AQA AS Physical Chemistry - Atomic Structure PDF

AS CHEMISTRY 3.1.1 ATOMIC STRUCTURE EVOLUTION OF ATOMIC STRUCTURE The scientific model of the atom has been developed over the last 200 years. New discoveries have meant that scientists are better equipped to build more accurate models....

AS CHEMISTRY 3.1.1 ATOMIC STRUCTURE EVOLUTION OF ATOMIC STRUCTURE The scientific model of the atom has been developed over the last 200 years. New discoveries have meant that scientists are better equipped to build more accurate models. 1803 | The Solid Sphere John Dalton proposed that atoms are solid spheres and that the atoms in any given element were identical and could not be divided. 1904 | The Plum Pudding + - J.J. Thompson discovered - + - + electrons. This lead him to the - + idea that atoms are made up - + + of a ball of positive charge with negative electrons 1911 | The Nuclear Model embedded in it. Ernest Rutherford fired alpha radiation particles at gold foil and discovered that most of an atom was empty space, with the 1913 | The Planetary Model positive charge centred in a nucleus. x Niels Bohr then discovered that x electrons existed in orbits x around the nucleus at fixed distances. We know these as x x x x x x energy levels or “shells”. He x backed this up with theoretical calculations. 1932 | Subatomic Particles Ernest Rutherford’s experiments proved that the nucleus contained two types of subatomic particles. Protons that have a positive charge and neutrons that had no charge. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.1.1 ATOMIC STRUCTURE FUNDAMENTAL PARTICLES Atoms are very small, typically around 0.1 nanometers in size. That’s about 0.0000001 mm! It is made up of a central nucleus which contains protons and neutrons. Electrons orbit the nucleus. The radius of the nucleus is about 1/10,000th of that of the atom, so most of the atom is empty space! Almost all of the mass of an atom is in the nucleus. Electrons X Nucleus Protons X Neutrons X Relative Mass Charge Proton 1 +1 Neutron 1 0 Electron ≈ (very small) -1 HINTS | TIPS | HACKS Atoms always have the same number of electrons as they do protons. The charges cancel each other out! The number of neutrons in an atom of an element can vary and is not related to the number of protons or electrons. Atoms of the same element that have different numbers of neutrons are known as isotopes. Ions are atoms that have either gained or lost electrons. e.g. in theory, if an atom of “X” has 12 electrons.. Charge X3- X2- X- X X+ X2+ X3+ no. of 15 14 13 12 11 10 9 electrons AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.1.1 ATOMIC STRUCTURE How to Calculate Mass Number Particle Numbers = total number of protons + neutrons 7 3 Li Atomic Number = number of protons RELATIVE ATOMIC MASS (Ar) You will see that some mass numbers in the periodic table are not whole numbers. That is because this is actually their relative atomic mass, which is an average mass of the isotopes of that element. Isotopes: Atoms that have the same number of protons, but a different number of neutrons. Isotopes all have very similar physical properties as they all have the same bonding. Isotopes all have very similar chemical properties as they all have the same electronic configuration. The Relative Atomic Mass (Ar) of an element is the average mass of these different isotopes. It takes into account both their mass and their relative abundance (how common they are). Relative Atomic Mass (Ar) = ∑ (isotope mass x % abundance) 100 Most elements have a 3 or 4 different isotopes. To calculate relative atomic mass: Multiply the mass of each isotope by its abundance Add up these values Divide by 100 Check your answer. It should be between the lowest and highest isotope mass you used. It is an average after all! AQA www.chemistrycoach.co.uk © scidekick ltd 2024