Periodic Trends

There are many ways to use the periodic table Trends are based on electronic structure The trends we will discuss are:

shielding atomic mass atomic radius ionization energy metallic character ionic radius properties of the metals and non-metals melting point

Valence Shell

Def: the orbitals in the highest energy level

on any one row on the periodic table – s & p

valence electrons are only in these orbitals

core electrons are ALL the electrons between the valence electrons and the nucleus

Valence Shell (Cont.) for each row on the periodic table, the outermost

energy levels are always the s and p orbitals (check it out by comparing/contrasting the electron configurations for S, Se, Te, and Po)

for each period (row), the highest energy levels only have s or p as their orbital paths!

exs: S: [Ne] 3s2 3p4 ← Highest energy level: 3rd

only orbitals in level: s & p Se: [Ar] 4s2 3d10 4p4 ← Highest energy level: 4th

only orbitals in level: s & p Te: [Kr] 5s2 4d10 5p4 ← Highest energy level: 5th

only orbitals in level: s & p Po: [Xe] 6s2 5d10 4f14 6p4 ←Highest energy

level: 6th

only orbitals in level: s & p

Shielding

There is a rough cancellation of core electrons and protons

Effective nuclear charge is the positive charge felt after one-for-one cancellation of core e-s and protons

For example, Na has an effective nuclear charge of +1 the electron configuration for Na: [Ne] 3s1 it has 1 valence electron and 10 core electrons 11 protons – 10 core (shielding) electrons +1 effective nuclear charge

Periodic Trends

Atomic Mass: increases down a group (column) each time you go down one box in a group, the number

of protons increases as you add protons to an atom, the mass goes up you also need to add neutrons to keep the nucleus

stable, increasing the mass even more Atomic Mass: increases as you go across a row

each time you go across one box in a row, the number of protons increases

as you add protons to an atom, the mass goes up you also need to add neutrons to keep the nucleus

stable, increasing the mass even more

Periodic Trends

Atomic Radius: increases as you go down a group as you go down through each box in a group, you add a

new energy level and more shielding each new energy level wraps around all the previous

energy levels each new energy level increase the size of the atom

due to the shielding, the protons do not have an increased pull on the outer electrons

as the atom grows, so does the radius of the atom

Periodic Trends

Atomic Radius: decreases across each period as you travel across a row, the maximum number of

energy levels does NOT change, nor does the shielding as you travel across a row, the number of protons

DOES increase as the positive charge increases with the same

shielding, it attracts the e–s more strongly with increased pull from the nucleus, all energy levels

are pulled in closer to the nucleus with the energy levels closer to the nucleus, the atomic

radius shrinks

Periodic Trends

Atomic Radius comments: even though the number of protons increases as you go

down a group the atomic radius also increases the atomic radius increases in this case because the e−s

in the new energy level have to be significantly away from the electrons in the last energy level

across a row, the shrinking caused by the increase in protons is substantially smaller then adding a whole new energy level

Periodic Trends Ionization Energy: the amount of energy needed

to remove an e– from an atom even though ions can be made by adding or subtracting

e–s to(from) an atom, we are only considering removal of e–s here

as you travel across any period, the maximum energy level does not change (see last slide)

the attraction between the opposite charges in the atom changes based on the distance between the nucleus and the electrons

Big distance changes result in even larger energy changes: going out one energy level results in a big drop in energy holding electrons in place.

Periodic Trends

Ionization Energy: decreases as you go down a group as you add energy levels, the distance between the

nucleus and the outermost electrons increases this increase in distance decreases the ability of the

nucleus to hold the electrons in the atom that makes it easier to remove the electrons, decreasing

the amount of energy needed to remove an electron from the valence shell

that means the ionization energy drops

Periodic Trends

Ionization Energy: increases as you go across a period remember, as you go across a row, the atomic radius

shrinks AND the number of protons increases as the electrons get closer to the nucleus with an

increased positive charge, the attraction between the electrons and the nucleus increases

this requires more energy to remove any electron

that means the ionization energy increases, as a general

rule…

Periodic Trends

Going from the s orbital to the p orbital, the ionization energy drops, slightly, due to the slightly higher energy of the p orbitals (they are a little further from the nucleus)

The ionization energy drops very slightly after the fourth electron is added to the p orbital: the first pair of electrons in one orbital path The e−- e− repulsion increases b/c there are now 2 e−s in

the orbital. The extra pushing means the electrons are trying to get away from each other and less energy is required to remove the electron from the atom

Periodic Trends Reactivity – the ability of an element to form ionic

compounds For bonding purposes, metals lose electrons when

bonding to form compounds The more easily a metal will lose an electron, the more

metallic it is (the more reactive it is) Reactivity is a measure of how easily an element will

form a compound from all the other trends it should be clear that Fr is the

most reactive of all the metals: it is the largest element; it has the lowest ionization energy so, it will lose a valence electron most easily meaning it will form ionic bonds easily this makes it the most reactive metal

Next slide…

Periodic Trends

Reactivity (Continued) As a trend, the further you get from the steps on the

periodic table on the metals’ side, the more reactive the element is

This should make sense, b/c the steps are the metal/non-metal divider

Non-metals next…

Periodic Trends

Reactivity (Continued) For NONMETALS, there is also a definition for

reactivity The further you get from the step, the reactivity also

increases This is because the atoms there can more easily add an

electron because of the small radii and high ENC making them more reactive…

Periodic Trends Ionic radius – the radius of an ion as compared to

its neutral atomic radius As you make positive ions, the size tends to decrease The number of protons has not changed With fewer electrons, there is less repulsion pushing

the electrons apart With the same positive charge but lower repulsive

forces, the protons are able to draw the electrons closer This shrinks the atomic radius This is all based on the balance between repulsion

between the e−s and the attraction between the e−s and the nucleus

Periodic Trends

Ionic radius (continued) As you make negative ions, the size tends to increase The number of protons has not changed With more electrons, there is greater repulsion pushing

the electrons apart With the same positive charge but higher repulsive

forces, the electrons push away from each other more This increases the atomic radius This is again based on the balance between repulsion

between the e−s and the attraction between the e−s and the nucleus

Properties of the Metals Metals tend to be more malleable (able to be

pounded or rolled out in to thin sheets) Metals tend to be shiny Metals tend to be more lustrous (have a shimmer) Metals tend to have a heavier feel (have higher

density) for the same volume of material There are always exceptions to trends:

some metals are dull, feel light, and/or crumble when you try to make them into thin sheets, but this is not the majority of metals

Remember the majority of the metals behave as stated above

Properties of Non-Metals Non-metals tend to have a duller appearance when

solid Non-metals tend to crumble when pounded or

rolled out Non-metals tend to have a lighter feel (lower

density) when compared to the same volume of a metal

They are better electrical and thermal insulators They have more variety in their state, as a group