Periodic Trends
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1Periodic Trends
Term
Definition
Trend on the Periodic Table
Why?
Atomic Radius
The radius of an atom (since the
Across: Electrons added to the same
electron cloud accounts for the volume
energy level experience increasing
Decreases across a period
of the atom, this is primarily the radius
attraction to the nucleus due to
of the electron cloud)
successive addition of protons
Increases down a group
Down: Each period on the table adds
a new energy level to the electron
cloud.
Ionization Energy
The energy required to remove an
Across: Electrons are harder to
electron from an atom:
remove from small atoms because
Increases across a period
+
-
Na + 496 kJ
Na
+ e
they are closer to the nucleus
Ionization energy increases for
Decreases down a group
successive electrons removed from an
Down: Electrons are easier to
atom:
remove from large atoms because
+
2+
-
Na
+ 4562 kJ
Na
+ e
they are farther from the nucleus
Electronegativity
A measure of the ability of an atom in a
Across: Shared electrons are closer
chemical compound to attract electrons
to the nucleus in small atoms
Increases across a period
Down: Shared electrons are farther
Decreases down a group
from the nucleus in large atoms
Cation
A positively charged ion, formed when
Cations are smaller than the atom
Losing electrons decreases the size
an atom loses one or more electrons
from which they were formed
of the electron cloud, which reduces
the radius of the atom
Anion
A negatively charged ion, formed when
Anions are larger than the atom
Gaining electrons increases the size
an atom gains one or more electrons
from which they were formed
of the electron cloud, which
increases the radius of the atom
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