C1

• Atom


  The smallest part of an element that can exist
• Atoms


  • Consist of a nucleus containing protons and neutrons, surrounded by electrons in shells
• Atomic number


  The number of protons in the nucleus of an atom
• Mass number


  The total number of protons and neutrons in the nucleus of an atom
• The number of subatomic particles in an atom can be calculated from the atom's atomic number and mass number
• Isotopes


  Atoms of the same element with the same number of protons but different numbers of neutrons
• Relative atomic mass


  The average mass of the atoms of an element compared to the mass of a carbon-12 atom
• Early atomic models


  • John Dalton's model - atoms as tiny spheres that cannot be divided
  • J.J. Thomson's plum pudding model - atom as a ball of positive charge with negative electrons embedded in it
  • Rutherford's nuclear model - mass concentrated at the centre, nucleus is positively charged
• Rutherford's experiment with alpha particles scattered by gold foil led to the nuclear model of the atom
• A solution with a pH value of 7 is neutral (neither acidic nor alkaline).
• Acids have a pH less than 7, while bases or alkalis have a pH greater than 7.
• Acids have a pH less than 7.
• Alkalis or bases have a pH greater than 7.
• Strong acids completely dissociate into hydrogen ions and their conjugate base when they are dissolved in water.
• Bases or alkalis have a pH greater than 7.
• Neutral substances have a pH equal to 7.
• Isotopes are atoms with different numbers of neutrons but same number of protons
• Strong acids dissociation


  When strong acids dissolve in water, they completely dissociate into hydrogen ions (H+) and their conjugate base. This process increases the concentration of H+ ions, leading to a decrease in pH.
• Atom


  Consists of a nucleus containing protons and neutrons, surrounded by electrons in shells
• Subatomic particles in an atom

  Can be calculated from the atom's atomic number and mass number
• Niels Bohr's nuclear model of the atom


  • Electrons orbit the nucleus in shells at certain distances from the nucleus
  • Calculations agreed with experimental observations
• Proton


  Subatomic particle with a positive charge and a relative mass of 1
• Neutron


  Uncharged subatomic particle, with a mass of 1 relative to a proton
• James Chadwick found evidence for the existence of neutrons in the nucleus
• Atom


  Consists of a nucleus containing protons and neutrons, surrounded by electrons in shells
• Nucleus


  The central part of an atom, containing protons and neutrons, and having most of the mass of the atom
• Electron


  Subatomic particle with a negative charge and a negligible mass relative to protons and neutrons
• Subatomic particles in the nucleus

  • Protons
  • Neutrons
• Proton


  Subatomic particle with a positive charge and a relative mass of 1
• Neutron


  Uncharged subatomic particle, with a mass of 1 relative to a proton
• Relative mass


  The number of times heavier a particle is, compared to another
• The mass of an electron is very small compared to a proton or a neutron, and most of the mass of an atom is concentrated in its nucleus
• Protons and electrons have electrical charges that are equal and opposite
• Atom


  Consists of a nucleus containing protons and neutrons, surrounded by electrons in shells
• Atomic number


  The number of protons in the nucleus of an atom
• Mass number


  The total number of protons and neutrons in the nucleus of an atom
• Atoms of different elements have different numbers of protons
• Atoms have equal numbers of protons and electrons, so they have no overall electrical charge
• Calculating numbers of subatomic particles in an atom

  1. Use the atom's atomic number and mass number

  2. Number of protons = atomic number

  3. Number of electrons = atomic number

  4. Number of neutrons = mass number - atomic number
• Isotopes


  Atoms of the same element with the same atomic number but different mass numbers