Chemistry -Year 9

• What is the smallest particle of matter?

  Atom
• What does the mass number represent?

  Total number of protons and neutrons
• What is the atomic number?

  Number of protons in the nucleus
• What is the relationship between protons and electrons in an atom?

  They have the same number
• What is the approximate radius of an atom?

  0.1 nm
• What surrounds the nucleus of an atom?

  Shells
• What is the radius of the nucleus?

  $1 \times 10^{-14} \text{ m}$
• What is the electron structure of an atom in terms of shells?

  • Shell 1: 2 electrons
  • Shell 2: 8 electrons
  • Shell 3: 8 electrons
  • Shell 4: 2 electrons
• What did the plum pudding model propose about the atom?

  It was a ball of positive charge with electrons
• What did alpha particle scattering reveal about the atom?

  Mass is concentrated in the nucleus
• Who adapted the nuclear model of the atom?

  Niels Bohr
• What did Niels Bohr suggest about electrons?

  They exist in orbits at set distances
• What did experiments show about the nucleus?

  It is made of smaller particles with positive charge
• Who discovered the existence of neutrons?

  James Chadwick
• What does the group number in the periodic table indicate?

  Number of electrons in the outer shell
• What does the period number in the periodic table indicate?

  Number of electron shells in the element
• What charge do Group 1 elements form when they gain an electron?

  +1 (positive ion)
• What charge do Group 2 elements form when they gain electrons?

  +2 (positive ion)
• What charge do Group 7 elements form when they lose electrons?

  -2 (negative ion)
• What charge do Group 6 elements form when they lose an electron?

  -1 (negative ion)
• What do Group 1 metals react with water to form?

  Hydroxide and hydrogen gas
• What happens when alkali metals react with water?

  They form a hydroxide and hydrogen gas
• What happens to alkali metals when they react?

  They lose their outer shell electron
• Why does sodium lose its electron quickly?

  Its nucleus is further apart
• What do alkali metals form when they react with non-metals?

  Ionic compounds that are white solids
• What happens to sodium's electron attraction as the nucleus is further apart?

  The attraction becomes weaker
• What do halogens do with electrons?

  They gain electrons
• What are halogens composed of?

  Diatomic molecules (pairs of two)
• How does reactivity change in halogens as you go down the group?

  Reactivity decreases
• What is halogen displacement?

  • A more reactive halogen displaces a less reactive halogen from a compound
  • Example reactions:
  • Fluorine + potassium iodide → potassium fluoride + iodide
  • Chlorine + potassium bromide → potassium chloride + bromide
  • Bromine + sodium iodide → sodium bromide + iodide
• What happens to fluorine after forming a compound?

  It becomes fluoride
• Why does reactivity increase in halogens with more shells?

  Outer shells are further from the nucleus