Section 5-2: Electron Configuration and the Periodic Table

1. Section 5-2:Electron Configuration and the Periodic Table Coach Kelsoe Chemistry Pages 138-149

2. Section Objectives • Describe the relationship between electrons in sublevels and the length of each period of the periodic table. • Locate and name the four blocks of the periodic table, as well as explain the reason for these names. • Discuss the relationship between group configurations and group numbers. • Describe the locations in the periodic table and the general properties of the alkali metals, the alkaline-earth metals, the halogens, and the noble gases.

3. Periods and Blocks of the Periodic Table • Remember that elements are arranged vertically in groups and horizontally in periods. • Elements in the same group share chemical properties. • The length of each period is determined by the number of electrons that can occupy the sublevels being filled in that period.

4. Periods and Blocks of the Periodic Table • The first period consists of two elements because the 1s sublevel can only 2 electrons. • In the second period, the 2s sublevel can hold two electrons and the 2p sublevel can hold 6, so the second period has 8 elements. • The same applies to the third period. • At the fourth period, the 4s sublevel can hold 2 electrons, the 3d sublevel can hold 10 electrons, and the 4p sublevel can hold 6.

5. Periods and Blocks of the Periodic Table • The period of an element can be determined from the element’s electron configuration. • For example, arsenic (As) has the Noble Gas configuration [Ar]3d104s24p3. The 4 in the 4p3 indicates that the highest occupied energy level is the fourth energy level.

6. Periods and Blocks of the Periodic Table • Based on the electron configurations of the elements, the periodic table can be divided into four blocks, the s, p, d, and f blocks. • The name of each block is determined by whether an s, p, d, or f sublevel is being filled in successive elements.

7. Important Notice • It is important to realize that not all periodic tables have the information arranged in the same way. • Atomic numbers will never have a decimal and will always be in numerical order.

8. The s-Block Elements: Group 1 & 2 • The elements of the s block are chemically reactive metals. • Group 1 elements are extremely reactive because of how easily they lose their electron. • Using n for the number of the highest occupied energy level, the outer, or group, configurations of the Group 1 and 2 elements are written as ns1 and ns2 respectively.

9. Alkali Metals • The elements of Group 1 of the periodic table (lithium, sodium, potassium, rubidium, cesium, and francium) are known as the alkali metals. • In pure state, all have a silvery appearance and are soft enough to be cut with a knife.

10. Alkali Metals • Properties of alkali metals: • Silvery appearance • Soft in texture • Not found in nature as free elements because they combine with other elements. • Combine vigorously with most nonmetals • React strongly with water to produce H2 gas and alkalis.

11. Alkali-Earth Metals • The elements of Group 2 of the periodic table (beryllium, magnesium, calcium, strontium, barium, & radium) are called the alkali-earth metals. • Atoms of alkali-earth metals contain a pair of electrons in their outermost s sublevel.

12. Alkali-Earth Metals • The Group 2 metals are harder, denser, and stronger than the alkali metals. • They also have higher melting points. • They are less reactive than alkali metals, but they too are too reactive to be found free in nature.

13. Hydrogen and Helium • Hydrogen and helium are special cases in the periodic table. • Hydrogen has an electron configuration of 1s1, but it does not share the same properties as the elements of Group 1. • Helium is also different from the Group 18 elements. It is very stable because its outermost energy level is filled by 2 electrons.

14. Sample Problem • Without looking at the periodic table, give the group, period, and block in which the element with the electron configuration [Xe]6s2 is located. • Group 2, Period 6, Block s • Without looking at the periodic table, write the electron configuration for the Group 1 element in the 3rd period. Is this element likely to be more active or less active than the previous? • 1s22s22p63s1; it is likely to be more reactive

15. The d-Block Elements: Groups 3-12 • For energy level n, there are n possible sublevels, so we don’t see the d sublevel until the 3rd energy level. • Remember that the 3d sublevel is higher in energy than the 4s, so they will fill up in order of 4s3d. • The d sublevel is made up of 5 orbitals that can hold a total of 10 electrons.

16. The d-Block Elements: Groups 3-12 • The group configuration for Group 3 is (n-1)d1ns2. • The group configuration for Group 12 is (n-1)d10ns2. • There are a few exceptions. For elements like Palladium and Platinum, those lower energy levels do not fill up first.

17. The d-Block Elements: Groups 3-12 • The d-block elements are metals with typical metallic properties and are often referred to as transition elements. • They are good conductors of electricity, have a high luster, and are less reactive than alkali and alkali-earth metals.

18. Essentials for Life • These elements are essential for life and make up over 96% of the human body. • Carbon • Hydrogen • Oxygen • Phosphorus • Sulfur • Nitrogen

19. Sample Problem • An element has the electron configuration [Ar]3d84s2. Without looking at the periodic table, identify the period, block, and group in which this element is located. • 4th Period – indicated by the highest occupied energy level • d-block – indicated by the (n-1)d1-10ns0-2 notation • Group 10 – indicated by the total number of electrons in the outer energy level.

20. The p-Block Elements: Groups 13-18 • The p-block elements consist of all the elements of Groups 13-18 except Helium. • Electrons add to a p sublevel only after the s sublevel in the same energy level is filled. • Atoms of all p-block elements contain two electrons in the ns sublevel.

21. The p-Block Elements: Groups 13-18 • The p-block elements and the s-block elements are called the main-group elements. • For Group 13, the group configuration is ns2np1. • For Group 18, the group configuration is the ns2np6.

22. The p-Block Elements: Groups 13-18 • For atoms of p-block elements, the total number of electrons in the highest occupied level is equal to the group number minus 10. • In the p-block elements, there are metals, metalloids, and nonmetals.

23. The Halogens • The elements of Group 17 (fluorine, chlorine, bromine, iodine, and astatine) are known as the halogens. • The halogens are the most reactive nonmetals. • They react with most metals to form salts. • For all atoms, reactivity is based on the presence of electrons in the outermost energy level.

24. The Halogens • Characteristics of some of the halogens: • Fluorine and chlorine are gases at room temperature. • Bromine is a reddish liquid. • Iodine is a dark purple solid. • Astatine is a synthetic element prepared in only very small quantities.

25. Metalloids • Metalloids are semiconducting elements that are mostly brittle solids with some properties of metals and some of nonmetals. • The metalloids have electrical conductivity intermediate between that of metals and nonmetals.

26. Properties of p-Block Elements • The p-block elements are generally harder and denser than the s-block elements, but softer and less dense than the d-block elements. • With the exception of bismuth, these metals are sufficiently reactive to be found in nature only in the form of compounds.

27. Sample Problem • Without looking at the periodic table, write the outer electron configuration for the Group 14 element in the second period. Then name the element. • It is in the p-block because its group is higher than 12 • The total number of electrons in the highest occupied s and p sublevels is equal to the group number minus 10, so 14-10=4 • Being in the 2nd period, it must be 2s22p2.

28. The f-Block Elements: Lanthanides and Actinides • The f-block elements are wedged between Groups 3 and 4 in the 6th and 7th periods. • With seven 4f orbitals to be filled with two electrons each, there are a total of 14 f-block elements between lanthanum and hafnium. • There are also 14 f-block elements between Actinium and Rutherfordium.