6.2 Classifying the Elements Read the lesson title aloud to students.

Using the Periodic Table: Entries Atomic number Electrons in each energy level Element symbol Tell students that every element has a one- or two-letter symbol. For aluminum, it’s “Al.” Click to label the two-letter symbol. Explain that the atomic number is the number of protons in the nucleus of the atom. Ask: Based on the information given in the periodic-table square for aluminum, what is the atomic number of aluminum? Answer: The atomic number must be an integer, so it is 13. Click to label the atomic number. Tell students to now consider the bottom number. Click to reveal the write-on line for the bottom number. Ask for a student to fill in the blank for the bottom number. Click to label the atomic mass. Ask: How many grams is a mole of aluminum? Answer: From the atomic mass of aluminum, a mole of aluminum has a mass of about 27 grams. Ask: What are the three numbers for in the upper-right corner? Answer: The numbers in the upper-right corner give the number of electrons in each occupied energy level. Click to reveal the label. Atomic mass

Using the Periodic Table: Colors Meaning of text color: phase (solid, liquid, gas) Tell students that the element symbols are written in different colors. They can be black, red, blue, or grey. Ask: Can you name an element whose element symbol is written in black? Answer: There are many elements written in black: gold, iron, and copper are three examples. Click to circle these elements. Ask: Can you name an element whose element symbol is written in red? Answer: There are several: nitrogen, neon, and hydrogen are three examples. Ask: Can you name an element whose element symbol is written in blue? Answer: There are two element symbols written in blue: mercury and bromine. Ask: Can you name an element whose element symbol is written in grey? Answer: There are several such elements: plutonium, mendelevium, and californium are three examples. Ask: What do you think these color codes represent? Answer: At standard temperature and pressure, the black elements are solids, the red elements are gases, and the blue elements are liquids. The grey elements do not occur in nature but are man-made. Click to reveal the response. Explain that the periodic table has a legend to remind you what the text color means. Click to reveal the legend. Ask: Where are most of the red elements found on the periodic table, and what does this tell you about them? Answer: There are mostly in the upper-right corner and are all in the blue section of the table, so they are nonmetals. Ask: Where are the black elements found, and what does this tell you about them? Answer: With the exception of hydrogen, bromine, and the grey elements, they occupy the entire table except for the upper-right corner, so they are metals and metalloids.

Using the Periodic Table: More Colors Chemical families are color coded on the periodic table. Halogens Explain that you can use the periodic table to identify chemical families by the colors of the squares. Ask: What do the blue squares, green squares, and light-beige squares indicate? Answer: The blue squares are nonmetals, the light-beige squares are metals, and the green squares are metalloids. Click to reveal the legends for the blue, green, and light-beige squares. Ask: What are the characteristics of the elements in the purple squares? Answer: These elements all have filled electron shells, so they are chemically inert. Ask: What is the group of elements in the purple squares called? Answer: This group is called the noble gases. Click to reveal the noble gas legend. Explain that the two shades of orange are used for the metals in Groups 1A and 2A. The elements in Group 1A are called alkali metals. The name alkali comes from the Arabic al aqali, meaning “the ashes.” Wood ashes are rich in compounds of the alkali metals sodium and potassium. Click to reveal the legend for alkali metals. Explain that the elements in Group 2A are called alkaline earth metals. The term “earth” is an old term that was given to compounds containing these elements before it was realized that the compounds were, in fact, compounds. Click to reveal the legend for alkaline earth metals. Explain that some groups of nonmetals also have special names. The nonmetals of Group 7A are called halogens. The name halogen comes from the combination of the Greek word hals, meaning “salt,” and the Latin word genesis, meaning “to be born.” Click to label the halogens.

Elements are divided into 2 categories; representative & transitional Explain that you can use the periodic table to identify chemical families by the colors of the squares. Ask: What do the blue squares, green squares, and light-beige squares indicate? Answer: The blue squares are nonmetals, the light-beige squares are metals, and the green squares are metalloids. Click to reveal the legends for the blue, green, and light-beige squares. Ask: What are the characteristics of the elements in the purple squares? Answer: These elements all have filled electron shells, so they are chemically inert. Ask: What is the group of elements in the purple squares called? Answer: This group is called the noble gases. Click to reveal the noble gas legend. Explain that the two shades of orange are used for the metals in Groups 1A and 2A. The elements in Group 1A are called alkali metals. The name alkali comes from the Arabic al aqali, meaning “the ashes.” Wood ashes are rich in compounds of the alkali metals sodium and potassium. Click to reveal the legend for alkali metals. Explain that the elements in Group 2A are called alkaline earth metals. The term “earth” is an old term that was given to compounds containing these elements before it was realized that the compounds were, in fact, compounds. Click to reveal the legend for alkaline earth metals. Explain that some groups of nonmetals also have special names. The nonmetals of Group 7A are called halogens. The name halogen comes from the combination of the Greek word hals, meaning “salt,” and the Latin word genesis, meaning “to be born.” Click to label the halogens.

Using the Periodic Table: Transitions Inner transition metals Transition metals Explain that the elements are further divided into two main groups: representative elements and transition elements. Ask: Which elements do you think are the transition elements? Answer: The transition elements are the transition metals and the inner transition metals. Click to label the transition and inner transition metals and reveal their legends. Explain that the “representative” elements are all the elements that are not “transition” elements. In other words, the representative elements are those on the left and right regions of the periodic table. Explain that the representative elements are all the rest of the elements. Click to circle the legends for the representative elements.

Electron Configurations An element’s location in the periodic table gives information about its electron configuration. Energy sublevels Oxygen Silicon 14 2 Principal energy levels Iron 26 1 3 4 5 6 7 8 Explain that you can use the periodic table to identify and explain the properties of chemical families, including alkali metals, alkaline earth metals, halogens, noble gases, and transition metals. An element’s location in the periodic table gives information about its electron configuration. Electrons play a key role in determining the properties of elements, so there should be a connection between an element’s electron configuration and its location in the periodic table. Explain that you can use the periodic table to help determine electron configurations of elements. Each period on the periodic table corresponds to a principal energy level. Click to label principal energy levels. Explain that the periodic table can be divided into sections, or blocks, that correspond to the highest occupied sublevels. The s block contains the elements in Groups 1A and 2A and the noble gas helium. The p block contains the elements in Groups 3A, 4A, 5A, 6A, 7A, and 8A, with the exception of helium. The transition metals belong to the d block, and the inner transition metals belong to the f block. Click to label sublevels. Explain that to determine the electron configuration of a given element, you assign one electron to each square of the table from left to right, top to bottom until you have used up all the electrons in the (neutral) element. Take oxygen as an example. It has eight electrons, so you fill the squares of the table as follows. Click to show the animation to determine electron configuration of oxygen. Ask: A neutral silicon atom has 14 electrons. Where would the element Si appear on the periodic table? Click to show Si. Ask for a student to circle the square on the screen where iron (26 electrons) appears. Click to reveal the response.

Noble Gases Noble gases are called inert because the rarely take part in chemical reactions. They have full s & p orbitals. Group 8A Helium (He) 1s2 Neon (Ne) 1s22s22p6 Argon (Ar) 1s22s22p63s23p6 Krypton (Kr) 1s22s22p63s23p63d104s24p6 Explain that the noble gases neon and argon are used to make the colors in the neon sign, and helium is used in helium balloons. Noble gases are sometimes called inert gases because they rarely take part in a chemical reaction. The electron configurations for the first four noble gases in Group 8A are listed in the table shown. Ask: What is the highest occupied energy level for each element? Click to highlight the highest occupied energy level for each element. Explain that the s and p sublevels are completely filled with electrons—two electrons in the s sublevel and six electrons in the p sublevel. This makes the electron configuration very stable, as will be explained in the next chapter. This is why these elements are very stable and do not readily undergo chemical reactions.

Representative Elements Groups 1A-7A Representative Elements Groups 1A-7A. The s & p sub levels are partially full. Tell students that these are the representative elements that are the part of the periodic table containing Groups 1A through 7A. On the screen, the transition elements have been removed to concentrate on the representative elements. Elements in Groups 1A through 7A are often referred to as representative elements because they display a wide range of physical and chemical properties. Some elements in these groups are metals, some are nonmetals, and some are metalloids. Most of them are solids, but a few are gases at room temperature, and one, bromine, is a liquid. Explain that this group contains metals, metalloids, and nonmetals. (Transition elements removed)

Representative Element Examples Lithium, silicon Sulfur Explain that these images show examples of some representative elements or items that use them. Ask: What representative element is used in making the laptop and cell phone? Answer: Lithium is used to make the batteries, and silicon is used to make the integrated circuits. Click to reveal the answer. Ask: What representative element is used to make the jug? Answer: The jug is made of tin because tin resists corrosion. Ask: What representative element is being ejected by this underwater vent? Answer: Sulfur is being ejected, along with other elements and compounds. Tin

Transition Elements Transition metals have electrons in the d orbitals, inner transition metals have electrons in the f orbitals. Transition metals Explain that in the periodic table, the B group elements separate the A groups on the left side of the table from the A groups on the right side. Elements in the B groups are referred to as transition elements. There are two types of transition elements—transition metals and inner transition metals. They are classified based on their electron configurations. Ask for a student to show on the screen where the Group A elements are situated. Click to show where the Group A elements are situated. Explain that the transition metals are the Group B elements that are usually displayed in the main body of a periodic table. Ask for a student to show on the screen where the transition metals are situated. Click to highlight the transition metals. Tell students that copper, silver, gold, and iron are transition metals. Transition metals are characterized by the presence of electrons in d orbitals. Ask: What is the highest occupied sublevel for transition elements? Answer: Transition metals are in the “d” block, so the highest occupied sublevel is a “d” sublevel. Explain that the inner transition metals are the elements that appear below the main body of the periodic table. They are characterized by the presence of electrons in f orbitals. Click to highlight the inner transition metals. Explain that before scientists knew much about inner transition metals, people referred to them as rare-earth elements. This name is misleading because some inner transition metals are more abundant than other elements. Notice that some of the inner transition metals and transition metals are not found in nature. Inner transition metals