Developing the Periodic Table

Early Element Classification

Mendeleev’s First Periodic Table

Mendeleev’s First Periodic Table

Mendeleev’s Periodic Table● Arranged by increasing atomic mass

○ Some elements did not follow the trend, why?

○ Their atomic numbers were in different orders than their atomic masses

○ Modern periodic tables are arranged by atomic number, why did Mendeleev arrange his by

atomic mass?

○ Rutherford discovered the nucleus in 1911, 40 years after Mendeleev first arranged the

elements

● Grouped by properties○ Fluorine, Chlorine, Bromine, and Iodine were all placed into the same group because they had

similar properties and bonded with other elements in the same ratios

Adding to Mendeleev● In 1894, the gas argon (Ar) was discovered by John William Strutt and Sir

William Ramsay● The next year, the gas helium (He) was proven to exist on earth● Sir Ramsay proposed a new group, the noble gases, be added to the periodic

table ● Krypton (Kr), xenon (Xe), and radon (Rn) were all added to the noble gases as

they were discovered

Modern Periodic Table● Arranged by increasing atomic number● A vertical column, known as a group contain elements with similar properties

● A horizontal row, known as a period, adds an energy level to the atom for each

row

Group 1 - The Alkali Metals● Have one valence electron● Soft and silvery in color● Metals which are good conductors of heat and electricity● Low densities, low boiling points, low melting points● React violently with water● https://www.youtube.com/watch?v=m55kgyApYrY

X

Group 2 - The Alkaline Earth Metals● Have two valence electrons● Are lustrous and silvery-white● Are somewhat reactive● React with water to form hydroxides which are basic

X

Groups 3-12 Transition Metals● Have various numbers of valence electrons● We indicate the charges of their ions with Roman numerals

○ Iron (IV) = Fe4+

○ Copper (II) = Cu2+

● Are less reactive than alkali metals

Group 17 or 7A - The Halogens● Have seven valence electrons● Very good at stealing an electron from other compounds which make them great

oxidizers● Known as halogens because they react with metals to create salts● At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine is a

solid

X

Group 18 or 8A - The Noble Gases● Have full valence energy levels● Are inert (unreactive) because they are so stable● Gases at room temperature

XHe

Metals, Metalloids, and NonmetalsMetalloids:

● Boron● Silicon● Germanium● Arsenic● Antimony● Tellurium● Polonium

Metals = Left Nonmetals = Right + Hydrogen

Diatomic ElementsSome elements form diatomic (two atoms) molecules in their elemental form.These include:

● Hydrogen● Nitrogen● Oxygen● Fluorine● Chlorine● Bromine● Iodine

Oxidation NumbersThe oxidation number is the charge that an ion of a group in the periodic table will usually have.

Write these on your white periodic table

Oxidation NumbersOxidation numbers are related to the number of valence electrons

Valence electrons are the number of electrons in the outermost energy level of an atom

The Roman numerals next to the As in the column heading tell how many valence electrons are in that group

PracticeWhich element is in group 2 and period 7 of the periodic table?

Which element is in group 3A and period 3 of the periodic table?

Which element is in group 18 and period 1 of the periodic table?

Practice

Which set of elements contains a metalloid?

A. K, Mn, As, Ar

B. Li, Mg, Ca, Kr

C. Ba, Ag, Sn, Xe

D. Fr, F, O, Rn

PracticeThe most reactive family of metals is the

A. Transition metalsB. Alkaline earth metalsC. Alkali metals

Which of the following is most likely to have similar properties to calcium?

A. PotassiumB. BariumC. Scandium

PracticeWhich of the following is most likely to have an ion with a charge of +3?

A. SodiumB. AluminumC. Silicon

Which of the following is most likely to have an ion with a charge of -2?

A. FluorineB. KryptonC. Oxygen

PracticeName a main group element with 6 valence electrons.

Name a main group element with 1 valence electron.

Name a main group element with 3 valence electrons.

Practice: Average Atomic Mass

Find the average atomic mass of chlorine given 35Cl is 75.77% abundant and 37Cl is 24.23% abundant.

Find the average atomic mass of iodine given 127I is 80% abundant, 126I is 17% abundant, and 128I is 3% abundant.