A look at ionic, covalent and metallic bonds Chemical Bonds A look at ionic, covalent and metallic bonds

Atom – the smallest unit of matter Helium atom

Electron Shells Atomic number = number of Electrons Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. Electron shells determine how an atom behaves when it encounters other atoms

Electrons are placed in shells according to rules: The 1st shell can hold up to two electrons. Each shell thereafter can hold up to 8 electrons.

H would like to C would like to N would like to O would like to Gain 1 electron Gain 4 electrons Gain 3 electrons Gain 2 electrons

IONIC BOND A bond formed between two elements by the transfer of electrons

Formation of Ions from Metals Ionic compounds result when metals react with nonmetals Metals lose electrons to gain a full outer electron shell (the next electron shell becomes the new outer shell) Positive ions form when electrons are lost Group 1A metals  ion +1 Group 2A metals  ion +2 Group 3A metals  ion +3

Formation of Ions from Nonmetals Nonmetals gain electrons to gain a full outer electron shell Negative ions form when electrons are gained Group 5A nonmetals  ion -3 Group 6A nonmetals  ion -2 Group 7A nonmetals  ion -1 Group 8A elements do not gain or lose electrons since they already have a full outer shell.

The formation of sodium chloride (salt)

Ionic Bonds: One Big Greedy Thief Dog!

1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

Properties of Ionic Compounds Individual atoms are bound tightly together forming crystal structures High melting points High boiling points Conduct electricity when melted or in solution Many can be dissolved in water

COVALENT BOND A bond formed between two elements by the sharing of electrons.

How to Draw Covalent Bonds 1. Draw dot diagrams for each element Figure out how many electrons need to be SHARED Show sharing of electrons by connecting the dots. Ex: Hydrogen and Oxygen. H needs 2 valence e to be stable, O needs 8 total but only has 6. They need to share electrons because they are both non-metals.

Example: Carbon + Chlorine

Covalent Bonds

when electrons are shared equally NONPOLAR COVALENT BONDS when electrons are shared equally H2 or Cl2

Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)

when electrons are shared but shared unequally POLAR COVALENT BONDS when electrons are shared but shared unequally H2O

Polar Covalent Bonds: Unevenly matched, but willing to share.

Water is a polar molecule because oxygen has a stronger charge than hydrogen, and therefore electrons are pulled closer to oxygen.

Properties of Covalent Compounds Form irregular structures (no set geometric shapes like crystals) Low melting and boiling points Poor conductors of electricity in all phases Many do not dissolve in water

METALLIC BOND Bond found in metals which holds metal atoms together very strongly

Metallic Bond Formed between atoms of metallic elements Electron cloud around atoms Good conductors at all states, hard, very high melting points Examples; Na, Fe, Al, Au, Co

Metallic Bond: A Sea of Electrons

Metallic Bonds: Mellow dogs with plenty of bones to go around.

Metals Form Alloys Metals do not combine with metals. They form alloys which is a solution of a metal in a metal. Three common examples are steel, brass, and bronze.

Examples of metal alloys