Types of Chemical Bonds IONIC BONDS Occur between

Types of Chemical Bonds

IONIC BONDS �Occur between an element with low ionization energy (a metal) and an element with high ionization energy (a non-metal). �An actual transfer of electrons from the metal (becoming a cation) to the non-metal (becoming an anion) occurs. �This transfer results in the formation of 2 oppositely charged ions. �The electrostatic interaction between the 2 ions holds the compound together. �ie. Na. Cl and Mg. Br 2

Properties of Ionic Compounds �Solids at room temperature because the attraction between the ions is very strong. �Atoms are arranged in a highly ordered crystal lattice structure which maximizes the attractive forces between oppositely charged ions and minimizes the repulsion between like charged ions. �Many are soluble in water (the ions will dissociate [break apart] in water). �Will conduct electricity as a liquid or aqueous solution because the ions are free to move to oppositely charged electrodes.

COVALENT BONDS � Occur between 2 atoms with high ionization energies (i. e. 2 non-metal atoms). � Result from a sharing of electrons to obtain a full outer energy level (octet rule). � Not all sharing of electrons is equal. A measure of an atoms ability to pull on a shared pair of electrons is called electronegativity. � The greater the difference in electronegativities the more unequal the sharing. � EN = the difference in electronegativities. � The trend in electronegativities on the periodic table follow most other trends. Low in bottom left, high at top right. � The actual values are listed on the periodic table.

Types of Covalent Bonds the EN between the two atoms is less than 0. 4, the bond is a true covalent bond and the electrons are shared equally. �If the EN between the two atoms is between 0. 4 and 1. 7, the bond is polar and there is an unequal sharing of electrons. �If the EN is greater than 1. 7, the bond exhibits more of an ionic character. �If

Types of Covalent Molecules �Molecules can be either polar or non-polar. �An area of a molecule can have excess negative charge and an area of deficient negative charge as a result of unequal sharing. ( EN) �Two factors determine the polarity of a molecule: 3 D SHAPE and BOND TYPE

Determining Molecule Shape �The 3 D shape of the molecule can be approximated by building a model. �First draw a Lewis dot diagram of the molecule, trying to have all molecule obtain a full octet. �Using a molecular model kit, construct the molecule and approximate the 3 D shape.

Model Building Molecule H 2 Cl 2 O 2 CH 4 NH 3 H 2 O CO 2 Lewis Structure Sketch of Molecule Name of Shape

Determining Types of Bonds the EN for each of the bonds within the molecule and draw an arrow towards the atom with the higher EN. �Calculate

Putting it Together �The molecule will be polar if it is asymmetrical and contains polar covalent bonds. ie. NH 3 �The molecule will be non-polar if it is symmetrical and contains either polar covalent bonds or true covalent bonds. �ie. CCl 4 and F 2

Properties of Non-Polar Covalent Compounds �Have low melting and boiling points and are usually gases at room temperature. �If solid at room temperature, the solid is usually soft and waxy. �Soluble in non-polar solvents such as ethers. �Will not conduct electricity in any form due to the fact that there are no ions present.

Properties of Polar Covalent Molecules �Since these compounds exhibit polarity or dipoles, their intermolecular forces will be greater than non-polar covalent compounds. �These compounds will have higher melting and boiling points and are more likely to be liquids or solids at room temperature (may even exhibit a crystal lattice like sugar). �May dissolve in polar solvents(ie. sugar in water). � Will not conduct electricity when liquid or aqueous solution.