Atomic Structure & the Periodic Table

1. Atomic Structure & the Periodic Table

2. Atoms Atom smallest particle that has the properties of an element Democritus PROPERTIES Atoms are the building blocks of molecules John Dalton’s 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

3. What is an Atom? Nucleus the center of an atom; made up of protons & neutrons Water Three main Subatomic Particles a positively charged subatomic particle in the nucleus of an atom Proton Neutron a neutral subatomic particle in the nucleus of an atom Electron a tiny negatively charged subatomic particle moving around outside the nucleus of an atom 4 miles

5. Atoms have no overall charge? Atoms do not have a charge because they have an equal number of protons & electrons whose charges exactly cancel. Atomic Models Bohr’s model electrons in an atom move in set paths around the nucleus (like the planets orbiting the sun) Energy level / shell any of the possible energies an electron may have in an atom

6. Atomic Models e- Cloud Modern Theory Bohr’s model It is impossible to determine both the exact location of an electron (e- )in an atom & its speed & direction e- cloud Visual method uses an… Shaded region used to demonstrate the possible location of an e-

7. Atomic Number Mass Number Isotopes

8. Model of Helium

9. What does an atom really look like? • The Electron Cloud Model is the current accepted model of the atom • This model illustrates the nucleus and the electrons in a cloud around the nucleus

10. Electron Orbitals • Electrons occupy the lowest energy levels available in an atom • Within each energy level, e- occupy orbitals w/the lowest energy • s, p, d, f – order of orbit strength (weakest to strongest) Valence Electrons Valence electron Electron(s) in the outermost energy level of an atom 2e- 8e-

11. How do the structures of atoms differ? Atomic number (Z) • the number of protons in the nucleus • Note: All atoms of the same element have the same atomic number/protons. • In a neutral atom the number of protons is equal to the number of electrons Atomic Mass (A) the total number of protons and neutrons in the nucleus of an atom Because atomic masses are averages, many of them are decimals instead of whole #’s.

12. ISOTOPES Does changing the number of neutrons affect the number of p+ & e- ? Isotopes any atoms having the same number of protons but different numbers of neutrons • have different mass #’s Calculating neutrons How many neutrons are in radioactive uranium-235?

13. Mass of an Atom atomic mass unit (amu) a quantity equal to one-twelfth of the mass of a carbon-12 atom average atomic mass the weighted average of the masses of all naturally occurring isotopes of an element

14. EX: Determine each of the following given this picture… # e- # p + # n Atomic # Mass # Element Name Element Symbol Now Complete the handout “I/S Atomic Structure Worksheet”… Then, let’s go over the intro packet (first couple of pages…).

15. IONS Atoms of Group 1 elements are reactive, why? • because their outermost energy levels are only partially filled Ionization process of adding e- to or removing e- from an atom or group of atoms Ion an atom or group of atoms that has lost or gained one or more e- and therefore has a net electric charge Cation an ion w/a positive charge Li +

16. IONS Anion an ion w/a negative charge F - How do the structures of atoms differ? Atomic number (Z) the number of protons in the nucleus Mass number (A) the total number of protons and neutrons in the nucleus of an atom

17. Periodic Table • elements are represented by their symbols • arranged by # of protons found in the nucleus Periodic Law properties of elements tend to change in a regular pattern when elements are arranged in order of increasing atomic # (# of protons in their atoms)

18. Periodic Table Dmitri Mendeleev Mendeleev arranged the elements into rows in order of increasing mass so that elements w/similar properties were in the same column ? Why couldn’t Mendeleev make a complete periodic table? Gallium

19. Periodic Table Period a horizontal row of elements in the periodic table • the # of p+ & e- increase by one, moving from left to right Group (family) a vertical column of elements in the periodic table • group members have the same # of valence e- • have similar properties

20. Element Families • elements are classified as either metals or nonmetals Metals the elements that are good conductors of heat & electricity Nonmetals the elements that are usually poor conductors of heat & electricity Semiconductors the elements that are intermediate conductors of heat & electricity

21. Metals (4 types) Alkali metals highly reactive metallic elements located in Group 1 of the periodic table Are alkali metals often found in nature as elements? reactive metallic elements located in Group 2 of the periodic table Alkaline-earth metals

22. Metals Transition metals metallic elements located in Groups 3-12 of the periodic table radioactive nuclei of the atoms are continually decaying to produce different elements

24. Nonmetals • include some elements in Groups 13-16 & all in Groups 17-18 Carbon is usually found as what, in its’ pure state?

25. Nonmetals The most plentiful gases in the air are… Odorless yellow solid? N&O Halogens highly reactive elements located in Group 17 of the periodic table Poisonous yellow-green gas? Cl is widely used to kill bacteria

26. Nonmetals I is used in table salt to prevent goiters from forming (enlarged thyroid gland) Fl is used in some toothpastes & added to drinking water to help prevent tooth decay unreactive gaseous elements located in Group 18 of the periodic table Noble Gases Ne is responsible for… Why are the noble gases so unreactive? He is lighter than air & gives balloons lift Ar prevents filaments from burning

27. Semiconductors Semiconductors (metalloids) nonmetals exhibiting some metallic properties under certain circumstances Silicon is the most familiar semiconductor, making up 28% of the earth’s crust

28. Electron Orbitals Orbital a region in an atom where there is a high probability of finding electrons Four Orbital Types d p s Simplest… max 2 e- /orbital (5) shaped like a sphere max 2 e- dumbbell-shaped max 2 e- /orbital (3) f max 2 e- /orbital (7)

29. Energy Levels, Orbitals, and Electrons Energy Level # of Orbitals Max # of Electrons 1 1 2 2 8 4 3 9 18 4 16 32

30. Electron Orbitals

31. Question? • Atoms are mostly________? • A. Protons • B. Neutrons • C. Electrons • D. All of these • E. None of these

32. Answer • E. None of these • Atoms are 99.999% empty space, essentially a vacuum. • There is the nucleus and the electrons circling around it • Between the nucleus and circling electrons there is absolutely nothing! • The nucleus makes up 99.9% of the atom’s mass.

33. Facts • The radius of the electron cloud is 10,000 times larger than the nucleus of the atom • Even with this huge cloud, it contains almost none of the total mass of an atom • The volume of an atom is 1 trillion times larger than the nucleus