Periodicity: Ionisation Energy | A-level Chemistry | OCR, AQA, Edexcel

Periodicity: Ionisation Energy in a Snap! Unlock the full A-level Chemistry course at http://bit.ly/2jUm1En created by Ella Buluwela, Chemistry expert at SnapRevise. SnapRevise is the UK’s leading A-level and GCSE revision & exam preparation resource offering comprehensive video courses created by A* tutors. Our courses are designed around the OCR, AQA, SNAB, Edexcel B, WJEC, CIE and IAL exam boards, concisely covering all the important concepts required by each specification. In addition to all the content videos, our courses include hundreds of exam question videos, where we show you how to tackle questions and walk you through step by step how to score full marks. Sign up today and together, let’s make A-level Chemistry a walk in the park! The key points covered in this video include: 1. What is Ionisation Energy? 2. Factors Influencing Ionisation Energy 3. Trends in Ionisation Energy a. Across a Period b. Down a Group 4. Successive Ionisation Energies What is Ionisation Energy? It is a measure of the energy required to completely remove an electron from an atom of an element. To form an ion. First Ionisation Energy. The energy required to remove one electron from each atom in one mole of the gaseous element to form one mole of gaseous 1+ ions. Second Ionisation Energy. Factors Influencing Ionisation Energy The negative electrons are attracted to the tiny positive nucleus. This attraction keeps the electrons held in their shells. When an ion is formed, energy is supplied to remove an electron(s). The electrons in the outer shell are lost first. They experience the smallest amount of nuclear attraction, They require the smallest ionisation energy. Ionization energy is largely influenced by Atomic Radius. Atomic radius itself is largely influenced by 2 other factors: Nuclear Charge, Electron shielding. Factors Influencing Ionisation Energy: Atomic Radii Atomic radius is the distance from the centre of the atom to the edge of the electron cloud. The boundary of the electron cloud is not incredibly well defined, Instead, a value for the distance between 2 nuclei is found and halved. Atomic Radii show Periodicity. Across a Period the radius decreases, Down a group, the radius increases. Across a Period: The number of protons in the nucleus increases, As this increases, the effective nuclear charge also increases, The nucleus becomes more positive. Down a Group: The number of shells increases, Inner shells of electrons repel the outer-shell of electrons, Electrons are negative and will tend to repel each other. This is shielding. As we move across a period, elements increase in both the number of protons and electrons. As we move across a period, elements increase in both the number of protons and electrons. As more electrons are added to the shell, there is an increase in repulsion, This is offset by the increase in effective nuclear charge and resulting attractive forces. Factors Influencing Ionisation Energy: Atomic Radii The larger the atomic radius, the further away the outer electrons are held from the nucleus. The further away the outer electrons are held, the smaller the nuclear attraction for the outer electrons will be. Summary: Factors Influencing Ionisation Energy Atomic Radii: The larger the atomic radius, the further away the outer electrons are held from the nucleus. The further away the outer electrons are held, the smaller the nuclear attraction for the outer electrons will be. Nuclear Charge: The greater the nuclear charge, the greater the attractive force on the outer electrons. Shielding: Electrons are negative and will tend to repel each other. Inner shells of electrons repel the outer-shell of electrons. This is shielding. Trends in Ionisation Energy We see a trend on the Ionisation Energy of Elements. Shows Periodicity. Across a Period. General increase in first ionisation energy. Down a Group. There is a general decrease in the first ionisation energies down a group. Trends in Ionisation Energy: Across a Period Across a Period we observe an increase in the first ionisation energy. Period 2. This is because: The number of protons in the nucleus increases, The number of electrons in the outer shell increases. The outer shell is drawn inwards. Shielding does not change. There are the same number of shells. Trends in Ionisation Energy: Down A Group Down a group we observe a decrease in the first ionisation energy. Group 1. This is because: The number of shells increases. Atomic radius increases, Shielding increases. Although the number of protons does increase, this is outweighed by the increase in atomic radius and shielding.