1. ATOMIC BONDING

2. INTRODUCTION OK, so we know that atoms can combine into compounds, and that when they do, they combine chemically during a chemical reaction. But what does that mean? How many ways does that happen? Why do they stick together? Let’s find the answer.

3. INTRODUCTION Atoms that combine chemically into a new substance can do so in two ways, ionicly and covalently. Either way that it happens, the new substance stays together unless energy, or a solvent, is used to separate them.

4. INTRODUCTION Let’s look at ionic bonds first. Ionic bonds happen between a metal and a non metal, like chlorine and sodium.

5. INTRODUCTION Atoms with 5, 6, or 7 valence electrons usually become more stable when this number increases to eight. Likewise, most atoms with 1, 2, or 3 valence electrons can lose electrons and become more stable.

6. INTRODUCTION When these two types of atoms combine, electrons are transferred from one atom to another. The transfer makes both types of atoms more stable.

7. INTRODUCTION When an atom loses an electron, it loses a negative charge and becomes a positive ion. When an atom gains an electron, it gains a negative charge band becomes a negative ion.

8. INTRODUCTION Because oppositely charged particles attract, the negative ion and the positive ion attract each other. An ionic bond is formed. The compound that results is called an ionic compound.

9. INTRODUCTION Ionic compounds are hard brittle crystals that have high melting points. When dissolved in water, or melted, they conduct electricity, really well.

10. INTRODUCTION Covalent bonds form between atoms of nonmetals. Covalent bonds form when two atoms share electrons between them, like hydrogen and oxygen.

11. INTRODUCTION By sharing atoms, each atom will have a more stable valence shell. The force of attraction that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons.

12. INTRODUCTION Most nonmetals can bond with another atom of the same element, like fluorine.

13. INTRODUCTION When atoms bond covalently, a covalent compound is created. Examples of covalent compounds would be: sugar, water, and butter.

14. INTRODUCTION Covalent compounds have lower melting points and lower freezing points than ionic compounds, and they don’t conduct electricity when dissolved in water.

15. OBJECTIVES Describe and contrast ionic and covalent bonds. Explain that compounds form when two or more atoms bond.

16. IN QUESTION Solid ice melts to liquid water, is this an example of a physical change or a chemical change? Explain.

17. VOCABULARY ion—an atom that has lost or gained electrons in its outer energy level. Ionic bond – bond where one atom gives up an electron and another atom takes in the electron. Covalent bond – bond where atoms share an electron, or electrons.

18. NOTES Atoms held together by chemical bonds. Valence electrons determine an element’s ability to bond or form ions 2 types of chemical bonds – Ionic – Covalent

19. NOTES Ionic bonds – Atom loses electron or takes in electron – Atom that loses electron has overall positive charge, cation – Atom that gains electron has overall negative charge, anion – Oppositely charged ions attract & form bond – Bonds can be broken easily in a solution – Bonds usually form between metal and nonmetal

20. NOTES Ionic Compounds – Salt is an ionic compound – Ionic compounds tend to be brittle – They have high melting points – They are solids at room temperature – Conduct electricity well when in a solution – As a solid they don’t conduct electricity

21. NOTES Covalent bonds – Atoms share electrons – Electrons spend more time between atoms than anywhere else – Negative charge of electrons attracts positive nuclei of the atoms – Bonds usually form between two nonmetals

22. NOTES Covalent Compounds – Butter, water, sugar are covalent compounds – Have a lower melting point – Most don’t break down in water easily – Don’t conduct electricity well if they are in a solution (sugar)

23. OUT QUESTION A solid log turns to ash and smoke, is this a physical change or a chemical change? Explain.