The Periodic Table

The Modern Periodic Table

Basic Information about its construction
◦ The symbol for each element is shown in a separate box, in order of increasing atomic number from 1 to 118.
 Each box shows the atomic symbol with the atomic number above the symbol and the atomic mass below:

The Modern Periodic Table
◦ Each row is called a period & may contain from 2 to 32 elements.
◦ Each column is called a group & elements within groups have similar physical and chemical properties.
 Within a group, the closer elements are to each other, the more similar they are.
 On the PT, the groups are generally numbered, but
NOT on the PT provided for the AP Test.

The Modern Periodic Table

The Modern PT- as on the test

The Modern Periodic Table

Atomic Symbols
◦ Each element is designated by a 1 or 2 letter symbol.
◦ Most symbols are abbreviations of the elements’ English names.
◦ Some derive from the elements’ names in other languages.

The Modern Periodic Table
Non-English Chemical Symbols
Sodium Na Silver Ag Gold Au
Potassium K Tin Sn Mercury Hg
Iron Fe Antimony Sb Lead
Copper Cu Tungsten W
Pb

The Modern Periodic Table

When chemists use atomic symbols for formulas, ions, & isotopes, they add subscripts & superscripts to the 4 corners of the symbol to represent various features of the atom.
A
Z
Ca charge subscript
A – the mass # of an isotope
Z – the atomic #
Charge – charge of an ion that results when an electron is lost or gained
Subscripts- used in writing chemical formulas to show # atoms of each element

The Modern Periodic Table

Electrons, Protons, & Neutrons
◦ The PT can be used to quickly determine the # e & # p + in a particular elements.
◦ The # n 0 may be calculated only if a specific isotopic mass of an element is known.
◦ Protons - # p + is always equal to the atomic #
◦ Electrons-
 #e - is always equal to the atomic # for an atom
 #e - is the atomic # - charge of the ion for an ion
◦ Neutrons - #n 0 depends on knowing the specific isotope of the element in question. Why?
 B/c atomic masses are weighted averages of all the isotopes of an element, you cannot determine the #n 0 from it.
 BUT, if you know the mass of that specific isotope, then
 #n 0 = A – Z (mass number – atomic number)

The Modern Periodic Table

Isotopes – atoms with the same # p +
BUT different # n 0 .

The Modern Periodic Table

Mass Spectrometry

The Modern Periodic Table

Atomic Masses
◦ Weighted average mass of all isotopes of an element based on each isotope’s relative abundance.
n
◦ Ave. atomic mass = Σ(mass isotope i
)(abundance isotope i
) i=1

Periodic Properties of the Elements

Names of important groups on the PT
Alkali Metals
Alkaline Earth Metals
Chalcogens
Halogens
Noble Gases
Lanthanides
Actinides

Periodic Properties of the Elements

Each element in a group has the
◦ Same # of valence electrons
◦ Causes similarities in physical & chemical properties
◦ Ex. The Noble Gases have completely filled s & p sublevels, giving them extraordinary stability
◦ Ex. The Halogens are missing 1 p electron, otherwise they would be electronically the same as the Noble
Gases.
 Halogens tend to react so that they can gain that one p electron.
 Similarly, Alkali metals & alkaline earth metals have 1 & 2 s electrons respectively. They readily give up those electrons to become electrically identical (isoelectronic) with a noble gas

Periodic Properties of the Elements

Metals and Metalloids
◦ Metals dominate the PT, there are more metals than any other type of element on it.
◦ Metalloids border the line between metals and nonmetals.
 They exhibit some properties of metals and some properties of nonmetals.
 The metallic character of the elements increases from the top of the PT to the bottom as the group containing nitrogen shows.

Periodic Properties of the Elements

Periodic Properties of the Elements

Alltropes
◦ Elements that have 2 or more distinct sets of chemical and physical properties.

Periodic Properties of the Elements

Variation of Physical Properties
◦ Many properties vary regularly on the PT
 Melting & Boiling points of metals tend to decrease from top to bottom of a group.
 Melting & Boiling points of nonmetals tend to increase from top to bottom down a group.
 Similar trends in electrical properties, densities, & specific heats also occur in each group.

Periodic Properties of the Elements

Variation of Physical Properties
K
Rb
Cs
Element Specific Heat,
J/gK
Li
Na
3.56
1.23
.75
.363
.24

Periodic Properties of the Elements

Atomic Radii
◦ You do not get a chart/table/graph of the atomic radii for the elements
◦ What you need to remember…
 Atomic radius increases from top to bottom of a group b/c each increase in period # involves another larger, energy level.
 Atomic radius decreases left to right across a period because of an increase in the effective nuclear charge.

Periodic Properties of the Elements

Effective Nuclear Charge
◦ Core electrons (non-valence electrons) shield the valence electrons from an equal amount of positive nuclear charge. At the same, valence electrons do not shield other valence electrons from the remaining nuclear charge.
The result is an increase in nuclear charge from left to right in any given period.

Periodic Properties of the Elements
Effective Nuclear Charge

Periodic Properties of the Elements

◦ Energy needed to remove an electron from an atom completely.
 Always endothermic!
◦ 1 st ionization energy- removing the 1 st electron from an atom.
 For most elements decreases as from the top to the bottom of a group.
 It generally increases from left to right across a period, although relatively small decreases are seen when a shell is full or half-full
◦ Removing more than 1 electron reveals that valence electrons have relatively low ionization energy compared to core electrons.

Periodic Properties of the Elements

Ionization Energy
Ionization Energies (kJ/mol) of Selected Elements
Metal 1 st electron 2 nd electron 3 rd electron
Na
Mg
K
Ca
496
737
419
590
4563
1450
3051
1145
6913
7731
4411
4912

Periodic Properties of the Elements

Photoelectron Spectroscopy
◦ When high energy beams (ultraviolet, X-rays, or even visible light) are trained on the surface of the elements, electrons can be ejected. This is called the photoelectric effect.
 It’s how solar calculators work!
Light hits the solar cell, which ejects a steady stream of electrons. This causes a flow of electrons, which can power the calculator.

Periodic Properties of the Elements

Photoelectron Spectroscopy
◦ Photoelectron spectrometers measure the kinetic energies of the ejected electrons. They are also set up to bathe the sample in light of very specific energy.
 The difference between the energy of the incoming beam and of the outgoing photoelectrons tells how strongly the electrons are held in the atom, called binding energy.
 Binding energy = E incoming photon
 Similar to ionization energy
– E emitted photoelectron

Periodic Properties of the Elements

Photoelectron Spectroscopy
◦ The photoelectron spectra allows chemists to compare the energy levels within the atom so they can make correlations with effective nuclear charge, relative size of the atom, etc.

4 Types of Spectroscopy

1. UV-Vis(ible)
◦ Electronic
◦ Machine is called a spec-20
 Changes the quantum level, exciting e so it can move atoms/molecules

4 Types of Sprectroscopy

2. IR
◦ Vibrational
 Machine is a heat lamp
 Changes the dipole (partial charges) in molecules like CO
2
& H
2
O.

4 Types of Spectroscopy

3. μ waves
◦ Rotational
◦ Machine is a microwave
 Excites the rotation of H
2
O in food.

http://www.youtube.com/watch?v=MiL0wCZr0Mw http://www.youtube.com/watch?v=DZTXa4qerI4 (start at 2:40)
4 Types of Spectroscopy

X-ray
◦ Nuclear
◦ Machine is an X-ray machine
 Removes e from atoms
 nmr
◦ Nuclear
 Machine is a mri
 Uses a superconducting
Nb-alloy which only works below 30K. So its cooled by liquid He (4K).

4 Types of Spectroscopy
– μ wave – IR –
–

Periodic Properties of the Elements

Electron Affinity
◦ The energy change that accompanies the addition of an electron to an atoms.
 Some atoms readily attract electrons (halogens!), so their electron affinities have a negative value. The energy is released.
 Most atoms do not accept electrons readily
(remember most of the PT is made of metals!), so their electron affinities have a positive value. Energy must be added to the electrons.
 F has the highest affinity for electrons and Fr has the lowest.

Periodic Properties of the Elements

Electronegativity
◦ Developed by Linus Pauling to describe the attraction of electrons by individual atoms.
 Combination of ionization energy, electron affinity,
& other factors.
 Show the same diagonal trend as electron affinity does.

Periodic Properties of the Elements

Ionic Radii
◦ 2 types of ions, cations & anions
 cations – lost 1 or more electrons
 Always smaller than their neutral atoms. Usually about half the size of their neutral atoms + they have more protons than electrons.
 Anions – gain 1 or more electrons
 Always larger then their neutral atoms. Many are twice the size of their neutral atoms. More electrons than protons increases the repulsive force between each electron, which makes the ion bigger.

Periodic Properties of the Elements