1. What is Chemistry?
Learning goals 3 & 4

2. What is Chemistry?
Chemistry is the science of matter and the changes it undergoes
A large part of chemistry involves understanding the way chemicals react with each other.
Living things require chemical reactions to survive
Examples: Respiration, digestion, photosynthesis

3. Levels of Chemical Organization
Atoms
Nucleus—central core of atom
In the nucleus there are…
Protons—positively charged particles
Neutrons—particles with NO charge
Atomic number—number of protons in nucleus
Atomic mass—number of protons and neutrons combined
What makes up an atom’s atomic mass? The number of protons and neutrons combined.

4. Levels of Chemical Organization
Atoms
Energy levels—orbital regions around the nucleus that contain electrons
Electrons—negatively charged particle
Describe an energy level. Energy levels (shells) are the limiting regions in which orbitals are arranged.

5. Structure of an Atom
Models of the atom. The nucleus—protons (+) and uncharged neutrons—is at the core. Electrons inhabit outer regions called energy levels (A), which look more like a cloud because the electrons do not stay in one place (B). This is a carbon atom, a fact that is determined by the number of its protons. All carbon atoms (and only carbon atoms) have six protons.(One proton in the nucleus is not visible in this illustration.)

6. Levels of Chemical Organization
Element—a pure substance; made up of only one kind of atom
Molecule—a group of atoms bound together in a group
Compound—substances whose molecules have more than one kind of atom

7. Element, Molecule, or Compound
Hydrogen H H2

8. Element, Molecule, or Compound
H2O Na

9. How Many Elements and Atoms??
NaOH 3
NaCl 2 H2 2

10. Chemical Bonding Chemical bonds form to make atoms more stable
Atoms react with one another in ways that make their outermost energy level full
Atoms may share electrons or donate or borrow them to become stable
What is a chemical bond? The energy that holds two atoms together.

11. Ionic Bonds Ionic bonds
Ionic bonds form when positive and negative ions attract each other
What is dissociation? Occurs when molecules dissolve in water because water molecules wedge between the ions and force them apart.

12. Ionic Bonds An Ion is an atom the has gained or lost electrons
Positive ion—has lost electrons; as in Na+ or Ca++
Negative ion—has gained electrons; as in Cl–
How is an ion formed? Ions form when an atom gains or loses an electron to become stable.

13. Ionic Bonds
Ionic bonding. A, The sodium atom donates the single electron in its outer energy level to a chlorine atom having seven electrons in its outer level. Then both have eight electrons in their outer shells. Because the electron/proton ratio changes, the sodium atom becomes a positive sodium ion. The chlorine atom becomes a negative chloride ion. The positive-negative attraction between these oppositely charged ions is called an ionic bond. B, A cube-shaped crystal of sodium chloride (table salt).

14. Covalent Bonds
A covalent bond forms when atoms share their outer electrons
Covalent bonds do not easily break down in water
Covalent bonding is used to form all of the major organic compounds found in the body
What is covalent chemical bonding? Bonding that forms when atoms fill up their energy levels by sharing electrons rather than donating or receiving them.

15. Covalent Bonds
Covalent bonding. Two hydrogen atoms move together, overlapping their energy levels. Although neither gains nor loses an electron, the atoms share the electrons, thereby forming a covalent bond.

16. Hydrogen Bonds Hydrogen bonds do not create new molecules
Hydrogen bonds weakly bond to surrounding molecules
Hydrogen bonds are present in
1) water
2)DNA
3)proteins