Chapter #1 - Atomic Structure Atomic Theories Democritus (460-340 BC) Democritus believed that all matter consisted of extremely small particles that could not be divided. He called them atoms from the Greek word atomos meaning "uncut". John Dalton (1766-1844) Dalton's model was that the atoms were tiny, indivisible, indestructible particles, and that each one had a certain mass, size, and chemical behavior that was determined by what kind of element they were. Dalton's Atom Model
Ch. 1 Atomic structure September 11, 2016 J.J Thomson (1856-1940) - atom is a ball of positive charge containing a number of electrons. Plum Pudding model Experiment: Cathode Ray Tube Cathode Ray Tubes were in nearly every home in the old TV and computer monitors. Ernest Rutherford (1871 1937) Gold Foil Experiment. Discovery of the nucleus 1908 Atoms an atom is the smallest unit of matter. Each kind of atom is called an element.
Atoms are mostly empty space most of an atom s mass is concentrated in a small positively charged region called the nucleus. Niels Bohr - proposed the Planetary Model for the hydrogen atom in 1913. Electrons move in definite orbits around the nucleus, like planets. He proposed that each electron moves in a specific energy level.
Electron Shells - Energy Levels Draw the Bohr energy levels diagrams for H, Li, and Na.
Ch. 1 Atomic structure September 11, 2016 An electron in an atom can move from one energy level to another when the atom gains or loses energy. Light Energy Atomic Line Spectrum
Atomic Line Spectrum Each type of atom (H 2, O 2 He, ) gives off a unique set of colors. The colored lines (or Spectral Lines) are a kind of "signature" " fingerprints" for the atoms. Schrodinger developed the Wave Model which suggests that electrons behave in a wave-like manner Electron Cloud the space around the nucleus of an atom which describes the possible location of where the electrons can be found. Schrodinger's view of the atom can be seen as "layers within layers" in terms of the electron shells. Each electron shell is made up of a number of subshells. The number of subshells in a shell is the same as the shell number. Schrodibger's cat BB These subshells can be further subdivided into orbitals, and each orbital is a distinct region of space that can contain a maximum of two electrons.
Heisenberg "Uncertainty Principle" The uncertainty principle states that the position and velocity cannot both be measured,exactly, at the same time The exact location of the electrons within an orbit could not be precisely calculated. The Cloud Model, Electrons do NOT move about the atom in a definite path and it is impossible to determine the exact location of an electron. Scientists can only predict the probable location of an electron. Bohr's idea of energy levels, however, is still used. Summary Models of the Atom
Energy Levels and Orbitals (shells) Building Model Energy Atomic Orbitals are mathematical descriptions of where the electrons are in an atom (or molecule) are most likely to be found. Each orbital can only hold 2 electrons. Each orbital has a name. The orbital occupied by the hydrogen electron is called a 1s orbital. The "1" represents the fact that the orbital is in the first energy level. The "s" tells you about the shape of the orbital. "s" orbitals are spherically symmetric around the nucleus Every energy level has an "S" orbital
At the first energy level, the only orbital available to electrons is the 1s orbital, but at the second level, as well as a 2s orbital, there are also orbitals called 2p orbitals. At any one energy level there are three absolutely equivalent p orbitals. These are given the symbols px, py and pz. p orbitals begin at the second energy level At the third level, there is a set of five d orbitals as well as the 3s and 3p orbitals (3px, 3py, 3pz). At the third level there are a total of nine orbitals altogether. At the fourth level, as well the 4s and 4p and 4d orbitals there are an additional seven f orbitals - 16 orbitals in all. Atomic Orbitals s, p, d and f orbitals are then available at all higher energy levels as well.
Electron Configurations The arrangement of electrons in the orbitals of an atom. Shorthand Electron Configuration To simplify the writing of lengthy electron configurations, the symbol of a noble gas may be substituted for the appropriately filled shells and orbitals.
Pauli Exclusion Principle An orbital can hold a maximum of 2 electrons. They must spin in opposite directions, they are said to be paired. The blue electrons are paired The red electrons are unpaired Hund s Rule electrons will not pair in an orbital until all orbital of equal energy contain one electrons.
Subatomic Particles Protons - are positively charged particles, have a mass of 1 amu, found in the nucleus. They determine which element an atom is. Neutrons - are neutral particles, have a mass of 1 amu, found in the nucleus. Electrons - are negatively charged particles, have a mass of 1 amu. They orbit the nucleus
Atomic Number is the number of protons in the nucleus of an atom. (also represent the number of electrons in the neutral atom) Mass Number = the number of protons + neutrons in the element s nucleus. Used to identify isotopes. Practice: Ion An atom with an overall positive or negative charge. Cation - When a neutral atom loses an electron(s), it has more positive protons than negative electrons. This results in an overall positive charge. Anion - When a neutral atom gains an electron(s), it has less positive protons than negative electrons. This results in an overall negative charge.
Isotopes are atoms of the same element whose nuclei contain the same number of protons but different number of neutrons. Isotopes of hydrogen One element may have several different isotopes. Various Isotopes: Stable Stable Unstable