Covalent Bonding and Molecules

Atoms and Stability  Atoms bond with other atoms to become stable. 

Sections in a Periodic Table

Types of Bonding  Type of BondingDescriptionExample IonicBetween metal ions (cations) and non-metal ions (anions) via electrostatic attraction Salts - Sodium chloride, calcium hydroxide, magnesium oxide, etc. MetallicBetween metal atoms due to a ‘sea of delocalised electrons’ around them. Any metal; copper, iron, zinc, magnesium, aluminium CovalentBetween non-metal atoms via sharing of valence electrons Gases, water, alcohol, diamond, graphite, sugars,….

Covalent Bonding  Covalent bonding occurs when pairs of electrons are shared by atoms.  They share electrons to have a fully filled valence shell and hence become stable.  Atoms need 8 electrons in their valence shell except for hydrogen that needs 2 electrons to become stable.  Non-metal atoms are held by covalent bonds.  It differs from ionic bonds in that there is no transfer of electrons  A group of atoms joined by covalent bonds is called a molecule.  To assist in covalent bonding, need to draw electron dot diagram.

Electron Dot Diagrams

Lewis Diagram of Water molecule

Example 2: Hydrogen chloride (HCl) molecule  Name: Hydrogen chloride  Formula: HCl  Atoms bonded via covalent bonds: 1H and 1 Cl  Electron dot diagrams (shows only the valence electron):  Hydrogen (1 e) H  chlorine (17e)  Arrange the atoms…… H will take its e’ to the site where Cl has unpaired electron (that is, to the right side of Cl).

Lewis Diagram of a HCl molecule

Terminology  Bonding Electrons.  Are unpaired electrons take part in covalent bonding.  Lone pair Electrons  Are paired electrons do not take part in bonding.  Aka non-bonding electrons.

Lewis Diagrams  Diagrams of molecules that show electrons in terms of dots and crosses either as bonding or non-bonding electrons.  A way to show covalent bonding.  Don’t draw dash lines.

Lewis Diagram  Example:

Structural formula  Diagram of molecules with dash lines to represent covalent bonds between atoms.  Often shows the non-bonding e’s.

Structural Formula  Example:

Activity: Complete the worksheet

Double and Triple Bonds  For some molecules, merely a single bond is not enough to make them achieve a fully filled valence shell and become stable.  They form a double or a triple bond to gain stability.

Double and Triple Bonds

How to draw Double and Triple Bonds  TIP  Draw the electron dot diagrams  Move atoms to share one unpaired e’  Check for octet (do the atoms have 8 e’s?)  If not, utilise another unpaired e’  Check for octet  Repeat if necessary.

Double and Triple Bonds