Atomic Structure

  • Created by: Manyah
  • Created on: 04-05-20 10:09
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    • Chemical Symbols
      • All substances are made from tiny particles called atoms
      • An atom is the smallest part of an element that can exist
      • Some non-metal elements exist as molecules that are made up of two atoms joined together
      • A compound is a substance that contains two or more elements that are chemically combined
      • A chemical formula can be used to represent a compound
        • The number of atoms of each element in a unit of the compound
        • The symbols for each element in a compound
      • Many compounds exist naturally. They can also be formed from their elements in chemical reactions.
        • In a chemical reaction, one or more new substances are formed. most chemical reactions involve energy changes
      • Reactants are substances that react together in a chemical reaction. In a chemical reaction, the atoms or ion in reactant separate from one another
        • A balanced chemical equation represents a chemical reaction using the formulae of the reactants and products
    • Balancing equations
      • this means that chemical reactions can be represented by symbol equations. A balanced symbol equation has the same number of atoms of each element on both sides of the arrow
      • To balance an equation, add numbers to the left of one or more formulae. Here is one way to work out how to do this for the reaction between nitrogen and hydrogen
    • Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells.
      • The number of subatomic particles in an atom can be calculated from the atom's atomic number and mass number
    • ideas about atoms have changed over time. Scientists developed new atomic models as they gathered new experimental evidence
      • John Dalton published his ideas about atoms in 1803. He thought that all matter was made of tiny  particles called atoms
        • Nearly 100 years later, J J Thomson carried out experiments and discovered the electron. This led him to suggest the plum pudding model
          • In 1909 Ernest Rutherford designed an experiment to test the plum pudding model. In the experiment, positively charged alpha particles were fired at thin gold foil
            • Niels Bohr adapted Ernest Rutherford's nuclear model. Bohr did calculations that led his to sugest that electrons orbit the nucleus in shells
              • In 1932 James Chadwick found evidence for the existence of particles in the nucleus with mass but no charge. These particles were names neutrons
    • Structure of the atom
      • An atom has a central nucleus. This is surrounded by electrons arranged in shells
        • The nucleus is tiny compared to the atom as a whole
          • The radius of an atom is about 0.1nm
          • The nuclei of all atoms contain subatomic particles called protons. The nuclei of most atoms also contains neutrons
          • The masses of subatomic particles are very tiny.
            • Instead of their actual masses in kilograms, we often use their relative masses. The relative mass of a proton is 1, and a particle with a relative mass smaller than 1 has less mass
    • The mass of an electron is very small compared to a proton or a neutron
      • Since the nucleus contains protons and neutrons, most of the mass of an atom is concentrated in its nucleus
    • The number of protons in an atom of an element is its atomic number
      • All atoms of a given element have the same number of protons
        • Atoms of different elements have different numbers of protons
    • an atom contains equal numbers of protons and electrons. Since protons and electrons have equal and opposite charges, this means that atoms have no overall electrical charge
    • Atoms of the same element must have the same number of protons, but they can have different numbers of neutrons.
      • Atoms of the same element with different numbers of neutrons are called isotopes
        • Isotopes of an elements have: The same atomic number and different mass numbers
      • Mass numbers are always whole numbers (Protons and neutrons can't be split into parts)
        • Relative atomic masses are often rounded to the nearest whole number, but are not actually whole numbers


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