Transcript Ch.2_000
Atoms & the Periodic Table Abundance of Elements Abundance of elements in the universe and in Earth’s crust (in atom percent) Elements in the body Elemental Composition of the Human Body Elements & Compounds • Element Symbols • English • Latin • German (H, O, N, C, Cl, Ne, Mg, etc.) (Na, Fe, Ag, Au, Hg, Pb, Sn, etc.) (W) • Compound Formulas (based on LDP) • SymbolsubscriptSymbolsubscript • Identity of elementnumber of atoms • H2O, CO2, NaCl, H2O2, Mg(OH)2 The known elements ← Elements (names & symbols) Periodic Table • Dmitri Mendeleev --> Chemist 1869 • Henry Moseley Physicist 1924 Modern PT The periodic table of the elements is a graphical way to show relationships among the elements. In this periodic table, elements 58 through 71 and 90 through 103 are shown in their proper sequential positions. John Dalton’s Atomic Theory 4 postulates: 1. All matter is made of atoms. Atoms are indivisible and indestructible. 2. All atoms of a given element are identical in mass and properties 3. Compounds are formed by a combination of two or more different kinds of atoms. 4. A chemical reaction is a rearrangement of atoms. A boy & his atom Each element is composed of a unique type of atom (Dalton’s Atomic Theory)! • So, what makes Oxygen’s atoms oxygen atoms!?? Subatomic Particles The protons (discovered in 1919 by E. Rutherford) and neutrons (discovered in 1932 by J. Chadwick) of an atom are found in the central nuclear region, or nucleus, and the electrons (discovered in1897 by JJ Thomson) are found in an electron cloud outside the nucleus. However, not all atoms of an element are identical (how does this notion fit with Dalton’s Atomic Theory?) Atomic Properties Element Atomic # Mass # # of p+ Sodium # of no 12 35 8 17 16 17 8 # of e- Symbol Isotopes • Isotopes are “forms” of an element that have varying #s of neutrons (n˚). • Ex. Boron (Z = 5) has two isotopes • Boron 10 (approximately 20 %) • Boron 11 (approximately 80%) • The atomic weight of an element is the average of the masses of all the isotopes of that element. Examples of Isotopes Atomic Weight • Weighted (by %) average of the mass of the naturally occurring isotopes of a particular element (reported in AMU). • Example: Element Mass (amu) Abundance • V-50 • V-51 49.95 50.94 0.250% 99.750% Metals vs. Nonmetals on PT Atomic Theories in History • • • • • Dalton’s Thomson’s Rutherford’s Bohr’s Quantum Mechanical (QM) • Heisenberg; Schrodinger; Planck; Einstein, etc. Electron Arrangement (the Quantum Mechanical Model of the Atom) • The chemistry/behavior of elements is largely determined by the number & arrangement of electrons in their atoms. • Electrons move about the nucleus (therefore have kinetic energy). • The amount of energy each electron has allows it to occupy a defined spatial region at a certain distance from the nucleus. • The further from the nucleus, the greater the number of electrons that can “share” the space. • What are the limitations of the space & number of electrons? (Hint: consider atomic forces) QM numbers • Principal (n) - defines the energy of the electron • Shell (1,2,3, etc.) = distance from nucleus • Azimuthal (l) - defines the shape of the region of space • Subshell (s,p,d,f) = periodic • Magnetic (ml) - defines the alignment in space of each particular shaped region • Orbital (x,y,z, etc.) • Spin (ms) - defines the direction of spin on an axis of each electron (one axis, therefore 2 spins possible) • Clockwise (+1/2) • Counterclockwise (-1/2) Subshells = Orbital Shape An s orbital has spherical shape; a p orbital has two lobes; a d orbital has four lobes; and an f orbital has eight lobes. Subshell arrangement The number of subshells within a shell is equal to the shell number. Orbitals = Alignments in Space Orbitals within a subshell differ mainly in orientation. Relationship of Quantum Numbers Electron Configuration The order of filling various electron subshells. Subshells of different shells “overlap.” This overlap is due to the relative energies required for electrons to move about in particularly shaped regions of space. Configuration Order The order of filling various electron subshells with electrons follows the same order given by the arrows in this diagram. Using the PT to help remember the Order Electron configuration and the positions of the elements in the periodic table. Writing Electron Configurations expressing what you know! • Each element has a unique arrangement of electrons. • However, this arrangement has a consistent pattern (use the PT to know the pattern). • Thus, you can describe the electron arrangement for any atom of any element. Examples • O • Br • Na • Zn • Ca • Pb • Fe • Cd Valence electrons • The electrons • Ex. Elements in periods 2 & 3 in the outermost shell = valence electrons! Electron Configuration Shortcut expressing the arrangement of valence electrons • Use the Noble Gas in the row immediately prior to the element to represent the “core” electrons • Sr • U • W • Xe Relationship between electron configuration and periodic properties of elements Classification scheme for the elements based on their electron configurations Periodic Trends of Properties • Atomic size: based on atomic radius • Group/column • Period/row • Ionization Energy: energy needed to remove an electron from a neutral atom • Group/column • Period/row Review • Atomic structure • • • • • Nucleus contains p+ & no (IDs the mass #) Electrons (e-) “surround” the nucleus Atoms have #p+ = #e- (atomic #) Nuclear Symbols ex. Hydrogen-1 vs. Hydrogen-2 Isotopes • Atoms of an element w/ varying # of no • Average atomic weight calculations • Electron configurations • QM model & configuration information • Periodicity & Periodic Table!