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Atomic Structure 1 What is an atom? 1 AMU 1 AMU ++ 1 AMU 1 AMU An atom is the smallest particle of an element. Atoms make up all matter. 2 Basic Structure of the Atom • Nucleus - center of the atom that contains: – Protons - (p+) - positively charged – Neutrons - (n) - no charge • Energy Levels / Orbits - paths that electrons (e-) travel around the nucleus – Electrons – (e-) – negative charge - In a neutral atom: Number of protons (+)= Number of electrons (-) Nucleus with Protons & Neutrons + +o o Energy Levels with Electrons 3 Basic Structure of an Atom AMU is an atomic mass unit. 1 AMU 1 AMU + o 1 AMU + o 1 AMU •Each proton and neutron has 1 AMU •Electrons do not have much mass compared to protons and neutrons so we don’t count any mass for them 4 Where did the Atomic Theory come from? • John Dalton (1766-1844) – Published detailed theory in 1808 – Elements are composed of atoms – Atoms of different elements have different properties – Atoms are NOT changed by chemical reactions, just rearranged – Compounds are defined by the number, type and proportion of atoms 5 Expanding the Theory • Thomson (1856-1940) – Identified the electron – Found it had a negative charge – Positive sphere and negative electrons embedded – Atom is neutral-positive cancels negative 6 Expanding the Theory • Rutherford - discovered that atom has a nucleus • Bohr-discovered electrons orbit nucleus • Schrodinger-discovered electron cloud • Chadwick-discovered neutrons 7 8 What Do You Notice? 1 H 1.01 3 4 5 6 7 8 2 He 4.0 9 10 Ne Li Be B C N O F 6.94 9.01 10.81 12.01 14.01 16.00 19.00 11 12 13 14 15 16 17 Na Mg 22.99 24.31 19 20 K Ca 39.10 40.08 Al 26.98 20.18 18 Si P S Cl Ar 28.09 30.97 32.07 35.45 39.95 You should notice the numbers are getting bigger from left to right and from top to bottom. 9 Let’s take a closer look at all those numbers… 10 Element Name Atomic Number (# of protons and # of electrons) Element Symbol (capital & lower case letters) Atomic Mass Beryllium 4 Be 9.01 (total # of protons and neutrons) 11 Beryllium 4 Chemical Symbols Be 9.01 •Abbreviated way to write the name of an element •One capital letter or one capital letter and one lower case letter •Some symbol abbreviations are for the LATIN name for the element 12 Beryllium 4 Be 9.01 If the atomic number tells me the # of Protons and # of Electrons… How do I figure out the number of Neutrons? Use the formula below: Atomic Mass - Atomic Number = # of Neutrons P= 4 E= 4 N= 9-4=5 ? 13 Beryllium 4 Okay – If this tells me the # of Protons and the # of Electrons… Be How do I figure out the number of Neutrons? 9.01 Easy – use the formula below: Atomic Mass - Atomic Number = # of Neutrons P=4 E=4 9-4=5 N = 5 Neutrons 14 Let’s Practice. Nitrogen Fluorine 7 9 17 N F Cl 14.01 18.98 Chlorine 35.45 What are the numbers of protons, electrons and neutrons? 15 What is an Isotope? A given Element usually has differing amounts of neutrons. These different forms are called isotopes. 16 Isotopes - Continued Let’s take hydrogen as an example: As you can see from the atomic mass (1.01) the most naturally abundant form of hydrogen does not have a neutron. However, in rare instances isotopes form. Below are the isotopes of hydrogen: 1 Hydrogen H 1.01 Protium Deuterium Tritium …. are isotopes of hydrogen. 17 Isotope Notation C 12 6 Mass number superscript – superman flying Atomic Number subscript - submarine Mass Number Atomic Number Carbon - 12 Mass Number How many protons, electrons and neutrons? Protons = 6 Electrons = 6 Neutrons = 12 – 6 = 6 18 Isotope Notation - Continued Mass Number Atomic Number C 14 6 Carbon - 14 How many protons, electrons and neutrons? Protons = 6 Electrons = 6 Neutrons = 14 – 6 = 8 19 How many protons, electrons and neutrons? Which example(s) are isotopes? Example 1: Example 2: Example 3: How many e-? N 16 7 Magnesium - 24 10 Neutrons What element? Write this element as demonstrated in Examples 1 & 2. 20 What are Bohr Models? Neils Bohr devised a method for drawing models to represent the atoms nucleus and their electron arrangement because the atoms are too small to see. These models are easy to draw – if you follow the steps! 21 Drawing Bohr Models Step 1: Determine the number of protons, electrons and neutrons for each atom’s element. Fluorine = F Fluorine 9 F 18.98 (Atomic Number) #Protons = 9 (Atomic Number) #Electrons = 9 # Neutrons = atomic mass – atomic # # Neutrons = 19 – 9=10 22 Drawing Bohr Models - Continued Step 2: Draw a nucleus inserting the # of protons and # of neutrons that are inside. Fluorine = F P= 9 N = 10 # Protons = 9 # Electrons = 9 # Neutrons = 10 23 Drawing Bohr Models - Continued Step 3: Determine the number of electron rings to draw around the nucleus by what row it is in on the Periodic Table. # of rings = row number P= 9 N = 10 Fluorine is in row #2 so, I need to draw 2 rings around the nucleus. 24 Drawing Bohr Models - Continued Step 4: Place the electrons on the correct energy ring – filling each to capacity. 3 Energy Levels are Identified as: 4 1st Level –holds 2e2 9 P= 9 N = 10 1 5 2nd Level –holds 8e- 6 3rd Level –holds 8eRemember we need to have 9 electrons total for fluorine! 8 7 25 Complete Bohr Model Fluorine = F 3 4 # Protons = 9 # Electrons = 9 # Neutrons = 10 5 2 9 P= 9 N = 10 8 7 6 1 Energy Level Max # of Electrons 1 2 2 8 3 8 26 Happy / Stable Elements Elements that have a full outer ring of electrons are called “happy” atoms. Max # of Energy Level Meaning that – that ring can’t hold any more electrons. So, if the 2nd ring has 7 electrons in its outer ring – it is still hungry for the 8th electron – needing it to be “happy.” Electrons 1 2 2 8 3 8 27 Happy / Stable Elements The last ring or outer shell of the atom is called the . . . Energy Level Remember the # of rings that you drew in the Bohr model is equal to the Row number that the element is in on the Periodic Table. 2 He 4.0 5 6 7 8 9 10 Ne B C N O F 10.81 12.01 14.01 16.00 19.00 13 14 15 16 17 Al 26.98 20.18 Fluorine = Row 2 Fluorine Energy Level = 2 18 Si P S Cl Ar 28.09 30.97 32.07 35.45 39.95 28 Happy / Stable Elements The number of electrons in that last ring or outer shell is called the . . . Valence Electrons 2 Fluorine = Column VIIA Fluorine Valence # = 7 He 4.0 5 6 7 8 9 10 Ne B C N O F 10.81 12.01 14.01 16.00 19.00 13 14 15 16 17 Al 26.98 20.18 18 Si P S Cl Ar 28.09 30.97 32.07 35.45 39.95 29 What are Lewis Dot Diagrams? G.N. Lewis, an American chemist, developed this shorthand system using only the element’s symbol and dots. The symbol represents the element’s nucleus. The dots represent the #of valence electrons of that element. F Fluorine Valence # = 7 or 7 electrons in outside shell 30 Drawing Lewis Dot Diagrams Nitrogen Chlorine 7 17 N Cl 14.01 35.45 Using just your periodic table, draw Lewis Dot Diagrams for each of the above elements. 31