1. Structure of Matter The branch of science that explains how matter is put together is known as chemistry.

2. Historical View of Matter Democritus (in the 4 th century B.C.) realized if one could continue to slice a piece of bread into smaller pieces until it could be sliced no more. Democritus (in the 4 th century B.C.) realized if one could continue to slice a piece of bread into smaller pieces until it could be sliced no more. Atom originates from the Greek word atomos, which means “cannot be cut”. Atom originates from the Greek word atomos, which means “cannot be cut”.

3. The Atomic Theory An English scientist named John Dalton (1766-1844) realized that different types of atoms existed from experimentation.

4. John Dalton’s Atomic Theory 1. All matter is made of atoms. 2. All atoms of an element are identical in mass and properties 3. Compounds are formed by two or more different kinds of atoms. 4. A chemical reaction is a rearrangement of atoms.

5. J.J. Thomson (1897) Performed the Cathode Ray Tube Experiment He discovered electrons, which are negatively charged particles within the atom

6. JJ Thomson’s Experiment Thomson concluded the cathode ray consists of a beam of negatively charged particles (electrons) and that electrons are constituents of matter.

7. Ernest Rutherford’s Experiment Early 1900’s, proved the existence of the atomic nucleus. Early 1900’s, proved the existence of the atomic nucleus. Shot particles of matter at a piece of gold foil. Shot particles of matter at a piece of gold foil. Most particles continued on a straight line, a few deflected. Most particles continued on a straight line, a few deflected.

8. Why the Atomic Theory? Humans have never seen an atom directly because they are so small!

9. How Small Are Atoms? If all humans on Earth were shrunk to the size of an atom, we could fit easily on the head of a pin! If all humans on Earth were shrunk to the size of an atom, we could fit easily on the head of a pin! The most powerful microscopes cannot see atoms because they are too small! The most powerful microscopes cannot see atoms because they are too small! In 12 grams of Carbon, there are 6 x 10 23 atoms! In 12 grams of Carbon, there are 6 x 10 23 atoms!

10. The Emptiness of Matter The space between an atom’s center and its edge is enormous. The space between an atom’s center and its edge is enormous. If an atom’s nucleus was expanded to the size of a penny and placed on the pitcher’s mound at Fenway Park, then the closest electron would be somewhere along the Green Monster! If an atom’s nucleus was expanded to the size of a penny and placed on the pitcher’s mound at Fenway Park, then the closest electron would be somewhere along the Green Monster!

11. Basic Structure of Matter Elements are the simplest form of matter and cannot be broken down any further by chemical changes. Elements are the simplest form of matter and cannot be broken down any further by chemical changes. Elements are made of atoms. Elements are made of atoms.

12. Sub-Atomic Particles Atoms are not indestructible, they are made of smaller pieces of matter. Atoms are not indestructible, they are made of smaller pieces of matter. These subatomic particles are protons, neutrons, and electrons. These subatomic particles are protons, neutrons, and electrons.

13. The Nucleus Where the protons and neutrons exist. Over 99% of an atom’s mass is found within the nucleus. Each particle in nucleus has a mass of 1 AMU (Atomic Mass Unit)

14. Protons The number of protons in an atom determine the identity of an element. The number of protons in an atom determine the identity of an element. Atomic number – Number of protons in nucleus. Atomic number – Number of protons in nucleus. Protons carry a positive electrical charge. Protons carry a positive electrical charge.

15. Neutrons Found in nucleus Found in nucleus Same mass as a proton with no charge (neutral) Same mass as a proton with no charge (neutral) Mass number = Atomic number + # of Neutrons.

16. Electrons Electrons orbit the nucleus of an atom in what is called an electron cloud. Electrons orbit the nucleus of an atom in what is called an electron cloud. Electrons have a negative electrical charge. Electrons have a negative electrical charge. Electrons are attracted to the positively charged nucleus (from the protons) of an atom. Electrons are attracted to the positively charged nucleus (from the protons) of an atom.

17. Isotopes Isotopes – two atoms of same element (same atomic number) with different numbers of neutrons in the nucleus. Isotopes – two atoms of same element (same atomic number) with different numbers of neutrons in the nucleus.

18. Reading the Periodic Table Chemical Symbol Chemical Symbol Atomic Number (# of protons) Atomic Number (# of protons) Average atomic mass (rounded to the nearest whole = mass number) Average atomic mass (rounded to the nearest whole = mass number) Number of Neutrons is determined by subtracting atomic number from mass number Number of Neutrons is determined by subtracting atomic number from mass number 1.00197 (rounded to 1) – 1 = 0 neutrons

19. Apply what you just learned How many protons in an iron atom? How many protons in an iron atom? How many neutrons in an iron atom? How many neutrons in an iron atom? Why do you suppose iron’s chemical symbol is Fe and not something like Ir? Why do you suppose iron’s chemical symbol is Fe and not something like Ir?

20. How Electrons are Arranged Atoms will usually have the same number of electrons as they do protons to balance the overall electrical charge. Atoms will usually have the same number of electrons as they do protons to balance the overall electrical charge. Electrons are arranged in energy levels. Each energy level can only hold a certain number of electrons. Electrons are arranged in energy levels. Each energy level can only hold a certain number of electrons. Energy Level Number of Electrons 12 28 38 418 518

21. Bohr Model – Helium Atom Valence Electrons- Amount of electrons in the outermost energy level; i.e Helium has two valence electrons. Carbon has 4 valence electrons (See next Slide)

22. Bohr Model - Carbon