Bellwork: What information can be used for identifying where you live? How are YOU identified?

Transcription

1 Wednesday, October 3rd Bellwork: What information can be used for identifying where you live? How are YOU identified? Power of the mind and intellectual thought were the primary avenues to the truth. Curiosity sparked the interest of scholarly thinkers known as philosophers who considered many of life's mysteries. As the speculated about the nature of matter, many philosophers formed explanations based on their own life experiences. 1

2 Democritus -matter was made up of tiny individual particles called atomos (we derive our English word, atom) which move through empty space Aristotle -rejected the idea of atoms (denied their existence), he didn't believe empty space could exist. -matter is made of earth, fire, air, and water -because he was very influential people rejected Democritus -No one challenged him for 2,000+ years! 2

3 Dalton -could actually do experiments -Created Dalton's atomic theory *matter is composed of extremely small particles called atoms *atoms are divisible and indestructible *atoms of a given element do not always have the same properties and can have slightly different masses *atoms of a specific element are different from those of another element *different atoms combine in simple wholenumber ratios to form compounds *in a chemical reaction, atoms are separated, combined, or rearranged. -conservation of mass in chemical reactions is the result of separation, combination, or rearrangement of atoms (not created, destroyed, or divided) Atom-smallest particle of an element that retains the properties of the element. -idea of its size: world population = 6.5x10 9 in The penny has 2.9x10 22 atoms. (5 trillion times world population!) -They can be seen! You have to use a scanning tunneling microscope (STM) to see individual atoms. Once people were convinced that the atom existed -it led to more questions being asked just like all good experiments. 3

4 -Scientists began to make connections between matter and electric charge. -Some wondered how electricity might behave in the absence of matter. -Used the newly invented vacuum pump to pass electricity though glass tubes from which most of the air had been removed. -tubes are called cathode ray tubes. (positive end is called anode, negative end is called cathode) Note: anions are negative, and cations are positive shows direction charges want to move. Crooks -saw a spark of green light when the electricity struck zinc sulfide coating in the tube (some sort of radiation was produced) -Cathode ray was the name given to this spark of light, this eventually led to the invention of the tv. -Conclusions: streams of charged particles were passing through the tube, they carried a negative charge. 4

5 J.J. Thomson -he concluded that the mass of the charged particle was much less than the hydrogen atom, the lightest known atom. -This meant that there were particles smaller than an atom. -Dalton was incorrect! -He had identified the first subatomic particle - the electron Millikan -did oil drop experiment and determined the charge of an electron. -His setup was so good that it is within 1% of the current accepted value! -then knowing the charge and the known charge-tomass ratios, he calculated the mass of an electron Two major questions were then asked: If electrons mass is so small, what accounts for the rest of the mass in an atom? & If an electron is negative, how is it that all matter is neutral? 5

6 J.J. Thomson proposed a model of the atom known as the plum pudding model -said there was positive charge throughout and that negative electrons sat with in -his model didn't last long. Rutherford -studied how positively charged particles interacted with solid matter. -conducted an experiment to see if alpha particles would be deflected as they passed through a thin piece of gold foil -Hypothesis: it wouldn't alter the path of alpha particles and that they would see slight altered paths when collisions happened with an electron. 6

7 Results: most past right through with no deflection, some were deflected at large angles and some came straight back. -Kind of like firing a large artillery shell at a sheet of paper and the shell coming back at the cannon! Concluded: -Plum pudding model was wrong, -atom is mostly empty space through which electrons move -most of atom's positive charge and almost all of its mass were contained in a tiny dense region in the center of the atom-called the nucleus -negative particles are held within the atom by their attraction to positive nucleus Nucleus is very dense. IF it was the size of the dot on an exclamation point mass would be as much as 70 automobiles! If its diameter was 2 football fields, nucleus would be the size of a nickel. Neutral Nature of Matter: the positive charge in the nucleus is balanced out by the negative electrons but didn't account for atomic mass. 7

8 Proton carries an equal but opposite charge of an electron. Rutherford discovered it Chadwick discovered that nucleus also has neutrons Neutron mass = mass of proton Neutrons have NO CHARGE Henry Moseley discovered atoms of each element contain a unique positive charge in the nuclei number of protons in an atom identifies the atom we call this atomic number The periodic table is organized left to right and top to bottom by increasing atomic number. All atoms are neutral; therefore, #p + = #e 8

9 Summary: All atoms are made up of 3 fundamental subatomic particles: protons, neutrons, and electrons Atoms are spherically shaped, small, dense nucleus of positive charge surrounded by negative charge (1 or more) Most of an atom is fast moving electrons traveling through empty space that surrounds the nucleus. electrons are held by their attraction to positive charge in the nucleus nucleus contains protons and neutrons and they make up 99.97% of the mass of an atom. atom is neutral: #protons = # electrons Subatomic particles are made up of quarks Thursday, October 4th Bellwork: Complete the worksheet (front and back) that you picked up for 4.1 and 4.2 as a way of reviewing all of the history from yesterday. 9

10 Homework: 4,6,7 4. Explain how Dalton's theory of the atom and the conservation of mass are related. Dalton explained that atoms are neither created nor destroyed in chemical reactions, only rearranged. 6. Design a concept map that compares and contrasts the atomic ideas proposed by Democritus and Dalton. See next page. 7. Describe the structure of a typical atom. Identify where each subatomic particle is located. A typical atom consists of a central, small, dense nucleus containing protons and neutrons. The nucleus is surrounded by a cloud of negatively charged electrons. 8. Compare and Contrast Thomson's plum pudding atomic model with Rutherford's nuclear atomic model. Thomson's plum pudding model describes atoms as spherical particles with uniformly distributed positive charge in which individual, negatively charged electrons are located in fixed positions. In contrast, Rutherford's model states that an atom is mostly empty space, with a small, dense, central nucleus containing all of an atom's positive charge and most of its mass. The negatively charged electrons move through the empty space and are held in the atom by their attraction to the positively charged nucleus. matter composed of extremely small particles called atoms all atoms of a given element are identical but differ from the atoms of other elements atoms could not be created, divided, or destroyed Democritus Dalton matter is composed of empty space through which atoms move differing properties of atoms are due to the size, shape, and movement of the atoms different kinds of atoms come in different sizes and shapes different atoms combine in simple whole-number ratios to form compounds 10

11 Refer back to Dalton's atomic theory: States that 'atoms of a given element do not always have the same properties and can have slightly different masses.' Number of neutrons can be different Atoms with the same number of protons but different numbers of neutrons are called isotopes. atoms with more neutrons have more mass Isotopes of same element all have the same chemical behavior. the number of electrons is the only thing that chemical behavior is dependent upon. Each isotope of an element is identified with a number called mass number. Mass # = atomic number(# of protons) + neutrons Example: Copper 63, Copper 65 *remember: atomic number (protons) doesn't change! In nature elements are found as mixtures of isotopes. How much each isotope occurs in any given substance is constant Due to mass of p +, n o, and e being so small chemist developed a method for measuring the mass of an atom relative to mass of a specific atomic standard. The standard is Carbon 12 Carbon has exactly 12 amu so 1 amu = 1 / 12 the mass of a carbon 12 atom = almost the mass of one proton. Atomic mass of an element is a weighted average of the isotopes of that element. Sometimes you can gain an understanding of which isotope may be more common if the amu (atomic mass unit) is close to a whole number it indicates that isotope is more common (not always) 11

12 Use what you've learned to complete the table below: Element Atomic Number Ne 10 Protons 35 Electrons 19 ANSWERS Element Atomic Number Protons Electrons K Br Ne

13 Standard Notation: written as a way to express the chemical symbol, the mass number, charge (if any), and the atomic number(#of protons) Examples: Carbon-12 Carbon-13 Carbon-14 The three carbon molecules above represent isotopes. Ion-Charged element, one that has either gained electrons (become negative) or lost electrons (become positive). Cu 2+ Cl - Ni 3+ O 2- How do you know how many electrons are gained or lost? Using what you know and have learned...try completing the table on atomic structure. You will want to use a periodic table. 13

14 Friday, October 5th Bellwork pg 116: How many protons and electrons are in each atom? a. radon b. magnesium a. 86p, 86e b. 12p, 12e 13. An atom of an element contains 66 electrons. Which element is it? dysprosium 14. An atom of an element contains 14 protons. Which element is it? silicon 15. Do the atoms shown in the figure have the same atomic number? yes, there are nine With a person other than your lab partner: Complete Practice Problems 16 19, 21,23, 24 14

15 16. Determine the number of protons, electrons, and neutrons for isotopes b f in the table above. Name each isotope and write its symbol. Element Atomic # Mass # Protons & Electrons Neutrons Isotope Name Symbol b. Calcium Calcium-46 c. Oxygen Oxygen-17 d. Iron Iron-57 e. Zinc Zinc-64 f. Mercury Mercury An atom has a mass number of 55. Its number of neutrons is the sum of its atomic number and five. How many protons, neutrons, and electrons does this atom have? What is the identity of this atom? 25 protons, 25 electrons, 30 neutrons. Manganese 18. Boron has two naturally occuring isotopes: boron-10 (19.8% abundant, mass amu) and boron-11 (80.2% abundant, mass amu) Calculate the atomic mass of boron amu 19. Nitrogen has two naturally occurring isotopes, N-14 and N-15. Its atomic mass is Which isotope is more abundant? Explain your answer. N-14 is most likely more abundant because the atomic mass is closer to 14 than Which subatomic particle identifies an atom as that of a particular element? the proton 15

16 23. Copper has two isotopes: Cu-63 (abundance 69.2%, mass = amu). Cu-65 (abundance 30.8%, mass = amu). Calculate the atomic mass of copper. 63.5amu 24. Three magnesium isotopes have atomic masses and relative abundances of amu (78.99%), anu (10.00%), and (11.01%). Calculate the atomic mass of magnesium amu Complete the worksheets on atomic structure and isotopes/average atomic mass. -Finish for homework -Snackium lab Prep-homework 16

17 Tuesday, October 9th Bellwork Refresh your memory, what is a chemical reaction? A chemical reaction is the change of one or more substances into new substances -this only involves the electrons. Nuclear Reaction- can change one element into another element by creating a change in the nucleus of the atom. -We realized its existence in a process called radioactivity where radiation was spontaneously emitted. Radiation- rays or particles emitted by radioactive material. Why do they emit radiation? -their nuclei are unstable -Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay. -the primary factor in determining an atom's stability is its ratio of neutrons to protons 17

18 3 types of radiation-based on their electrical charge. alpha particles (2p+, 2no) = 2+ charge -Ernest Rutherford, an English scientist, discovered alpha particles in 1899 while working with uranium. -occur naturally in the environment in soils, rocks, and water Uses of alpha particles: *Radium-226 may be used to treat cancer, by inserting tiny amounts of radium into the tumorous mass. *Polonium-210 serves as a static eliminator in paper mills and other industries. The alpha particles, due to their positive charge, attract loose electrons, thus reducing static charge. *Some smoke detectors use the alpha emissions from americium-241 to help create an electrical current. beta particles (e ) = 1 charge Henri Becquerel is credited with the discovery of beta particles. In 1900, he showed that beta particles were identical to electrons, which had recently been discovered by J. J. Thompson. energy can break chemical bonds and form ions. used in medical diagnosis, imaging, and treatment harmful to cells and the environment people who have taken radioactive iodine will emit beta particles. Radioactive iodine may enter the environment during a nuclear reactor accident and find its way into the food chain. 18

19 Gamma Rays - no mass, no charge, usually accompany alpha or beta radiation, and they account for most energy lost during decay. -Henri Becquerel discovered them, shortly after x-rays were discovered. He said uranium emitted similar invisible light energy. -Gamma photons have about 10,000 times as much energy as the photons in the visible range of the electromagnetic spectrum. -They can pass through many kinds of materials, including human tissue...lead is often used to help shield us against them. What's the difference between x-rays and gamma rays? -Gamma rays originate in the nucleus. X-rays originate in the electron fields surrounding the nucleus or are machine-produced. 19