The periodic table of elements developed as chemists tried to classify the elements. It arranges them in a pattern in which similar elements are grouped together.
Newlands' table put the elements in order of atomic mass but failed to take account of elements that were unknown at the time.
Mendeleev's periodic table left gaps for the unknown elements, and so provided the basis for the modern periodic table.
1 of 5
The Modern Periodic Table
The atomic (proton) number of an element determines its position on the periodic table.
The number of electrons in the outmost shell (highest energy level) of an atom determines its chemical properties.
The group number in the periodic table equals the number of electrons in the outmost shell
We can explain trends in reactivity as we go down a group in terms of:
the distance between the outmost electrons and the nucleus
the number of occupied inner shells (energy levels) in the atoms.
2 of 5
Group 1 -The Alkali Metals
The elements in Group 1 of the periodic table are called the alkali metals.
Their melting points 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 disolve in water, giving colourless solutions.
The reactivity of the alkali metals increases going down the group.
3 of 5
The transition elements
Compared with the alkali metals, transition elements have much higher melting points and densities. They are also stronger 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
4 of 5
Group 7- The Halogens
The halogens all form ions with a single negative charge in their ionoic compounds with metals
The halogens form covalent compounds by sharing electrons with other non- metals
A more reactive halogen can displace a less reactive halogen from a solution of one of its salts
The reactivity of the halogens decreases going down the group because it is harder for them to gain an electron as they are further away from the nucleus.
Comments
No comments have yet been made