Covalent BONDS Chapter 4 Section 2

Covalent Bonds Covalent Bonds – electrons are shared between two atoms Both atoms “claim” the other’s electron as their own The number of covalent bonds an atom can form depends on the number of valence electrons it needs to complete its outer shell.

O Covalent Bonds Ex) Water (H2O) H H 2H2 + O2  2H2O Oxygen has 6 v.e.  it can form 2 covalent bonds (octet rule) Hydrogen has 1 v.e.  it will form 1 covalent bond (only needs 2) A covalent bond forms between each hydrogen and the oxygen atom O 2H2 + O2  2H2O H shows a shared pair of e- H

Hydrogen Because hydrogen only has one valence electron and needs 1 more, it tends to form covalent bonds easily… even with itself!

Double Bonds Sometimes atoms share two pairs of electrons…

Triple Bonds Sometimes they share three pairs…

POLAR MOLECULES Some atoms will pull more strongly on shared electrons than other atoms The electron moves closer to the stronger pull, causing a slight electrical charge

Polar Molecules Non-Polar Molecule – atoms pull equally on the shared electrons Polar Molecule – covalent bond in which electrons are shared unequally creating a partial charge on either end

Naming Covalent Molecules prefix  1st element  prefix  2nd element Note: if 1st element only has one atom, no prefix is used Prefixes are based on the number of atoms present: Examples: 1 = mono CO2 2 = di H2O 3 = tri CF4 4 = tetra carbon dioxide dihydrogen monoxide carbon tetrafluoride

Properties of Covalent Molecules Low Melting Point Covalent molecules tend to melt at lower temperatures Poor Conductors Most covalent molecules are poor conductors of electricity (electrons do not flow easily)

Ionic vs. Covalent Type of Bond Electrons are… Forms Between… Held Together by… Ionic Given or Taken Metals and Non-Metals Opposing charges Covalent Shared Non-Metals Shared Electron Pairs