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ATOMS

ATOMS. THE BUILDING BLOCKS OF MATTER. Do Atoms Exist?. Democritus – First person known to suggest that matter can be broken down into small particles that he named: ATOMS In the 1790s, chemists are using better instruments and are able to make better measurements.

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ATOMS

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  1. ATOMS THE BUILDING BLOCKS OF MATTER

  2. Do Atoms Exist? • Democritus – First person known to suggest that matter can be broken down into small particles that he named: ATOMS • In the 1790s, chemists are using better instruments and are able to make better measurements. • Using these instruments, theories about matter are developed. Some of which are still valid today. • In the late 19th century and early 20th century,some fundamental discoveries were made about the atom due to the further development of instruments. • What did Einstein propose? ___________________________________________________________________________________________________

  3. What happens to Atoms When a Chemical Change Happens? From illustration, what can we determine about what happens to the particles before and after a chemical reaction?

  4. WHAT DOES THE LAW STATE? • Law of Conservation of Mass says: • Mass is neither destroyed nor created during ordinary chemical reactions or physical change. • Example: • If you have 50 grams of matter before a chemical reaction or physical change, the total mass will be 50 grams after the chemical reaction or physical change.

  5. How do Atoms Combine in a Compound? • What is the formula for water? • A chemical compound contains the same elements in exactly the same proportions by mass even if the size of the samples change. It is the law of Definite Proportions • Other example: • Carbon dioxide is always 1 Carbon and 2 Oxygen atoms • Carbon Monoxide is always 1 Carbon and 1 Oxygen atoms • Hydrogen Peroxide is always 2 Hydrogen and 2 Oxygen atoms • What is the ratio of elements in Hydrogen Peroxide and how is that different from Water?

  6. Law of Multiple Proportions What is different between the two examples? What is the same? What is the ratio between the mass of Oxygen in the first example and that in the second example?

  7. What does the Law Say? • The Law of Multiple Proportions says: • If we have two different substances that have the same two elements, if we combine the second element with the same amount of the first, the ratio of the elements are always small whole numbers • 2:1, 3:1, 3:2, etc…. • In the examples below, find the whole number ratio between: • C2H2 and C2H6 • H2O2 and H2O

  8. Dalton's Theory Vs. Modern Theory of the Atom Dalton’s Atomic Theory year 1808 Today - 2010 • Matter made of extremely small particles called atoms • Atoms of an element are identical in: mass, size and other properties • Atoms cannot be subdivided, created or destroyed • Atoms combine in simple whole number ratios to for chemical compounds • In chemical reactions, atoms combine, separate or are rearranged • Statement 1, 4 and 5 are still accepted today • Statement 2 has been modified because we now know that atoms of an element can differ. A given element can have atoms of different masses • Statement 3 is incorrect. Atoms can be subdivided and have been

  9. How were the Particles of the Atom Discovered?

  10. What are Scientists Certain About the Atom What is the difference between the charge of a proton and an electron? Which particle has the least mass? By how much less? Which of them is neutral and where is it located?

  11. Set up of Rutherford’s Experiment Screen to detect deflected particles Thin gold foil Lead box containing radioactive source of fast-moving particles

  12. Illustration of Rutherford’s Experiment

  13. Strong Nuclear Forces Proton-Proton Attraction Neutron-Neutron Attraction • Protons are closely packed at the center of the atom • When protons are extremely close, there is a STRONG ATTRACTION between them. More than 100 protons can exist close together in the nucleus • Similar attraction between neutrons in the nucleus The forces that hold the protons and neutrons together are referred to as NUCLEAR FORCES

  14. Why is matter mostly empty space? Hint: look at the radius difference between the atomic radius and nucleus radius) Homework: Are there other sub particles in the atom? If there are, give some examples.

  15. Counting Atoms

  16. Two ways of writing isotopes: • Hyphen notation: example: • Chlorine-37; uranium-235; carbon-14 • Nuclear Symbol: example: • 235 U the top number is the atomic mass 92 and the bottom number is the atomic number Formula Top number or mass number – the bottom number or atomic number = the number of neutrons Example Find the number of protons, neutrons and electrons of: Chlorine-37:

  17. Solution Find the atomic number from the Periodic Table. The atomic number = Number of protons = number of electrons Mass number = number of neutrons +atomic number Atomic number from the Periodic Table = 17 The number of electrons is = 17 The number of neutrons is: 37 – 17 protons = 20 neutrons. Calculate: How many protons, neutrons and electrons are there is atom of bromine-80?

  18. Atomic Mass Unit • The standard used by scientists to apply to atomic mass is based on an atom: carbon-12 nuclide. • The mass assigned to this nuclide is 12 atomic mass units • One atomic mass unit or 1 amu is 1/12 the mass of a carbon-12 amu • Definition: A Nuclide is a general term for a specific isotope of an element

  19. Calculating Average Atomic Mass Average Atomic Mass Example • Weighted average of the atomic masses of the naturally occurring isotopes of an element • Copper has two naturally occurring isotopes: • 69.17% of Copper-63 with a mass of 62.929599 amu and 30.83% of Copper-65 with atomic mass 64.927793 amu. • Calculating> • .6917 X 62.929599 amu + .3083 X 64.927793 amu = 63.55 amu

  20. Three Ways to Count

  21. What is the mass in grams of 3.50 mol of the element copper, Cu? Given: 3.50 mol Cu Unknown: mass of Cu in grams Solution: the mass of an element in grams can be calculated by multiplying the amount of the element in moles by the element’s molar mass. The molar mass of copper from the periodic table is rounded to 63.55 g/mol.

  22. A chemist produced 11.9 g of aluminum, Al. How many moles of aluminum were produced? Given: 11.9 g Al Unknown: amount of Al in moles The molar mass of aluminum from the periodic table is rounded to 26.98 g/mol.

  23. How many moles of silver, Ag, are in 3.01  1023 atoms of silver? Given: 3.01 × 1023 atoms of Ag Unknown: amount of Ag in moles Solution:

  24. What is the mass in grams of 1.20  108 atoms of copper, Cu? Given: 1.20 × 108 atoms of Cu Unknown: mass of Cu in grams The molar mass of copper from the periodic table is rounded to 63.55 g/mol.

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