Modern Atomic Theory

Electromagnetic Radiation Electromagnetic radiation – forms of radiant energy (light in all its varied forms) Electromagnetic spectrum – a continuous range of wavelengths and frequencies of all forms of electromagnetic radiation

11.2 Electromagnetic Radiation Radiation energy – has wavelike properties Frequency (υ, Greek nu) – the number of peaks (maxima) that pass by a fixed point per unit time (s-1 or Hz) Wavelength (λ, Greek lambda) – the length from one wave maximum to the next Amplitude – the height measured from the middle point between peak and trough (maximum and minimum) Intensity of radiant energy is proportional to amplitude

Electromagnetic Radiation

11.3 Emission of Energy by Atom How does atom emit light? Atoms absorbs energy Atoms become excited Release energy Higher-energy photon –>shorter wavelength Lower-energy photon -> longer wavelength

11.4 The Energy Levels of Hydrogen Excited state: atom with excess energy Releasing energy by emitting a photon Different wavelengths of light carry different amounts of energy Energy contained in the photon corresponds to the change in energy that the atom experiences Ground state: the lower energy level of an atom The level of energy of hydrogen and all other atoms are quantized

The energy level

11.5 The Bohr Model of the Atom the Bohr model created by Niels Bohr depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity Describe the behavior of electrons in an atom

11.6 The Wave Mechanical Model of the Atom Schröndinger’s quantum mechanical model of atomic structure is frame in the form of a wave equation; describe the motion of ordinary waves in fluids. i. Wave functions or orbitals (Greek, psi , the mathematical tool that quantum mechanic uses to describe any physical system ii.  2 gives the probability of finding an electron within a given region in space iii. Contains information about an electron’s position in 3- D space defines a volume of space around the nucleus where there is a high probability of finding an electron say nothing about the electron’s path or movement

11.7 The Orbitals Orbital: the probability map for hydrogen electrons The principal quantum number (n): Shell a. describes the size and energy level of the orbital a. positive integer (n = 1, 2, 3 …..) as the value of n increases the number of allowed orbital increases size of the orbital increases the energy of the electron in the orbital increases

The Orbitals As the value of n increases, the number of allowed orbitals increases and the size of the orbitals become larger, thus allowing an electron to be far from the nucleus, because it takes energy to separate a negative charge from a positive charge E.gn = 3  third shell (period #3) n = 5  fifth shell (period # 5) n = 2  2 nd shell (period 2)

The Orbitals Orbitals are grouping in group according to the angular-momentum quantum number l is called subshells. Types of orbitals Notations: s, p, d, f

The shape of the orbitals S orbital P orbital

Summary Subslevels (type of orbitals) Present 1s (1) 2s (1) 2p (3) 3s (1) 3p (3) 3d (5) 4s (1) 4p (3) 4d (5) 4f (7)

11.8 The Wave Mechanical Model Pauli exclusion principle: an atomic orbital can hold a maximum of two electrons, and those two electrons must have opposite spins unoccupied orbital orbital with 1 electron orbital with 2 electrons

Electron Arrangements in the First Eighteen Atoms on the Periodic Table Recall: Atomic number (Z) = # electrons = # protons Electron configuration: describes the orbitals that are occupied by the electrons in an atom Orbital diagrams: describe the orbitals with arrows representing electrons a. Arrows are written up or down to denote electron’s spin He = 1 s 2 Z = 2

Example Write the full electron configuration and orbital filling diagram for: O, Na, Si, Ar, Cr

Electrons Configuration Shorthand version – give the symbol of the noble gas in the previous row to indicate electrons in filled shells, and then specify only those electrons in unfilled shells E.g Shorthand version of P: [Ne] 3s 2 3p 3 The valence-shell electrons are the outer most shell of electron E.gValence electrons of P is 5

11.10 Electron Configurations and the Periodic Table Write the full electron configuration short hand notation Determine the valence electrons F, Mg, As

11.11 Atomic Size A.Periodicity is the presence of regularly repeating pattern found in nature B.Atomic radius is distance between the nuclei of two atoms bonded together C.Atomic radius increases down a group, decreases across a period i. Larger n, larger size of orbital

Examples In each of the following sets of elements, indicate which element has the smallest atomic size Ba, Ca, Ra P, Si, Al

11.11 Ionization Energies Ionization energy (Ei) – the amount of energy required to remove the outermost electron from an isolated neutral atom in the gaseous state Which has higher ionization energy (Ei)? K or Br S or Te