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Periodic Trends

Periodic Trends. Periodic Trends. You can use the periodic table to figure out the properties of elements The properties that change in a systematic way as you move either across a row in the periodic table or down a group are called periodic trends. Trend 1: Atomic Radii.

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Periodic Trends

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  1. Periodic Trends

  2. Periodic Trends • You can use the periodic table to figure out the properties of elements • The properties that change in a systematic way as you move either across a row in the periodic table or down a group are called periodic trends

  3. Trend 1: Atomic Radii • Atoms are basically spherical (round), so their sizes are described by their atomic radius • The atomic radius is half the distance between 2 atoms of the same element • For example, if the distance between 2 atoms of the same element is 120 nm (picometers), the atomic radius of that element is 60 nm. THE TREND • As you move left to right across the PT, the radius of the elements decreases – this is because there are more negative charges for the positive nucleus to act on, so the electrons get pulled closer to the nucleus • As you move down a group, the radius of the elements increases – the electrons are being added to higher energy levels, so they have bigger orbitals

  4. Trend 2: Ionization Energy • The ionization energy of an element is the amount of energy it takes to pull one electron off of an atom • As you move left to right, the ionization energies of elements increase – remember that elements on the L side of the PT want to lose electrons • As you move down the periodic table, the ionization energies of elements decreases – this is because the nucleus can not hold on as strongly to electrons farther away

  5. Multiple Ionizations • If you want to pull off more than one electron, more energy is required than to pull off only one. • This is why the alkaline-earth metals are less reactive than the alkali metals • This is especially true, as soon as an element reaches the amount of valence electrons of a noble gas Practice: which is easiest to remove 1 electron, 2?

  6. Trend 3: Electronegativity • Electronegativity measures how hard an element tries to pull electrons away from other atoms it is bonded to • Elements on the R side of the PT want to grab electrons so they have HIGH electronegativity • Elements on the L side of the PT want to lose electrons, so they have LOW electronegativity • Noble gases have no electronegativity

  7. The Glue • There are a bunch of periodic trends. Most of them involve the octet rule, which says that all elements want to gain or lose electrons to be like the nearest noble gas.

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