Periodic Trends
Horizontal & vertical trends can be seen in the elements for:
• atomic radius
• ionization energy
• electron affinity
• electronegativity
ATOMIC RADIUS
To find atomic radius, atoms are assumed to be spheres. The electron cloud size determines the atomic
radius for an atom. The radius values are only estimates. These values are measured by finding the distance
between 2 nuclei and dividing the distance by 2.
GROUP TREND: Atomic radius increases as you move from top to bottom in a family. This is because
major energy levels (1-7) are being filled with more & more electrons. The electrons get farther & farther
from the nucleus.
PERIOD TREND: Atomic radius generally decreases from left to right as atomic number increases. This
is because extra electrons are entering the same level while the nucleus gets larger & more positive. This
draws the electron cloud in towards the nucleus.
[Atomic Size of Elements] [Atomic Size of Ions]
ATOMIC RADIUS OF IONS: When an atom loses an electron it has a positive charge. The radius of the
atom decreases because there’s a smaller electron cloud. When an atom gains an electron it has a negative
charge. The radius of the atom increases because the electron cloud is larger.
Horizontal & vertical trends can be seen in the elements for:
• atomic radius
• ionization energy
• electron affinity
• electronegativity
ATOMIC RADIUS
To find atomic radius, atoms are assumed to be spheres. The electron cloud size determines the atomic
radius for an atom. The radius values are only estimates. These values are measured by finding the distance
between 2 nuclei and dividing the distance by 2.
GROUP TREND: Atomic radius increases as you move from top to bottom in a family. This is because
major energy levels (1-7) are being filled with more & more electrons. The electrons get farther & farther
from the nucleus.
PERIOD TREND: Atomic radius generally decreases from left to right as atomic number increases. This
is because extra electrons are entering the same level while the nucleus gets larger & more positive. This
draws the electron cloud in towards the nucleus.
[Atomic Size of Elements] [Atomic Size of Ions]
ATOMIC RADIUS OF IONS: When an atom loses an electron it has a positive charge. The radius of the
atom decreases because there’s a smaller electron cloud. When an atom gains an electron it has a negative
charge. The radius of the atom increases because the electron cloud is larger.
