Lecture 1 Analytical Chemistry

Topics: Atom, Electron, Ion Pages: 7 (1929 words) Published: February 5, 2012
Analytical chemistry

Analytical chemistry is the branch of chemistry that deals with the separation, identification and determination of components in a sample. Analytical chemistry can be divided into two branches, qualitative and quantitative.

Qualitative analysis
It deals with the identity of the constituents that are in an analytical sample.

Quantitative analysis
It deals with the determination of how much of a given substance is in the sample. The quantitative analyses are classified into several methods of analysis according to the process of the final measurements:

1. Volumetric Analysis
It deals with determination the concentration of a solution by titration against a solution of known concentration (standard).

2. Gravimetric Analysis
In whichthe substance being determined is converted into an insoluble precipitate which is collected and weighed

3. Instrumental Analysis
Determination of a final form by measuring some physical properties that is quantitatively related to the concentration of the analyzed sample by using an instrument; these include spectrophotometry, potentiometry, polarography, optical rotation etc. ..

Atomic struture

The basic building block of all matter is called an atom. Atoms are a collection of various subatomic particles containing negatively charged electrons, positively charged protons and neutral particles called neutrons. Each element has its own unique number of protons, neutrons and electrons. Both protons and neutrons have mass, whereas the mass of electrons is negligible. Protons and neutrons exist at the centre of the atom in the nucleus. Electrons move around the nucleus, and are arranged in shells at increasing distances from the nucleus. These shells represent different energy levels, the outermost shell being the highest energy level.

The number of protons that an atom has in its nucleus is called the atomic number. The total number of protons and neutrons in the nucleus of an atom is known as the mass number. For example, a carbon atom containing six protons and six neutrons has a mass number of 12.

Elements are substances containing atoms of one type only, e.g. O2, N2 and Cl2.Compounds are substances formed when atoms of two or more elements join together, e.g. NaCl, H2O and HCl.

Orbitals and electronic configurations
It is important to understand the location of electrons, as it is the arrangement of the electrons that creates the bonds between the atoms, and chemical reactions are just that to form new bonds. Electrons are involved in the chemical bonding and reactions of an atom. Electrons are said to occupy orbitals in an atom. An orbital is a region of space that can hold two electrons. Electrons do not move freely in the space around the nucleus but are confined to regions of space called shells. Each shell can contain up to 2n2 electrons, where n is the number of the shell. Each shell contains subshells known as atomic orbitals. The first shell contains a single orbital known as the 1s orbital. The second shell contains one 2s and three 2p orbitals. These three 2p orbitals are designated as 2px, 2py and 2pz. The third shell contains one 3s orbital, three 3p orbitals and five 3d orbitals. Thus, the first shell can hold only two electrons, the second shell eight electrons and the third shell up to 18 electrons, and so on. As the number of electrons goes up, the shell numbers also increase. Therefore, electron shells are identified by the principal quantum number, n¼1, 2, 3 and so on.

The electronic configuration of an atom describes the number of electrons that an atom possesses, and the orbitals in which these electrons are placed. The arrangements of electrons in orbitals, subshells and shells are called electronic configurations. Electronic configurations can be represented by using noble gas symbols to show some of the inner electrons, or by using Lewis structures in which the valence electrons are represented by dots....
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