1. Introduction to Chemistry
Lecture #11
Honors Biology
Ms. Day

2. Composition of Matter
Matter - everything in universe is composed of matter (“stuff”)
Matter is anything that occupies space or has mass
Mass – quantity of matter an object has
Weight – pull of gravity on an object
Volume – amount of space something takes up

3. Elements Pure substances that cannot be broken down
Made of a single type of atom
More than 100 elements (92 naturally occurring)

4. Atoms smallest piece of matter Can NOT be broken down
Atom have 3 subparticles:
Protons
+ charged particle
Neutrons
Neutral (0) charged particle
Electrons
- charged particle

5. The Nucleus Middle of the atom
Holds positive charged protons and neutral neutrons (p’s + n’s)
Positively charged
Contains most of the mass of the atom p n

6. Protons All atoms of a given element have the same number of protons
# of protons = also known as the atomic number
# of protons (+’s) = # of electrons (-’s)
If you change the PROTON #, you change the atom!!

8. Most Common Elements
90% of the mass of an organism is composed of 4 elements (carbon, oxygen, hydrogen and nitrogen  “COHN”)
Each element unique chemical symbol
Consists of 1-2 letters
First letter is always capitalized

9. Neutrons The number varies slightly among atoms of the same element
Different number of neutrons produces isotopes of the same element
Neutron # = Mass # - # protons (atomic #)

10. Radioactive Isotopes Natural or artificially created isotope UNSTABLE
Nucleus decays (breaks down) until stable
Uses include:
1) kill or inhibit (stop) specific abnormal cells
2) treat abnormal cell growth
3) Radioactive tracers

11. Electrons
Negatively charged high energy particles with little or no mass
# electrons = # protons
Travel at very high speeds in different energy levels
Energy levels are different distances from the nucleus

12. Ions Ions are atoms that have EXTRA or MISSING electrons
# electrons = # protons
Examples:
Na+ is MISSING 1 electron
It has 1 extra positive charge (+)
Ca+2 is MISSING 2 electrons
It has 2 extra positive charges (+2)
Cl- has 1 extra electron
It has 1 extra negative charge (-)

13. Compounds Most atoms do not exist by themselves
Atoms combined with other atoms to form compounds
2 types of compounds:
1) molecules
2) ionic (salts)

14. Compounds
A compound is a pure substance made up of atoms of two or more elements
Chemical formula shows the kind and proportion of atoms of each element that occurs in a particular compound
EX: C6H12O6 (glucose) or H20 (water)

15. Chemical Formulas 2H202  2H2O + O2
Subscript after a symbol tell the number of atoms of each element
H20 has 2 atoms of hydrogen & 1 atom of oxygen
Coefficients before a formula tell the number of molecules
3O2 represents 3 molecules of oxygen or (3x2) or 6 atoms of oxygen

16. Bonds Molecular “glue” Holds atoms together to form compounds
Valence (outermost) electrons are involved in bonding

17. Bonds Single Double Triple
Bonds SIZE decreases as you increase # of bonds
Bonds STRENGTH increases as you increase # of bonds

18. Types of Bonds: 1) Covalent Bonds
Formed when two atoms share one or more pairs of electrons in a compound
“Co” means “together”
Found in molecules
Ex: water

19. Types of Bonds: 2) Ionic Bonds
Bond involves the electrical attraction between oppositely charged ions (+ and -)
Some atoms become stable by losing or gaining electrons
Atoms that lose electrons are called positive ions (Ex: Na+)
A.k.a= a cation
Atoms that gain electrons are called negative ions (Ex: Cl-)
A.k.a= an anion

20. Ionic Bonds (Con’t)
Because positive and negative electrical charges attract each other ionic bonds form

21. Covalent vs. Ionic Bonds

22. Types of Bonds: 3) Hydrogen Bonds
An attraction between a hydrogen (H) atom and another atom (usually O, N or F)
Found between molecules
Ex: water or in middle of DNA

23. Bonds vs. Strength Covalent bonds are the STRONGEST!
Hydrogen bonds are the WEAKEST!

24. States of Matter Atoms are in constant motion (called kinetic energy)
The rate at which atoms or molecules in a substance move determines its state