The Development of the Periodic Table
- 1864- John Newland tried to put periodic table together. Only 63 elements were known. Many were still undiscovered.
- He arranged them in order of atomic weight.
- Noticed repeated patterns. Missing elements caused problems.
- Order of atomic weight created problems. Some elements were in the wrong place.
- Dmitri Mendeleev realised elements were still to be found.
- 1869-he created his table and left gaps for their discovery.
- Elements were placed in a vertical column (groups) that had similar properties.
- Mendeleev used his periodic table to predict the existance and properties of new elements.
- Later discovery revealed that Mendeleev had organised the elements in order of increasing atomic number (number of protons).
- Element in group 0 are known as Noble Gases.
- They have full outer shell of electrons.
- This means they have very stable electron configuration.
- They also are very unreactive non-metals.
- Boiling point increasesas you go down the group.
- Element in group 1 are known as Alkali Metals.
- One electron in their outermost shell
- Low melting point. Boiling point decreases as you go down the group
- More reactive as you go down the group
- Outer electron gets further away from the influence of the nucleus. Can get lost more easily.
- They are stored in oil-react very vigorously with oxygen and water, including moist in air.
- When reacted with water a metal hydroxide is formed and hydrogen gas is given off.
Potassium + water --> potassium oxide + hydrogen
- They have low density-lithium, sodium and potassium are less dense than water.
- When a metal oxide is dissolved in water, an alkaline solution is produced.
Continuation with Group 1
- Alkaline Metals react with non-metals to form ionic compounds.
- When this happens, metal atom loses one electron to form metal ion with positive charge (+1).
Sodium + chlorine --> sodium chloride
- They are non-metals. Known as Halogens. They have seven electron in their outermost shell.
- Consists of molecules made of pairs of atoms.
- Reactivity decreases down the group-outer shell gets further away from nucleus. Harder to gain an electron.
- As you go further down the group, the higher its relative molecular mass, melting point and boiling point is.
- Reacts with metals to produce ionic salts.
- When this happens, gains one electron to form a halide ion with negative charge.
Chlorine + potassium --> potassium chloride
The Transition Metals
- Centre of the periodic table - group 2 and 3.
- Form coloured compounds.
- Ions with different charges, e.g Fe^2 and Fe^3.
- Used as catalysts to speed chemical reactions.
- They are good conductors of heat and electricity.
- Be easily bent or hammered into shape.
Quick Test Questions
1) Name the Russian Chemist who designed the periodic table.
2) Why are Group 0 elements unreactive?
3) Why are the alkali metals stored in oil?
4) Give three properties of the transition metals.
Quick Test Answers
1) Dmitri Mendeleev
2) They have full outer shell of electrons
3) They react vigorously with oxygen and water
4) They have different charges,
Speed chemical reaction
Good conductors of heat and electricity