1. How do elements bond?

2. How do elements bond?
Chemical bond – a force that holds two atoms together.
Atoms form bonds with other atoms by using their outer electrons.
Three types of chemical bonds:
Ionic bond
Covalent bond
Metallic bond

3. Ionic Bonds
Strong attraction between atoms that holds the atoms very close together.
Electrons are gained or lost from an atom to form ions.
Gain / Loss of electrons makes each atom STABLE!!!!

4. Ionic Bonds Chlorine Ion (Cl-) Chlorine (Cl) Sodium (Na)
Sodium Ion (Na+)

5. Ionic Bonds
Ex. Salt = Na + Cl Na Cl
[Na]+
[Cl]- +  +

6. Covalent Bonds
When atoms don’t “want” to gain or lose outer level electrons, they must SHARE electrons to become stable.
Covalent bond - Chemical bond formed from atoms sharing electrons.
Molecule – Particle formed from atoms in a covalent bond. The smallest component of a compound that still has the properties of that compound.
Pd 1, 2, 5

7. Covalent Bonds
Ex. Hydrogen molecule = H + H H H H H +

8. Chemical Reactions
Every chemical formula is made up of reactants and products.
Reactants – “ingredients” that are needed to make something.
Products – what is made
Reactants make products

9. Chemical Formulas Reactant + reactant  product + product
Ice cream + banana + chocolate syrup + cherry + whip cream  banana split
Ex. Na + Cl  NaCl
sodium and chlorine makes sodium chloride
Ex. O2 + C6H12O6  CO2 + H2O
oxygen and glucose make carbon dioxide and water

10. CO2 + H2O H2CO3 Thermodynamics of a Chemical Reaction
Bond energy is the amount of energy needed to break a bond between two atoms.
Energy is added to break bonds.
Energy is released after the bonds form.
A reaction is balanced when the total bond energy of the reactants and is equal to the total energy in the products.
CO2 + H2O H2CO3

11. Thermodynamics of a Chemical Reaction
Exothermic reactions release more energy than they absorb.
Reactants have higher bond energies than products.
Excess energy is released by the reaction.

12. Thermodynamics of a Chemical Reaction
Endothermic reactions absorb more energy than they release.
Reactants have lower bond energies than products.
Energy is absorbed by the reaction to make up the difference.