Developments of the Periodic Table

The Early Periodic Table

Key Points

1. The periodic table of elements classifies elements by arranging them according to their properties

2. Early versions of the periodic table failed to realise that not all elements had been discovered

3. Mendeleev's table took account of undiscovered elements, so provided a basis for the modern periodic table

Key Figures

1. Dalton - Arranged elements in order of their mass

2. Newlands - Arranged elements according to his law of octaves but this only worked until Calcium

3. Mendeleev - Arranged in order of atomic masses but left space for undiscovered elements

The Modern Periodic Table

Key points

1. The group that an element is in is determined by its atomic (proton) number

2. The number of electrons in the highest energy level of the atom determines its chemical properties

3. We can explain trends in reactivity as we go down a group in terms of the number of energy levels in the atoms

4. Elements in the same group have similar properties because their atoms have the same number of electrons in the highest occupied shell

5. Larger atoms (atoms with more energy levels between the outer shell and nucleus) :

- Lose electrons more easily

- Gain electrons less easily

The Alkali Metals

Group 1

Key Points

1. The elements in Group 1 of the Periodic table are called the alkali metals

2. The metals all react with water to produce hydrogen and an alkaline solution containing the metal hydroxide

3. The reactivity of the elements increases as we go down the group

4. They have low melting and boiling points (the further down the table the lower)

5. They are very reactive and have to be stored in oil

6. They always form ionic compounds with non-metals by losing their single outer electron and becoming metal ions with 1+ charges (Na+)

The Halogens

Group 7

Key Points

1. The Halogens exist as diatomic particles (ie- F2 = F-F)

2. The halogens all form ions with a single negative charge

3. The halogens form covalent compounds by sharing electrons with other non-metals (ie - HCl)

4. The reactivity of the halogens decreases going down the group

Key Properties

1. The halogens have low melting and boiling points

2. They are poor conductors of heat and electricity

3. All poisonous non-metals with coloured vapours

The Transition Elements

Key Points

1. Nearly all the transition elements have high melting points (except Mercury which is a liquid at room temperature) and high densities.

2. Thetransition metals are strong and hard, and are good conductors of heat and electricity

3. The transition metals do not react vigorously with oxygen and water

4. They have a typical metallic structure. The metal's atoms are held together by metallic bonds, and the outer electrons of each atom can move about freely within the metal

5. Many of the transition metals form coloured compounds (ie - Copper Sulphate is blue)