The electron pair will be pulled toward the chlorine atom because the chlorine nucleus contains many more protons than the sodium nucleus. The bond can be considered covalent, composed of a pair of shared electrons. Picture a bond between a sodium atom and a chlorine atom. Each of these elements has a very low electronegativity when compared with fluorine, and the electronegativities decrease from lithium to cesium. It is usually measured on the Pauling scale, on which the most electronegative element (fluorine) is given an electronegativity of 4.0 ( Table A2).Ī graph showing the electronegativities of the Group 1 elements is shown above. However, the distance between the nucleus and the outer electrons increases down the group electrons become easier to remove, and the ionization energy falls.Įlectronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. As mentioned before, in each of the elements Group 1, the outermost electrons experience a net charge of +1 from the center. the distance between the outer electrons and the nucleus.ĭown the group, the increase in nuclear charge is exactly offset by the increase in the number of inner electrons.the amount of screening by the inner electrons,.Ionization energy is governed by three factors: Notice that first ionization energy decreases down the group. \Ī graph showing the first ionization energies of the Group 1 atoms is shown above. The first ionization energy of an atom is defined as the energy required to remove the most loosely held electron from each of one mole of gaseous atoms, producing one mole of singly charged gaseous ions in other words, it is the energy required for 1 mole of this process: Therefore, the atoms increase in size down the group. More layers of electrons take up more space, due to electron-electron repulsion. The only factor affecting the size of the atom is the number of layers of inner electrons which surround the atom. This is true for each of the other atoms in Group 1. This effect is illustrated in the figure below: The positive charge on the nucleus is canceled out by the negative charges of the inner electrons. In each element, the outer electron experiences a net charge of +1 from the nucleus. The attraction the outer electrons feel from the nucleusĬompare the electronic configurations of lithium and sodium:.The number of layers of electrons around the nucleus. ![]() The radius of an atom is governed by two factors: The chart below shows the increase in atomic radius down the group. Rubidium and caesium are denser than water.\) Lithium, sodium and potassium are less dense than water and therefore can float on water. Similarly, on the application of heat the free moving electrons in the outermost shells gain a lot of energy and transfer this through the metal via collisions with the other free moving electrons. On the application of an electric field the large numbers of free flowing electrons in the outer shells conduct electricity through the metal. The outer electron can drift further from the nucleus and move relatively freely. ![]() ![]() It is the reduced interatomic forces in these elements that make them relatively soft.Īlkali metals are extremely good conductors of electricity and heatĪlkali metals have one electron in their outermost shell which is held very weakly by the nucleus. Freshly cut alkali metals are shiny but tarnish rapidly due to reaction with oxygen in the air. Alkali Metals are softĪlkali metals are soft metals that can be cut with a knife and silvery coloured. The increasing atomic radius means weaker forces between the atoms and so a lower melting and boiling point. The decrease in melting and boiling points down the group can be explained by the additional shell being added to the previous element causing the atomic radius to increase. It is these weaker attractive forces due to the large atomic radii between neighbouring atoms of Group 1 elements that result in lower melting and boiling points when compared to other metals. The large atomic size results in weaker forces between neighbouring atoms. This results in Group 1 elements having larger atomic radii than those elements that follow them in their respective periods. This electron can drift further from the nucleus than in most atoms of other elements. ElementĪlkali Metals have lower melting and boiling PointsĪll Group 1 elements have one electron in their outermost shell which is held very weakly by the nucleus. ![]() The table below summarises the physical properties of the Group 1 elements.
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