1. The Atom, the Elements, & the Periodic Table

2. 2 Democritus (460-370 BC) John Dalton (1766-1844) Joseph John Thomson (1856-1940) Published the atomic theory: 1.Elements made of atoms. 2.Atoms of the same element are identical. 3.Atoms of different elements have different properties. 4.Atoms DON’T CHANGE, but can be combined and rearranged with other atoms. 5.Compounds are formed when atoms of more than one element combine in specific ratios. Proposed that matter was made of small particles he called atoms. In Greek this means indivisible or cannot be divided. He believed different atoms would vary in size and would be in constant motion. Atom as solid object Extremely small particles in motion Identified the electron, which carries a negative charge. He thought that electrons were embedded in the atom like blueberries in a muffin. Atom as solid object with a positive center and electrons embedded in the atom

3. 3 Neils Bohr (1885-1962) James Chadwick (1891-1974) Ernest Rutherford (1871-1937) Used high speed lightweight atoms called alpha particles to bombard very thin gold foil. Most of these alpha particles passed through the gold foil. The fact that these particles went through the foil lead to his theory that atoms have mostly empty space. Alpha particles went through spaces. Described the electrons moving around the nucleus in fixed orbits. Each orbit has a set amount of energy. We use this model for a basic understanding of the atom’s structure. Solved the problem of “missing mass” in the atom by discovering the neutron.        However, more recent research has shown that electrons move around the nucleus in waves rather than elliptical orbits. Electrons are better represented as an “electron cloud.”      Electrons move so fast that scientists prefer the atom model where electrons are represented by a cloud.

4. 4 Basic Structure of an Atom Proton Electron Neutron + + Positive Charge No Charge Negative Charge 1 AMU

5. Atomic Number This refers to how many protons an atom of that element has. No two elements, have the same number of protons. Wave Model

6. Atomic Mass Atomic Mass = the “weight” of the atom. Number of protons plus number of neutrons. This is a helium atom. Its atomic mass is 4 (protons plus neutrons). What is its atomic number?

7. Atomic Mass Unit (AMU) The unit of measurement for an atom is an AMU. One AMU = the mass of one proton.

8. Atomic Mass Unit (AMU) There are 6 X 10 23 or 600,000,000,000,000,000,000,000 amus in one gram. (Remember that electrons are 2000 times smaller than one amu).

9. 9 Be 9.01 Beryllium 4 Element Name Atomic Number Element Symbol Atomic Mass (# of protons and electrons) (Average mass of all the isotopes of that element) + + + +

10. 10 N 14.01 Nitrogen 7 Nitrogen-14 14 is the mass number. Mass number = #p + #n #p = 7 (atomic number) #e= 7 (equal to the number of protons) #n = 7 (mass # - # p) What are the numbers of protons, electrons and neutrons in a Nitrogen-14 atom?

11. 11 K 39.098 Potassium 19 20 P = E = N = What are the numbers of protons, electrons and neutrons in a potassium-39 atom ( remember 39 is the mass number)?

12. 12 Cl 35.4 Chlorine 17 18 P = E = N = What are the numbers of protons, electrons and neutrons in a chlorine-36 atom?

13. Energy Levels of Electrons Energy levelMaximum # of electrons 12 28 318 432 550

14. 14 Atoms of a given element with different numbers of neutrons. All isotopes will have the same atomic number but different mass numbers. Mass number = #p + #n Shown below are three isotopes of hydrogen. The letter after the name tells you the mass number. The most common isotope of hydrogen is Hydrogen-1. 1 Hydrogen H 1.01  Hydrogen-1  Hydrogen-2  Hydrogen-3

15. The mass of an element is the mass of the element compared to an isotope of carbon, Carbon 12. –Carbon 12 is assigned an atomic mass of 12.00 g. –12.00 is one atomic mass unit The number of protons and neutrons in an atom is its mass number. Atomic numbers are whole numbers Mass numbers are whole numbers The atomic mass is not a whole number.

16. Periodic Table of Elements

17. Patterns in the Elements Dmitri Mendeleev noticed a pattern in the properties of the elements when he arranged the elements in order of increasing atomic mass. He is credited for developing the first periodic table.

18. Mendeleev left blank spaces in his table when the properties of the elements above and below did not seem to match. The existence of unknown elements was predicted by Mendeleev on the basis of the blank spaces. When the unknown elements were discovered, it was found that Mendeleev had closely predicted the properties of the elements as well as their discovery.

19. The Periodic Law –Similar physical and chemical properties recur periodically when the elements are listed in order of increasing atomic number.

21. –Chemical Symbols There are about a dozen common elements that have single capitalized letter for their symbol The rest, that have permanent names have two letters. –the first is capitalized and the second is lower case. Some elements have symbols from their Latin names. Ten of the elements have symbols from their Latin or German names.

22. Introduction –The periodic table is made up of rows of elements and columns. –An element is identified by its chemical symbol. –The number above the symbol is the atomic number –The number below the symbol is the rounded atomic weight of the element. –A row is called a period –A column is called a group or family

24. Other information Many periodic tables include a zig-zag line that separates the metals from the non- metals. The metals are to the left of the line, the non-metals to the right.

25. Properties of Metals Physical properties include: –Malleable – ability to be hammered or rolled into flat sheets or other shapes. –Ductile – ability to be pulled out or drawn into a wire. –Good Conductors – of heat & electricity

26. Other Properties of (some) Metals Shiny appearance / metallic luster Solids High density Magnetic React with other elements by LOOSING electrons. Corrosion

27. Properties of Non-Metals Lack the properties of metals (opposites) Poor conductors Brittle (not malleable or ductile) –Non-metals will generally break, crumble or powder when hit with a hammer.

28. Other properties of Non-Metals Dull appearance Gases Low density Characteristic color React with other elements by GAINING OR SHARING electrons.

29. Properties of Metalloids Metalloids (metal-like) have properties of both metals and non-metals. They are solids that can be shiny or dull. They conduct heat and electricity better than non- metals but not as well as metals. They are ductile and malleable. Semi-conductors – computer chips, transistors, lasers Silicon

30. Organization The properties of an element can be predicted based on the location within the periodic table. Periods – horizontal rows –Indicates the number of shells

31. Organization Groups –Indicates the number of valence electrons –Shows how reactive an element is. Groups/families share similar characteristics or properties

32. Valence Electrons The number of valence electrons an atom has may also appear in a square. Valence electrons are the electrons in the outer energy level of an atom. These are the electrons that are transferred or shared when atoms bond together.

33. Families Periods Columns of elements are called groups or families. Elements in each family have similar but not identical properties. For example, lithium (Li), sodium (Na), potassium (K), and other members of family IA are all soft, white, shiny metals. All elements in a family have the same number of valence electrons. Each horizontal row of elements is called a period. The elements in a period are not alike in properties. In fact, the properties change greatly across even given row. The first element in a period is always an extremely active solid. The last element in a period, is always an inactive gas.

35. Hydrogen The hydrogen square sits atop Family AI, but it is not a member of that family. Hydrogen is in a class of its own. It has one valence electron in its one and only energy level. It’s a gas at room temperature. Hydrogen only needs 2 electrons to fill up its valence shell.

36. Alkali Metals The alkali family is group 1. Atoms of the alkali metals have 1 valence electron that they lose when forming bonds. They are shiny, have the consistency of clay, and are easily cut with a knife.

37. Alkali Metals They are the most reactive metals. They react violently with water. Alkali metals are never found as free elements in nature. They are always bonded with another element.

38. What does it mean to be reactive? We will be describing elements according to their reactivity. Elements that are reactive bond easily with other elements to make compounds. Some elements are only found in nature bonded with other elements. What makes an element reactive? –An incomplete valence electron level. –All atoms (except hydrogen) want to have 8 electrons in their very outermost energy level (This is called the rule of octet.) –Atoms bond until this level is complete. Atoms with few valence electrons lose them during bonding. Atoms with 6, 7, or 8 valence electrons gain electrons during bonding.

39. 5

42. Alkaline Earth Metals The alkaline earth family is group 2. They have two valence electrons that they lose when forming bonds. They are never found uncombined in nature and very reactive. Alkaline earth metals include magnesium and calcium, among others.

43. Transition Metals Transition Elements include those elements in families 3-12. Transition elements valence electrons vary, but many have 1 or 2 valence electrons, which they lose when they form bonds with other atoms. Some transition elements can lose electrons in their next-to-outermost level. They are good conductors of heat and electricity.

44. Transition Metals The compounds of transition metals are usually brightly colored and are often used to color paints. These are the metals you are probably most familiar: copper, tin, zinc, iron, nickel, gold, and silver.

45. Boron Family The Boron Family is family 13. Atoms in this family have 3 valence electrons that are typically shared when forming bonds. This family includes a metalloid (boron), and the rest are metals. This family includes the most abundant metal in the earth’s crust (aluminum).

46. Carbon Family The Carbon family is family 14. There are 4 valence electrons that are typically shared when forming bonds.. This family includes a non- metal (carbon), metalloids, and metals. The element carbon is called the “basis of life.” There is an entire branch of chemistry devoted to carbon compounds called organic chemistry.

47. Nitrogen Family The nitrogen family is family 15, named after the element that makes up 78% of our atmosphere. Atoms in the nitrogen family have 5 valence electrons. They tend to share electrons when they bond. This family includes non-metals, metalloids, and metals. Other elements in this family are phosphorus, arsenic, antimony, and bismuth.

48. Oxygen Family Oxygen family is family 16. Atoms of this family have 6 valence electrons. They tend to share or gain electrons when they bond. Oxygen is the most abundant element in the earth’s crust. It is extremely active and combines with almost all elements.

49. Halogen Family Halogen family is family 17. Halogens have 7 valence electrons, and will gain an electron when forming bonds. This explains why they are the most active non- metals. They are never found free in nature. They react with alkali metals to form salts. The elements in this family are fluorine, chlorine, bromine, iodine, and astatine.

50. Inert Gases Noble Gases are family 18. One important property of the noble gases is their inactivity. They are inactive because their outermost energy level is full, with 8 valence electrons. They are colorless gases that are extremely un-reactive. The family of noble gases includes helium, neon, argon, krypton, xenon, and radon. All the noble gases are found in small amounts in the earth's atmosphere.

51. Rare Earth Elements The thirty rare earth elements are composed of the lanthanide and actinide series. One element of the lanthanide series and most of the elements in the actinide series are called trans-uranium, which means synthetic or man-made.