does atomic radius increase down a group

The higher the attraction, the higher the electron affinity. The electron affinity is a measure of the attraction between the incoming electron and the nucleus. The tendency is for the electron affinities to decrease (in the sense that less heat is given out), but the fluorine value is out of line. Notice that the trend down the Group isn't tidy. If you choose to follow this link, use the BACK button on your browser to return quickly to this page. The current page duplicates much of that material, but you might like to read it again in different words. Note: You will find electron affinity covered in detail in another part of this site. The first electron affinities of the Group 7 elements

By convention, the negative sign shows a release of energy. For example, the first electron affinity of chlorine is -349 kJ mol -1. It is the energy released (per mole of X) when this change happens.įirst electron affinities have negative values. This is more easily seen in symbol terms. The first electron affinity is the energy released when 1 mole of gaseous atoms each acquire an electron to form 1 mole of gaseous 1- ions. In other words, as you go down the Group, the elements become less electronegative. The larger pull from the closer fluorine nucleus is why fluorine is more electronegative than chlorine is.Īs the halogen atoms get bigger, any bonding pair gets further and further away from the halogen nucleus, and so is less strongly attracted towards it. That means that it won't be as strongly attracted as in the fluorine case. (This is exactly the same sort of argument as you have seen in the atomic radius section above.) However, in the chlorine case, the nucleus is further away from that bonding pair. The bonding pair of electrons between the hydrogen and the halogen feels the same net pull of 7+ from both the fluorine and the chlorine. This is easily shown using simple dots-and-crosses diagrams for hydrogen fluoride and hydrogen chloride. The atoms become less good at attracting bonding pairs of electrons.Įxplaining the decrease in electronegativity

Notice that electronegativity falls as you go down the Group. Note: You will find electronegativity covered in detail in another part of this site. It is usually measured on the Pauling scale, on which the most electronegative element (fluorine) is given an electronegativity of 4.0. That means that the atoms are bound to get bigger as you go down the Group.Įlectronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. Obviously, the more layers of electrons you have, the more space they will take up - electrons repel each other. The only factor which is going to affect the size of the atom is therefore the number of layers of inner electrons which have to be fitted in around the atom. The outer electrons always feel a net pull of 7+ from the centre. This is equally true for all the other atoms in Group 7. The positive charge on the nucleus is cut down by the negativeness of the inner electrons. In each case, the outer electrons feel a net pull of 7+ from the nucleus. The pull the outer electrons feel from the nucleus. The number of layers of electrons around the nucleus You can see that the atomic radius increases as you go down the Group. Note: You will find atomic radius covered in detail in another part of this site. The same ideas tend to recur throughout the atomic properties, and you may find that earlier explanations help to you understand later ones. H-Cl)Įven if you aren't currently interested in all these things, it would probably pay you to read the whole page. There is also a section on the bond enthalpies (strengths) of halogen-halogen bonds (for example, Cl-Cl) and of hydrogen-halogen bonds (e.g. You will find separate sections below covering the trends in atomic radius, electronegativity, electron affinity, melting and boiling points, and solubility.

This page explores the trends in some atomic and physical properties of the Group 7 elements (the halogens) - fluorine, chlorine, bromine and iodine. Atomic and physical properties of Periodic Table Group 7 (the halogens)ĪTOMIC AND PHYSICAL PROPERTIES OF THE GROUP 7 ELEMENTS (THE HALOGENS)

Does atomic radius increase down a group