F, Cl and Br are the elements each having seven valence electrons. Which of these (i) has the largest atomic radius, (ii) is most reactive? Justify your answer stating reason for each.
(i) The number of valence electrons determines the group of the element. F, Cl and Br have valence electrons 7 and belong to group 17. As we go down the group, new atomic shells are added. So, atomic size increases. Therefore, Br has the largest atomic radius as compared to Cl and F which has 3 and 2 shells respectively.
(ii) F is most reactive due to smaller size, high effective nuclear charge and high electro-negativity.
A star sometimes appears brighter and some other times fainter. What is this effect called? State the reason for this effect.
An element 'M' has atomic number 11.
(a) Write its electronic configuration.
(b) State the group to which 'M' belongs.
(c) Is 'M' a metal or a non-metal.
(d) Write the formula of its chloride.
When we place a glass prism in the path of a narrow beam of white light a spectrum is obtained. What happens when a second identical prism is placed in an inverted position with respect to the first prism? Draw a labelled ray diagram to illustrate it.
Define homologous series of organic compounds. List its two characteristics. Write the name and formula of the first member of the series of alkenes.
