The Modern Period Table of Elements
An element is a pure substance that cannot be broken down into simpler substances by chemical
composed entirely of only one kind of atom
Elements that conduct heat/electricity, are malleable, ductile, and lustrous are classified as metals.
Elements that are non-conductive and brittle as solids are classified as nonmetals.
Elements that have share metallic and nonmetallic properties are classified as metalloids.
Modern periodic law states that when elements are
arranged in order of their increasing atomic number,
their properties show a periodic recurrence and gradual
A group is a vertical column in the periodic table
with elements that share similar chemical
A period is a horizontal row of elements whose
properties change from metallic on the left to
nonmetallic on the right.
alkaline earth metals
Groups and Series of Elements
Representative elements (most closely follow periodic law)
alkali metals soft, silver coloured metals Li
(Group 1) solids at room temperature Na
exhibit metallic properties K
react violently with water
react with halogens
stored under oil to prevent reaction with air
alkaline earth light, reactive metals Mg
metals (Group 2) solids at room temperature Ca
exhibit metallic properties Sr
react violently with acids
form oxide coatings when exposed to air
halogens solids, liquids, or gases F
(Group 17) exhibit nonmetallic properties Cl
extremely reactive with hydrogen and metals Br
noble gases gases at room temperature He
(Group 18) extremely unreactive Ne
Kr, Xe, and Rn reluctantly form compounds with F Ar
radon is radioactive
transition metals strong, hard metals with high mps Fe
conduct heat and electricity Cu
variable reactivity Ag
many react with oxygen to form oxides Zn
some react with acids to form hydrogen gas Co
lanthanides elements with atomic nos. 57-70 Ce
actinides elements with atomic nos. 89-102 U
Developing a Model of the Atom
Empirical knowledge comes directly from observations and experimentation.
Theoretical knowledge is knowledge based on ideas created to explain observations.
A theory is a comprehensive set of ideas that attempts to explain a law or related observations.
A model is a mental or physical representation of a theoretical concept.
The smallest particle of an element that has all the properties of that element is an atom.
The small, positively charged centre of an atom is the nucleus.
A proton is a positively charged subatomic particle in the
nucleus of an atom.
An electron is a negatively charged subatomic particle.
A neutron is an uncharged subatomic particle in the nucleus
of an atom.
Understanding Atomic Mass
Atomic number (Z) is the number of protons present in the nucleus of an atom of a given element.
The number of electrons equals the number of protons in an atom.
Atomic mass (A) is the sum of the number of protons and neutrons present in the nucleus of an atom.
number of neutrons = mass number – atomic number
N represents the number of neutrons. A collective term for protons and neutrons, the elementary
particles found in the nucleus, is nucleons.
Isotopes are atoms of an element that differ from each other only in the number of neutrons in their
mass number A 14 12
atomic number ZX C C
A naturally or artificially produced element that is capable of
spontaneously emitting radiation in the form of particles and/or
gamma rays is a radioisotope.
The majority of nuclei are unstable and exhibits radioactivity.
radioactive means capable of spontaneously emitting radiation in the form of particles and/or
Each type of unstable nuclei has a characteristic rate of decay, which varies from fractions of a second
to billions of years.
When nuclide of one element decays, it changes into nuclide of a different element.
The decaying nuclide is called the parent, and the product nuclide is called the daughter. Nuclear
decay produces a nuclide of lower energy as the excess energy is emitted as radiation.
During any transmutation event, the total Z (number of protons) and total A (sum of protons and
neutrons) of reactants must equal those of the products.
Total Z Reactants TotalA
Total Z Products
Modes of Radiation and Radioactive Decay
Alpha particles (symbolized or 4 He ) are dense, positively charged particles identical to helium
released during alpha decay
92 U 90Th 2 He
238 234 4
reactant product + particle
parent daughter + (2n+2p)
Beta particles (symbolized or 1 e ) are negatively charged
particles identified as high-speed electrons.
released during beta decay
6C 7 N 1e
14 14 0
reactant daughter + particle
0 n 1p 1e
1 1 0
Gamma rays (symbolized or 0 ) are very high-energy photons, about 105 times as energetic as
released during gamma emission (accompanies most other types of decay)
U 234 Th 4 He 2 0
92 90 2 0
parent daughter + particle + 2 gamma rays
Measuring Radioactive Decay
All radioactive material decays at a characteristic rate, regardless of the chemical substance in which
the rate of decay is called the activity and can be measured with a Geiger counter
the SI unit of activiy is the becquerel (Bq), defined as one disintegration per second (1 Bq = 1 d/s)
the curie (Ci) is equal to the number of nuclei disintegrating each second in 1 g of radium-226
1 Ci = 3.70 x 1010 Bq
Half-life (t1/2) is the time it takes for half of the nuclei present
The amount of nuclei remaining is halved after each half-
Every radioisotope has its own characteristic value for
half-life, and can be measured in seconds (s), minutes
(min), hours (h), or years (a).
6 C 14
7 N 0
1 e t 1/ 2 5730 a
application of radioisotopes naturally present to determine the age of an object
the accuracy of the method diminishes after 6 half-lives and specific radioisotopes can be used for
different substances and various lengths of time
A technique that uses radioactive carbon-14 to identify the date of death of once living material is
called carbon-14 dating.
14C : 12C ratio is determined based on radioactivity of the sample, from which the elapsed time can
t A is the measured activity
A A0 2 t1/2 A0 is the normal activity
t is the time elapsed
t1/2 is the half-life
potassium-40 and uranium-238 can be used to date non-living materials with much greater ages
Continuous spectrum is the pattern of colours observed when a narrow beam of white light is passed
through a prism or spectroscope.
contains all wavelengths of visible light
Line spectrum is the pattern of distinct lines, each of which corresponds to light of a single
produced when light consisting of only a few distinct wavelengths is passed through a prism or
When the atoms of elements are energized, they emit characteristic patterns to their line spectra.
each line corresponds to a specific quantity of energy as an electron returns to its original energy
Modern Atomic Theory
The orbitals of an electron are actually regions of fixed energy in which an electron is allowed to move
and orbit the nucleus.
energy levels (or energy shells)
Features of the First Four Shells
Number of Maximum number of electrons per Maximum Number of electrons per
subshells shell subshell
1 1 2 (2)
2 2 8 (2 + 6)
3 3 18 (2 + 6 + 10)
4 4 32 (2 + 6 + 10 +14)
Ground state is the lowest energy level that an electron can occupy.
Transition is a movement from one energy level to another.
Valence electrons are those electrons in the highest energy level of an atom.
Trends in the Periodic Table
the distance between the nuclei of bonded or adjacent atoms of
the same element divided by two
down a group, the atomic radius gets larger (adds on extra
across a period, the atomic radius gets smaller (more electrons
in valence shell, attracts to nucleus)
a measurement of the size of an ion
positive ions are smaller than atoms (same positive
charge in nucleus pulls electrons tighter)
negative ions are larger than atoms (greater number of
electrons, more negative charge, nucleus cannot hold as
Trends in the Periodic Table
the amount of energy required to REMOVE an electron from
an atom or ion in the gaseous state
X(g) + IE1 X+(g) + 1e-
Moving down a group,
increase in number of orbitals
increase in atomic radius
since the electrons are further from the nucleus, they are more loosely held and easier to
The first ionization energy decreases down a group.
Moving across a period,
increase in number of protons in the nucleus
decrease in atomic radius
since the electrons are closer to the nucleus, they are more tightly held and harder to remove
The first ionization energy increases across a period.
Second Ionization Energy
By removing a second electron from the cation formed in the gaseous state, the second ionization
energy is measured.
+ IE1 + IE2 + IE3
atom +1 ion +2 ion
after the removal of first electron, ionic radius is smaller as electrons are held more tightly
more energy is required to remove second electron
second ionization energy is larger
IE1 < IE2 << IE3 <<< IE4
the energy released when an electron is accepted by an atom in the gaseous state
X(g) + 1e- X-(g) + EA1
The stronger an atom holds its valence electrons, the more likely that atom will want to gain another
[EXCEPTION: noble gases already have a full octet]
As atomic radius increases, the atom has looser hold on
electrons, the electron affinity decreases.
down a group, EA decreases
As atomic radius decreases, the atom has tighter hold on
electrons, the electron affinity increases.
across a period, EA increases
Reactivity is a chemical property of an element that indicates the tendency of the element to form a
an element that forms compounds easily has high reactivity
an element that does not form compounds has low reactivity
An activity series is a list of elements in order of their reactivity, based on evidence gathered from
single displacement reactions.
Ionic compounds are pure substances
composed of ions and formed from a metal
and a nonmetal.
Ionic bonds are a type of chemical bond
created by the electrostatic attraction
between positive and negative ions.
Octet rule states that representative elements
want a stable octet consisting of a full shell
of eight electrons in their outer energy level.
metallic elements lose electrons (positive
nonmetallic elements gain electrons
Molecular compounds are pure substances composed of two
or more nonmetals.
Covalent bonds are a type of chemical bond created by an
attractive force between two atoms when they share
nonmetallic elements want to gain electrons and are
involved with covalent bonding
Properties of Compounds
The simplest whole number ratio of ions in an ionic compound is called the formula unit.
ions actually form a crystal lattice – a regular, ordered arrangement of ions
Properties Ionic Molecular
Melting point High Low
No conductivity No conductivity
in solid state
in liquid state Conductivity
Consistency of solid Hard, brittle Soft, waxy or flexible
Intramolecular force is the attractive force between atoms and ions within a compound.
strong intramolecular force in ionic solids
Intermolecular force is the attractive force between molecules.
experienced by molecules of molecular compounds
a representation of an atom or ion, made up of the chemical symbol and dots indicating the number
of electrons in the valence energy level
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
In the formation of ionic compounds, show the movement of electrons with a full arrow:
. . +2 .. -2
[Mg] [ O ]
Mg + O ..
In the formation of molecular compounds, show the movement of electrons with a half arrow:
.. .. .. .. .. ..
Cl + Cl Cl . . Cl Cl Cl
.. .. .. .. .. ..
the covalent bond is shown with a solid line
Drawing Lewis Structures and Structural Formulae for Molecular Compounds
Step 1 Place the element with the highest bonding capacity in the central position and arrange
the symbols of the other elements around it.
Step 2 Add up the number of valence electrons available in each of the atoms. For polyatomic
ions, add one electron for each unit of negative charge, or subtract an electron for each
unit of positive charge.
Step 3 Place one pair of electrons between each adjacent pair of electrons, forming single
Step 4 Place pairs of the remaining valence electrons as lone pairs on the peripheral atoms
Step 5 If octets are not complete, move lone pairs into bonding position between those atoms
and the central atom until all octets are complete.
Step 6 If the peripheral atoms all have complete octets and there are pairs of electrons
remaining, place these electrons as lone pairs on the central atom.
Step 7 To give the structural formula, remove the dots representing the lone pairs and replace
bond dots with dashes.
Step 8 If you are representing a polyatomic ion, place brackets around the entire structure and
write the charge outside the brackets.
Coordinate Covalent Bond
Molecular compounds often have pairs of electrons that are not involved with bonding called lone
Lone pairs can be used to form covalent bonds, in which one atom donates both electrons to be
coordinate covalent bonds
A B A B
A B A B bond
The ammonium ion (NH4+) is an example of coordinate covalent bond.
H+ .. H
H N H
H N H
Identifying Coordinate Bonds
Draw the Lewis structure for the compound.
Count the number of bonds between the central atom and the peripheral atoms.
Compare the number of bonds to the bonding capacity of the central atom.
If the number is more than the bonding capacity, one or more of the bonds is coordinate covalent.
To identify which ones, remove the peripheral atoms one at a time.
If you can do this and leave the central structure with a complete octet, you have identified
coordinate covalent bonds.
Within a covalent bond, the electronegativity (Pauling) of each bonding atom affects the type of bond.
electronegativity is a property of an atom within a covalent bond describing its ability to attract
the electrons in the bond to its nucleus
Nonpolar covalent bond results from a zero difference in electronegativity between the bonded atoms
and has equal sharing of bonding electrons.
Polar covalent bond results from a difference in electronegativity between the bonded atoms and the
electrons are not shared equally.
results in partial positive and negative ends of the bond called dipoles (+ and -)
When the electronegativity difference is high, the bonding pair of electrons is mostly with one
atom/ion resulting in an ionic bond.
the greater the difference in electronegativity, the more ionic character of the bond
Both the polarity of the bonds and the shape of the molecule determine if the molecule is polar or
A nonpolar molecule has either all nonpolar bonds or polar bonds whose bond dipoles cancel,
such that there is no positive/negative ends.
Symmetrical molecules with polar bonds are generally nonpolar since the sum of the bond
dipoles is zero.
A polar molecule has polar bonds with dipoles that do not cancel and create positive and negative
ends of the molecule.
the force of attraction and repulsion between molecules
generally much weaker than covalent and ionic bonds (intramolecular forces)
1. dipole-dipole forces
a force of attraction between polar molecules where the oppositely charged dipoles attract one
the greater the polarity of the molecule, the greater the strength of the dipole-dipole force
2. hydrogen bonds
special dipole-dipole forces involving N-H, O-H, and F-H bonds
highly polar bonds and molecules, resulting in strong intermolecular forces between the
hydrogen atom and the lone pair of N, O, or F
3. London dispersion forces
weak intermolecular forces in nonpolar molecules
due to the simultaneous attraction of the elecrons of one molecule by the positive nuclei in the
by increasing the number of electrons in the molecule, the strength of London forces