Periodic Trends

Ionic radii When an atom forms an ion electrons are either gained or lost. If electrons are gained the electron-electron repulsions increase while the number of protons stays the same and therefore the ionic radius will increase. Therefore negative ions will be larger than their atoms.

If electrons are lost then a whole electrons shell is lost and therefore the ionic radii will decrease. Therefore positive ions will be smaller than their atoms.

Explaining electronegativity As we go across the periodic table (left to right) electronegativity increases (ie atoms hold their electrons more tightly). This is because protons increase across the periodic table and the more protons there are, the higher the attraction for the electrons.

As we go down a group of the periodic table electronegativity decreases (ie atoms cannot hold onto their own valence as well). This is because: The outside electrons are being shielded from the pull of the protons by all the inner layer of electrons There are more layers of electrons so they are further away from the nucleus and again feel less pull from the protons

Explaining trends in electronegativity State the general trend. Compare the: Electron shells and / or Number of protons Therefore ___ has a higher electronegativity than ___.

Explain why Fluorine has a higher electronegativity than Oxygen As we go across the periodic table the electronegativity increases. F and O are in the same period which means the have the same number of electron shells so there is no shielding effect. As F has more protons than O, there will be a higher attraction of the nucleus for the electrons. This means the electronegativity of F is higher than that of O.

Explain why Fluorine has a higher electronegativity than Chlorine As we go down the periodic table the electronegativity decreases. F and Cl are in the same group of the periodic table but different periods which means that they have different numbers of electron shells. Because Cl has more electron shells than F, the valence electrons are being shielded from the pull of the protons in the nucleus by the inner layer of electrons.

Because Cl has these extra electron shells, the valence electrons are also further away from the nucleus and again feel less pull from the protons. Therefore F will have a higher electronegativity than Cl.

Ionisation energy This is “the minimum amount of energy required to remove an electron from one mole of an atom or ion in the gaseous state”. Learn this definition

Ionisation trend down a group As we go down the periodic table ionisation energy decreases. This is because the electron lost is further away from the nucleus, and there is more shielding from the nuclear attraction by the increased number of inner electrons.

Ionisation energy across a period As we go across the periodic table ionisation energy increases. This is because as atomic number increases there are more protons in the nucleus so there is a stronger attraction on electrons. It becomes more difficult to remove an electron from a non-metal than a metal in the same period (row).