The Periodic Table


The Development of the Periodic Table

- the periodic table of elements developed as chemists tried to classify the elements. It arranges them in order in which similar elements are grouped together

- the table is so named because of the regularly repeating patterns in the properties of elements

- Mendeleev's periodic table left gaps for the unknown elements, which when discovered matched his predictions, and so his table was accepted by the scientific community

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Electronic Structures and the Periodic Table

- the atomic (proton) number of an element determines its position in the periodic table

- the number of electrons in the outermost shell (highest energy level) of an atom determines its chemcial propperties

- the group number in the periodic table equals the number of electrons in the outermost shell

- the atoms of metals tend to lose electrons, whereas those of non-metals tend to gain electrons

- the noble gases in Group 0 are unreactive because of their very stable electron arrangements

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Group 1- Alkali Metals

- the elements in Group 1 of the periodic table are called the alkali metals

- their melting and boiling points decrease going down the group

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

- they form 1+ ions in reactions to make ionic compounds, these are generally white and dissolve in water, giving colourless solutions

- the reactivity of the alkali metals increases going down the group

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Explaining Trends

- can explain trends in reactivity as you go down a group in terms of the attraction between electrons in the outermost shell and nucleas, this electrostatic attraction depends on:

    the distance between the outermost electrons and the nucleas

    the number of occupied inner shells (energy levels) of electrons, which provide shielding effect

    the size of the positive charge on the nucleas (called the nucleas charge)

- deciding how easy it is for atoms to lose or gain electrons from their outermost shell, these factors are taken into account. The increased nuclear charge, due to extra protons in the nucleas, going down a gorup is outweighed by the other 2 factors

-therefore electrons are easier for the larger atoms to lose going down a group, and harder for them to gain going down a group

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Transition Elements

- compared with the alkali metals, transition elements have much higher melting points and densities. They are also stonger and harder but are much less reactive

- the transition elements do not react vigorously with oxygen or water

- a transition element can form ions with different charges, in compounds that are often coloured

- transition elements and their compounds are important industrial catalysts

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