/*
 *                    BioJava development code
 *
 * This code may be freely distributed and modified under the
 * terms of the GNU Lesser General Public Licence.  This should
 * be distributed with the code.  If you do not have a copy,
 * see:
 *
 *      http://www.gnu.org/copyleft/lesser.html
 *
 * Copyright for this code is held jointly by the individual
 * authors.  These should be listed in @author doc comments.
 *
 * For more information on the BioJava project and its aims,
 * or to join the biojava-l mailing list, visit the home page
 * at:
 *
 *      http://www.biojava.org/
 *
 * Created on 29.04.2010
 *
 */
package org.biojava.bio.structure;

import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;

/**
 * Element is an enumeration of the elements of the periodic table. In addition,
 * several attributes of each element are accessible.
 * <B>Note:</B> Deuterium and Tritium are treated as separate elements D and T,
 * respectively. Sometimes part of a molecule is represented as an R-group, which
 * is represented as the element R.
 * 
 *  
 * @author Peter Rose
 * @version %I% %G%
 * @since 3.0
 * 
 */

public enum Element implements Serializable {

	// most frequently used elements first
    H(1, 1, 39, 1.10f, 0.32f, 1, 1, 1, 1, 1, 1.008f, 0, 1, new int[] {1}, 2.20f, ElementType.OTHER_NONMETAL),
    C(6, 2, 0, 1.55f, 0.77f, 4, 4, 4, 4, 4, 12.011f, 2, -4, new int[] {-4,-3,-2,0,-1,1,2,3,4}, 2.55f, ElementType.OTHER_NONMETAL),
    N(7, 2, 57, 1.40f, 0.75f, 5, 2, 5, 3, 4, 14.007f, 2, -3, new int[] {-3,-2,-1,0,1,2,3,4,5}, 3.04f, ElementType.OTHER_NONMETAL),
    O(8, 2, 65, 1.35f, 0.73f, 6, 1, 2, 2, 2, 16.000f, 2, -2, new int[] {-2,-1,0,1,2}, 3.44f, ElementType.OTHER_NONMETAL),
    /**
     * Deuterium
     */
    D(1, 1, 27, 1.10f, 0.32f, 1, 1, 1, 1, 1, 1.008f, 0, 1, new int[] {0,1}, 2.20f, ElementType.OTHER_NONMETAL), // need to edit properties!
    /**
     * Tritium
     */
    T(1, 1, 90, 1.10f, 0.32f, 1, 1, 1, 1, 1, 1.008f, 0, 1, new int[] {0,1}, 2.20f, ElementType.OTHER_NONMETAL), // need to edit properties!
    He(2, 1, 40, 2.20f, 1.60f, 2, 0, 12, 0, 0, 4.003f, 2, 0, new int[] {0}, 0.0f, ElementType.NOBLE_GAS), // electroneg not reported
    Li(3, 2, 50, 1.22f, 1.34f, 1, 0, 12, 0, 1, 6.940f, 2, 1, new int[] {0,1}, 0.98f, ElementType.ALKALI_METAL),
    Be(4, 2, 12, 0.63f, 0.90f, 2, 0, 12, 2, 2, 9.012f, 2, 2, new int[] {0,1,2}, 1.57f, ElementType.TRANSITION_METAL),
    B(5, 2, 10, 1.55f, 0.82f, 3, 3, 5, 3, 4, 10.810f, 2, 3, new int[] {0,1,2,3}, 2.04f, ElementType.METALLOID),
    F(9, 2, 32, 1.30f, 0.72f, 7, 0, 1, 1, 1, 18.998f, 2, -1, new int[] {-1,0,1}, 3.98f, ElementType.HALOGEN),
    Ne(10, 2, 61, 2.02f, 1.12f, 8, 0, 12, 0, 0, 20.170f, 10, 0, new int[] {}, 0.00f, ElementType.NOBLE_GAS), // electroneg not reported
    Na(11, 3, 58, 2.20f, 1.54f, 1, 0, 1, 0, 0, 22.990f, 10, 1, new int[] {-1,0,1}, 0.93f, ElementType.ALKALI_METAL),
    Mg(12, 3, 54, 1.50f, 1.30f, 2, 0, 2, 0, 2, 24.305f, 10, 2, new int[] {0,1,2}, 1.31f, ElementType.ALKALINE_EARTH_METAL),
    Al(13, 3, 4, 1.50f, 1.18f, 3, 0, 5, 0, 4, 26.982f, 10, 3, new int[] {0,1,2,3}, 1.61f, ElementType.POST_TRANSITION_METAL),
    Si(14, 3, 86, 2.20f, 1.11f, 4, 4, 4, 4, 4, 28.086f, 10, 4, new int[] {-4,-3,-2,-1,0,1,2,3,4}, 1.90f, ElementType.METALLOID),
    P(15, 3, 67, 1.88f, 1.06f, 5, 3, 5, 3, 5, 30.974f, 10, 5, new int[] {-3,-2,-1,0,1,2,3,4,5}, 2.19f, ElementType.OTHER_NONMETAL),
    S(16, 3, 82, 1.81f, 1.02f, 6, 2, 6, 2, 6, 32.060f, 10, -2, new int[] {-2,-1,0,1,2,3,4,5,6}, 2.58f, ElementType.OTHER_NONMETAL), 
    Cl(17, 3, 21, 1.75f, 0.99f, 7, 0, 1, 1, 1, 35.453f, 10, -1, new int[] {-1,0,1,2,3,4,5,6,7}, 3.16f, ElementType.HALOGEN),
    Ar(18, 4, 6, 2.77f, 1.54f, 8, 0, 12, 0, 0, 39.948f, 18, 0, new int[] {0}, 0.00f, ElementType.NOBLE_GAS), // electroneg not reported
    K(19, 4, 47, 2.39f, 1.96f, 1, 0, 12, 0, 0, 39.102f, 18, 1, new int[] {-1,0,1}, 0.82f, ElementType.ALKALI_METAL),
    Ca(20, 4, 17, 1.95f, 1.74f, 2, 0, 2, 0, 0, 40.080f, 18, 2, new int[] {0,1,2}, 1.00f, ElementType.ALKALINE_EARTH_METAL),
    Sc(21, 4, 84, 1.32f, 1.44f, 3, 0, 12, 3, 0, 44.956f, 18, 3, new int[] {0,1,2,3}, 1.36f, ElementType.TRANSITION_METAL),
    Ti(22, 4, 96, 1.95f, 1.36f, 4, 2, 4, 3, 4, 47.880f, 18, 4, new int[] {-1,0,1,2,3,4}, 1.54f, ElementType.TRANSITION_METAL),
    V(23, 4, 100, 1.06f, 1.25f, 5, 0, 12, 3, 0, 50.040f, 18, 5, new int[] {-1,0,1,2,3,4,5}, 1.63f, ElementType.TRANSITION_METAL),
    Cr(24, 4, 24, 1.13f, 1.27f, 6, 0, 12, 2, 0, 51.996f, 18, 3, new int[] {-2,-1,0,1,2,3,4,5,6}, 1.66f, ElementType.TRANSITION_METAL),
    Mn(25, 4, 55, 1.19f, 1.39f, 7, 0, 12, 0, 0, 54.938f, 18, 2, new int[] {-3,-2,-1,0,1,2,3,4,5,6,7}, 1.55f, ElementType.TRANSITION_METAL),
    Fe(26, 4, 33, 1.95f, 1.25f, 3, 0, 8, 0, 0, 55.847f, 18, 3, new int[] {-2,-1,0,1,2,3,4,5,6}, 1.83f, ElementType.TRANSITION_METAL),
    Co(27, 4, 23, 1.13f, 1.26f, 3, 0, 12, 0, 0, 58.933f, 18, 2, new int[] {-1,0,1,2,3,4,5}, 1.88f, ElementType.TRANSITION_METAL),
    Ni(28, 4, 62, 1.24f, 1.21f, 3, 0, 12, 0, 0, 58.710f, 18, 2, new int[] {-1,0,1,2,3,4}, 1.91f, ElementType.TRANSITION_METAL),
    Cu(29, 4, 26, 1.15f, 1.38f, 2, 0, 4, 0, 0, 63.546f, 18, 2, new int[] {0,1,2,3,4}, 1.90f, ElementType.TRANSITION_METAL),
    Zn(30, 4, 106, 1.15f, 1.31f, 2, 0, 2, 0, 0, 65.380f, 18, 2, new int[] {0,1,2}, 1.65f, ElementType.TRANSITION_METAL),
    Ga(31, 4, 36, 1.55f, 1.26f, 3, 1, 4, 2, 4, 69.720f, 28, 3, new int[] {0,1,2,3}, 1.81f, ElementType.POST_TRANSITION_METAL),
    Ge(32, 4, 38, 2.72f, 1.22f, 4, 0, 12, 4, 4, 72.590f, 28, 4, new int[] {-4,-3,-2,-1,0,1,2,3,4}, 2.01f, ElementType.METALLOID),
    As(33, 4, 7, 0.83f, 1.19f, 5, 0, 12, 3, 5, 74.922f, 28, -3, new int[] {-3,0,1,2,3,5}, 2.18f, ElementType.METALLOID),
    Se(34, 4, 85, 0.90f, 1.16f, 6, 0, 12, 2, 6, 78.960f, 28, 4, new int[] {-2,0,1,2,4,6}, 2.55f, ElementType.OTHER_NONMETAL),
    Br(35, 4, 15, 1.95f, 1.14f, 7, 0, 1, 1, 1, 79.904f, 28, -1, new int[] {-1,0,1,2,3,4,5,7}, 2.96f, ElementType.HALOGEN),
    Kr(36, 4, 48, 1.90f, 1.60f, 8, 0, 12, 0, 0, 83.800f, 28, 0, new int[] {0,2}, 3.00f, ElementType.NOBLE_GAS),
    Rb(37, 5, 77, 2.65f, 2.11f, 1, 0, 12, 0, 0, 85.467f, 36, 1, new int[] {-1,0,1}, 0.82f, ElementType.ALKALI_METAL),
    Sr(38, 5, 89, 2.02f, 1.92f, 2, 0, 12, 2, 0, 87.620f, 36, 2, new int[] {0,1,2}, 0.95f, ElementType.ALKALINE_EARTH_METAL),
    Y(39, 5, 103, 1.61f, 1.62f, 3, 0, 12, 3, 0, 88.806f, 36, 3, new int[] {0,1,2,3}, 1.22f, ElementType.TRANSITION_METAL),
    Zr(40, 5, 105, 1.42f, 1.48f, 4, 0, 12, 4, 0, 91.220f, 36, 4, new int[] {0,1,2,3,4}, 1.33f, ElementType.TRANSITION_METAL),
    Nb(41, 5, 59, 1.33f, 1.37f, 5, 0, 12, 3, 0, 92.906f, 36, 5, new int[] {-1,0,1,2,3,4,5}, 1.60f, ElementType.TRANSITION_METAL),
    Mo(42, 5, 56, 1.75f, 1.45f, 6, 1, 6, 3, 0, 95.940f, 36, 6, new int[] {-2,-1,0,1,2,3,4,5,6}, 2.16f, ElementType.TRANSITION_METAL),
    Tc(43, 5, 93, 1.80f, 1.56f, 7, 0, 12, 6, 0, 98.910f, 36, 7, new int[] {-3,-1,0,1,2,3,4,5,6,7}, 1.90f, ElementType.TRANSITION_METAL),
    Ru(44, 5, 81, 1.20f, 1.26f, 8, 0, 12, 3, 0, 101.070f, 36, 4, new int[] {-2,0,1,2,3,4,5,6,7,8}, 2.20f, ElementType.TRANSITION_METAL),
    Rh(45, 5, 79, 1.22f, 1.35f, 4, 0, 12, 3, 0, 102.906f, 36, 3, new int[] {-1,0,1,2,3,4,5,6}, 2.28f, ElementType.TRANSITION_METAL),
    Pd(46, 5, 70, 1.44f, 1.31f, 4, 0, 12, 2, 0, 106.400f, 36, 2, new int[] {0,1,2,4}, 2.20f, ElementType.TRANSITION_METAL),
    Ag(47, 5, 3, 1.55f, 1.53f, 1, 0, 6, 0, 0, 107.868f, 36, 1, new int[] {0,1,2,3,4}, 1.93f, ElementType.TRANSITION_METAL),
    Cd(48, 5, 18, 1.75f, 1.48f, 2, 0, 12, 0, 0, 112.400f, 36, 2, new int[] {0,1,2}, 1.69f, ElementType.TRANSITION_METAL),
    In(49, 5, 45, 1.46f, 1.44f, 3, 0, 12, 3, 0, 114.820f, 46, 3, new int[] {0,1,2,3}, 1.78f, ElementType.POST_TRANSITION_METAL),
    Sn(50, 5, 88, 1.67f, 1.41f, 4, 0, 12, 2, 4, 118.690f, 46, 4, new int[] {-4,0,2,4}, 1.96f, ElementType.POST_TRANSITION_METAL),
    Sb(51, 5, 83, 1.12f, 1.38f, 5, 0, 12, 4, 5, 121.750f, 46, -3, new int[] {-3,0,3,5}, 2.05f, ElementType.METALLOID),
    Te(52, 5, 94, 1.26f, 1.35f, 6, 0, 12, 2, 6, 127.600f, 46, 4, new int[] {-2,0,2,4,5,6}, 2.10f, ElementType.METALLOID),
    I(53, 5, 44, 2.15f, 1.33f, 7, 1, 1, 1, 1, 126.905f, 46, -1, new int[] {-1,0,1,3,4,5,7}, 2.66f, ElementType.HALOGEN),
    Xe(54, 5, 102, 2.10f, 1.70f, 8, 0, 12, 0, 0, 131.300f, 46, 0, new int[] {0,1,2,4,6,8}, 2.60f, ElementType.NOBLE_GAS),
    Cs(55, 6, 25, 3.01f, 2.25f, 1, 0, 12, 0, 0, 132.905f, 54, 1, new int[] {-1,0,1}, 0.79f, ElementType.ALKALI_METAL),
    Ba(56, 6, 11, 2.41f, 1.98f, 2, 0, 12, 0, 0, 137.340f, 54, 2, new int[] {0,2}, 0.89f, ElementType.ALKALINE_EARTH_METAL),
    La(57, 6, 49, 1.83f, 1.95f, 3, 0, 12, 3, 0, 138.905f, 54, 3, new int[] {0,2,3}, 1.10f, ElementType.LANTHANOID),
    Ce(58, 6, 19, 1.86f, 1.03f, 4, 0, 12, 3, 0, 140.120f, 54, 3, new int[] {0,2,3,4}, 1.12f, ElementType.LANTHANOID),
    Pr(59, 6, 73, 1.62f, 0.90f, 4, 0, 12, 3, 0, 140.908f, 55, 3, new int[] {0,2,3,4}, 1.13f, ElementType.LANTHANOID),
    Nd(60, 6, 60, 1.79f, 0.99f, 3, 0, 12, 3, 0, 144.240f, 56, 3, new int[] {0,2,3,4}, 1.14f, ElementType.LANTHANOID),
    Pm(61, 6, 71, 1.76f, 0.98f, 3, 0, 12, 3, 0, 145.000f, 58, 3, new int[] {0,2,3}, 1.13f, ElementType.LANTHANOID),
    Sm(62, 6, 87, 1.74f, 0.96f, 3, 0, 12, 2, 0, 150.400f, 59, 3, new int[] {0,2,3}, 1.17f, ElementType.LANTHANOID),
    Eu(63, 6, 31, 1.96f, 1.09f, 3, 0, 12, 2, 0, 151.960f, 60, 3, new int[] {0,2,3}, 1.20f, ElementType.LANTHANOID),
    Gd(64, 6, 37, 1.69f, 0.94f, 3, 0, 12, 3, 0, 157.250f, 61, 3, new int[] {0,1,2,3}, 1.20f, ElementType.LANTHANOID),
    Tb(65, 6, 92, 1.66f, 0.92f, 4, 0, 12, 3, 0, 158.925f, 61, 3, new int[] {0,1,2,3,4}, 1.10f, ElementType.LANTHANOID),
    Dy(66, 6, 28, 1.63f, 0.91f, 3, 0, 12, 3, 0, 162.500f, 62, 3, new int[] {0,2,3,4}, 1.22f, ElementType.LANTHANOID),
    Ho(67, 6, 43, 1.61f, 0.89f, 3, 0, 12, 3, 0, 164.930f, 64, 3, new int[] {0,2,3}, 1.23f, ElementType.LANTHANOID),
    Er(68, 6, 29, 1.59f, 0.88f, 3, 0, 12, 3, 0, 167.260f, 65, 3, new int[] {0,2,3}, 1.24f, ElementType.LANTHANOID),
    Tm(69, 6, 98, 1.57f, 0.87f, 3, 0, 12, 3, 0, 168.934f, 66, 3, new int[] {0,2,3,4}, 1.25f, ElementType.LANTHANOID),
    Yb(70, 6, 104, 1.54f, 0.86f, 3, 0, 12, 2, 0, 173.040f, 67, 3, new int[] {0,2,3}, 1.10f, ElementType.LANTHANOID),
    Lu(71, 6, 52, 1.53f, 0.85f, 3, 0, 12, 3, 0, 174.970f, 68, 3, new int[] {0,3}, 1.27f, ElementType.LANTHANOID),
    Hf(72, 6, 41, 1.40f, 1.58f, 4, 0, 12, 4, 0, 178.490f, 68, 4, new int[] {0,2,3,4}, 1.30f, ElementType.TRANSITION_METAL),
    Ta(73, 6, 91, 1.22f, 1.38f, 5, 0, 12, 5, 0, 180.850f, 68, 5, new int[] {-1,0,2,3,4,5}, 1.50f, ElementType.TRANSITION_METAL),
    W(74, 6, 101, 1.26f, 1.46f, 6, 0, 12, 6, 0, 183.850f, 68, 6, new int[] {-2,-1,0,1,2,3,4,5,6}, 2.36f, ElementType.TRANSITION_METAL),
    Re(75, 6, 78, 1.30f, 1.59f, 7, 0, 12, 4, 0, 186.200f, 68, 7, new int[] {-3,-1,0,1,2,3,4,5,6,7}, 1.90f, ElementType.TRANSITION_METAL),
    Os(76, 6, 66, 1.58f, 1.28f, 8, 0, 12, 2, 0, 190.200f, 68, 4, new int[] {-2,-1,0,1,2,3,4,5,6,7,8}, 2.20f, ElementType.TRANSITION_METAL),
    Ir(77, 6, 46, 1.22f, 1.37f, 6, 0, 12, 3, 0, 192.220f, 68, 4, new int[] {-3,-1,0,1,2,3,4,5,6,8}, 2.20f, ElementType.TRANSITION_METAL),
    Pt(78, 6, 74, 1.55f, 1.28f, 4, 0, 6, 0, 0, 195.090f, 68, 4, new int[] {-2,-1,0,1,2,3,4,5,6}, 2.28f, ElementType.TRANSITION_METAL),
    Au(79, 6, 9, 1.45f, 1.44f, 3, 0, 6, 0, 0, 196.967f, 68, 3, new int[] {-1,0,1,2,3,5}, 2.54f, ElementType.TRANSITION_METAL),
    Hg(80, 6, 42, 1.55f, 1.32f, 2, 0, 12, 1, 2, 200.59f, 78, 1, new int[] {0,1,2,4}, 2.00f, ElementType.TRANSITION_METAL),
    Tl(81, 6, 97, 1.96f, 1.45f, 3, 0, 12, 1, 3, 204.3833f, 78, 1, new int[] {-1,0,1,3}, 1.62f, ElementType.POST_TRANSITION_METAL),
    Pb(82, 6, 69, 2.16f, 1.47f, 4, 0, 12, 2, 4, 207.200f, 78, 2, new int[] {-4,0,2,4}, 2.33f, ElementType.POST_TRANSITION_METAL),
    Bi(83, 6, 13, 1.73f, 1.46f, 5, 0, 12, 3, 3, 208.981f, 78, 3, new int[] {-3,0,1,3,5}, 2.20f, ElementType.POST_TRANSITION_METAL),
    Po(84, 6, 72, 1.21f, 0.67f, 6, 0, 12, 4, 2, 209.000f, 78, 4, new int[] {-2,0,2,4,5,6}, 2.0f, ElementType.METALLOID),
    At(85, 6, 8, 1.12f, 0.62f, 7, 0, 12, 1, 1, 210.000f, 78, -1, new int[] {-1,0,1,3,5,7}, 2.20f, ElementType.HALOGEN),
    Rn(86, 6, 80, 2.30f, 1.90f, 8, 0, 12, 0, 0, 222.000f, 78, 0, new int[] {0,2,6}, 0.0f, ElementType.NOBLE_GAS), // electroneg not reported
    Fr(87, 7, 35, 3.24f, 1.80f, 1, 0, 12, 0, 0, 223.000f, -1, 1, new int[] {0,1}, 0.70f, ElementType.ALKALI_METAL),
    Ra(88, 7, 76, 2.57f, 1.43f, 2, 0, 12, 2, 0, 226.000f, -1, 2, new int[] {0,2}, 0.9f, ElementType.ALKALINE_EARTH_METAL),
    Ac(89, 7, 2, 2.12f, 1.18f, 3, 0, 12, 4, 0, 227.000f, -1, 3, new int[] {0,2,3}, 1.1f, ElementType.ACTINOID),
    Th(90, 7, 95, 1.84f, 1.02f, 4, 0, 12, 1, 0, 232.038f, -1, 4, new int[] {0,2,3,4}, 1.30f, ElementType.ACTINOID),
    Pa(91, 7, 68, 1.60f, 0.89f, 5, 0, 12, 4, 0, 231.036f, -1, 5, new int[] {0,2,3,4,5}, 1.50f, ElementType.ACTINOID),
    U(92, 7, 99, 1.75f, 0.97f, 6, 0, 12, 4, 0, 238.029f, -1, 6, new int[] {0,2,3,4,5,6}, 1.38f, ElementType.ACTINOID),
    Np(93, 7, 64, 1.71f, 0.95f, 6, 0, 12, 4, 0, 237.048f, -1, 5, new int[] {0,3,4,5,6,7}, 1.36f, ElementType.ACTINOID),
    Pu(94, 7, 75, 1.67f, 0.93f, 6, 0, 12, 3, 0, 244.000f, -1, 4, new int[] {0,3,4,5,6,7,8}, 1.28f, ElementType.ACTINOID),
    Am(95, 7, 5, 1.66f, 0.92f, 6, 0, 12, 3, 0, 243.000f, -1, 3, new int[] {0,2,3,4,5,6,7}, 1.13f, ElementType.ACTINOID),
    Cm(96, 7, 22, 1.65f, 0.91f, 3, 0, 12, 3, 0, 248.000f, -1, 3, new int[] {0,3,4}, 1.28f, ElementType.ACTINOID),
    Bk(97, 7, 14, 1.64f, 0.90f, 4, 0, 12, 3, 0, 247.000f, -1, 3, new int[] {0,2,3,4}, 1.30f, ElementType.ACTINOID),
    Cf(98, 7, 20, 1.63f, 0.89f, 3, 0, 12, 4, 0, 251.000f, -1, 3, new int[] {0,2,3,4}, 1.30f, ElementType.ACTINOID),
    Es(99, 7, 30, 1.62f, 0.88f, -1, 0, 12, 4, 0, 254.000f, -1, 3, new int[] {0,2,3}, 1.30f, ElementType.ACTINOID),
    Fm(100, 7, 34, 1.61f, 0.87f, -1, 0, 12, 4, 0, 257.000f, -1, 3, new int[] {0,2,3}, 1.30f, ElementType.ACTINOID),
    Md(101, 7, 53, 1.60f, 0.86f, -1, 0, 12, 4, 0, 256.000f, -1, 3, new int[] {0,2,3}, 1.30f, ElementType.ACTINOID),
    No(102, 7, 63, 1.59f, 0.85f, -1, 0, 12, 4, 0, 254.000f, -1, 3, new int[] {0,2,3}, 1.30f, ElementType.ACTINOID),
    Lr(103, 7, 51, 1.58f, 0.84f, -1, 0, 12, 4, 0, 257.000f, -1, 3, new int[] {0,3}, 0.00f, ElementType.ACTINOID), // electroneg not reported
    /**
     * R-group to represent generic groups that are sometimes present in MDL .sdf
     * files.
     */
    R(104, 0, 105, 0.0f, 0.0f, 0, 0, 4, 1, 0, 0.000f, -1, 3, null, 0.00f, ElementType.UNKNOWN); // this is an R-group
    // should these be declared final?
    private int atomicNumber;
    private int period;
    //private int hillOrder;
    private float VDWRadius; // in Angstroms
    private float covalentRadius; // in Angstroms
    private int valenceElectronCount;
    private int minimumValence;
    private int maximumValence;
    private int commonValence;
    private int maximumCovalentValence;
    private float atomicMass;
    private int coreElectronCount;
    private int oxidationState;
    private int[] allOxidationStates;
    // Pauling electronegativity: http://en.wikipedia.org/wiki/Electronegativity
    private float paulingElectronegativity;
    // Element type: http://www.ptable.com/
    private ElementType elementType;
    //private static final Element[] hillOrderIndex;
    
//
//    static {
//        hillOrderIndex = new Element[Element.values().length + 1];
//        for (Element e : Element.values()) {
//            hillOrderIndex[e.getHillOrder()] = e;
//        }
//        hillOrderIndex[Element.H.getHillOrder()] = Element.H; // special case for hydrogen
//    }

    private static final Map<String,Element> allElements ;
   
	static {
    	allElements = new HashMap<String,Element>();
    	for (Element e : Element.values()){
    		allElements.put(e.toString().toLowerCase(), e);
    	}
    }
    private Element(int atomicNumber,
            int period,
            int hillOrder,
            float VDWRadius,
            float covalentRadius,
            int valenceElectronCount,
            int minimumValence,
            int maximumValence,
            int commonValence,
            int maximumCovalentValence,
            float atomicMass,
            int coreElectronCount,
            int oxidationState,
            int[] allOxidationStates,
            float paulingElectronegativity,
            ElementType elementType) {

        this.atomicNumber = atomicNumber;
        this.period = period;
        //this.hillOrder = hillOrder;
        this.VDWRadius = VDWRadius;
        this.covalentRadius = covalentRadius;
        this.valenceElectronCount = valenceElectronCount;
        this.minimumValence = minimumValence;
        this.maximumValence = maximumValence;
        this.commonValence = commonValence;
        this.maximumCovalentValence = maximumCovalentValence;
        this.atomicMass = atomicMass;
        this.coreElectronCount = coreElectronCount;
        this.oxidationState = oxidationState;
        this.allOxidationStates = allOxidationStates;
        this.paulingElectronegativity = paulingElectronegativity;
        this.elementType = elementType;
        
       
    }
    
    /**
     * Returns a list of all oxidation states the element is found in.
     * The set is by Greenwood and Norman in "Chemistry of the Elements (ISBN:0080379419).
     * @return An array of oxidation states sorted from most negative to most positive.
     */
    public int[] getAllOxidationStates() {
		return allOxidationStates;
	}

    /**
     * Returns the atomic number of this Element.
     * @return the atomic number of this Element.
     */
    public int getAtomicNumber() {
        return atomicNumber;
    }

    /**
     * Returns the period in the periodic table of this Element.
     * @return the period in the periodic table of this Element.
     */
    public int getPeriod() {
        return period;
    }

    /**
     * Returns the Hill Order of this Element. The Hill Order represents the
     * priority by which elements are sorted in molecular formulas.
     * The Hill system is a system of writing chemical formulas such that the
     * number of carbon atoms in a molecule is indicated first, the number of
     * hydrogen atoms next, and then the number of all other chemical elements
     * subsequently, in alphabetical order. When the formula contains no carbon,
     * all the elements, including hydrogen, are listed alphabetically.
     * <p>
     * Edwin A. Hill, "On A System Of Indexing Chemical Literature;
     * Adopted By The Classification Division Of The U. S. Patent Office".
     * J. Am. Chem. Soc. 1900, 22(8), 478-494.
     * <p>
     * <a href="http://en.wikipedia.org/wiki/Hill_system">
     * http://en.wikipedia.org/wiki/Hill_system</a>
     * <p>
     * @return the Hill Order of this Element.
     */
    public int getHillOrder() {
    	throw new RuntimeException("Not implemented, yet!");
    	//throw new NotImplementedYetException();
        //return hillOrder;
    }

    /**
     * Returns the van der Waals radius of this Element.
     * @return the van der Waals radius of this Element, measured in Angstroms.
     */
    public float getVDWRadius() {
        return VDWRadius;
    }

    /**
     * Returns the covalent radius of this Element.
     * @return covalent radius, measured in Angstroms.
     */
    public float getCovalentRadius() {
        return covalentRadius;
    }

    /**
     * Returns the number of valence electrons for this Element.
     * @return the number of valence electrons for this Element.
     */
    public int getValenceElectronCount() {
        return valenceElectronCount;
    }

    /**
     * Returns the minimum valence for this Element.
     * @return the minimum valence of this atom.
     */
    public int getMinimumValence() {
        return minimumValence;
    }

    /**
     * Returns the maximum valence for this Element.
     * @return the maximum valence for this Element.
     */
    public int getMaximumValence() {
        return maximumValence;
    }

    /**
     * Returns the common valence for this Element.
     * @return the common valence for this Element.
     */
    public int getCommonValence() {
        return commonValence;
    }

    /**
     * Returns the maximum valence for this Element.
     * @return the maximum valence of this element.
     */
    public int getMaximumCovalentValence() {
        return maximumCovalentValence;
    }

    /**
     * Returns the atomic mass for this Element.
     * @return the atomic mass for this Element, measured in g/mol.
     */
    public float getAtomicMass() {
        return atomicMass;
    }

    /**
     * Returns the number of core electrons for this Element.
     * @return number of core electrons for this Element.
     */
    public int getCoreElectronCount() {
        return coreElectronCount;
    }

    /**
     * Returns a typical oxidation state for this Element. This information is mostly
     * useful for metals.
     * @return a typical oxidation state for this Element.
     */
    public int getOxidationState() {
        return oxidationState;
    }

    /**
     * Returns the Pauling electronegativity for this Element.
     * @return the Pauling electronegativity for this Element.
     */
    public float getPaulingElectronegativity() {
        return paulingElectronegativity;
    }

    /**
     * Returns the Element Type for this Element.
     * @return the Element Type for this Element.
     */
    public ElementType getElementType() {
        return elementType;
    }
    
    /**
     * Returns the Element that corresponds to the specified element symbol. The case
     * of the element symbol is ignored. Example: FE, fe, Fe represent iron.
     * @param elementSymbol element symbol to specify Element.
     * @return the Element specified by the element symbol.
     */
    public static Element valueOfIgnoreCase(String elementSymbol) throws IllegalArgumentException {

    	Element e = allElements.get(elementSymbol.toLowerCase());
        if ( e != null)
        	return e;
        throw new IllegalArgumentException("Invalid element symbol: " + elementSymbol);
    }

	/**
	 * Returns <code>true</code> if this Element is Hydrogen.
	 * <p>
	 * <b>Note:</b> Deuterium ({@link #D}) and Tritium ({@link T}) will return
	 * <code>true</code> to this method.
	 * 
	 * @return <CODE>true</CODE> if the Element is Hydrogen.
	 */
	public boolean isHydrogen() {
		return this == H || this == D || this == T;
	}

	/**
	 * Returns <CODE>true</CODE> is the Element is an not Hydrogen (or an
	 * isotope of Hydrogen).
	 * <p>
	 * This method is the exact opposite of {@link #isHydrogen()}.
	 * 
	 * @return <CODE>true</CODE> is Element is not Hydrogen.
	 */
	public boolean isHeavyAtom() {
		return !isHydrogen();
	}

    /**
     * Returns <CODE>true</CODE> if Element is not Hydrogen and not Carbon.
     * @return <CODE>true</CODE> if Element is not Hydrogen and not Carbon.
     */
    public boolean isHeteroAtom() {
        return !(this == C || this == H);
    }

	/**
     * Returns <CODE>true</CODE> if ElementType is a metal.
     * @return <CODE>true</CODE> if ElementType is a metal.
     */
	public boolean isMetal() {
		return elementType.isMetal();
	}
	
	/**
     * Returns <CODE>true</CODE> if ElementType is a metalloid.
     * @return <CODE>true</CODE> if ElementType is a metalloid.
     */
	public boolean isMetalloid() {
		return elementType.isMetalloid();
	}
	
	/**
     * Returns <CODE>true</CODE> if ElementType is a non-metal.
     * @return <CODE>true</CODE> if ElementType is a non-metal.
     */
	public boolean isNonMetal() {
		return elementType.isNonMetal();
	}
	
	/**
     * Returns <CODE>true</CODE> if Element is a halogen (F, Cl, Br, I, At).
     * @return <CODE>true</CODE> if Element is a halogen.
     */
    public boolean isHalogen() {
        return elementType.equals(ElementType.HALOGEN);
    }
    
    /**
     * Returns <CODE>true</CODE> if Element is a chalcogen (O, S, Se, Te, Po).
     * @return <CODE>true</CODE> if Element is a chalcogen.
     */
    public boolean isChalcogen() {
        return (this == O || this == S || this == Se || this == Te ||
                this == Po);
    }

    /**
     * Returns the Element that corresponds to the specified Hill Order.
     * @param index the Hill Order.
     * @return the Element that corresponds to the specified Hill Order.
     * @see #getHillOrder()
     */
    public static Element getElementFromHillIndex(int index) {
    	throw new RuntimeException("Not implemented, yet!");
        //return hillOrderIndex[index];
    }
}
