The Atom, the Elements, & the Periodic Table

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

2. Development of Atomic Theory: Democritus (460-370 BC) Extremely small particles in motion 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. John Dalton (1766-1844) • Published the atomic theory: • Elements were composed of atoms. • Atoms of a given element are identical. • Atoms of different elements have different properties. • Atoms don’t change, but can be combined and rearranged with other atoms. • Compounds are formed when atoms of more than one element combine. Atom as solid object Joseph John Thomson (1856-1940) Atom as solid object with a positive center and electrons embedded in the atom Identified the electron, which carries a negative charge. He thought that electrons were embedded in the atom like raisins in raisin bread or chocolate chip cookie.

3.             Development of Atomic Theory: 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. Neils Bohr (1885-1962) 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. Electrons move so fast that scientists prefer the atom model where electrons are represented by a cloud. 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.” James Chadwick (1891-1974) Solved the problem of “missing mass” in the atom by discovering the neutron.

4. 1AMU 1AMU 1AMU 1AMU Basic Structure of an Atom Proton Positive Charge + + Neutron No Charge Electron AMU is an atomic mass unit. Electrons do not have much mass compared to protons and neutrons. Negative Charge

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

6. Atomic Mass • Atomic Mass refers to the “weight” of the atom. • It is derived at by adding the number of protons with the number of neutrons. This is a helium atom. Its atomic mass is 4 (protons plus neutrons). What is its atomic number? H

7. Atomic Mass Unit (AMU) • The unit of measurement for an atom is an AMU. It stands for atomic mass unit. • One AMU is equal to the mass of one proton.

8. Atomic Mass Unit (AMU) • There are 6 X 1023 or 600,000,000,000,000,000,000,000 amus in one gram. • (Remember that electrons are 2000 times smaller than one amu).

9. What’s in a square? • Different periodic tables can include various bits of information, but usually: • atomic number • symbol • atomic mass • number of valence electrons • state of matter at room temperature.

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

11. What are the numbers of protons, electrons and neutrons in a Nitrogen-14 atom? 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) Nitrogen 7 N 14.01

12. What are the numbers of protons, electrons and neutrons in a potassium-40 atom ( remember 40 is the mass number)? Potassium 19 K P = E = N = 19 19 20 39.098

13. What are the numbers of protons, electrons and neutrons in a chlorine-36 atom? Chlorine 17 Cl P = E = N = 17 17 18 35.45

14. Atomic Energy Levels (orbits) 1st Level = 2 electrons 2nd Level = 8 electrons 3rd Level = 18 electrons 4th Level = 32 electrons 5th Level = 52 electrons Magnesium Atomic # = 12 Atomic mass = 24 1st = 2 2nd = 8 3rd = 2

15.    Hydrogen-1 Hydrogen-2 Hydrogen-3 Isotopes 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

16. Atomic Structure Review • A molecule is a particle that is composed of two or more atoms held together by a chemical bond. • Isotopes are atoms of an element with identical chemical properties, but different masses due to a difference in the number of neutrons. • The atomic massof an element is the average of all the atomic masses of the isotopes. • an isotopes contribution is determined by its relative abundance.

17. 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.

18. Chemical Symbols • There are about a dozen common elements that have a 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.

19. Periodic Table of Elements

20. 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.

21. 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.

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

23. Notice the Pattern of the Periodic Table.

24. What Do You Notice? 1 H 1.01 2 He 4.0 3 Li 6.94 4 Be 9.01 5 B 10.81 6 C 12.01 7 N 14.01 8 O 16.00 9 F 19.00 10 Ne 20.18 11 Na 22.99 12 Mg 24.31 13 Al 26.98 14 Si 28.09 15 P 30.97 16 S 32.07 17 Cl 35.45 18 Ar 39.95 19 K 39.10 20 Ca 40.08

26. 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/family

27. Element Data • Each square on the periodic table represents information about one atom of an element. Each square tells… • Atomic number • Chemical symbol • Element name • Atomic mass

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

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

30. 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.

32. 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.

33. 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. • GoodConductors – transfers heat or electricity

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

35. 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.

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

37. REVIEW • In what order did Mendeleev arrange the elements in the first periodic table? • How are they arranged today? • What does an elements location in the periodic table tell you about that element?

38. REVIEW 4. What properties of metals do the following terms describe? conductivity malleability ductility 5. What property of metals led to the use of plastic or wood handles on many metal cooking utensils?

39. 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

42. 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. Families Periods

43. Families