Atomic Structure

What is an atom? An atom is the smallest particle of an element. + 1 AMU An atom is the smallest particle of an element. Atoms make up all matter.

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 Nucleus with Protons & Neutrons Electrons – (e-) – negative charge - In a neutral atom: Number of protons (+)= Number of electrons (-) + o Energy Levels with Electrons

Basic Structure of an Atom AMU is an atomic mass unit. 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 1 AMU 1 AMU + + 1 AMU 1 AMU o Many students likely know this information. While going through this slide be sure ask students to tell you what they know before “telling” them the answers. Page down, page down: Direct students to write the notes as they appear. Explain of a proton and it’s placement in the atom Explanation of a Neutron and it’s placement in the atom Page down (4 times): Explanation of Electron and it’s placement in the atom Page down (5 times) - display the charges of sub-particles Page down: Talk about the relative masses of each of the sub-particles. “If you weighed yourself once and then took off your watch, would it make much difference in your weight?” is a good illustration of how miniscule the mass is of an electron. Be sure to point out that protons and neutrons weigh about 1 AMU. This helps later when trying to figure out the number of neutrons there are in an atom.

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

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

Expanding the Theory Rutherford - discovered that atom has a nucleus Bohr-discovered electrons orbit nucleus Schrodinger-discovered electron cloud Chadwick-discovered neutrons

Let's look at the Periodic Table. Have them watch the next slide carefully and then page down.

What Do You Notice? 3 Li 6.94 11 Na 22.99 12 Mg 24.31 19 K 39.10 20 Ca 40.08 16 S 32.07 17 Cl 35.45 18 Ar 39.95 10 Ne 20.18 9 F 19.00 13 Al 26.98 14 Si 28.09 15 P 30.97 5 B 10.81 6 C 12.01 7 N 14.01 8 O 16.00 1 H 1.01 4 Be 9.01 2 He 4.0 You should notice the numbers are getting bigger from left to right and from top to bottom. Page down if necessary. Have them look at the top numbers (atomic numbers) as they go across. It is likely that they will not be able to see them very well so you might have to read them aloud. Page up to do it again if necessary. Explain that the atomic number tells us how many protons an atoms has. You might ask the question (using the classroom periodic table) How many protons does carbon have. And them switch back and say, “If an atom has 5 protons, what is it it?” Continue questioning until you feel that they understand. Explain the atom mass is the total weight (on average…). Ask them how much a proton weighs (1 amu), how much an electron weighs (too small to weigh) and neutron weighs (1 amu). Page down to the next slide.

Let’s take a closer look at all those numbers…

Be 4 Element Name Atomic Number Element Symbol Atomic Mass 9.01 Beryllium 4 Element Name Atomic Number (# of protons and # of electrons) Element Symbol (capital & lower case letters) Have the students Draw the box “of Be” on their page. Have them refer to a periodic table. Ask them to find “Be” on the table. Ask someone to give the element name. Page Down: Beryllium, The element name, Page Down: Atomic Number, Page Down: Atomic Symbol, Page Down: Atomic mass. Have students copy this down. If their periodic table has them listed in a different places within the “box”, ask them how they might be able to determine difference between each. Page Down: Explain that the atomic number tells us the number of protons and electrons an element has. Page Down again. Ask “if there are the same number of protons and neutrons, then what is the overall charge of an atom?” Page Down:Have them write down “tell us the number of neutrons” and then say, “But it does it indirectly. We know that each proton weighs 1 AMU. How many protons does beryllium have? (4). So how much do the protons weigh? (4). So if the protons take up 4 of the 9.01, what is left over? (5.01) Do electrons take up any of that mass? (no) So what else is taking up that mass? (the neutrons) So if the neutrons weigh 1 AMU, then how many neutrons are there? (5) Page down 3 times Make sure that the students have copied everything down. Atomic Mass (total # of protons and neutrons)

Chemical Symbols 4 Be Abbreviated way to write the name of an element Beryllium Chemical Symbols 4 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

4 Be 9 - 4 = 5 Atomic Mass - Atomic Number = # of Neutrons ? 9.01 Beryllium 4 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 9 - 4 = 5 P = 4 E = 4 N = ?

4 Be 9 - 4 = 5 Atomic Mass - Atomic Number = # of Neutrons Beryllium 9.01 Beryllium 4 Okay – If this tells me the # of Protons and the # of Electrons… How do I figure out the number of Neutrons? Easy – use the formula below: P = 4 E = 4 N = Atomic Mass - Atomic Number = # of Neutrons 5 Neutrons

N F Cl Let’s Practice. 7 9 17 What are the numbers of protons, 14.01 Nitrogen 7 F 18.98 Fluorine 9 Cl 35.45 Chlorine 17 Have the students figure out the number of protons, electrons and neutrons. There is a 90 second delay until the answers appear. You can use page down to have them come in sooner. What are the numbers of protons, electrons and neutrons?

What is an Isotope? A given Element usually has differing amounts of neutrons. These different forms are called isotopes.

H Isotopes - Continued …. are isotopes of hydrogen. 1 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.

C Isotope Notation Carbon - 12 12 6 Mass Number Atomic Number Mass number superscript – superman flying Atomic Number subscript - submarine Carbon - 12 Mass Number How many protons, electrons and neutrons? Protons = 6 Electrons = 6 Neutrons = 12 – 6 = 6

C Isotope Notation - Continued Carbon - 14 14 6 Mass Number Atomic Number Carbon - 14 How many protons, electrons and neutrons? Protons = 6 Electrons = 6 Neutrons = 14 – 6 = 8

N Magnesium - 24 16 7 Example 1: Example 2: Example 3: How many protons, electrons and neutrons? Which example(s) are isotopes? N 16 7 Example 1: Example 2: Magnesium - 24 Example 3: 10 Neutrons How many e-? What element? Write this element as demonstrated in Examples 1 & 2.

These models are easy to draw – if you follow the steps! 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!

F Drawing Bohr Models 9 Step 1: Determine the number of protons, electrons and neutrons for each atom’s element. Fluorine = F F 18.98 Fluorine 9 (Atomic Number) #Protons = 9 (Atomic Number) #Electrons = 9 # Neutrons = atomic mass – atomic # # Neutrons = 19 – 9=10

Drawing Bohr Models - Continued Step 2: Draw a nucleus inserting the # of protons and # of neutrons that are inside. # Electrons = 9 # Protons = 9 # Neutrons = 10 Fluorine = F N = P = 10 9

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 Fluorine is in row #2 so, I need to draw 2 rings around the nucleus. N = P = 10 9

Drawing Bohr Models - Continued Step 4: Place the electrons on the correct energy ring – filling each to capacity. Energy Levels are Identified as: 3 4 N = P = 10 9 1st Level –holds 2e- 2nd Level –holds 8e- 5 2 1 3rd Level –holds 8e- 6 9 Remember we need to have 9 electrons total for fluorine! 8 7

Complete Bohr Model P = 9 N = 10 Fluorine = F # Protons = 9 2 3 4 5 6 7 8 # Protons = 9 # Electrons = 9 # Neutrons = 10 2 Max # of Electrons Energy Level 8 1 3

Happy / Stable Elements Elements that have a full outer ring of electrons are called “happy” atoms. 2 Max # of Electrons Energy Level 8 1 3 Meaning that – that ring can’t hold any more electrons. Page Down: In making a diagram of an element scientists used to use a model called the Bohr Model. Although it does not completely describe the structure of an atom, it is a useful tool for understanding the interactions of matter. First you would write down the # of protons and neutrons the atom has. Page Down: First energy level - can hold up to 2 electrons. Page down Page Down: Second energy level - can hold up to 8 electrons. Page Down: Because the atoms are spinning around the nucleus it is important to put the out of each other’s path. The first two are paired. The next three are distributed around the energy level one at a time. The next three are paired with the previous three. Teacher Note: The rationale for teaching this is to help them understand the Lewis Dot diagrams later. Page Down: Third energy level - Similar to the 2nd level… however in reality the students will learn more about this level in chemistry. Page down. Make sure that the students have copied this slide. 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.”

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. 16 S 32.07 17 Cl 35.45 18 Ar 39.95 10 Ne 20.18 9 F 19.00 13 Al 26.98 14 Si 28.09 15 P 30.97 5 B 10.81 6 C 12.01 7 N 14.01 8 O 16.00 2 He 4.0 Fluorine = Row 2 Fluorine Energy Level = 2

Happy / Stable Elements The number of electrons in that last ring or outer shell is called the . . . Valence Electrons 16 S 32.07 17 Cl 35.45 18 Ar 39.95 10 Ne 20.18 9 F 19.00 13 Al 26.98 14 Si 28.09 15 P 30.97 5 B 10.81 6 C 12.01 7 N 14.01 8 O 16.00 2 He 4.0 Fluorine = Column VIIA Fluorine Valence # = 7

F 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. F The dots represent the #of valence electrons of that element. Fluorine Valence # = 7 or 7 electrons in outside shell

Drawing Lewis Dot Diagrams 14.01 Nitrogen 7 Cl 35.45 Chlorine 17 Using just your periodic table, draw Lewis Dot Diagrams for each of the above elements.