Chemical Bonding Joining atoms together to make compounds

 Chemical Bonding: combining atoms of elements together to form new substances  Bond: force that holds atoms together to form molecules

Molecules   Two or more atoms that form a new substance   Smallest part of a compound

Review of atomic structure  Atoms: electrons, protons, neutrons  Electrons are negatively charged  Protons are positively charged  Neutrons have no charge  Electrons are in energy levels  First level = 2 electrons  Second level = 8 maximum electrons  Third level = 18 maximum electrons

 Valence electrons: the outermost electrons  Determine how and with what the atom will bond  Electrons and energy levels video Electrons and energy levels video Electrons and energy levels video

FACT: Atoms become stable (won’t react chemically) when they have a full outer energy level.

Bohr model review Bohr model review  Start with a circle (nucleus)  Put in proper number of protons (atomic number)  Calculate number of neutrons  Atomic mass – mass of protons = neutrons  Place electrons:  Start in inner ring, fill first then move to next  Start at “12:00”, then “3”, then “6”, then “9”  Once shell is half full, electrons pair up

Electron Dot Diagrams  Electron dot diagrams used to show how many valence electrons are in an element Rules: 1.Start with the symbol for the element –Represents nucleus and “inner” energy levels 2.Count how many valence electrons are in the outer shell 3.Place one dot at a time working around the symbol, usually start at “3:00” position o- -

Electron dot diagrams Examples

 Octet Rule: Fill the outer shell to give a total of 8 shared electrons  Makes a stable molecule, will not react further

Types of Bonds  Ionic Bonds: transfer of electrons from one atom to another  Ions: Positively or negatively charged atoms  Since negatives and positives attract, the atoms bond to each other  Usually happens between a metal and a nonmetal  Ionic Bonding video Ionic Bonding video Ionic Bonding video

Which elements do you think will bond together?

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 Salt video Salt video Salt video

 Covalent bonding: Sharing electrons equally between two or more atoms  Example: Hydrogen has one valence electron so it needs one more to fill up its energy level  Covalent bonds often happen between like elements  Usually happens in non-metals  Cl 2, H 2, O 2 Covalent Bonds Covalent Bonds video

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Structural Formula:  shows the actual arrangement of the molecule  replace dots between atoms with lines to indicate the bonds