C1 - Atomic Structure and the Periodic Table

• What is the approximate radius of an atom?

  ≈ 0.1 nm
• What is the approximate radius of a nucleus?

  ≈ 1 × 10^{-15} m
• Why do atoms have no overall charge?

  Because the number of protons equals the number of electrons
• What does the mass number represent in a nuclear symbol?

  The total number of protons and neutrons in an atom
• What does the atomic number represent in a nuclear symbol?

  The number of protons in an atom
• How many different elements are there approximately?

  About 100
• What is the relative mass and charge of a proton?

  Relative mass: 1, Relative charge: +1
• What is the relative mass and charge of a neutron?

  Relative mass: 1, Relative charge: 0
• What is the relative mass and charge of an electron?

  Relative mass: very small, Relative charge: -1
• What defines an element?

  Substances made up of atoms with the same atomic number
• What are isotopes?

  Atoms with the same number of protons but different numbers of neutrons
• What is relative atomic mass (Aᵣ)?

  The average mass number for an element
• How is relative atomic mass calculated?

  Aᵣ = sum of (isotope abundance × isotope mass number) / total abundance of all isotopes
• What is a compound?

  • A substance formed from two or more elements chemically bonded together
  • Fixed proportions
  • At least one new substance is made in a chemical reaction
• What is a molecule?

  A particle containing two or more non-metal atoms bonded covalently
• What does a chemical formula show?

  The proportion of atoms of each element in a compound
• What does a chemical equation represent?

  The overall change in a reaction
• What must be true for a chemical equation to be balanced?

  There must be the same number of each atom on each side
• What are mixtures?

  • Substances made up of different elements or compounds
  • Not chemically bonded
  • Can be separated by physical methods
• What is an example of a mixture?

  Air
• What is paper chromatography?

  • A method to separate components of a mixture
  • Uses filter paper and a solvent
  • Components separate as they move up the paper
• How do the chemical properties of a substance change when part of a mixture?

  The chemical properties are not affected
• What is filtration?

  • A method to separate insoluble solids from liquids
  • Can purify a liquid by removing insoluble impurities
• What is evaporation?

  • A method to separate soluble salts from a solution
  • Crystals form as the solvent evaporates
• What is crystallisation?

  • A method to separate soluble salts from a solution
  • Large crystals form as the solution cools
• What is simple distillation?

  • A method to separate liquids based on boiling points
  • The part with the lowest boiling point evaporates first
• What is fractional distillation?

  • A method to separate liquids with similar boiling points
  • Uses a fractionating column
• How were atoms described at the start of the 1800s?

  As solid spheres that can't be divided
• What is the "plum pudding" model of the atom?

  A model where a ball of positive charge contains small negative electrons
• What does the nuclear model of the atom state?

  Mass is concentrated in a positive nucleus with a cloud of electrons
• What is the Bohr model of the atom?

  A model where electrons orbit the nucleus in fixed shells
• Who provided evidence that neutrons are neutral particles found in the nucleus?

  James Chadwick
• What do electrons occupy in an atom?

  Shells, also called energy levels
• How do electrons fill shells in an atom?

  They fill each shell up before occupying a new one, starting with the lowest energy
• What is Mendeleev's Table of Elements?

  • Elements grouped using their properties
  • Gaps were left for undiscovered elements
  • New elements discovered later fit into the gaps
• How are elements ordered in the modern periodic table?

  By increasing atomic number
• What are periods and groups in the periodic table?

  • Horizontal rows are called periods
  • Vertical columns are called groups
• What does the position of an element in the periodic table indicate?

  The electronic structure of the element
• What are metals?

  Elements that can form positive ions when they react
• What are non-metals?

  Elements that don't generally form positive ions