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• Periods –
• horizontal rows on the PT
• Increase by atomic number
• Group/Family –
• vertical column on the PT
• contain elements with similar properties
Alkali Metals –
• 1st 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
• Form 2:1 ratio oxide compounds
Alkaline Earth Metals
• 2nd column on Left (Group 2)
• Reactive metals
• Form 1:2 ratio chloride compounds
• Form 1:1 ratio oxide compounds
Noble Gases
• Far right column on the PT
• Very unreactive (Chemically inert) elements
• All gases
• Xenon (Xe) and Krypton (Kr) can form
some compounds
• Column next to noble gases
• Highly reactive nonmetals
• Form binary compounds with Hydrogen
• Binary compounds – made of 2
By knowing the major properties of a
certain chemical family, you can predict
some properties of any element in that
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.
• Given that the density of silicon (Si) is 2.3 g/cm3 and the
density of tin (Sn) is 7.3 g/cm3, 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/cm3.
• When germanium was discovered in 1886, its density was
found to be 5.3 g/cm3, 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 (CO2).
• 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 CO2, a logical—and
quite correct—prediction would be CS2 (carbon
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 (SiCl4)
existed. Predict the formula for the compound formed by
germanium and chlorine.
• Here are formulas for several known
compounds: Nal, MgCl2, CaO, Al2O3, and CCl4. Using that
information, predict the formula for a compound formed
• 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?

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