Atoms: The Building Blocks of Matter

1. Chapter 4 Atoms

2. Atoms • The smallest particle that has the properties of an element.

3. Dalton’s Atomic Theory • Every element is made of tiny, unique, particles called atoms that cannot be subdivided. • Atoms of the same element are exactly alike. • Atoms of different elements can join to form molecules or compunds

4. Parts of an Atom • Nucleus – small, dense center of an atom made up of 2 subatomic particles that are identical in size and mass. • Protons – have a positive charge • Neutrons – have no charge

5. Parts of an Atom cont. • Electrons – are tiny subatomic particles that have very little mass that moves around the outside of the nucleus. These particles are negatively charged and form a “cloud” around the nucleus.

6. The number of protons and electrons an atom has is unique for each element.

7. Atomic Charge • Atoms have no overall charge because the protons (+) cancel out the electrons (-). Helium 2 protons - +2 2 neutrons - 0 2 electrons --2 total charge 0

8. Protons • positive (+) charge • Found in the nucleus • # of protons = atomic # • The number of protons identify the element (atomic #)

9. Neutrons • no charge • Found in the nucleus • Along with protons makes up atomic mass • Atomic Mass – atomic number = # of neutrons (rounded to whole #)

10. Electrons • negative (–) charge • travel in orbitals (or energy levels) around the nucleus. (electron cloud) • Equals atomic number in neutral atoms • valence electrons - the # of electrons in the outer shell and relates to the oxidation #

11. Unit of measure for atomic particles is Atomic mass unit (amu) protons and neutrons = about 1 amu (electrons are about 1/2000 of the size of protons and neutrons))

12. Chemical symbols • The one or two letter abbreviation of the element name. • Some are based on Latin name • ALL 1st letter is upper case • ALL 2nd letter is lower case

13. Mass Number or Atomic Mass • the sum of the number of protons and the number of neutrons in the nucleus of an atom. • # of neutrons = mass # - atomic # Neutrons Protons +

14. Atom Summary • Atomic Number = protons = electrons • Atomic Mass = Protons + Neutrons • Neutrons = atomic mass – atomic number • Atomic symbols • First letter is ALWAYS upper case • Second letter is ALWAYS lower case • Example: Oxygen element 6 with mass 16 P = 8 E = 8 N = 16-8 = 8

15. Isotopes • Atoms of the same element that have a different # of neutrons and a different atomic mass. (identified by the element name followed by the mass # ) • ex. C-12, C-14, B-10, B-11) Carbon 14 = 8 neutrons 6 protons 6 electrons 6 electrons 6 protons Carbon 12 = 6 neutrons