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Periodic Trends

Ellen D'Astous

Period Trends
  • Periodic Trend - Left to Right
  • Group Trend - Up and Down
Atomic Radius
  • Periodic trend - decreasing
  • Group Trend - increasing
  • Factors
    • Nuclear Charge - the charge in the nucleus (comes from the # of protons)
    • period and group increase
    • Shielding Effect
    • period stays the same, group increases
  • Exceptions
    • p³p⁴ exception
    • p⁴ should be bigger, but the atom prefers to be fully half filled
  • Effective Nuclear Charge
    • The difference between the nuclear charge and the shielding effect
    • Zeff - Z=atomic # eff=effective nuclear charge
    • Z = NC - SE (NC = nuclear charge & SE = shielding effect
Ionization Energy
  • The energy required to take away an electron from the atom
  • Periodic Trend - increasing
  • Group Trend - decreasing
  • Factors
    • Atomic Radius
    • the closer to that nucleus, the harder it is to remove an electron 
    • (more pull towards nucleus)
  • Exceptions
    • s²p¹ - easier to take an electron from than         
    • electrons prefer to be paired in an orbital
    • p³p⁴ - prefers to be fully half full
    • fully filled orbitals require more energy to eliminate an electron
    • cause peaks in graph
  • it’s easier to get rid of an electron from higher orbitals (higher energy, electrons further from nucleus)
  • Cations are a result of ionization
Electron Affinity
  • The energy released when an electron is added
  • becomes more stable (shows stability by releasing energy)
  • Metals have low electron affinity
  • Electrons move from atoms with low ionization energy to an atom with high electron affinity
  • The closer the element is to the noble gases, the higher electron affinity
  • noble gases are fully filled ➜ preferred state (low/positive electron affinity)
Ionic Radii
  • The distance from the center of the ion to the outermost electron
  • ion = a charged particle
    • cation (+) - atom has lost an electron, radius gets smaller (less repulsion, lower energy level, more shrinking effect - proton-electron ratio increases)
    • anion (-) - atom has gained an electron, radius gets bigger (more repulsion, more electrons ➜ proton-electron ratio in favour of enlarging effect of electrons)
  • Periodic Trend -  decreases (metals), (non-metals, closer to F) increases
  • Group Trend - increases
  • Metals have lower ionization energy than non-metals
    • The ion of a metal will always be smaller than the original metal
    • The ion of a non-metal will always be bigger than the original atom
Electronegativity
  • Measures an atoms attraction towards electrons in a bond
  • Electrons move from atoms with low ionization energy to atoms with high electron affinity
  • Tells you how equally/unequally the atoms share the electrons in a bond
  • Cs (lowest electronegativity) F (highest electronegativity)
  •   smaller atoms have ‘more custody’ - closer to nucleus ➜ more pull / more nuclear charge
  • When two atoms are bonded, they share a pair of electrons
  • noble gases don’t like bonds, halogens always have the highest electronegativity in their periods
Metallic Character
  • Tendency to lose an electron (similar process and inversely related to ionization energy)
  • Group Trend - increases
  • Periodic Trend - decreases
Valence Electrons
  • Electrons in the highest/outermost energy level
  • Electrons with the highest energy
  • Group Trend - increases (within main group elements)
  • Periodic Trend - stays the same 
  • use electron configuration to determine valence electrons
Important Names
  • Representative/Main Group - Group 1A-Group 8A
  • Alkaline Earth Metals - Group 2A
  • Halogens - Group 7A
  • Noble/Inert Gases - Group 8A
  • Rare Earth Metals - f-block elements
  • Lanthanide Series - elements in 4f series (atomic # 57-70)
  • Actinide Series - elements in 5f series (atomic # 89-102)
  • Metalloids/Semi-Metals - Se, Ga, As, Sb, Te, Be
  • Metals - left side of the Periodic Table
  • Non-Metals - right side of the Periodic Table
  • Transition Metals - D-block
Lab - Reactivity of Alkaline Earth Metals
  • Properties of Alkaline Earth Metals
    • They react with water and phenolphthalein 
    • They turn purple or pink
    • Mainly white
    • Typically react with water to make hydroxide and hydrogen gas
    • Valence Electrons - 2 (make ions with 2+ charges)
  • Hazards/Precautions
    • going down the group, they are very reactive
    • they may react with your skin and clothes and corrode them
    • the gas (the product of Ca reacting with water) may be very flammable
    • Cover the gas
    • Wear Goggles!
  • If the metal reacts with oxygen, does the product have a greater or lesser mass than the reacting metal? Why?
    • Greater, because you’re adding oxygen to the metal and making it larger
  • What does the pink colour of phenolphthalein solution indicate?
    • The alkaline earth metals have reacted with the water
  • How should you dispose of the products of the reaction of calcium and water?
    • First neutralize it, to lower the pH and make it safe to release
    • You can neutralize it with a base
  • Calcium and Magnesium (unreacted) are shiny when they are pure. If the metals you worked with weren’t shiny, explain why this is so.
    • They may have reacted with the air or the water in the air
  • Is the reaction of calcium in water exothermic or endothermic? Use your observations 
    • Endothermic, because they didn’t release energy (no smoke/heat)
  • Phenolphthalein is pink in base/alkaline solutions. Did the reactions of the alkaline     earth metals with water produce alkaline solutions?
    • No, because the liquid was not pink
  • When a solution of calcium hydroxide becomes saturated, a white solid, calcium     hydroxide appears. Did your calcium hydroxide become saturated?
    • Yes, the solids in the pink liquid were not turning pink or dissolving
  • Did magnesium react with water to form a gas and an alkaline solution?
    • No, even though the liquid was pink, the magnesium didn’t really change, and it wasn’t covered
  • Groups of metals change in reactivity from top to bottom. What evidence do you have      that there was a pattern in the reactivity of alkaline earth metals?
    • With Ca, it reacted with just water, but Mg did not react with water. Thus, you can conclude that as you go down the periodic table, they get more reactive.
  • Was there any evidence that aluminum reacted with water?
    • No, no visual changes or evidence
  • Are Mg and Ca more reactive with water than Aluminum? 
    • Yes, because the calcium was not shiny and the magnesium and aluminum were very shiny.
  • What can you conclude from the colour of the solutions made from the magnesium    and aluminum oxides when phenolphthalein was added?
    • They react differently, they don’t have similar chemical properties
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