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The Atom and the Periodic Table From

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1 The Atom and the Periodic Table From

2 Atoms Everything in the Universe is made of stuff (also known as matter). The building blocks are the same, whether we are looking at Stars or Starbursts.

3 Atoms Matter is made up of Atoms. Atoms are the smallest particle of an element. They are so small that:  1 sheet of paper = 10,000 atoms thick  1 drop of water has 2 trillion atoms of oxygen and 4 trillion atoms of hydrogen. The three parts of an atom are:  Protons  Neutrons  Electrons

4 Atoms – Protons There are three types of particles that make up atoms The first type of particle is called the PROTON. Protons are found in the nucleus of an atom. Protons have a positive (+) charge. Protons have a mass of 1 a.m.u.

5 Atoms - Neutrons Another particle is the NEUTRON. Neutrons are also found in the nucleus of an atom. Neutrons have no charge. We call this neutral. Neutrons have a mass of 1 a.m.u. Neutrons act like the glue that holds the nucleus together.

6 Atoms - Electrons Electrons are the third type of particle inside of an atom. They are very small, and exist outside of the nucleus in the electrons clouds or shells. Electrons have a negative charge (-) and have almost no mass at all.

7 Atomic Structure Atoms are made up of three subatomic particles: Subatomic = smaller than an atom Live where? Have mass? What charge? Protons Neutrons Electrons In nucleus Outside nucleus 1 a.m.u No, negligible + - none

8 Atomic Structure Video

9 Elements Substances made of only one type of atom Identified by atomic number (protons!!!) Can not be broken down into simpler substances

10 Element Symbols Shorthand name of the element Most are based on the Latin name  Ex: Gold = Au The symbol is either: 1. One capital letter -ex: Carbon = C 2. Two letters…one capitol, one lower case -ex: Krypton = Kr

11 Atomic Number Top Number indicates Atomic Number Atomic Number = Number of Protons  Hydrogen: Atomic Number 1 = 1 proton  Magnesium: Atomic Number 12 = 12 protons  Lead: Atomic Number 82 = 82 Protons IF YOU CHANGE THE NUMBER OF PROTONS OF AN ATOM, YOU CHANGE ITS IDENTITY!!!!!!!! 1H1H 12 Mg 82 Pb

12 Atomic Mass Bottom Number indicates Atomic Mass Atomic Mass = Total Mass (Number of Protons + Number of Neutrons)  Hydrogen: 1 (Protons + Neutrons)  Magnesium: 24 (Protons + Neutrons)  Lead: 207 (Protons + Neutrons) If we take the Atomic Mass and subtract the Atomic Number, we can figure out the number of neutrons.  Pb – (Atomic Mass) 207 – (Atomic Number) 82 = 125 H1H1 Mg 24 Pb 207

13 Atomic Structure (cont.) Atomic Mass Average mass of an element, based on amount of each isotope found in nature Not a whole number because it is an average Atomic number Number of protons in an element Also, number of electrons when it is neutral (has no charge) 7 N

14 Atomic Structure (cont.) For a lithium (Li) atom:  What is the atomic number? How many protons? How many electrons since it is neutral?  What is the atomic mass? How many neutrons? rounded to 7 Usually 4

15 Atomic Structure (cont.) Practice Problem #1 For a sodium atom:  What is the atomic number? How many protons? How many electrons since it is neutral?  What is the atomic weight? How many neutrons? rounded to 23 Usually 12

16 Atomic Structure (cont.) Practice Problem #2 For a boron atom:  What is the atomic number? How many protons? How many electrons since it is neutral?  What is the atomic weight? How many neutrons? rounded to 11 Often 6

17 Atomic Structure (cont.) Helium Atomic Number: 2 Protons: 2 Electrons: 2 Atomic Mass: Atomic Mass rounded to: 4 Neutrons: 2

18 Isotopes Is an atom of a given element that has different numbers of neutrons and a different mass number.  It has gained or lost neutrons  Examples: Carbon—12 Carbon—14 Mass

19 Carbon-12 #p + 6 #e - 6 #n 0 6 Mass12 Carbon-14 #p + 6 #e - 6 #n 0 8 Mass14

20 Radioisotopes Is an isotope with an unstable nucleus Examples: uranium, Plutonium Isotopes of all elements above #83 are radioactive producing radioisotopes Ex. U-238 is naturally occuring U-235 is a radioisotope

21 Writing Isotope Symbols Hyphen Notation- is the element symbol with the atomic mass hyphenated. Example C-12 and C-14

22 Writing Isotope Symbols continued Atomic Symbol Notation: Atomic Mass Atomic # = # protons Chemical Symbol of Element

23 The Periodic Table Organized by trends and patterns  “periodic” means repeating This allows you to make predictions about the atoms’ behavior based on where they are on the table

24 Periods The elements are arranged on the periodic table of elements Going horizontal across the table are the PERIODS (Left to right) Period # = # of valence shells Starting from the left, the periods go from metals  metalloids  nonmetals

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26 Periodic Table - History Dimitry Mendeleev was a Russian (actually Siberian) scientist that lived in the late 19 th Century.

27 Periodic Table - History When Mendeleev arranged them by Atomic Mass, he was able to predict the properties of elements that had not yet been discovered. This is the basis of the Periodic Table that we use today.

28 Periodic Table - History Now the Periodic Table that we use is arranged by Atomic Number instead of Mass. Henry Moseley reordered the Periodic Table by Atomic Number

29 Groups and Families The columns on the periodic table are called groups and families. The groups are the numbers; the families are the names They are organized by the number of valence electrons

30 Metals Lose electrons to form positive ions Ductile & Malleable  What do these words mean? Good conductors of heat and electricity MOST are solid at room temperature

31 Nonmetals Gain electrons to form negative ions Brittle Good insulators Found as solid, liquid, or gas at room temp

32 Metalloids (semi-metals) Found directly on either side of side-step line  Except Al (this is a metal!!!) Properties of both metals and nonmetals  Less conductive than metals, but poorer insulators than nonmetals Electrons held more tightly than metals, but can be freed with heat

33 Alkali Metals Group 1A Only one valence electron VERY reactive!!!! Hydrogen is NOT included +1 charge

34 Alkaline Earth Metals Group 2A Two valence electrons Not as reactive as the alkali metals Named because of where they are found on Earth +2 charge

35 Transition Metals Found in the middle of the table In the “B Groups” Can change their number of valence electrons Bottom Rows are also known as the Rare Earth Metals!!!

36 Halogens Group 7A Seven valence electrons VERY reactive!!!! They react with alkali metals to form salts -1 charge

37 Noble Gases Group 8A 8 valence electrons—outer energy level is full Very UNREACTIVE— what do they need to be 0 charge

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40 Electron Clouds The different layers of clouds hold different numbers of electrons  1 st cloud = 2  2 nd cloud = 8  3 rd cloud = 8 These cloud layers conveniently match the rows on the periodic table: 1 st row = 2 elements 2 nd row = 8 elements 3 rd row =8 elements… And then it gets complicated

41 Electron Clouds (cont.) To draw the electron clouds:  Figure out how many total electrons  Fill in the electrons starting with the first cloud Sulfur has:  16 electrons

42 Electron Clouds (cont.) Practice Problem  Draw the electron clouds for an Al atom This is WAY too much work…there must be a simpler way!

43 Lewis Dot Structures A smart man named Gilbert Newton Lewis figured out an easier way!  For Lewis Dot Structures draw only the important electrons…are called the outer, or valence, electrons Just draw the outer electrons around the atomic symbol S

44 Lewis Dot Structures (cont.) Practice Problem #4  Draw Lewis Dot Structures for:  A Calcium atom  A Chlorine atom  An Oxygen atom CaOCl

45 Octet Rule Noble gases are what all elements aspire to be like electronically These elements have 8 electrons in highest energy level 8 is GREAT

46 Lewis Dot Structures (cont.) All elements want to be full of electrons:  So they gain or lose electrons until they are full  This gives the atom a charge Negative charge if they gain electrons Positive charge if they lose electrons Charged atoms are called ions: cations if they are positive and anions if they are negative

47 Atomic Number Continued Also equal to number of electrons if the atom has no charge If the Element has a positive charge  Take the atomic number and Subtract the charge to find # of electrons K  (Atomic Number)  19 --  (Charge) 11 ==  18 Electrons Ca ?? If the element has a negative charge  Take the atomic number and Add the charge to find the number of electrons Cl  17 ++ 11 ==  18 Electrons +1 K +2 Ca Cl

48 Ions How many valence electrons in Li? Is it easier to gain or lose to become full? How many will it gain or lose? What charge will it become? 1 lose 1 +1

49 Ions How many valence electrons in O? Is it easier to gain or lose to become full? How many will it gain or lose? What charge will it become? 6 gain 2 -2

50 Ions Magnesium Sulfur-33-2 Phosphorus NameSymbolAtomic #Mass #ProtonsNeutronsElectronsCharge

51 Atomic Tables Rules  Name Comes from Periodic Table WITH Mass Number  Symbol Comes from Periodic Table  Atomic Number Top Number, Same as number of Protons  Mass Number Equal to Number of Protons + Number of Neutrons (Usually Bottom Number of Periodic Table Rounded)

52 Atomic Tables Continued  Protons Equal to Atomic Number (Top)  Neutrons = Mass Number – Number of Protons  Electrons If No Charge  Equal to Number of Protons If Has a Positive Charge  Subtract Charge from Number of Protons If Has a Negative Charge  Add Charge to Number of Protons

53 Practice Problems Name Symbol Atomic Number Mass Number ProtonsNeutronsElectronsCharge Na Nitrogen Neon-20Ne FeIron-56 Sodium Sulfur-32S3216 7N


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