The Periodic Table of the Elements 1869~Dmitri Mendeleev 1944~Glenn Seaborg

Mendeleev’s Periodic Table Was organized by two characteristics: 1.Atomic weight or “atomic mass” 2.Their “combining capacity” with other elements, especially with oxygen and chlorine. (The “O in oxide” and “Cl in chloride)

Vocabulary  Atomic Number – the number of protons in an atom’s nucleus  Mass Number- the number of protons and neutrons an atom has.

Vocabulary  Isotope- An element (same proton)that has different numbers of neutrons.  This is one lithium’s isotope.  It has 3 protons and 4 neutrons.  92.5 % of Lithium exists in this isotope.  The other 7.5 % exists in the isotope with 3 protons and 3 neutrons.  This has no effect on the charge.

Vocabulary  Ion – An atom that has gained or lost electrons.  Shown by + or – symbol in top right corner  An atom that has one or more electrons than protons will have a negative charge  An atom that has one or more protons than electrons will have a positive charge.

Metals, Metalloids, Nonmetals

Periodic Variation in Properties  Horizontal rows are called PERIODS  Vertical columns are called GROUPS or FAMILIES. The elements in each group have similar properties.  ALKALI METALS—1 st column; highly reactive  ALKALINE EARTH—2 nd column  TRANSITION METALS—3 rd through 12 th column  HALOGEN—17 th column (2 nd from right); readily form 1- anions  NOBLE GASES—18 th column (far right column); very unreactive

What determines properties?  Mostly it is the number and arrangement of the atom’s electrons.

Predicting Properties  Mendeleev used the average of properties of elements just above and below an unknown element to predict its properties.  Average is found by adding all the numbers together then dividing the sum by the number of numbers.  Average for 2,4, and 6  = 18  18/3 = 6

 Element #32 was unknown to Mendeleev, but the density of silicon (the element above it on the table) is 2.3 g/cm 3 and tin’s (the element below it on the table) density is 7.3 g/cm 3. Make an estimate of element #32’s density.  2.3 g/cm³ g/cm³ = x  x/2 = Estimation Predicting Properties

 When germanium (element #32) was discovered in 1886, its density was found to be 5.3 g/cm 3, only about 10% different than the prediction!

Predicting Properties  Formulas for chemical compounds can also be predicted. We know that carbon and oxygen form carbon dioxide (CO 2 ). What formula would you predict for a compound of carbon and sulfur? Since oxygen and sulfur are in the same group (16), we can predict that the compound would be carbon disulfide (CS 2 ).

Your turn! 1.Krypton (Kr) wasn’t known in Mendeleev’s time. Given that the boiling point of argon (Ar) is -186°C and of xenon (Xe) is -112°C, estimate the boiling point of Kr. 2.The melting points of potassium and cesium (Cs) are 337 K and 302 K respectively. (a) Estimate the melting point of rubidium (Rb). (b) Do you expect the melting point of sodium to be higher or lower than that of rubidium? Explain the evidence you used for your prediction.

Solutions to questions degrees C K; Higher because the melting points within this group of elements decrease as you go from top to bottom.

3.Mendeleev knew that silicon tetrachloride (SiCl 4 ) existed. Using his periodic table, he predicted an element just below silicon (germanium). Predict the formula for the compound formed by this predicted element and chlorine. 4.Given these formulas for known compounds– NaI, MgCl 2, CaO, Al 2 O 3, and CCl 4 –predict the formula for a compound formed from: (a) C and F(b) Al and S (c) K and Cl(d) Ca and Br (e) Sr and O

Solutions to questions 3. GeCl 4 4. a) CF 4 ; b) Al 2 S 3 ; c) KCl; d) CaBr 2 ; e) SrO

Reading the periodic table  Find the following for Ti (titanium) 1.Atomic Number, or Protons 22 2.Atomic Mass 48 3.Number of Neutrons 26 4.Number of Electrons 22