http://www.ck12.org Chapter 6. The Periodic Table
two electrons, there are ten elements in each period of the d-block. The general electron configuration for elements
in the d-block is (n- 1)d^1 −^10 ns^2. The d sublevel being filled belongs to a principal energy level that is one lower than
the s sublevel that has just been filled. For example, the configuration of zirconium (Zr) is [Kr]4d^2 5s^2. The group
number can easily be determined from the combined number of electrons in thesanddsublevels. Zirconium is in
Period 5 and Group 4.
Because electrons in the d sublevel do not belong to the outermost principal energy level, they are not valence
electrons. Most d-block elements have two valence electrons, which are the two electrons from the outermost s
sublevel.
The f-block
The first of the f sublevels is the 4f sublevel. It fills after the 6s sublevel, meaning that f sublevels are two principal
energy levels behind. The general electron configuration for elements in the f-block is (n- 2)f^1 −^14 ns^2. The seven
orbitals of the f sublevel can each accommodate two electrons, so the f-block is 14 elements in length. It is usually
shown pulled out of the main body of the periodic table and is placed at the very bottom. Because of that, the
elements of the f-block do not belong to any of the numbered groups; they are wedged in between Groups 3 and
- Thelanthanidesare the 14 elements from cerium (atomic number 58) to lutetium (atomic number 71). Most
lanthanides have a partially filled 4f sublevel. They are all metals and are similar in reactivity to the Group 2 alkaline
earth metals.
Theactinidesare the 14 elements from thorium (atomic number 90) to lawrencium (atomic number 103). Most
actinides have a partially filled 5f sublevel. The actinides are all radioactive elements, and only the first four have
been found to occur naturally on Earth. All of the others have only been artificially made in the laboratory.
Lesson Summary
- An element’s placement in the periodic table is determined by its electron configuration.
- Valence electrons (those in the outermost principal energy level) dictate the chemical behavior of each element.
Their relatively large distance from the nucleus makes them more available to interact with other atoms. - Core electrons are the electrons that are closer to the nucleus and therefore do not participate in bonding.
- The periodic table is divided into 4 blocks (s, p, d, and f) based on which sublevel is in the process of being
filled. - Alkali metals, alkaline earth metals, halogens, and noble gases are the common names of groups 1, 2, 17, and
18. - Transition elements are members of the d-block, while the f-block consists of the lanthanides and the actinides.
Lesson Review Questions
- Sketch a periodic table, labeling the s, p, d and f blocks.
- What can be said about the elements within a given group of the periodic table?
- How do valence electrons and core electrons differ?
- What blocks of the periodic table make up the representative elements?
- Describe the relationship between the electron configuration of the alkali earth metals and their reactivity.
- How do alkaline earth metals differ from the alkali metals?
- Describe the properties of hydrogen and helium?
- Why are the noble gases almost completely unreactive?
- What are some unique properties of transition metals?