Topic 1b - The Periodic Table

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Dmitri Mendeleev in 1969 was the first to sort the periodic table because of their relative atomic mass and their physical and chemical properties, rather than their relative atomic mass or physical and chemical properties. He was correct to take notice of their properties, because of isotopes (which were discovered in the early 20th century). Isotopes have different atomic masses but the same chemical properties, so occupy the same position on the periodic table. He left gaps for undiscovered elements he predicted would fit in.

The periodic table: The table is laid out in order of increasing atomic number so that elements with similar properties form columns called groups, and rows are called periods. Relative atomic mass is used. Group number represents the amount of electrons in the outer shell, except group 0, which is always full. Reactivity increases going down the groups.

Metals and non-metals: Metals: Elements that can form positive ions when they react. Most found further down the periodic table and on the left-hand side. The elements in the centre of the periodic table are known as the transition metals. The majority of the periodic table. Strong, malleable, great conductors of heat and electricity, generally have high bps and mps, so tend to be solids at room temp.

Non-metals: Elements which don't form positive ions when they react, either form negative ions in ionic compounds or bond covalently with other non-metals. Right-hand side only. Tend to be more dull looking and more brittle, lower bps and mps, so aren't always solids at room temp, don't generally conduct electricity, often have a lower density than metals. Wide variety of different structures so have a large range of chemical properties.

Positive ions: Cations. Negative ions: Anions.

Hydrogen is the exception as it is a non-metal that forms positive ions.

Group 1 - The alkali metals: lithium, sodium, potassium, rubidium, caesium and francium. Silvery solids. Have to be stored in oil and handled with forceps. One electron in their outer shell. Low density, first three in group less dense than water. Reactivity increases down the group. Lose the 1 electron in the outer shell, but further down the group, the electron is further away from the nucleus, so has a weaker attraction and is easier lost. Mps and bps decrease further down the group. Relative atomic mass increases down the group.