Trends of the Periodic Table

Background Electrons can jump between shells (Bohr’s model supported by line spectra) The electrons can be pushed so far that they escape the attraction of the nucleus Losing an electron is called ionization

Ions An electrically charged particle formed when an atom or molecule loses or gains an electron. Q: what would the charge be on an atom that lost an electron? Q:Gained two electrons? A: +1 (because your losing a -ve electron) called a cation A: -2 (because you gain 2 -ve electrons) called an anion

Ionization energy Ionization energy is the energy required to remove one outer electron from an atom. 11p + 12n ° + Ionization Energy Na + 1e - +1 Most weakly held + E ionization Na +1 (g) + 1e -

Predict… Is there an IE trend in the PT of E? Down a group? Across a period? I.E. DECREASES because: oMore energy levels, resulting in a decrease in attractive forces between the nucleus and valence electrons. Removing one electron becomes easier. I.E. INCREASES because: oElectrons are added along the same energy level, increasing the attractive forces between protons and valence electrons requiring more IE to remove them.

Ionization energy vs. atomic number

Electrostatic Force Theory (EFT) The degree of attraction or repulsion experienced by two charged particles depends on TWO main factors: 1. The distance between them 2. The magnitude of the charge. As the # of protons in the nucleus increases, the electrons will experience a greater electrostatic attraction for the nucleus. As electrons are positioned in energy shells further from the nucleus, they will experience less electrostatic attraction from the positive nucleus.

What does this mean? Look at the arrangement of electrons Sodium BUT is ‘shielded’ by 10 electrons in front of it 11p + 12n ° Is being ‘pulled’ in by the 11 protons Chlorine BUT is ‘shielded’ by 10 electrons in front of it 17p + 18n ° Is being ‘pulled’ in by the 17 protons More protons means greater attraction between nucleus and outer electron thus higher ionization energy.

Electron Affinity The energy released when a free electron is added to the lowest available energy shell of an atom in the gas phase. + Electron Affinity Cl + 1e - + E.A. Cl -1 (g) + 17p + 18n ° 1e -

Predict… Is there an EA trend in the PT of E? Down a group? Across a period? EA. DECREASES because: oMore energy levels are added increasing the distance between the nucleus and valence electrons. EA. INCREASES because: oMore energy is released as atoms become more stable. For example, elements in group 7 are very stable with the addition of 1 e -, thus a higher EA. Elements in group 1 become less stable with the addition of 1 e -, thus a lower EA.

Atomic Radius the estimated distance from the centre of the nucleus to the outer edge of the atom. Typically radii = 100 pm (picometer) »1 pm = 1 x m

Predict… Is there a trend in Atomic Radii in the PT of E? Down a group? Across a period? Atomic size INCREASES because: oEnergy levels are added, therefore electrons are at a greater distance from the nucleus. oThere is an increase in shielding effect due to the inner electrons. Atomic size DECREASES because: oElectrons are added along the same energy level, so are protons, therefore overall attraction increases, atomic radius decreases.

Atomic radius vs. atomic number

Classwork/Homework Trends Worksheet Follow directions on the sheet and answer the questions. Hint: Ignore Hydrogen when looking at trends. Look at many periods/groups when summarizing trends.