Alkali metal: an element in Group 1 of the periodic table
Alkaline earth metals: an element in Group 2 of the periodic table.
Atom: the atom is the smallest unit of an element that retains the chemical properties of that element
Atomic mass: the relative mass of an atom on a scale on which the mass of one atom of carbon-12 is exactly 12 u.
Atomic number (Z): the number of protons present in the nucleus of an atom of a given element.
Atomic radius: a measurement of the size of an atom in picometers.
Compound: a pure substance that can be broken down by chemical means two or more pure substances. A substance containing atoms of more then one element combined in fixed proportions.
Continuous spectrum: the pattern of colours observed when a narrow beam of white light is passed through a prism or spectroscope.
Electron: a negatively charged subatomic particle.
Electron affinity: the energy change that occurs when an electron is accepted by an atom in the gaseous state.
Electronegativity: a number that describes the relative ability of an atom when bonded, to attract electrons
Element: a pure substance that cannot be broken down into simpler substances by chemical means. OR. A substance composed of entirely of only one kind of atom.
Energy level: a state with definite and fixed energy in which an electron is allowed to move.
Ground state: the lowest energy level that an electron can occupy.
Ion: a charged entity formed by the addition or removal of one or more electrons from a neutral atom.
Isotope: atoms of the same element that have the same number protons and neutrons; there may be several isotopes of the same element that differ from each other only in the number of neutrons in the nuclei.
IUPAC: the International Union of Pure and Applied Chemistry; An international body that approves chemical names, symbols and units.
Law of conservation of mass: the law stating that during a chemical reaction matter is neither created nor detroyed.
Line spectrum: a pattern of distinct lines, each of which corresponds to light of a single wavelength, produced when light consisting only a few distinct wave length passes through a prism or spectroscope.
Mass Number: the sum of the number of protons present and neutrons present in the nucleus.
Metalliod: an element that is a good conductor of electricity, malleable, ductile, and lustrous.
Neutron: An uncharged subatomic particle in the nucleus of an atom.
Principal quantum number: a number specifying the theoretical energy level of an electron in an atom.
Proton: A positively charged subatomic particle.
Radioisotope: a radioactive isotope of an element, occurring naturally or produced artificially.
Valence electrons: those electrons that occupy the highest shell of an atom and are used by the atom to form chemical bonds

History of the Atom
Orginal idea Ancient Greece (400 B.C)
Democritus and Leucippus-Greek philosphers
Aristole-famous philospher
4 elemenets= fire, water, air, earth
John Dalton-Teacher ( late 1700)
summarized results of his experiments and those of others
Dalton's Atomic Theory
1.) All matter is made of tiny indivisible particles called atoms
2.) Atoms of the same element are identical, those of diffrent elements are diffents
3.)Atoms of diffrent combine in whole number ratios to form ccompounds
4.) Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed
Parts of the Atom
*J.J. Thompson-English Physicist (1897)
made a piece of equipment called a carthode ray tube. It is a vacuum tube which means all the air has been pumped out


*Proton- postively charged pieces that are 1840 times heavier than the electron- by E. Goldstein
*Neutron- no charge but the same mass as a proton- by J. Chadwick

Rutherfords Model of the Atom

Electromagnetic Radiation
  • microwave O
  • infra red R
  • ultra violet
  • radio waves Y
  • x-rays I
  • visible light
  • gamma rays



Wavelength is large - energy is small
Wavelength is small - energy is large

Frequency --> how many times/a period of time


Spectroscopes: instruments used to measure the behaviour of radiation

Bohr Model of Atom


Ground State Electrons: electrons in the lowest energy level

Drawback of Rutherford Model of Atoms
1) The atom is not stable due to continuous emission of radiation(EMR)
2) Cannot explain the line spectra of Hydrogen like atoms

Quantised: Fixed Energy. Every orbit(shell or energy level) has a fixed value for its energy. (It will not change).

Energy will be absorbed or emitted in discrete quantities.

RAM: Relative Atomic Mass

Unified Atomic Mass: a unit of mass for atoms; 1/12 of the mass of carbon- 12 atom( theortical definition)14= 1/12 of C-12 ( Isotope of C)


Quantum Mechanical Model of an Atom
Orbital: It is a 3 dimensional space around the nucleus where there is a very high probability of locating the electrons.

Hesembergs Uncertanity Principle: It is impossible to determine both the position and momentum of an electron with 100% accuracy.

Quantum Numbers: These are a set of 4 integers necessary to specify the energy, position, shape, size and orientation of orbital's to which electrons belong.

Principle Quantum Number "n": It specifies the location and energy of an electron, It is a measure of the effective volume or size of the electron cloud denoted by "n" and can have values 1,2,3,4..........

Azimuthal Quantum Number"l": It determines the shape of the orbital. It takes integral values from 0 (n-1) where "n" id the principle quantum number. When "l" = 0,1,2, the shapes of the orbital's are "s" Spherically symmetrical, "p" dumbbell, and "d" double dumbbell

Sphercally Symmetrical
Double Dumbell

Magnetic Moment Quantum Number 'm': (2l+1) values It gives the orientation of the orbital's in space. It takes integral values ranging from -l......0.......+l or 's' orbital has got one orientation, 'p' orbital has got 3 orientations, 'd' orbital has got '5' orientatios and 'f' orbital has got 7 orientations.

Spin Quantum Number 's': it indicates the direction in which the electron spins on its own axis or the magnetic property that is associated with it. This value is quantised the two values htat are permitted are +1/2 and -1/2 where g=gyro magnetic constant.

a well defined circular path around the nucleus in which the electron revolves
a region in 3D space around the nucleus where there is a very high probability of locating the electron
circular in shape
's', 'p' and 'd' orbital's are spherical, dumbell and double dumbell in shape respectively
represents the movement of an electron around the nucleus on one plane
represents the movement of an electron around the nucleus in a 3D space
states with certainty the momentum and position of an electron. Violates the Heisenberg's uncertainty principle
a consequence of Heisenberg's uncertainty priciple. i.e. The posision and momentum cannot be known with certainty
the maximum number of electrons in an orbital is 2n2
the maximum number of electrons in an orbital is 2

Degenerate Orbital's: The orbital's of the same sub shell having equal energy are called degenerate orbital's. e.g. Px, Py, Pz orbital's. The 5 'd' orbital's are degerate but can lose their degeneracy under the infulence of and external electrical or magnetic field.

Nodal Plane: The plane passing through the nucleus on which the probability of finding the electron is almost zero.

Type of Information
Principal Quantum Number 'n'
Azimuthal Quantum Number 'l'
Magnetic Moment Quantum Number 'm'
Spin Quantum Number 's'
Why is it required?
To explain the main lines of spectra
To explain the fine structure of line spectra
To explain the splitting of lines in the magnetic field
To explain the magnetic properties of substances.

external image msword.png Principal Quantum Number.doc

Electron Configuration of atoms: rules governing the filling up of electrons in the different orbital's of an atom

Orbital's: arranged in the increasing order of energy which is based on Aufbau order and can be verified using the (n+1) rule.

Aufbau Order: the number of electrons that can be accomodated in an 'orbit' is 2n2 where n is the principal quantum number.
1s,2s,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p,7s or 1s2,2s2,3s2,3p6,4s2,3d10,4p6,5s2,4d10,5p6,6s2,4f14,5d10,6p6,7s2

PEP or Pauli's Exclusion Principle: No two electrons in an atom can have all the four quantum numbers alike or an orbital can accommodate a maximum of 2 electrons in an atom.

Hund's Rule of Maximum Multiplicity: Electrons pairing will not take place in orbital's of the same energy (same sub shell) until each orbital is singly filled.

*Exceptional Electronic Configuration*
Cu, Cr, Mo, Ag, W and Au have got exceptional electronic configuration.
Half filled 'd' orbital configurations are preferred because
  • there is a extra stability because of the symmetrical distribution of the electrons in the orbitals.
  • the exchange energy is high for Cr, Mo and W
  • exchange energy can be calculated using the following equation. where 'n' is the number of electons having parallel spins. In the equation given below 'n' stands for the number of unpaired electrons in the 'd' orbital.

SATP: Standard Ambient Temperature and Pressure. Corresponds to 25 c

STP: Standard Temperature and Pressure used to measure gas density and volume.

Isoelectronic: refers to a group of atoms ot ions having the same number of electrons. For excample, F-, Ne, Na+, are all isoelectronic.


Atomic elements which have the same atomic number but different mass number.
Isotopes show same chemical reactivity because they have the same number of electons.
The number of neutrons in the different isotopes differ.

C- 12 and C-14

Ionisation Energy:

The energy required to remove an elctron fron the neutral gaseous atom.

Na+ IE ----------------> Na+ e-
1s2,2s2,2p6,3s1+IE 1s2 ,2s2,2p6 + e-
(less stable ) ( more stable)

Na+ is more stable than Na because it has a configuration of a Noble Gas.

Mg- 1S², 2S², 2P⁶, 3S²
First Ionization Energy Mg + IE--------------> Mg+ + e-
Second Ionization Energy Mg + IE---------------> Mg 2+ + e-

Second Ionization Energy is the energy needed to make it unipositive ion.

Electron Affinity

It is the energy released when an electron's added to a neutral gaseous atom(usually non-metals)

F+ e-------->F-+ EA

Moving from left to right, the elesctrons are added to the same energy level and there is an increase in nuclear charge. Therefore the size of the atom decreases.


It is defined as the tendency of an atom to attract a shared pair of electrons.