ORGANIZATION OF THE PERIODIC TABLE Periods horizontal rows

ORGANIZATION OF THE PERIODIC TABLE

• Periods – • horizontal rows on the PT • Increase by atomic number • Group/Family – • vertical column on the PT • contain elements with similar properties

Alkali Metals – • 1 st Column on Left Side (Group 1) • Start with Lithium (Li) • Highly reactive metals (especially with water/water vapor) • Never found uncombined in nature • Form 1: 1 ratio chloride compounds (metal: Cl) • Form 2: 1 ratio oxide compounds (metal: O)

Alkaline Earth Metals • 2 nd column on Left (Group 2) • Reactive metals • Form 1: 2 ratio chloride compounds (metal: Cl) • Form 1: 1 ratio oxide compounds (metal: O)

Noble Gases • Far right column on the PT • Very unreactive (Chemically inert) elements • All gases • Xenon (Xe) and Krypton (Kr) can form some compounds

Halogens • Column next to noble gases • Highly reactive nonmetals • Form binary compounds with Hydrogen (H) • Binary compounds – made of 2 elements

So… By knowing the major properties of a certain chemical family, you can predict some properties of any element in that family!!!

Predicting properties • Periodic properties – properties that vary among elements according to trends that repeat as atomic number increases • Because of these trends, some element properties can be estimated by averaging info from other atoms in the same family. • Ex: Mendeleev predicted Ge based on the known properties of other elements in the family.

Example: • Given that the density of silicon (Si) is 2. 3 g/cm 3 and the density of tin (Sn) is 7. 3 g/cm 3, estimate the density of germanium (Ge). • These three elements are in the same group in the periodic table. Germanium is below silicon and above tin. The predicted density of germanium can be estimated by averaging the densities of silicon and tin, arriving at a calculated value of 4. 8 g/cm 3. • When germanium was discovered in 1886, its density was found to be 5. 3 g/cm 3, which is within ~10% of the earlier estimated density.

What else can be predicted? • Formulas for chemical compounds can also be predicted from relationships in the periodic table. For example, carbon and oxygen form carbon dioxide (CO 2). • What formula would be predicted for a compound of carbon and sulfur? • The periodic table indicates that sulfur (S) and oxygen (O) are in the same family. Knowing that carbon and oxygen form CO 2, a logical—and quite correct—prediction would be CS 2 (carbon disulfide).

Now it’s your turn. • The element krypton (Kr) was not known in Mendeleev’s time. Given that the boiling point of argon (Ar) is − 186 °C and of xenon (Xe) is − 107 °C, estimate the boiling point of krypton. • Estimate the melting point of rubidium (Rb). The melting points of potassium(K) and cesium (Cs) are 337 K and 302 K, respectively. • Do you expect the melting point of sodium (Na) to be higher or lower than that of rubidium (Rb)? Explain. On what evidence did you base your answer?

• Mendeleev knew that silicon tetrachloride (Si. Cl 4) existed. Predict the formula for the compound formed by germanium and chlorine. • Here are formulas for several known compounds: Nal, Mg. Cl 2, Ca. O, Al 2 O 3, and CCl 4. Using that information, predict the formula for a compound formed from: • C and F • Al and S • K and CI • Ca and Br • Sr and O

• Elemental nickel is white to light gray in color, highly ductile, lustrous, and resistant to tarnish. Which other element would you expect to share these properties: Pt, Cu, Rb, or Kr? Explain your choice. • Manganese, which has melting point 1519 K and is one of the metals used in the Presidential dollar coin, was the only known element in its family for 150 years. When rhenium, which has melting point 3459 K, was discovered in 1925, what could chemists predict about the melting point of element 43?