Chemical thermodynamics

1. Basic definitions – Elements structure - Reactivity –the Periodic table

2. Chemical thermodynamics – evolution of chemical systems- equilibrium –

3 . Acid -Base reactions – Oxido-reductions – Photo-chemistry

Microscopic scale

Macroscopic scale

Basic definitions

An atom consists of a nucleus made up of protons and neutrons (on the order of 20,000 times smaller than the size of the atom).

The outer part of the atom consists of a number of electrons equal to the number of protons, making the normal atom electrically neutral.

A chemical element consists of those atoms with a specific number of protons in the nucleus; this number is called the atomic number Z.

The atoms of an element may differ in the number of neutrons; atoms with different neutron numbers are said to be different isotopes of the element.

An atom can loose or gain electron in a chemical reaction. It is then called an ion and lose it neutrality.

Elements are represented by a chemical symbol, with the atomic number and mass number sometimes affixed as indicated below. The mass number is the sum of the numbers of neutrons and protons in the nucleus.

an atomic mass unit or amu is one twelfth of the mass of an unbound atom of carbon-12.

Periodic table (1)

This periodic law is represented in the periodic table.

The different isotopes of a given element have the same atomic number but different mass numbers since they have different numbers of neutrons. The chemical properties of the different isotopes of an element are identical ( why ?*) , but they will often have great differences in nuclear stability.

* Chemical reactions do not modify the nucleus but the electron configurationNuclear reactions modifies the nucleus

Isotopes

Biogeochemical applications ( can you cite some? ) use the knowledge of specific element radioactive decay and measurements of isotopic ratios.

Atomic mass or atomic weight is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element.

e.g. The atomic mass of carbon is 12.011 amu, the atomic mass of hydrogen is 1.0079 amu

In chemical reactions, atoms can combine to form molecules (simple or complex compounds) .

Compounds can then react together.

The number and nature of atoms are conserved in a chemical reaction ( hence so does the mass)

The atom energetic state can change according to certain rules . These rules basically define the possibility of formation of molecules at the microscopic scale and the existence of chemical reactions (we ‘ll see later a macrosopic or thermodynamic approach)

Chemical reactions : microscopic scale

What determines this reaction pattern ?

Atomic structure and reactivity

Atomic emission spectra

p

(Bohr)

The quantum mechanical atom

Quantum mechanics (Schrödinger, etc ) shows that the electron are organized within the atoms into shells , subshells and orbitals whose relation to one another depends on the energy state of the atoms defined by its principal quantum number

•Schell : or ‘energy level’ defined by its principal quantum number (1,2,3, …n)•Subschell : location within a schell (energy sublevel) defined by letters s,p,d,f•Orbital : region where the electron is most likely to be found (density of probability presence)

Building up an energetic representation of elements / electronic configurationImagine you want ‘build’ elements (starting from H) by adding electrons to nuclei that increase in proton number in the same way . Q.M establishes precise rules to do so :

Practical diagrams

Practical exercise:

What is electron configuration for

K:

P:

Periodic table 2 : relation between elements structure, period and properties

Valence layer, octet rule, Lewis symbols

Determines the reactivity of elements at the microscopic scale

To summarize a bit …

Dimensionless quantity (eg Pauling scale)

Formation of molecules

http://www.chem1.com/

Bond formation

Chemical bonding and physical properties of substances

Destruction of a bond corresponds to a release of energy .

Covalent bonding : single, double or triple

Covalent double or triple bond energies are higher than for single bonds.

Energetic aspects

Implication for the reactivity of compounds at the microscopic scale -- - why certain chemical reactions occurs and other never .

Alkanes (C-C single bonds) Alkenes (C-C double bonds)

etheneethane

Alkynes (C-C triple bonds)

ethyne Benzene

Aromatic compounds

Oxygenated hydrocarbons:Aldehydes, alcohols, ketones, etc…

CnH2n+2 CnH2n

CnH2n-2 CnH2n-6

ORGANIC MOLECULAR NOMENCLATURE based on covalent bonding

methanol Acetic acid acetaldehyde