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Chapter 3 – Atoms: The Building Blocks of Matter Section 3-1 – The Atom: From Philosophical Idea to Scientific Theory The first people to think about particle theory were the _____________ around ___________. Greeks 400 BC One in particular was __________. The word atom in Greek means _______. Democritus indivisible Following Democritus was _________. He didn’t believe in atoms. He thought matter was ___________. Aristotle continuous This idea succeeded for about _______years. Neither view was supported by __________ _________ until ________. 2000 experimental evidence The 18th century By the late ________, most people thought of an _______ as something that could not be broken down and that could _________ with other elements to form __________. 1800’s combine Atom compounds Scientists still weren’t sure, however if they always combined in the same ________. proportions In the late 1790’s scientists had better _________ which allowed them to study chemical reactions ___________. balances quantitatively This led to the law of _______________________. It essentially says that as long as nothing enters or leaves a chemical reaction, _______ remains constant. conservation of mass mass Antoine-Laurent de Lavoisier • He was obsessed with measuring mass during chemical reactions. • He observed that when chemical reactions are carried out in a closed system, the mass of the system is not changed. • He was obsessed with the latest equipment for measuring mass. • He spent a great deal of the French taxpayers money on this equipment. • He died in the French Revolution. It also lead to the law of __________________ which essentially says that regardless of the _________ or _________ of the sample, the elements that make it up are always there in the same ____________. definite composition size or source proportions Law of Definite Proportions Joseph Louis Proust (1754-1826) Joseph Louis Proust observed that Copper carbonate (CuCO3) occurs in nature as the mineral malachite (a), it forms as a patina on copper roofs (b) and bronze statues, and can also be synthesized in the laboratory (c). Regardless of its source, basic copper carbonate has the same composition. Since the composition of copper carbonate is the identical regardless of the source, Proust called this generalization as the law of definite proportions. Swedish chemist Berzelius heated certain amount of lead with various amount of sulfur. He found that when he used 1.55 g of sulfur (yellow) and 10.0 g of lead (gray) he got 11.55 of lead sulfide (black). Jons Jacob von Berzelius 1779-1848 If sulfur were taken in excess of 1.55g, Berzelius found that the excess amount of sulfur did not react. Similarly if had 1.55 g of sulfur and added lead in excess of 10.0 g, he found that the excess lead did not react The law of definite proportions – Berzelius View Definite proportions – A Closer Look The law of definite proportions. Berzelius' experiment with lead and sulfur are interpreted in terms of Dalton's atomic theory. The electrolysis of water Henry Cavendish (1731 - 1810) further illustrated the law of definite proportion by electrolyzing water. Electrolysis of water. During electrolysis, water decomposes to give hydrogen gas and oxygen gas always in a 2-to-1 volume ratio when energy is supplied by a battery or other source of direct current (dc). http://wps.prenhall.com/wps/media/objects/439/449969/Media_Portfolio/Chapter_04/Electrolysis_of_Water.MOV More complicated is the law of ______________. It says that if ______ or more different _______ are made of the same 2 elements, the ratio of the ________ element combined with a fixed mass of the 1st element is always a ________ of small ___________ numbers multiple proportions 2nd whole two ratio An example of this would be the compounds of ___________ and ___________. carbon dioxide carbon monoxide John Dalton’s Atomic Theory of Multiple Proportions Dalton theory multiple proportions: Elements can combine with each other in more than one set of proportions. For example, hydrogen and oxygen combine with each other in two different proportions and form two entirely different compounds. 2 H 2 O 2 2H 2 O Water John Dalton (1766-1848) 2H 2 2O 2 2H 2O 2 Hydrogen peroxide Although these two molecules contain only hydrogen and oxygen, they are not the same compound. These three laws prompted John Dalton to propose his atomic theory. It basically says: 1. All matter is made of ______________ ______________ called ____________ indivisible indestructible atoms 2. Atoms of the same ___________ are chemically and physically the ________. element same 3. Atoms of ___________ elements are chemically and physically the ________. different different 4. When atoms _______ in a chemical reaction, they do so in ___________, ____________ number ratios. combine small whole In a chemical reaction, atoms aren’t ____________ or ____________, they are simply _____________. created destroyed rearranged Section 3-2 – The Structure of the Atom Atoms consist of ___________________ regions. One of them contains the ___________________ and ___________________. It is called the ___________________. 2 protons neutrons nucleus The other area surrounds the nucleus. It contains ___________________ particles called ___________________. negatively charged electrons Actually ___________________, ___________________, and ___________________ are all ___________________. protons electrons neutrons subatomic particles The electron was discovered by working with a tube that contained a ___________________ at very low pressure. gas When ___________________ passed through it, it would light up. It is called a _________________________ ____________. an electrical current cathode ray tube The fact that the ray was deflected by a negative charged showed that the ray had a ___________________ charge. negative The fact that the ray could move a paddle wheel demonstrated the ___________________ nature of the ray. particle The ray was actually made of ___________________. electrons The scientist credited with naming the ___________________ was ___________________. electron JJ Thomson It stands to reason that where there is a negative charge, there must be a ___________________ charge to balance it. positive _________________________ and associates tried to bombard ___________________ with ___________________. Ernest Rutherford gold alpha particles They expected that most of the α particles would ________________________. go straight thru (92%) For the most part, this was true, but some were ___________________ and a very small percentage were actually _____________________. deflected (6%) shot straight back (2%) It took 2 years, but Rutherford developed a 2 part explanation. It was: • Atoms are mostly empty space • Atoms must have a densely packed positively charged nucleus. To summarize the ___________________, ___________________ are the lightest and can be found ______________________. They have a ________________ charge. subatomic particles electrons orbiting the nucleus negative ___________________ and ___________________ are the heaviest and are found in the ___________________. Protons neutrons nucleus ___________________ have a positive charge and ___________________ have ___________________ charge. Protons neutrons no Section 3-3 – Counting Atoms neutral, atomic number, chlorine, proton, 17, electron A neutral atom of chlorine would have 17 protons and 17 electrons if it is neutral. Because chlorine has an atomic number of 17, it would have 17 protons and assuming it is neutral, it would have 17 electrons. isotope, tritium, deuterium, protium, atomic mass, 1, 2, 3, hydrogen The three isotopes of hydrogen are protium with an atomic mass of 1, deuterium with an atomic mass of 2, and tritium with an atomic mass of 3. Hydrogen has 3 different isotopes. They are protium, deuterium, and tritium with atomic masses of 1, 2, and 3 respectively. nuclide, superscript, subscript, hyphen notation, uranium, nuclear symbol You can indicate nuclides 2 different ways; Hyphen notation means you write the symbol with a dash and the atomic mass or you could use the nuclear symbol method where you write the symbol and put the atomic mass as a subscript to the upper left and the atomic number as a subscript to the lower left. Example • U-238 238 92 U carbon-12, atomic mass unit An atomic mass unit is defined as one twelfth of a carbon-12 atom. average atomic mass, isotopes, percentage, naturally occurring The average atomic mass of an element takes into account the percentages of the naturally occurring isotopes. Average atomic mass can be calculated by multiplying the atomic masses of the isotopes by their naturally occurring percentage in a mixture. mole, carbon-12, Avogadro’s number, molar mass A mole is defined as 12 g of the carbon-12 isotope. It has Avogadro’s number of atoms. The molar mass of all other elements is compared to a mole of carbon12. Subatomic Particles The atoms of all elements consists of positively charged protons, neutral neutrons and negatively charged electrons. The protons and the neutrons together are called as nucleons and they are located at the nucleus of the atoms. The Atomic Number The number of protons in the nucleus of an atom determines the atomic number (Z) and indicates the element's identity. For a neutral atom, the atomic number also describes the number of electrons around the nucleus. Atomic Mass and Atomic Number Mass number A (sum of protons and neutrons) Atomic number Z (number of protons) = number of neutrons. Isotopes of hydrogen While the number of protons in the nucleus defines an element's identity, variations on the number of neutrons in the nucleus give rise to different isotopes of the same element. Mass Numbers and Atomic Numbers The atomic number is equal to the number of protons in an atom of that element. The mass number is the sum of the number of protons and neutrons.