Atomic Structure PDF

1.1 Nature of Chemistry and 1.2 Atomic Structure  Empirical knowledge: based on observable phenomena that is observed directly and is capable of being experimented on. Theoretical knowledge is created to explain observations based on ideas. It is an attempt to rationalize things we...

1.1 Nature of Chemistry and 1.2 Atomic Structure  Empirical knowledge: based on observable phenomena that is observed directly and is capable of being experimented on. Theoretical knowledge is created to explain observations based on ideas. It is an attempt to rationalize things we cannot see.  Theories are constantly being revised to make them fit the evidence that is being evaluated. Theories aim to describe, explain, and predict in the most concise manner possible.  IUPAC International Union Pure and Applied Chemistry – Established in 1919 – Role is to help regulate standards and procedures in chemistry Early Models of Matter  Democritus matter can be divided until you arrive at the smallest piece possible called it the atom atoms are in constant motion empty space between atoms The atomists held that there are two fundamentally different kinds of realities composing the natural world, atoms and void  Aristotle Thought Democritus’s idea of atomos was incorrect. Believed all matter was derived of four substance: earth, water, fire and air idea lasted for 2000 years  John Dalton “pool ball” model all matter is composed of tiny indivisible spheres called atoms all atoms of an element have the same properties atoms of different elements will have different properties atoms of two or more elements can combine in constant ratios to form new compounds atoms cannot be created, destroyed or subdivided in a chemical change  J. J Thomson “raisin bun” or “ plum pudding “ model first to come up with the idea that an atom consisted of positive and negative parts negatives were embedded in a positive sphere  Ernest Rutherford “nuclear” model gold foil experiment proved that the positive part of an atom was at the centre there was a lot of empty space in an atom that some electrons could be found amongst the empty space  Hantaro Nagaoka He proposed a “Saturnian or planetary model" of the atom (1904). The model was based on principles used to explain the stability of Saturn’s rings. – the rings are stable because the planet they orbit is very, very massive. Hantaro Nagaoka -Predictions – a very massive nucleus (analogous to a massive planet) – electrons revolve around the nucleus, bound by electrostatic forces (analogous to the rings revolving around Saturn, being bound by gravitational forces)  James Chadwick proved the existence of neutrons neutrons are heavy particles with no charge Neils Bohr (1885- 1962) Danish Physicist  Bohr’s Model Based on the element Hydrogen electrons orbit the nucleus at discrete energy levels these energy levels are at a fixed distance from the nucleus the electron travels along a three dimensional path called an orbit  these energy shells are designated by the principal quantum number n n=1,2,3 … electrons can transition between levels in order to jump it must receive that specific amount of energy that would put it to the next energy level  when an electron loses its gained energy, it falls back to its original orbit “ground state”  Assumptions an electron can travel indefinitely within an energy level without losing energy that the greater the distance between the nucleus of the atom and the energy level, the greater the energy required for an electron to travel in that energy level that an electron cannot exist between orbits, but can move to a higher unfilled orbit if it absorbs a specific quantity of energy and to a lower unfilled orbit if it loses energy  Experimental Evidence The basis for Bohr’s Theory came from observing line spectra line spectrum: a pattern of distinct lines, each of which corresponds to light of a single wavelength, produced when light consisting of only a few distinct wavelengths passes through a prism or spectroscope  How spectroscopy works!  This is the bright line spectrum for hydrogen  Symbo Particle Location Charge Mass l Orbiting the Electron Negative 9.11 × 10-31 kilograms e- nucleus Proton Nucleus Positive 1.67 × 10-27 kilograms p+ Neutron Nucleus Neutral 1.67 × 10-27 kilograms n0 Atomic Number and Mass Number  What is an atom's atomic number (Z)? number of protons in the nucleus each element has a unique number that identifies the number of protons Oxygen atoms contain 8 protons and has an atomic number of 8  What is an atom’s mass number (A)? derived from the number of protons and neutrons in an atom's nucleus. (N) = A- Z  The Mass of an Atom The mass of an atom is very small. Scientists compare the mass of an atom to that of a standard atom. As the mass of an atom is compared to that of another reference atom it is referred to as a relative atomic mass (Ar). The reference atom used to compare all other atomic masses is the stable and abundant isotope of carbon... carbon-12.  The C-12 atom is said to be 12 unified atomic mass units (u). Consequently, one atomic mass unit is equivalent to the mass of a nucleon (proton or neutron). Therefore, the atomic mass unit is defined as 1/12 the mass of a carbon-12 atom