Periodic Trends
Atomic Radius: Size of the atom.
Across a period: Atomic radius ___________________ moving from left to right.
WHY: A proton is added in each element on the same energy level, adding to the power of the nucleus to pull
electrons inward.
Down a group: Atomic radius ___________________ moving down a group.
WHY: Each orbit is overlapped by another larger orbit for each period moving downwards within a group.
Ionic Radius: Size of a _______________________.
Cation: When a stable cation forms (eg. Na1+) an entire energy level is lost and the ionic radius is _________.
Anion: When a stable anion forms (eg. F1-) there are now more electrons than protons. The electron-electron
repulsion increases and the nuclear charge remains the same. The anion gets __________.
Ionization Energy: The energy required to remove an electron from its outer shell.
Across a period: Ionization energy ____________________ moving from left to right across a period.
WHY: Increased number of protons increases the energy needed to pull electrons away from the nucleus. More
energy is needed for smaller atoms than larger atoms.
Down a group: Ionization energy ______________________ moving down a group.
WHY:
1) Distance from the positively charged nucleus is greater
2) Shielding effect: Inner electrons block the attraction of the nucleus to the outer electrons.
Electron Affinity: Attraction of an atom for an electron. (Electronegativity - Attraction of an atom for an
electron within a chemical bond.)
Across a period: Electron affinity ______________moving left to right across the periodic table (except group VIII).
WHY: Increased number of protons causes increased attraction to other electrons. Smaller atoms have a greater
ability to attract an electron. Noble gases have no room on their shell for an electron.
Down a group: Electron affinity _____________________ moving down a group.
WHY: Larger atom means nucleus is farther from the outer shell and attracts electrons less strongly.
Reactivity: Ability of an atom to react.
Across a period: Starting from the middle, reactivity _______________________ moving outwards towards
the ends of the periodic table, (noble gases not included).
WHY: Moving outwards, elements need to give or take fewer electrons to achieve a stable octet
Down a group: On the metallic side, reactivity _____________________ moving down the group.
WHY: Electrons are so easily removed. Large metals give up electrons easier since they are further from the
nucleus.
Down a group: On the non-metallic side, reactivity __________________________ moving up the group.
WHY: Nucleus has strong attraction to other electrons. Small non-metals gain electrons better and hold electrons
closer to its nucleus.