2. HISTORY
• Developed by Dmitri Mendeleev, Russian Scientist in 1869
• 63 elements
• Arranged by increasing atomic weight and properties.
• Today’s table has been modified based on the work of Rutherford and
Moseley.
• Arranged by atomic #, 115 elements
3. GROUPS – VERTICAL COLUMNS
• 1 – alkali metals
• 2 - alkaline earth metals
• 7 - halogens
• 0 – inert gases or noble gases
• Trends
• All elements in a group have the same number of valence electrons
• (exception noble gases have either 2 or 8)
• Valence electrons are mostly responsible for chemical properties of an element.
4. PERIODS – HORIZONTAL ROWS
• Numbered 1-7
• Transition metals are between groups 2 and 3
• Metals (<3/4) and nonmetals (<1/4)
• Metalloids – act like both metals and nonmetals
• Trends across a period
• From metal to nonmetal
• Increase in number of electrons in the outer energy shell
• Giant metallic through giant covalent to simple molecular
5. GROUP 1 – ALKALI METALS
• Lithium, sodium, potassium, rubidium, caesium and radioactive francium.
• Very reactive metals – stored in oil to prevent contact with air or water.
• Good conductors of electricity and heat
• Soft metals (lithium is hardest, potassium is softest)
• Low densities
• Shiny surfaces when freshly cut with knife
• Low m.p.
• Tend to lose one electron to form a stable outer energy level and a +1 charge
• More reactive as you go down the group because it takes more energy to remove an electron
closer to the nucleus.
• Burn in oxygen to form solid oxides
• Dissolve in water to form alkaline (basic) solutions of metal hydroxide.
• React vigorously with water to for alkaline solution and hydrogen gas.
• React vigorously with halogens to form metal halides.
