F321 - Topic 1 Atoms and Electron Structure 0.0 / 5 ? ChemistryAtoms, Bonds and GroupsASOCR Created by: SophieCreated on: 26-01-14 14:18 Atomic Structure Atomic Structure The nucleus contains almost all of the mass of an atom, as it cotains protons and neutrons. The nucleus of an atom contains all of the positive charge. The electrons orbit outside the nucleus. Electrons are negatively charged. Definitions Atomic number = number of protons in the nucleus. Mass number = number of protons and neutrons in the nucleus. Number of neutrons = mass number - atomic number. Number of electrons = number of protons (in a neutral atom) 1 of 10 Isotopes and Ions Isotopes Isotopes are atoms with the same number of protons but different number of neutrons. Isotopes of an element have the same chemical properties, as they have the same electron arangement. Ions Ions are formed when atoms gain or lose elctrons. E.g. An atom Cl has 17 electrons, a Cl- ion has gained one electron. 2 of 10 Relative Atomic Mass and Relative Isotopic Mass Relative Atomic Mass Average mass of an atom relative to 1/12 of the mass of a carbon-12 atom. To calculate relative atomic mass, add together (mass number x percentage/100). Example 75% of Cl atoms have a mass number of 35 25% of Cl atoms have a mass number of 37 Average mass of a Cl atom = (mass no x percent/100) + (mass no x percent/100) = (35 x 75/100) + (37 x 25/100) = 35.5 Relative Isotopic Mass Mass of a particular isotope relative to 1/12 of the mass of a carbon-12 atom. 3 of 10 Orbitals Orbitals An orbital is a region that can hold up to two electrons with opposite spins. Orbitals have different shapes called - s, p, d and f. S orbitals S orbitals are spherical in shape and come in sets of one. P orbitals P orbitals are hour - glass shaped and come in stes of three. D orbitals D orbitals come in sets of five which can hold up to 10 electrons. 4 of 10 Energy Levels E.g. Iron - 26 electrons - 1s2 2s2 2p6 3s2 3p6 4s2 3d6 5 of 10 Successive Ionisation Energies Successive Ionisation Energies Energy change when one mole of electrons is removed from one mole of gaseous positively charged ions. In an element, successive ionisation energies get bigger because the emaining electrons are held more tightly by the unchanged nuclear charge. First Ionisation Energy Energy change when one mole of electrons is removed from one mole of gaseous atoms. M(g) -----> M+(g) + e- Ionisation is easier if : The nuclear charge is smaller. The electron is further away from the nucleus. There is more shielding. 6 of 10 First Ionisation Energies - First 20 Elements First ionisation energy shows periodicity. Factors affecting the size of ionisation energy The size of that attraction will be governed by: The charge on the nucleus. The distance of the electron from the nucleus. The number of electrons between the outer electrons and the nucleus (shielding). Whether the electron is on its own in an orbital ( paired electrons are easier to remove). 7 of 10 The Pattern in Periods 2 and 3 Why the ionisation energy increases: There is an increasing number of protons in the nuceus. The increasing nuclear charge, drags the outer electrons in closer to the nucleus. 8 of 10 Trends in ionisation energy down a group Why: There is a bigger number of protons. But, the shielding and nuclear radius overcomes the nuclear charge. E.g. Li -1s22s11st I.E. = 519 kJ mol-1 Na -1s22s22p63s11st I.E. = 494 kJ mol-1 9 of 10 Blocks in the Periodic Table Blocks The s block is group 1 and 2. The p block is group 3 and 8. The d block is between the s and p blocks. 10 of 10
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