Date post: | 19-Jan-2016 |
Category: |
Documents |
Upload: | rosaline-georgia-mccoy |
View: | 216 times |
Download: | 1 times |
The Periodic Table of the Elements
1869~Dmitri Mendeleev1944~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—1st column; highly reactive ALKALINE EARTH—2nd column TRANSITION METALS—3rd through 12th column HALOGEN—17th column (2nd from right); readily
form 1- anions NOBLE GASES—18th 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
4 + 5 + 9 = 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/cm3 and tin’s (the element below it on the table) density is 7.3 g/cm3. Make an estimate of element #32’s density.
2.3 g/cm³ + 7.3 g/cm³ = x x/2 = Estimation
Predicting Properties
Predicting Properties
When germanium (element #32) was discovered in 1886, its density was found to be 5.3 g/cm3, 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 (CO2). 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 (CS2).
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
1. -149 degrees C
2. 320 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 (SiCl4) 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, MgCl2, CaO, Al2O3, and CCl4 –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. GeCl44. a) CF4;
b) Al2S3;
c) KCl; d) CaBr2;
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