Periodicity

• Periodic table


  Arranged in increasing atomic number, in vertical columns (groups) with same number of outer electrons + similar properties & horizontal rows (periods) giving number of highest energy electron shell
• Periodicity


  • Repeating, periodic pattern across a period
• Electron configuration across a period

  Period 2: 2s then 2p, period 3: 3s then 3p, period 4: 3d filled but highest energy is 4: 4s then 4p
• Periodic table blocks


  • s, p, d, f
• Periodic table groups


  • Group 1= alkali metals, 2=alkaline earth metals, 3-12=transition elements, 15=pnictogens, 16=chalcogens, 17=halogens, 18=noble gases
• First ionisation energy


  Energy required to remove one electron from one mole of gaseous atoms, forming one mole gaseous 1+ ions
• Factors affecting ionisation energies

  • Atomic radius (greater distance nucleus to outer electrons=less attraction, big effect), nuclear charge (more protons, more attraction), electron shielding (shielding effect- inner shell electrons repel outer shell electrons→ reduced attraction nucleus to outer electrons)
• Successive ionisation energies are greater
• Large increase successive ionisation energies→ electron has been removed from shell closer to nucleus with less shielding
• Successive ionisation energies allow predictions about: no. electrons outer shell, group in periodic table → element can be identified
• Trends in IE: general increase across period

  Sharp decrease between end of a period to the start of the next
• Down a group: atomic radius increases


  More inner shells so shielding increases, nuclear attraction on outer electrons decreases, 1st IE decreases
• Across a period: nuclear charge increases


  Same shell so similar shielding, nuclear attraction increases, atomic radius decreases, 1st IE increases. Exceptions period 2+3: group 2-3 fall (2p subshell higher energy than 2s, so 2p electron easier to remove) & group 5-6 fall (highest energy in 2p, but paired in 6- electrons repel making it easier for them to be removed)
• Semimetals/metalloids


  Elements near to metal/nonmetal divide (e.g. boron, silicon, germanium, arsenic, antimony) show in-between properties
• Metals


  • All solids at room temp except mercury, ranging properties of metals: tungsten- strong/hard, lead- soft, aluminium-light, osmium- very heavy
• Metallic bonding


  Strong electrostatic attraction between cations (+ve) and delocalised electrons. Cations fixed in position (maintains shape) & delocalised electrons mobile
• Metals w/ 2+ cations have 2x electrons
• Properties of metals


  • Electrical conductivity (electrons can move when voltage is applied), high mpt/bpt (high temp needed to overcome strong electrostatic attraction between cations/electrons) & insoluble (any interactions lead to reaction not dissolving)
• Giant covalent lattice


  Many billions of atoms held together by network strong covalent bonds (boron, carbon, silicon)
• Carbon (diamond) + silicon

  • Use 4 outer electrons forming covalent bonds with other atoms→ tetrahedral, 109.5°, can be shown w/ dot+cross diagram
• Properties of giant covalent lattices

  • High mpt/bpt (covalent bonds strong so high energy to break), insoluble in almost all solvents (bonds too strong to be broken by interactions w/ solvents), electrical conductivity (diamond/silicone no- no electrons not involved in bonding + graphene/graphite- yes)
• Graphene


  Single layer graphite, hexagonally arranged (planar 120°) carbons, conducts electricity & thinnest + strongest material in existence
• Graphite


  Parallel layers hexagonally arranged carbon atoms (planar 120°). Layers bonded by weak london forces, spare electron delocalised between layers→ conducts electricity
• Periodic trend mpts period 2+3


  Increases group 1-14, sharp decrease 14-15, comparatively low 15-18
• Most common reactions of group 2


  • Redox. They act as reducing agents
• Reaction with oxygen


  2M (s) + O​2​ (g) →2MO (s) (Mg burns w/ white light, MgO=white) (M=generic group 2 metal)
• Reaction with water


  M (s) + 2H​2​O (l) →M(OH)​2​ + H​2​ (g). Reaction more vigorous as reactivity increases down group
• Reaction with dilute acids


  Reactivity increases down group, metal + acid→salt + hydrogen e.g. M (s) + 2HCl (aq) →MCl​2​ (aq) + H​2​ (g)
• Reactivity increases down group

  Lose 2 electrons, requiring energy for 1st+2nd ionisation energies, these decrease down group b/c attraction decreases b/c atomic radius + shielding increase
• Oxides reaction with water


  MO(s) + H​2​O (l)→ M​2+​ (aq) + 2OH​-​ (aq), only slightly soluble so once solution saturated, any further ions: M​2+​ (aq) + 2OH​-​ (aq) -> M(OH)​2​ (s)
• Solubility hydroxides increases down group


  More OH​-​ ions→ more alkaline (higher pH)
• Compounds in agriculture


  • Ca(OH)​2​ (s) + 2H​+​ (aq) → Ca​2+​ (aq) + 2H​2​O (l)
• Compounds in medicine


  • Antacids to treat indigestion, 'milk of magnesia' suspension of white Mg(OH)​2​ in water. Mg(OH)​2​ (s) + 2HCl (aq) → MgCl​2​ (aq) + 2H​2​O (l) /// CaCO​3​ (s) + 2HCl (aq) -> CaCl​2​ (aq) + H​2​O (l) + CO​2​ (g)
• Appearance and state of halogens at RTP

  • F​2​: pale yellow gas (reacts w/ almost any substance), Cl​2​: pale green gas, Br​2​: red-brown liquid, I​2​: shiny grey-black solid, At​2​ never been seen (radioactive + decays rapidly)
• Trend in boiling point down group

  More electrons, stronger London forces, more energy to break intermolecular forces, bpt increases
• Most common reaction of halogens

  • Redox, oxidising agents
• Halogen-halide displacement reactions


  Cl​2 ​reacts with Br​-​ (Cl​2​ (aq) + 2Br​-​ (aq) →2Cl​-​ (aq) + Br​2​ (aq) orange), Cl​2 ​reacts with I​-​ (Cl​2​ (aq) + 2I​-​ (aq) → 2Cl​-​ (aq) + I​2​ (aq) violet), Br​2​ reacts with I​-​ only (Br​2​ (aq) + 2I​-​ (aq) → 2Br​-​ (aq)+ I​2​ (aq) violet), I​2 ​doesn't react at all
• Trend in reactivity down group

  Atomic radius increases, more inner shells so shielding increases, less nuclear attraction to capture another electron, reactivity decreases
• Become weaker oxidising agents down group
• Disproportionation


  Redox reaction where same element is both oxidised + reduced, e.g. Cl​2​ (aq) + H​2​O (l) → HClO (aq) + HCl (aq) (bacteria killed by chloric (I) acid/ions, chloric (I) acid acts as weak bleach- indicator paper will turn red then white), Cl​2​ (aq) + 2NaOH (aq)→ NaCl (aq) + H​2​O (l) + NaClO (household bleach)