Atomic Structure

De (United States of America)
PH Chem Chapter 4
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  1. atom
    the smallest component of an element
    All elements are composed of tiny indivisible particles called atoms.
    the smallest part of an element that retains its identity in a chemical reaction
  2. atomic theory
    a theory of the structure of the atom
    According to Dalton's atomic theory, atoms of different elements can physically mix together or chemically combine in simple whole-number ratios to form compounds.
    John Dalton, and English chemist and school teacher, used hypotheses and theories to form the first scientific theory of atoms.
  3. electron
    an elementary particle with negative charge
    Electrons are distributed around the nucleus of the atom and occupy almost all the volume of the atom.
    Electrons are negatively charged subatomic particles.
  4. cathode ray
    a beam of electrons emitted by the cathode of an electrical discharge tube
    A cathode ray is deflected by either a magnet or electrically charged metal plates.
    a glowing beam of electrons that passes from a cathode to an anode within a vacuum tube
  5. proton
    a stable particle with positive charge
    Protons and neutrons form the nucleus of an atom.
    protons are positively charged subatomic particles
  6. neutron
    a subatomic particle with zero charge
    Although protons and neutrons are exceedingly small, theoretical physicists believe that they are composed of yet smaller particle called quarks.
    neutrons are subatomic particles with no charge
  7. nucleus
    the positively charged dense center of an atom
    Protons are fundamental particles found inside the atomic nucleus that can be focused much more accurately than X-rays.
    The nucleus is the tiny central core of an atom and is composed of protons and neutrons.
  8. atomic number
    quantity of protons in the nucleus of an atom of an element
    The number of neutrons in an atom is the difference between the mass number and atomic number for that atom.
    The atomic number is the number of protons in the nucleus of an atom of that element.
  9. mass number
    the sum of the number of neutrons and protons in an atomic nucleus
    The composition of any atom can be represented in shorthand notation using atomic number and mass number.
    The total number of protons and neutrons in an atom is called the mass number.
  10. isotope
    atom with same atomic number, different number of neutrons
    Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.
    Isotopes are atoms that have the same number of protons but different numbers of neutrons.
  11. atomic mass unit
    unit of mass for expressing masses of atoms or molecules
    The mass of a single proton or neutron is about 1 amu (atomic mass unit).
    The atomic mass unit (amu) is defined as one twelfth of the mass of a carbon-12 atom.
  12. atomic mass
    the property of an atom that causes it to have weight
    You can calculate atomic mass given the number of stable isotopes of the element, the mass of each isotope, and the natural percent abundance of each isotope.
    The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.
  13. periodic table
    arrangement of chemical elements according to atomic number
    Each horizontal row of the periodic table is called a period.
    A periodic table is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties.
  14. period
    the interval to complete one cycle of a repeating phenomenon
    In the periodic table, the number of elements per period ranges from 2 (hydrogen and helium) in Period 1, to 32 in Period 6.
    Each horizontal row of the periodic table is called a period. There are 7 periods in the modern periodic table. Within a given period, the properties of the elements vary as you move across it from element to element. This pattern of properties then repeats as you move to the next period.
  15. group
    any number of entities (members) considered as a unit
    Group 2A contains the elements beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
    Each vertical column of the periodic table is called a group, or family. Elements within a group have similar chemical and physical properties. Each group is identified by a number and the letter A or B which represent specific trends in the periodic table.
Created on Sat Sep 21 10:07:05 EDT 2013 (updated Sat Sep 21 11:08:35 EDT 2013)

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