Chemistry: The Period Table

Chapter 3

Define groups

are elements with similar properties (vertical columns on the periodic table).

Define periods

are elements with principle energy levels (horizontal rows)

Triads

is a group of three elements with similar chemical properties, arranged in order of increasing atomic mass, where the atomic mass of the middle element is approximately equal to the average of the other two.

Law of Octaves

states that when elements are arranged in order of increasing atomic mass, the chemical properties repeat every eighth element.

Mendeleeve’s Periodic Law

states that when elements are arranged in order of increasing atomic weight, there’s a periodic occurrence of elements with similar properties.

What did Mosely discover?

Mosely arranged elements in order of increasing atomic number

Atomic number

of an atom is the number of protons in the nucleus of the atom

Modern Periodic Table

when elements are arranged in order of increasing atomic number, the properties of the element recur periodically.

State the properties of the Alkali Mentals?

• Reactivity increases going down the group from Lithium to Francium

• They are soft mentals, shiny when cut and have low densities

• Rapidly react with oxygen in the air to form metal oxides

2Na + ½ O₂ = Na₂ O

• Vigorous reaction with water to form metal hydroxide and hydrogen gas:

Na + H₂O = Na OH + ½ H₂

State the properties of the Alkaline Earth Mentals

• Reactivity increases going down the group

• Physically harder mentals than the alkali mentals

• React with water to form metal hydroxides and hydrogen gas:

Mg + H₂O = MgOH + ½ H₂

• Each alkaline earth mental is less reactive than its corresponding alkali metal.

State the properties of Halogens

• Very reactive non-metals

• Reactivity decreases going down the group

• Low melting and boiling points

• React easily with alkali metals to form salts:

2Na + Cl₂ = 2NaCl

• React with hydrogen to form compounds that dissolve in water to give acidic solutions:

H₂ + Cl₂ = 2HCl

• React with hydrogen to form compounds that dissolve in the water to give acidic solutions:

H₂ + Cl₂ = 2HCl

State the properties of the Nobel Gases?

• Very unreactive

• All gases at room temperature

• Boiling point and density increase going down the group