- Dalton’s atomic theory
- Main postulates
- Elements are made up of atoms
- Atoms can neither be created nor destroyed
- Atoms of the same element are alike
- Atoms combine in simple ratio
- Chemical reactions are due to combination or separation of atoms
- Main postulates
- Atomic structure
- Particles of atoms
- Proton wit positive charge
- Electron with negative charge
- Neutron with no charge
- Location
- Proton and neutron are in the nucleus
- Electrons revolve round the nuleus in shells or orbits
- Electron shells: K, L, M, N, O, P
- Atomic number and atomic mass
- The number of protons in the nucleus of an atom is the atomic number Z
- Mass number A is the sum total of the protons and neutrons in the nuleus of an atom.
- The difference between A and Z gives the number of neutrons
- Electronic configuration
- Shows how electrons are distributed in different shells ( K, L, M, N, O, P)
- Electonic shells have suborbits
- s-orbit ( spherical in shape), max electrons 2
- p-orbit ( shape of dumb-bell), max electrons 6
- d-orbit, max electrons 10
- f-orbit
- The rare gases are chemically stable because they have an octet structure.
- Particles of atoms
Table 3.1 electronic shells and their sub-orbits
Electronic shell | Suborbit | Max number of electrons |
K or 1 | S | 3 |
L or 2 | S, p | 8 |
M or 3 | S, p, d | 18 |
N or 4 | f | * |
- Chemical combinations/bonds
- Two major types
- Electronic or ionic
- Covalent
- Simple covalent
- Coordinate covalent
- Electrovalent combination
- Transfer of electrons from a donor atom to an acceptor atom
- Metals are usually donors, non-metals are acceptors
- Donors with one valence electron ( Na, K) are most reactive, acceptors with seven valence electrons (Cl )are most reactive.
- Donors become positively charged while acceptors negatively charged after the electron transfer.
- A strong electrostatic force binds the ions together to form the ionic bond
- Electrovalent compounds (NaCl, MgO, MgCl2, CaCO3)
- Solid structure
- High boiling and melting point
- Electrolytes
- Dissolve in polar solvent ( ethanol, water)
- Ordinary covalent combination/bond
- No transfer of electrons
- A pair of electrons is shared between the two reacting atoms
- Covalent bond exists between the atoms ( single, double, triple)
- Common in molecules of diatomic elements e.g O2, H2
- Covalent compounds ( N2, C2H2, CO2, CH4, H2O, NH3)
- Gases or volatile liquids
- Low melting and boiling point
- Non-electrolytes
- Dissolve in non-polar solvents ( benzene)
- Coordinate covalent combination
- A lone pair of electrons is donated for sharing by one of the reacting atoms.
- Example of compounds with coordinate covalent bond
- Ammonium ion
- Oxonium ion
- Chemical bonding forces
- Electrovalent bond
- Covalent bond
- Metallic bond
- Hydrogen bond
- Van der Waals forces
- Two major types
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