Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The building blocks of matter! The Atom: From Philosophical Idea to Scientific Theory A MODEL in science is often an explanation of how phenomena occur and how data or events are related. Models may be visual, verbal, or mathematical. Democritus called nature’s basic particle an atom, based on the Greek word meaning “indivisible.” The view of Democritus was not supported by experimental evidence. An atom is the smallest particle of an element that retains the chemical properties of that element. The smallest particle of an element that retains the chemical properties of the element is a (n) _____. molecule salt atom compound John Dalton (1766-1844) is the scientist credited for proposing the atomic theory. This theory explains several concepts that are relevant in the observable world: the composition of a pure gold necklace, what makes the pure gold necklace different than a pure silver necklace, and what occurs when pure gold is mixed with pure copper. The theories that Dalton used as a basis for his theory: the law of conservation of mass and the law of constant composition. Dalton’s Atomic Theory 1. 2. 3. 4. 5. All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed. Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged. J. J. Thomson In Thomson’s "Plum Pudding Model" each atom was a sphere filled with a positively charged fluid. The fluid was called the "pudding." Scattered in this fluid were electrons known as the "plums.” Fixed electrons surrounded by positive material Thomson’s experiment revealed that the electron has a very large charge for its tiny mass. Central positive center (nucleus) Surrounded by Electrons Ernest Rutherford Rutherford’s Gold Foil Experiment The Discovery of the Nucleus 1. Most of the alpha particles passed through the gold foil indicating most of the atom is empty space. 2. A few of the alpha particles rebounded back indicating there is a small dense central positive part of the atom called the nucleus. RUTHERFORD’S GOLD FOIL EXPERIMENT Positive center surrounded by electrons that travel in fixed orbits Neils Bohr Bohr Model 1st energy level K-shell max. 2 electrons 2nd energy level L-shell max. 8 electrons 3rd energy level M-shell max. 18 electrons Emission spectra •A diffraction grating and a spectrometer can be used to look at the emission spectrum from a light source. •If all possible wavelengths of light are present it would look like a continuous spectrum of colors. •However hot gases emit only particular characteristic colors of light. •Each line in the emission spectrum corresponds to an electron moving from a higher energy level to a lower energy level. •To do this it emits photon of light. •The energy of the photon of light is equal to the difference in the energy of the two energy levels. Positive nucleus surrounded by an electron cloud where electrons are likely found Which model best describes the structure of an atom? 1) Atoms are like tiny solid spheres like marbles. 2) Atoms have tiny particles orbiting the nucleus like planets in the solar system. 3) Atoms have tiny particles randomly traveling outside the nucleus. 4) Atoms are charged particles that make up all matter. http://www.colorado.edu/physics/2000/applets/a2.html (shows electrons , orbitals and nucleus Dalton turned Democritus' idea into a scientific theory that could be tested by experiment. Modern Atomic Theory Revised 1. Today we know that atoms are divisible into even smaller particles. (protons, neutrons, electrons) 2. We know that a given element can have atoms with different masses. (isotopes) GROUND STATE VS EXCITED STATE When an atom is in its lowest energy state, it is said to be in its ground state. When an atom absorbs a specific amount of energy, one of its electrons can “jump” into the next energy level. When this happens, the atom is said to be in the excited state. Atoms emit light as this excited electron returns to the ground state. A proton, neutron, and electron went out to dinner one night. After a luxurious meal, the waiter brought the check to the proton and the electron. The neutron was perplexed as to why the waiter didn't bring him his check. So, he summoned the waiter to the table and asked him about it. The waiter explained to the neutron, "For you, there's no charge!" Structure of the atom: Two main parts: 1. Nucleus A) made of two kinds of particles 1. Protons- positive charge (mass 1.673 x 10-27kg) 2. Neutrons-electrically neutral (mass1.675x10-27kg) 3. Mass of protons is a some less than the mass of neutrons B) Very small, dense central part of the atom C) Most of the mass of the atom 2. Electron cloud A) Probable location of the electron B) Most of the volume of the atom C) Electron-negative charge( mass 9.109 x 10-31kg) D) The electron has the least mass Identify in order from largest to smallest the relative size of each particle. p+, n0, ee-, p+, n0 p+, e-, n0 n0, p+, eMost of the volume of an atom is made up of the _____. nucleus nuclides protons electron cloud How would two protons in close proximity interact with each other? repel attract have no interaction How would one proton and one neutron in close proximity interact with each other? repel attract have no interaction How would one proton and one electron in close proximity interact with each other? repel attract have no interaction A positively charged particle found in the nucleus if called a (n) _____. proton neutron electron quark A nuclear particle that has no electrical charge is called a (n) _____. proton neutron electron quark Atoms are electrically neutral because they contain equal numbers of protons (charged positive) and electrons (charged negative). PROPERTIES OF ATOMS Atomic Number- Atomic number of an element is the number of protons in the nucleus of each atom of that element. • • • Mass Number- Mass number is the total number of protons and neutrons in the nucleus of an isotope. Mass number is the average atomic mass rounded to the nearest whole number. To figure out the number of neutrons in an atom, subtract the atomic number from the mass number. ATOMIC SYMBOLS 51 23 V 23 protons 28 neutrons 23 electrons The symbol tells you the number of each subatomic particle in one atom of the element. The number in the top left is the mass #. - The number of protons plus neutrons. The number in the bottom left is the atomic #. - The number of protons. Complete chemical symbols are written like this: atomic mass Symbol charge atomic # Don’t worry about this yet! Here is the periodic table entry for barium… 56 How many neutrons in a barium atom?______________ 81 How many electrons in a barium atom?______________ 56 How many protons in a barium atom?______________ What do you do with dead people? Barium! This information can be found on the periodic table… Atomic Number Atomic Mass Round it! The total number of protons and neutrons in the nucleus of an isotope is called its _____. mass number atomic mass unit atomic number molar mass The number of protons in the nucleus of an element is called its _____. atomic mass unit atomic number mass number molar mass The atomic number of nickel-60 is 28. The number of neutrons of the isotope is _____. 60 28 32 3 Carbon-14 has 8 neutrons. The atomic number of carbon-14 is _____. 32 8 14 6 An atom of silicon-30 contains 14 protons. The number of electrons it has is _____. 30 14 44 16 Isotopes are atoms of the same element that have different masses. Hydrogen-1 protium Hydrogen-2deuterium Hydrogen-3tritium Atoms of one element that have different masses are called _____. isotopes moles molecules Mixtures What is true when comparing isotopes carbon-12 and carbon-14 a) they have the same number of neutrons b) they are different elements c) they have the same number of protons d) they have the same mass Atoms of the same element can differ in _____. chemical properties mass number atomic number number of protons and electrons Law of conservation of mass states that mass is neither destroyed nor created during ordinary chemical or physical reaction. Example: A glass of ice cubes will have the same mass when the ice has completely melted into water even though its volume will change. The law of definite proportions states that a chemical compound contains the same element in exactly the same proportions by mass regardless of the size of the sample or source of the compound. 84.01 g of baking soda, NaHCO3, always contains 22.99 g of sodium, 1.01 g of hydrogen, 12.01 g of carbon, and 48.0 g of oxygen. What percentage of each of these elements is present in baking soda? _____________Na _____________C _____________H _____________O The law of multiple proportions: If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain masses of the first element is always a ratio of small whole numbers. An example of the law of multiple proportions is the existence of A) FeCl3 and Fe(S04)3 C) CO and CO2 B) O2 and O3 D) FeCl2 and Fe(NO3)2 For each compound, different elements combine in a simple numerical ratio. The illustration below describes this rule. The second equation for the reaction is incorrect because half of an atom does not exist. Atomic Radius: one-half the distance between the nuclei of identical atoms that are bonded together Relative Scale: One atomic mass unit , or 1 amu, is exactly 1/12 the mass of a carbon-12 atom. Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element. Calculating Average Atomic Mass Isotope Percentage Natural Abundance Uranium-234 0.005% Uranium-235 0.720% Uranium-238 99.275% Atomic mass (amu) 234.040947 235.043924 238.050784 •Oxygen has three naturally occurring isotopes in the following proportions: oxygen-16, 99.762% (15.99492 amu) oxygen-17, 0.038000% (16.99913 amu) oxygen-18, 0.20000% (17.99916 amu). •What is the average atomic mass of oxygen?