1. Chapter 4.1 Defining the Atom

2. Democritus (Greece 460 BCE) Believed that atoms were indivisible and indestructible. Believed that atoms were indivisible and indestructible. Did not explain chemical behavior. Did not explain chemical behavior. Did not test his ideas with scientific method. Did not test his ideas with scientific method.

3. Dalton’s Model (1808) Each element made of small atoms. Each element made of small atoms. Imagined atoms as tiny, solid balls. Imagined atoms as tiny, solid balls. Like marbles. Like marbles. Each element was different. Each element was different.

4. Dalton’s Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element.

5. 3. Atoms of different elements can physically mix together or can chemically combine in simple whole- number ratios to form compounds. 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element are never changed into atoms of another element as a result of a chemical reaction.

6. Chapter 4.2 Structure of the Nuclear Atom

7. Subatomic Particles Electrons Electrons Protons Protons Neutrons Neutrons

8. Subatomic Particles ParticleSymbolRelativeCharge Relative Mass Actual Mass Electron Proton Neutron

9. Electrons J.J.Thomson J.J.Thomson Discovered the existence of electrons. (1897) Discovered the existence of electrons. (1897) Tiny, negatively charged particles. Tiny, negatively charged particles.

10. Protons Ernest Rutherford (1911) Ernest Rutherford (1911) Discovered the location of protons in an atom. Discovered the location of protons in an atom. Positively charged particles. Positively charged particles. Identified the nucleus of an atom. Identified the nucleus of an atom. http://chemmovies.unl.edu/ChemAnime/RU ERFD/RUTHERFD.html http://chemmovies.unl.edu/ChemAnime/RU ERFD/RUTHERFD.html

11. Neutrons James Chadwick (1932) James Chadwick (1932) Discovered the existence of neutrons. Discovered the existence of neutrons. Neutral particles found in the nucleus of an atom. Neutral particles found in the nucleus of an atom.

12. Chapter 4.3 Distinguishing Among Atoms

13. Atomic Number: Atomic Number: The number of protons in an atom. The number of protons in an atom. This is what identifies each element on the periodic table. This is what identifies each element on the periodic table. Examples: Examples: C27Br 6Cobalt35

14. Mass Number Mass Number The total number of protons and neutrons in an atom. The total number of protons and neutrons in an atom. Mass number = protons + neutrons Mass number = protons + neutrons Atomic Mass/Atomic Weight Atomic Mass/Atomic Weight Average of all the isotope masses of an element. Average of all the isotope masses of an element. Found on Periodic Table Found on Periodic Table Round off to nearest whole number to calculate # of neutrons Round off to nearest whole number to calculate # of neutrons

15. Examples of Mass Number Examples of Mass Number C-14 11 B C-14 11 B

16. Calculating Protons, Electrons and Neutrons Protons = Atomic Number Protons = Atomic Number Electrons = # of Protons (for a neutral atom) Electrons = # of Protons (for a neutral atom) Neutrons = Mass Number - # of protons Neutrons = Mass Number - # of protons Mg-24 Ba-137 Mg-24 Ba-137

17. Shorthand Form: Shorthand Form: C 12 6

18. Practice… Shorthand Symbol Atomic Number ProtonsNeutronsElectrons Mass Number Ge73 2530 3950 75186

19. Isotopes Atoms that have the same number of protons (same element), but a different number of neutrons. Atoms that have the same number of protons (same element), but a different number of neutrons. They have gained or lost neutrons. They have gained or lost neutrons. They have different atomic masses. They have different atomic masses.

20. Ions An atom or group of atoms that has a positive or negative charge. An atom or group of atoms that has a positive or negative charge. How do atoms become ions? How do atoms become ions? They gain or lose electrons They gain or lose electrons Electrons have negative charges. Electrons have negative charges. Gain electron(s)  negative ion Gain electron(s)  negative ion Lose electron(s)  positive ion Lose electron(s)  positive ion

21. How do we write the symbol for isotopes and ions? How do we write the symbol for isotopes and ions? Shorthand Form: Shorthand Form: How many: How many: Protons: Protons: Neutrons: Neutrons: Electrons: Electrons: F 19 9 Atomic number Mass number Charge on ion 10 9