Forming CompoundsUsing Bohr and Lewis Diagrams to show how electrons can be

transferred or shared to form bonds

Compounds are of two basic types: IONIC and COVALENT

IONIC COMPOUNDS

• Contain a positive ion (usually a metal) and a negative ion (non-metal)

• In IONIC BONDING, one or more electrons TRANSFERS from each atom of the metal to each atom of the non-metal

Bohr Model:

Covalent Compounds

• Atoms of many non-metals SHARE electrons with other non-metal atoms.

• In COVALENT BONDING, atoms overlap slightly, and one unpaired electron from each atom will pair together. Both atoms are attracted to the same pair of electrons forming a COVALENT BOND

Representing Bonding with Lewis Dot DiagramsKey Concepts

• There are shorthand ways to represent how atoms form covalent or ionic bonds.

• Lewis dot diagrams use dots arranged around the atomic symbol to represent the electrons in the outermost energy level of an atom.

• Single bonds are represented by a pair of dots or one line between atoms.

• Double bonds are represented by two pairs of dots or two lines between atoms.

• Triple bonds are represented by three pairs of dots or three lines between atoms.

Lewis Dot Diagrams

• A Lewis dot structure is like a simplified electron energy level model.

• The Lewis structure contains the element symbol with dots representing electrons.

• The only electrons shown are those on the outer energy level or valence electrons.

• The electrons are placed around the element symbol, one at a time, clockwise or counterclockwise, and then grouped in pairs as more electrons are added.

Ionic Bonding of Sodium Chloride

• When sodium loses its only valence electron to become an ion, the Lewis structure shows it with no dots (electrons).

• The Na and Cl are near each other but the two dots from the Cl should not be interpreted as a covalent bond.

Ionic Bonding in Calcium Chloride

• When calcium loses its two valence electrons to become an ion, the Lewis structure shows it with no dots (electrons).

• The Ca and Cls are near each other but the two dots from each Cl should not be interpreted as a covalent bond.

Covalent Bonding in Hydrogen

• Lewis dot structures can also be used to show the bonded atoms in a molecule.

• The two dots together between the Hydrogens represent the electrons in the covalent bond between the hydrogen atoms.

• The line is a short-hand version of the two dots.

Covalent Bonding in Water

• The Lewis dot structure for water shows the electron from hydrogen and an electron from oxygen being shared in a covalent bond.

• The other four valence electrons in oxygen are in pairs at the bottom.

• The lines are a short-hand version of the two dots representing the covalent bonds.

Covalent Bonding in Oxygen

• The two pairs of dots between the Os represent the double covalent bond in the oxygen molecule.

• The two lines are a short-hand version of the two pairs of dots.

Covalent Bonding in Carbon Dioxide

• The two pairs of dots between the C and the Os represent the double covalent bond between the carbon and each oxygen atom in the carbon dioxide molecule.

• The two sets of two lines are a short-hand version to show the two double covalent bonds.

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