A substance that is made up of two or more different elements combined together chemically.
States that when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell.
Exceptions to the octet rule
1. Transition metals can have more or less than eight electrons in their outermost energy level.
2. The elements near helium in the Periodic Table tend to achieve the electronic arrangement of helium with two electrons in the outer shell rather than eight.
1. Contains a network of ions in the crystal.
2. Usually hard and brittle.
3. Have high melting points and boiling points.
4. Usually solid at room temperature.
5. Conduct electricity in molten state or when dissolved in water
A way of representing a compound using symbols for the atoms present and numbers to show how many atoms of each element are present
A group of atoms joined together. It is the smallest particle of an element or compound that can exist independently.
The number of atoms of hydrogen or any other monovalent element with which each atom of the element combines
1. Contains individual molecules.
2. Usually soft.
3. Have low melting and boiling points.
4. Usually liquids, gases or soft solids at room temperatures.
5. Do not conduct electricity
The relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond.
Scientist who studied the amounts of energy needed to break certain bonds and so set up a scale of relative values of electronegativity.
Bond where the electrons are equally shared. Electronegativity difference less than 0.4
Bond where the electrons are not equally shared. Electronegativity difference between 0.4 and 1.7 inclusive
Van der Waals forces
Weak attractive forces between molecules resulting from the formation of temporary dipoles. (The only forces of attraction that exist between non polar molecules. Their strength increases as the molecules get bigger due to the greater number of electrons in the electron clouds allowing the temporary dipoles to form more easily.)
Dipole dipole forces
Forces of attraction between the negative pole of one molecule and the positive pole of another. (Give rise to higher boiling points than those of similar non polar molecules.)
Particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine. (The hydrogen atom acts as a bridge between two electronegative atoms. The boiling points of H2O, HF and NH3 are much higher than other hydrogen compounds.)
Valence Shell Electron Pair Repulsion Theory - used to determine the shapes of molecules