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Atoms in a Nutshell All matter is made up of tiny particles called atoms. • There are about 92 naturally occurring elements. (The elements with numbers over 92 are man made.) • Atoms are made up of three main sub-atomic particles. – Protons – Neutrons – Electrons tells the number of protons and electrons Atomic number 19 Atomic Number 39 Atomic Mass Tells the number of protons and neutrons added Atomic together. Mass Protons and neutrons are found in the center of the atom. (Nucleus) Electrons are tiny particles that zoom around the space OUTSIDE the nucleus. Particle Charge Protons Mass (AMU) 1 Neutrons 1 Neutral Electrons Insignificant 1/1800th - + Rutherford Lab Purpose: to mimic Rutherford's famous gold foil experiment. Materials: marble (alpha particle), cardboard models, plain paper, ruler. Procedure: [Summarize procedure in 2 – 3 sentences] 1. Pick up a piece of plain paper from the supply area. 2. Center the paper on top of a cardboard model and tape it down to keep it in place. Don’t look under the box! 3. Roll the marble under one side of the box. Observe where the marble comes out and trace the approximate path on the white paper. 4. Working from all four sides of the black box, continue to roll the marble under the board, making observations and tracing the rebound path for each marble roll. Roll the marble at least 20 times from each side of the box. Vary the angles at which the marble is rolled into the box. 5. After sketching the apparent path of the marble from all sides and angles, the general size and shape of the unknown target should emerge in negative form from the area where there are no lines. 6. Form a working hypothesis of the unknown target by sketching the shape on your plain paper. Based on your hypothesis, repeat as many marble rolls as necessary to either confirm or revise your structure. Data: Make a 10 X 10 cm square to record your data. Rutherford Lab Conclusion Analysis: 1. Skim pages 111 to 112 in the textbook. In what ways does this activity simulate Rutherford’s experiment? 2. Briefly describe Rutherford’s experiment and what he observed. 3. As a result of his observations, what did Rutherford conclude about the structure of the atom? NIELS BOHR Atom Models Protons and Neutrons are found in the center of the atom. We call the area with the protons and neutrons the nucleus. Electrons are found zooming around the outside. They are in different energy levels. -Inner level has space for 2 electrons. -2nd level has space for 8 electrons. -3rd level has space for 18 electrons Things to KnOw… • Every element wants to have a full outer orbit – then they are stable – so… • if an element has it’s 1st orbit full and stable – it will have 2 valence e• if an element has it’s 2nd , or 3rd orbit full and stable – it will have 8 valence e- (we call that a Stable octet) • Everything wants to bind together to get a maximum of 8 valence e- shared between them – then they are stable!! Which Element is this? • Atomic # • Atomic Mass • Valence Electrons Which Element? Which Element? Bohr Models… Niels Bohr explained the structure of the atom in his “Bohr models”. His model of the atom resembles a solar system. P:9 N:19 So how do we draw a Bohr model …? • Start with a nucleus, and put in how many protons and neutrons are in sodium (look at your periodic table) • Next place some orbits around it P:11 N:12 P:11 N:12 • Next figure out how many e‐ are in sodium (look at your periodic table). Place them in dots in the orbits Sodium has 11 electrons !! they are the same as the protons P:11 N:12 • Bohr models show – the protons and neutrons in the nucleus. – the electrons in orbits or shells • Each orbit/shell can only hold a certain # of electrons and then it is full. P:3 N:4 Some Bohr models… Oxygen P:8 N:8 P:13 N:14 8p+ 8n 8e- Aluminium 13 p+ 14 n 13 e- Lewis Dot Diagrams… • Gilbert Lewis used a different model than Bohr, and he only showed the valence e‐ in it. • His model is called the Lewis dot structure . He put dots around the symbols so that we can see just the valence electrons for the elements (so we can easily see which e‐ are going to react) Lewis Model • Shows only the electrons in the outermost level. Called “Valence Electrons” • Valence Electrons determine how elements react. • Write the symbol with 1 – 8 dots around it. • Elements have a maximum number of 8 valence electrons. The red dots show you the VALENCE ELECTRONS in each element’s atoms See the difference??... Lewis just shows the valence e‐ P: 11 N:12 Bohr model of Sodium Atom Na Lewis Structure of Sodium Atom How to calculate atomic mass Problem #1: Carbon mass number --exact weight - percent abundance 12 --------------12.000000 ------98.90 13 --------------13.003355 ------1.10 To calculate the average atomic weight, each exact atomic weight is multiplied by its percent abundance (expressed as a decimal). Then, add the results together and round off to an appropriate number of significant figures. This is the solution for carbon: (12.000000) (0.9890) + (13.003355) (0.0110) = 12.011 amu Atomic Mass • • • • Magnesium has three isotopes. 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, 11.01 magnesium 26 with a mass of 25.9826 amu. What is the atomic mass of magnesium? Isotope Percent Abundance Mass Mg-24 78.99 23.9850 18.94575 Mg-25 10.00 24.9585 2.49585 Mg-26 11.01 25.9826 2.86068 24.304 amu Atomic Mass Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has Percent a mass of 64.93 amu. Isotope Mass Abundance Cu-63 69.1 62.93 43.48463 Cu-65 30.9 64.93 20.06337 63.548 A.A.M. (0.691)(62.93 amu) (0.309)(64.93 amu) A.A.M. 43.48463 amu 20.06337 amu A.A.M. 63.548 amu for Copper Cu 63.548 29