Chapter 2:Unit 8. Location of Elements in Periodic Table

Location of Elements in Periodic Table

Location of elements in the periodic table is related to its number of valence electrons. Valence electrons are the outermost shell electrons in an atom. Elements in the same group have the same number of valence electrons and similar electronic configurations. The group number (1A-8A) is equal to the number of valence electrons for main group elements (except Helium). The chemical properties of a group are similar because they contain same number of valence electrons and configurations. Thus the periodic table is organized into groups of elements with similar valence electronic configurations in the same column.

In the table below, we are trying to see electronic configuration of alkali metals.

It is evident from the table that all elements in group IA end with s1 configuration for the valence electrons (outermost shell). Similarly, all halogens valence configuration end with s2p5 configuration.

Considering electronic configuration, the periodic table can be classified in four blocks. The blocks are named according to the subshells that are filled with last electron of that element.

s block: Group IA and 2A, filling up s1-2 electrons.

p block: Group 3A-8A: filling up p1-6 electrons.

d block: 10 columns of transition metals, d1-10 electrons are filled up.

f block: two groups of 14 inner transition elements, f1-14 electrons are filled up

Electronic configuration of any element can be determined from the following table.

Here is the complete block diagram of periodic table.

Watch the following video.

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http://employees.oneonta.edu/viningwj/sims/periodic_table.html

Questions:

1. Identify the total number of electrons, the number of valence electrons and the name of the element
2. a. 1s2 2s2 2p6 3s2 3p2
3. b. 1s2 2s2 2p6 3s2 4s1

Ans: a. 14, 4, Si(silicon)

b. 19, 1, K(Potassium)

Activity:

Go to the above simulation and click on the electronic configuration of different elements. Click on any element from 1) main group, 2) Transition metal 3) Lanthanides and actinides and answer to the questions below.

• How the valence electrons number changes from left to right across the period?
• Which part on Periodic table have electronic configurations ending with “f” sublevel?
• Look at the orbital box diagram of Nitrogen. How many unpaired electrons are present?
• What is the noble gas notation for the electronic configuration of Ba?

The following activity has been taken from AACT

Electron Configuration and The Periodic Table

Pre-lab Questions

1. What is the Aufbau Principle?

2. How is bonding related to electron configuration?

Objective

You will learn how the periodic table can be used to predict the electron configuration of an atom and predict the reactivity of an atom based on its configuration and placement on the periodic table.

Procedure

1. In the table below, write the electron configurations of the following atoms using the aufbau principle according to your teacher’s instruction: H, Xe, Rb, Fe, Si, I, Hg, Ra, Mg, Eu, Zn, Ta, Ba, N, S, Co, He, Am, Y, Pd.
2. Check your electron configurations for accuracy with your shoulder partner.
3. For your assigned atom, write largely and legibly the valence shell configuration on a post-it note. Place the post-it note on top of your assigned atom on the periodic chart on the wall.
4. Make note or your observations of patterns on the chart indicated by the post-it notes and placement on the chart. Consider changes as you go up and down the periodic table or left to right on the periodic table in the total electrons, valence electrons, energy levels, periods, sublevels, blocks, and groups/families by considering the following questions.
5. Complete post-lab questions.
6. Prepare to discuss findings and explain trends to the class.

Data

Analysis

1. What trends do you see when considering total electrons, valence electrons, energy levels, periods, sublevels, blocks, and groups/families.

2. Explain how you can determine the electron configuration of an atom simply by looking at the periodic table:

3. What is the connection between the patterns you observed and the historical reasons for grouping elements in families?

4. Why is the periodic table shaped the way it is?

5. Which electron configurations are the most stable configurations? Why?

6. The most common reaction pattern for transition elements (d block) is losing two electrons. What does this fact suggest about how these elements lose electrons? A few sample electron configurations may be useful to reference in your answer.

Conclusion

Summarize your findings in your own words. In your summary, include your explanation for how you think the electron configuration of an atom is related to its reactivity.

Questions:

1. What is the generic configuration of alkali metals and halogens?

2. An element has 5 valence electron. What is the group number of the element?

3. An element is in group four and atomic number is 14. What block of elements does it represent?

4. Where are the transition metals located on the periodic table?

Ans:

1. Alkali metals: ns1, halogens: ns2np5
2. VA or 15.
3. p block element.
4. In the middle, d-block element