuclear charge increases, electrons are added more
strongly.
o Trend down group:
o Decreases as you go down the group
o Larger atoms have a weaker pull on valence electrons as they are
further away from the nucleus
What is Periodicity?
Periodicity refers to the recurring trends/repeating patterns in the
properties of elements as you move across periods (rows) and down
groups (columns) in the Periodic Table.
These trends are linked to electron configuration and how
the electrons interact with each other and the nucleus.
The Periodic Table Structure
Periods: Horizontal rows of the Periodic Table. As you move from
left to right across a period:
o The atomic number increases.
o Elements have more protons, more electrons, and
a larger nuclear charge.
Groups: Vertical columns. Elements in the same group have the
same valence electrons, leading to similar chemical properties.
Key Periodic Trends
a) Atomic Radius
Definition: The distance from the nucleus to the outermost
electron.
Trend Across a Period:
o Decreases from left to right.
o The electrons are pulled closer to the nucleus as the nuclear
charge increases.
Trend Down a Group:
o Increases as you go down a group.
o New electron shells are added, increasing the distance from
the nucleus.
b) Ionization Energy
, Definition: The energy required to remove one mole of electrons
from one mole of gaseous atoms.
Trend Across a Period:
o Increases from left to right.
o More protons = stronger nuclear attraction, making it harder
to remove electrons.
Trend Down a Group:
o Decreases as you go down a group.
o Outer electrons are further from the nucleus and experience
more shielding, so it’s easier to remove them.
c) Electronegativity
Definition: A measure of the ability of an atom to attract bonding
electrons.
Trend Across a Period:
o Increases from left to right.
o As the nuclear charge increases, atoms pull electrons more
strongly.
Trend Down a Group:
o Decreases as you go down a group.
o Larger atoms have a weaker pull on bonding electrons.
d) Electron Affinity
Definition: It is the amount of energy released when an electron is
added to a gaseous atom to form a negative ion (anion). i.e. X +e-
X-
Trend across the period:
o Increases from left to right
o As the nuclear charge increases, electrons are added more
strongly.
o Trend down group:
o Decreases as you go down the group
o Larger atoms have a weaker pull on valence electrons as they are
further away from the nucleus
