Regents Chemistry - Atomic Trends Includes information about atomic radius, ionization energy, electronegativity and electron affinity. Included are comprehension questions as well. Note that there is an Atomic Trends table on the Reference Tables for Chemistry Regents that is used for the questions.

1. Atomic Trends
NYS Regents Chemistry

2. Atomic Radius
 The atomic radius is one-half of the distance between
the nuclei of two elements.
 Atoms with the largest atomic radius are found in Group
I and the bottom of periods.
 As you go from left to right across a period, atomic
radius decreases. This is because of the increased
attraction of protons by the nucleus.
 As you go down a group, the radius increases because
the atoms are getting more electron shells.
 Atomic radius is measured in
picometers (pm).

3. Ionization Energy
 Ionization Energy is the energy required to completely
remove an electron from a gaseous atom or ion.
 The closer the electrons are to the nucleus, the more
tightly bound the electrons are, and the harder they will
be to remove.
 Ionization Energy is directly related to atomic radius. It
increases left to right in a period, and decreases down a
group.

4. Electronegativity
 Electronegativity is the measure of the attraction of an
atom for elements in a bond.
 Flourine has the highest electronegativity (4.0) of all the
elements, in the top of Group 17. Electronegativity
increases as you go left to right in a period and
decreases as you go down in a group.
 Electronegativity is a relative mesaure,
and is not measured in any units.
Electron Affinity
 Electron Affinity increases as you go left to right in a
period and decreases as you go down in a group.
 Electron Affinity is the ability of an atom to accept an
electron.

5. Trends Summary
 Moving Left → Right
 Atomic Radius Decreases
 Ionization Energy Increases
 Electron Affinity Increases (excluding Group 18)
 Electronegativity Increases
 Moving Top → Bottom
 Atomic Radius Increases
 Ionization Energy Decreases
 Electron Affinity Decreases Moving Down a Group
 Electronegativity Decreases

6. Introduction (Regents Information)
 Table S: Periodic Trends (Page 10-11 on the Chemistry
Reference Tables) can be used to double check any trend
for this chapter. The table includes Ionization Energy,
Electronegativity, and Atomic Radius.
 Following are questions about the material presented as
well as real regents questions based on the information.

7.  Find the ionization energy of F, Cl, Br, I and At (the
Halogens). What happens to the ionization energy as
you go down the group?
 Of Group 14, which element has the smallest atomic
radius? The largest?
 What is the atomic number of the element with the
highest electronegativity value?
 Rb has (a higher, a lower, the same) ionization energy
than Ru. Rb has (a higher, a lower, the same) ionization
energy than Li.
 The atomic radius of Mo is larger or smaller than the
atomic radius of Nb? What is the atomic radius of Mo
and Nb?
 Which of the following have the most similar chemical
properties?
A. Cobalt and Iron
B. Sodium and Magnesium
C. Mercury and Bromine
D. Lead and Tin

8. Added Notes: Group Behaviors
 Groups contain elements with the same amount of
valance electrons.
 Group 1: Alkali Metals
 Group 2: Alkaline Earth Metals
 Groups 3-12: Transition Metals
 Group 17: Halogens
 Group 18: Noble Gases
 Transition metals can form colored ions.
 Nobel gases have a full valance shell.
 Reactivity decreases as you go down the Halogens.
 Reactivity increases as you go down the Alkali Metals
and Alkaline Earth Metals.