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7 Trends
Trends and Patterns in the Periodic Table
Question | Answer |
---|---|
Atomic Radius | Atomic radius is defined as half the distance between the nuclei of atoms of the same element that are joined by a single covalent bond. |
Trends in Atomic Radius going down a group. 2 reasons | Atomic radius INCREASES. 1: A new shell is being added as we move down the table. 2: The screening effect of the extra electrons cancels out the pull of the growing nucleus/ decrease in effective nuclear charge |
Trends in Atomic Radius going left to right across a period. 2 reasons | Atomic radius DECREASES 1: Increasing nuclear charge due to an extra proton being added 2: There is no increase in screening effect as no new shell is being added/ Increase in effective nuclear charge |
Electronegativity | Is the measure of the relative attraction an atom has for the shared pair of electrons in a single covalent bond. Will predict how atoms combine chemically. Linus Pauling developed the electronegativity scale. |
Trends in Electronegativity going down a group. 2 reasons | Electronegativity DECREASES as we go down a group 1: Increasing atomic radius means the electrons are further away from the attractive force of the nucleus. 2: The screening effect of the inner negative electrons block the pull of the positive nucleus. |
Trends in Electronegativity going left to right across a period. 2 reasons | Electronegativity INCREASES going across a period. 1: Increasing nuclear charge means the nucleus has a stronger hold on the electrons. 2: Decreasing atomic radius: as no new shell is being added the stronger nucleus can hold the outer electrons tighter |
Ionization Energy | The first ionization energy of an atom is the minimum energy required to completely remove the most loosely bound electron from a neutral atom in a gaseous state. Noble Gases have the highest Ionization Energy, as they have full outer energy levels. |
Trends in Ionization energy going down a group: 2 reasons | Ionization Energy DECREASES going down a group. 1: As atomic radius increases the electrons are further away from the nucleus. 2: The screening effect of the inner electrons cancels out the pull of the nucleus. Decreasing effective nuclear charge |
Trends in Ionization energy going left to right across a period: 2 reasons | Ionization Energy INCREASE going across a period 1: Increasing nuclear charge means the nucleus has a better hold on the outer electrons. Increasing effective Nuclear Charge 2: Decreasing atomic radius means that the outermost shell is closer to the nucleus and is therefore held tighter. |
Reactivity of the Alkali Metals | Increases as we go down the group. All the elements have only 1 electron in their outer shell. Losing this electron gives them a full outer shell. This means they have a low ionisation energy and electronegativity. |
Properties of Alkali Metals | 1: Easier to cut as we move down the group. 2: Display more vigorous reaction with water as we move down the group. 3: Tarnish with air faster as we move down the group. 4. Extremely reactive. |
Reactivity of the Halogens | Reactivity increases moving up the group. 1: Decreasing atomic radius brings the outer shell closer to the nucleus. 2: Electronegativity increases as we move up the group. 3: All the halogens require only 1 electron to achieve noble gas structure. |
Effective Nuclear Charge | Is obtained by subtracting the effect of the screening electrons from the effect of the positive charge of the nucleus. |
Exceptions to general trend in Ionisation Energy across a period | Any orbital that is full or half-full has extra stability, so requires more energy to form a ion. |
Evidence for the existence of energy levels | There is a large jump in ionisation energy whenever an electron is removed from a new energy level & a slight increase when being removed from a new sublevel as full and half-filled sublevels have extra stability |
Ionisation energy increases as you remove more electrons | For each electron that is removed the size of the positive charge of the ion that is left behind increases by one. So there is greater attraction between the positive nucleus & the remaining electrons. |
Halogens - Displacement reactions | The more reactive Halogen displaces the less reactive Halogen from a solution of it's ions. |