Atomic Structure PDF

# Physical Inorganic Chemistry ## Atomic Structure Electron configuration - distribution of electrons in orbitals - Orbitals are regions in space where we are likely to find an electron. - Electron configuration of elements is obtained by putting electrons successfully in orbitals in order of inc...

# Physical Inorganic Chemistry ## Atomic Structure Electron configuration - distribution of electrons in orbitals - Orbitals are regions in space where we are likely to find an electron. - Electron configuration of elements is obtained by putting electrons successfully in orbitals in order of increasing energy, - the electrons enter first the sub-shells of lower energy. - The relative energy of the sub-shells are: 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p - Each sub-level holds only 2 electrons governed by the Pauli exclusion Principle which states that: - No two electrons in an atom can have the same values of the four quantum numbers. - The four quantum numbers are: - The principal quantum number - The azimuthal quantum number - The magnetic quantum number - The spin quantum number ## Electron Configuration of atoms using spdf notation The electron configuration of an atom tells us how the electrons are distributed among the various orbitals and is usually denoted nl^x where l indicates the subshells - The value of l: 0 1 2 3 - Subshell: s p d f - X - is the number of electrons ### Examples - Carbon -> 1s²2s²2p² - Sodium -> 1s²2s²2p⁶3s¹ - Magnesium -> 1s²2s²2p⁶3s² - Chlorine -> 1s²2s²2p⁶3s²3p⁵ - Manganese -> 1s²2s²2p⁶3s²3p⁶4s²3d⁵ ## Electromagnetic Spectrum - The electromagnetic radiation is the emission and transmission of energy through space in the form of waves - A wave can be thought of a vibrating disturbance by which energy is transmitted. - An electromagnetic wave is an electric field component and magnetic field component - this two components are at the same frequency and wavelength hence same speed. - Light is an electromagnetic radiation which is an emission of energy in the form of electromagnetic waves. - A feature common to all electromagnetic waves is the speed = 3.0 x 10⁸m/s; which is the speed of light in a vacuum. - The electromagnetic spectrum is the distribution of electromagnetic radiations according to frequency, energy or wavelength. - Frequency is the no. of waves or cycles that pass through a point in one second. - A wave of high frequency has a short wavelength and vice versa. - Wavelength is the distance btw two successive troughs or crests. ## Periodic Table It is a chart that categorizes elements by groups and periods and all elements are ordered by the atomic number. ### Groups - Groups are vertical columns in the periodic table of chemical elements that include elements with similar chemical properties. ### Periods - A period is a horizontal row in the table of elements that have the same number of electron shells. ### Atomic Radius and Ionic Radius - Atomic radius is the distance between the nucleus of an atom and its valence shell. - It tends to decrease across a period because the effective nuclear charge increases, thereby attracting the orbiting electrons and lessening the radius. - Effective nuclear charge (Z_eff) is the positive charge that an electron experiences from the nucleus. - Atomic radius increases down a group due to the addition of a new energy level/shell/ - Ionic radius is the distance between the nucleolus of an ion and the point where the nucleus exerts its influence on the electron cloud.. ### Ionization Energy / Ionization Potential - It is the energy needed to remove the outermost electron from a neutral atom in the gaseous state to form a positive ion. - It is measured in electron volts (eV) or kilojoules per mole of atoms (kJ/mol). - Atom(g) + Ionization Energy → Ion⁺(g) + e - Ionization energy decreases down a group, because due to increased atomic size. - Across a period, ionization energy generally increases, due to increased effective nuclear charge. ### Metallic Property - It decreases across a period with increase in number of valence elections as well as a decrease in atomic radius and it increases down the group with increase in number of shells and atomic radius. ### Electron Affinity - It is the energy change that occurs when an atom of a negative ion in the gaseous phase accepts an electron. - The first electron affinity applies to a neutral atom combining with an electron - the second electron affinity applies to a minus-one ion accepting an electron. - Atom (g) + electron → Anion (g) + energy - It increases from left to right across a period due to increase in effective nuclear charge for across the period. - Down a group, the electron affinity decreases because of a large increase in the atomic radius, electron-electron repulsion and 'shielding' effect of inner electrons against the valence electrons of the atom. ### Electronegativity - It is a qualitative measure of the ability of an atom in a chemical compound to attract shared electrons to itself - It increases across the periodic table from left to right due to a greater charge on the nucleus across the period, causing the electron bonding pairs to be strongly attracted to atom placed further right on the table. - Fluorine is the most electronegative element. - Electronegativity decreases down a group. This is caused by an increased amount of shielding or screening by the innermost electrons. It is also due to the longer distance between nucleus and valence electron shell, thereby decreasing the attraction due to less effective nuclear charge. ## Chemical Bonding - A chemical bond is an attractive or adhesive force that holds two or more atoms in a molecule or ion. ### Types of Bonding - Ionic bonding - Covalent bonding - Metallic bonding ### Metallic Bonding - It is the strong attraction between closely packed positive metal ions and free delocalized electrons.