Topic 3

• What is the difference between a group and a period in the periodic table?


  A period is the rows while groups are the columns.
• Which elements are metalloids?

  Boron, silicon, germanium, arsenic, antimony, tellurium, and astatine.
• Where are halogens located on the periodic table?

  Group 17
• What is effective nuclear charge?

  The charge experienced by the a valence electron of an element
• What are the trends in effective nuclear charge?

  Increases across a period and remains the approximately the same down a group.
• What is atomic radius?

  The size of an atom, typically measured as the distance from the nucleus to the outermost electron shell.
• What are the trends in atomic radius?

  Decreases across a period, increases down a group.
• Explain why atomic radius decreases across a period?

  The effective nuclear charge increases, so the attraction between the proton and electron is greater decreasing size of the atom.
• Explain why atomic radius increases down a group?

  The number of occupied principal energy levels increases.
• What are the trends in ionic radius?

  Ionic radius decreases across a period and increases down a group.
• Explain the trends in ionic radius.

  Positive ions are smaller than negative ions. Cations lose their outer shell, anions have greater electron repulsion.
• What is first ionisation energy?

  The energy required to remove one mol of an electron from one mol of a gaseous atom in their ground state.
• What are the trends of ionisation energy?

  Ionization energy generally increases across a period and decreases down a group on the periodic table.
• Explain why ionisation energy increases across a period.

  Increase in effective nuclear charge causes an increase in attraction between outer electrons and the nucleus, making electrons more difficult to remove.
• Explain why ionisation energy decreases down a group.

  The effective nuclear charge is the same, due to electron shielding. The increased distance between the valence electron and nucleus reduces the attraction between them.
• What are the exceptions to the trends in ionisation energy? Why do these occur

  -A drop between group 13 elements and group 2 elements. This is due to group 13 elements having a p orbital that has higher energy than an s orbital.

  -A drop between group 15 and 16 elements. Due to the an electron being removed from a group 16 element is taken from a double occupied p orbital making it easier to remove due to the repulsion of its partner.
• What is electron affinity?

  The energy change when one mole of electrons is added to one mole of gaseous atoms, forming one mole of gaseous ions.
• What is electronegativity?

  Electronegativity is the measure of an atom's ability to attract electrons in a covalent bond.
• What are the trends in electronegativity?

  Increasing across a period, decreasing down a group.
• Explain the trends in electronegativity.

  -Electronegativity increases across a period due to the increases in nuclear charge, leading to increased attraction between the nucleus and the bond electrons.

  -Electronegativity decreases down a group as the bonding electrons are furthest away from the nucleus causing reduced attraction
• Do metals have lower ionisation energies and electronegativity than non-metals?

  Yes
• Melting points decrease down group 1
• Melting points increase down group 17
• Melting points generally increase across a period


  Reaches a maximum at group 14
• Melting points reach a minimum

  At group 18
• In period 3 the bonding changes from metalic to giant covalent to weak van der Waal forces between simple molecules and single atoms
• All the period 3 elements are solids at room temperature except chlorine and argon
• What are the chemical properties of the noble gases?

  -Colourless gases

  -Very unreactive

  -Monatomic
• What are the chemical properties of the alkali metals?

  -Very reactive metals

  -Form ionic compounds with non-metals
• What are the physical properties of alkali metals?

  -Good conductors of electricity and heat

  -They have low densities

  -They have grey shiny surfaces when cut with a knife
• What gives alkali metals their ability to conduct electricity and heat so well?

  The mobility of their lone outer electron
• How do alkali metals react with water?


  Alkali metals react vigorously with water, producing hydrogen gas and an alkaline solution. The reaction becomes more vigorous as you go down the group.
• What are some observations that could be made when an alkali metal and water reacts?

  - Lithium metal reacts slowly, realising hydrogen gas.

  - Sodium reacts with a vigorous release of hydrogen. Heat produced causes the unreacted metal to melt, forming a small ball that moves excitedly on the water surface.

  - Potassium reacts very violently to produce sufficient heat to ignite the hydrogen produced, producing a lilac coloured flame, moving along the water surface.
• What are physical properties of the halogens?

  - they are coloured

  - they show a gradual change from gases (F, Cl) to liquids (Br) to solids (I, At)
• What are chemical properties of the halogens?

  - diatomic molecules

  - very reactive non-metals

  - form ionic compounds with metals and covalent compounds with non-metals
• How does reactivity change down the halogens?

  Decreases, as you go down atomic radius increases, causing attraction for outer electrons to decrease
• How do halogens react with group one metals?

  - form ionic halides, stable octet

  - opposite charge ions attract each other and make an ionic bond