4/14/2013 ATOMIC STRUCTURE THE ATOMIC MODEL

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1 ATOMIC STRUCTURE R E G E N T S C H E M I S T R Y M R S. T I L A R O HISTORY OF THE ATOM O L D A N D M O D E R N A T O M THE ATOMIC MODEL Model of the atom is based on indirect experimental data. Model of the atom changes as experimental abilities improve. Experimenting was limited to things that were visible with the unaided eye. Today we have accelerators. Machines that shoot high energy particles into atoms. Give us data that refines our understanding of the atom 1

2 PARTICLE ACCELERATOR IN CERN, SWITZERLAND THE GREEK MODEL Democritus Philosopher around the year 400BC. Concluded that matter could not be divided into smaller pieces. Used the word Atomos to describe the smallest piece of matter. Atomos = not to be cut, indivisible Greeks believed All matter on earth was made of four basic combinations Fire Air Water earth DALTON MODEL - SPHERE John Dalton - English chemist that proposed the Atomic Theory, in 1803 Law of Conservation of Mass Law of Definite Proportions Law of Multiple Proportions 2

3 LAWS OF CHEMISTRY LAW OF CONSERVATION OF MASS Law of Conservation of Mass = total mass of the reactants in any chemical reaction is exactly equal to the total mass of the product. IN OTHER WORDS Whatever amount you put in, you get out, Whatever amount of energy you put in, you get out. Whatever amount of molecules you put in, you get out. Etc. Etc. Etc. 3

4 LAW OF DEFINITE PROPORTIONS Law of Definite Proportions = compound always contains two or more elements combined in a definite proportion by mass. LAW OF MULTIPLE PROPORTIONS Law of Multiple Proportions = atoms of two or more elements may combine in different ratios to produce more than one compound. IN OTHER WORDS Compounds with definite proportions can be re-arranged to form other compounds with definite proportions. EX Water H 2 O Hydrogen peroxide H 2 O 2 4

5 POINTS OF DALTON S THEORIES 1. Elements are made of indivisible particles, atoms. 2. Atoms of the same element are alike in mass and size. 3. Atoms of different elements have different mass and size. 4. Chemical compounds are two or more atoms of different elements chemically combined. 5. Atoms combine to form compounds in simple numerical ratios. 6. Atoms of two elements combine in different ratios to form more than one compound. THOMSON S MODEL THE PLUM PUDDING J.J. Thomson English scientist who discovered electrons. Developed the plum pudding model after discovering negative charged particles in the atom. He knew that atom was neutral, but could not prove the atom had positively charged particles. Atom was positively charged material with negatively charged electrons scattered through it. RUTHERFORD MODEL - Ernest Rutherford British physicist who discovered atoms had a small, dense, positively charged Nucleus. His model proposed atoms are mostly empty space. He knew positive charges repel positive charges Positive charges were in the middle, known as the nucleus. Negative charges were scattered around the atom s edge. 5

6 BOHR MODEL Neils Bohr Danish scientist who proposed the planetary model of the atom. Electrons move in definite orbits around the nucleus like planets. Electrons move in a specific energy level Energy levels are located at certain distances from the nucleus Sir Chadwick discovered the neutron. WAVE MECHANICAL MODEL Based on wave mechanics model proposes that electrons have NO definite path in an atom. Location of electron is based on how much energy it has. More energy = further distance of electron from the nucleus The small positively charged nucleus is surrounded by a large enough space with elections to make the atom neutral. 6

7 WAVE MECHANICAL MODEL This meant that electrons, instead of traveling in defined orbits or hard, spherical shells, as Bohr proposed, travel in diffuse clouds around the nucleus. PRACTICE QUESTIONS The modern model of an atom shows that electrons are a) Orbiting the nucleus in a fixed path b) Found in regions called orbital c) Combined with neutrons in the nucleus d) Located in a solid sphere covering the nucleus In the wave mechanical model, the orbital is a region in space of an atom where there is a) High probability of finding an electron b) high probability of finding a neutron c) Circular path in which electrons are found d) Circular path in which neutrons are found PRACTICE PROBLEMS Which conclusion is based on the gold foil experiment and the resulting model of the atom? a) An atom has hardly any empty space, and the nucleus is positive charge b) An atom is hardly empty space, and the nucleus has positive charge c) An atom is mainly empty space, and the nucleus has a negative charge. d) An atom is mainly empty space, and the nucleus has a positive charge. 7

8 PRACTICE QUESTIONS Which group of atomic models is listed in order from the earliest to the most recent? a) Hard-sphere model, wave mechanical model, electron-shell model b) Hard-sphere model, electron-shell model, wavemechanical model c) electron-shell model, wave-mechanical model, hard-sphere model d) Electron-shell model, hard-sphere model, wavemechanical model PRACTICE QUESTIONS Subatomic particles can usually pass undeflected through an atom because the volume of an atom is composed mainly by a) Uncharged nucleus b) Unoccupied space c) Neutrons only d) Protons only Experiment evidence indicates that atoms a) Have uniform distribution of positive charges b) Have uniform distribution of negative charges c) Contains a positively charged, dense center d) Contains a negatively charged, dense center LAST PRACTICE QUESTION Compared to the entire atom, the nucleus of an atom is a) Smaller and contains most of atom s mass b) Smaller and contains little of atom s mass c) Larger and contains most of atom s mass d) Larger and contains little of atom s mass 8

9 THE ATOM atom is the smallest particle of an element that retains the chemical properties of that element element is defined as a substance that can t be broken down or separated into simpler substances through a chemical reaction. Elements contain just one type of atom, and each different element contains a different type of atom. ATOMS = 3 SUBATOMIC PARTICLES Protons, which are positively charged and situated at the center of the atom neutrons, which are electrically neutral (meaning that they have no charge) and are also in the nucleus of the atom electrons, which are negatively charged and are situated outside the nucleus. majority of the mass of an atom is contained in its nucleus because electron is 1/1836 amu THE SPACIOUS ATOM the nucleus of an atom is much, much smaller and more dense than the space occupied by an atom s electrons if an atom were the size of a football field, the nucleus would be the size of a flea on the 50-yard line! 9

10 THE PROTON Positively charged particle in the nucleus The number of protons an atom possesses is what gives the element its atomic number all of the sulfur atoms in the pile of sulfur we looked at have 16 protons in their nucleus. If they had one more proton in their nucleus, they would have a different identity they d be chlorine (Cl) atoms, and with one less, they d be phosphorus (P) atoms. s the atom its identity THE NEUTRON Neutrally charged particle in the nucleus of the atom Neutrons act like a glue for the protons Keeps positively charged nucleus from repelling ELECTRON Negatively charged particles Located outside the nucleus of an atom atoms have the same number of protons and electrons 1/1836 the size of a proton or neutron 10

11 PRACTICE QUESTIONS Which particles are found in the nucleus of an atom? a) Electrons, only b) Neutrons, only c) Protons and electrons d) Protons and neutrons Which is true of protons and neutrons? a) They have approximately the same mass and the same charge b) They have approximately the same mass but different charge c) They have different mass and different charge d) They have different mass but the same charge LAST PRACTICE QUESTIONS The electron has a charge of a) -1 and the same mass as a proton b) -1 and a smaller mass than a proton c) +1 and the same mass as a proton d) +1 and a smaller mass than a proton The mass of a proton is approximately a) 1/2000 times the mass of a neutron and a unit positive charge b) 1/2000 times the mass of a neutron and a unit negative charge c) 2000 times the mass of an electron and a unit positive charge d) 2000 times the mass of an electron and a unit negative charge SYMBOL: ATOMIC MASS AND NUMBER mass number (Z ), which is the number of the atom s protons plus the number of its neutrons, is indicated by the superscript atomic number (A), which is the number of protons the atom contains, is indicated by the subscript 11

12 SUMMARY OF RELATIONSHIP BETWEEN PARTICLES IN NEUTRAL ATOMS Protons = atomic # = nuclear charge = electrons = (mass # - neutrons) Electrons = atomic # = protons = (mass # - neutrons) Neutrons = (mass# - protons) = (mass# - atomic number)= (mass# - electrons) Mass# = (protons + neutrons) = (atomic# + neutrons) PRACTICE QUESTIONS The mass number of an element is always equal to the number of a) Protons plus electrons b) Protons plus positrons c) Neutrons plus protons d) Neutrons plus positrons The number of neutrons in the nucleus of an atom can be determined by a) Adding the mass # to the atomic # of the atom b) Adding the mass# to the # of electrons in the atom c) Subtracting the atomic # from the mass# of the atom d) Subtracting the mass# from the atomic # of the atom PRACTICE QUESTIONS A neutral atom contains 12 neutrons and 11 electrons. The number of protons in this atom is a) 1 b) 11 c) 12 d) 23 What is the number of electrons in a neutral atom of Fluorine? a) 9 b) 19 c) 10 d) 28 12

13 PRACTICE QUESTIONS The number of neutrons in a neutral atom with a mass number of 86 and 37 electrons is a) 86 b) 37 c) 123 d) 49 What is the atomic number of a neutral element whose atoms contain 60 neutrons and 47 electrons? a) 13 b) 47 c) 60 d) 107 LAST PRACTICE QUESTION What is the mass number of an atom that contains 19 protons, 18 electrons, and 20 neutrons? a) 19 b) 38 c) 39 d) 58 FOCUS ON BOHR MODEL Chlorine Total mass = 35amu Protons = 17 Neutrons = 18 Electrons 17 13

14 MAX ELECTRONS PER ENERGY LEVEL Energy levels can hold a certain number of electrons. FOCUS ON BOHR MODEL Lithium Total mass = 7amu Protons = 3 Neutrons = 4 Electrons = 3 ELECTRON CONFIGURATION Electron configuration - Shows how many electrons are in each principal energy level Chlorine is 2-8-7; 2 electrons in the first energy level, 8 in the second energy level, and 7 electrons in the third energy level. Valence electrons shows how many electrons are on the last energy level Chlorine has 7 valence electrons 14

15 BOHR MODEL & LEWIS DOT OF VALENCE ELECTRONS Octet happy = valence energy level is filled (AKA= 8 e-) Calcium electron configuration = (reference table) CHARGED ATOMS protons are positively charged and electrons are negatively charged, neutral atoms have no net electrical charge. Li = 3 protons 3 electrons = 0 charge Atoms with less electrons than protons = cation or positive charge Li +1 = 3 protons 1 electron = positive charge Atoms with more electrons than protons = anion or negative charge O -2 = 8 protons 10 electrons = negative charge IONS FILL IN THE BLANKS SHEET An atom is made up of protons and neutrons (found in the nucleus) Electrons (in the surrounding electron cloud) Atomic number = to the number of protons plus neutrons 15

16 ATOMS CAN BE EITHER: A neutral atom protons equal the number of electrons Charge on an ion indicates an imbalance between protons and electrons Too many electrons = negative charge Too few electrons = positive charge PRACTICE PROBLEMS A particle of matter contains 6 protons, 7 neutrons, and 6 electrons. This particle must be a a) Neutral carbon atom b) Neutral nitrogen atom c) Positively charged carbon ion d) Positively charged nitrogen ion Neutral atoms of 37 Cl and 35 Cl differ with respect to their number of a) Electrons b) Protons c) Neutrons d) positrons PRACTICE PROBLEMS Copper atom loses two electrons to become an ion. What is the proper symbols for this ion? Cu 2+ Iron atom loses three electrons to become an ion. What is the proper symbols for this ion? Fe 3+ Atomic ion for: a) Ca Ca 2+ b) K K + c) Ba Ba 2+ d) Li Li + e) Mg Mg 2+ f) H H + 16

17 ISOTOPES Atoms of a given element can, however, differ in the number of neutrons they contain atoms of the same element that have different numbers of neutrons are known as isotopes Most elements have at least two isotopes that occur naturally, although a few just have one. EXAMPLE OF ISOTOPES common isotopes of carbon can contain 5, 7, or 8 neutrons Isotopes can also be written as carbon-14, carbon-15, carbon-16, etc. or C-14, C-15, C-16, where the number represents the mass number of the atom. ATOMIC MASS Atomic mass weighted average mass of the naturally occurring isotopes of that element. the average is weighted according to the proportions in which the isotopes occur Ex: there are two isotopes of chlorine, 35 17Cl and Cl. There is 25% of natural occurring 37 Cl isotope and 75% of naturally occurring 35 Cl isotope 17

18 MOLECULAR MASS/WEIGHT Molecular weight of an element represents its average atomic mass based on the relative abundance of various isotopes of that element in nature. So, when we say that the atomic weight of carbon is = average weights of all isotopes of carbon that exist in nature, carbon-11, -12, -13, or -14, is Cesium 75% 133 Cs, 20% 132 Cs, 5% 131 Cs ( )+( )+( ) = = amu ATOMIC MASS UNIT The weight of elements Al 27amu Fe 56amu Zn 65 amu The weights of compounds NaCl (1 23) + (1 35) = 58amu H 2 O (2 1) + (1 16) = 18amu Ca(OH) 2 (1 40) + (2 16) + (2 1)= 74amu Atomic weights have the unit amu, or atomic mass unit GROUND AND EXCITED STATES Ground state - The periodic table is written in the ground state in order of Excited state electrons absorb energy or gotten more energy. Electrons jump ahead to a higher energy level, leaving one of the inner principal energy levels partly empty. EX: What is the electron configuration of Sodium in the ground state? Which electrons configuration represents an atom in the excited state? a) b) c) d)

19 PRACTICE QUESTIONS The excited atom has an electron configuration of 1-6. what atom is this? a) C b) N c) O d) F How many valence electrons does Mg have? a) 2 b) 4 c) 6 d) 10 GROUND AND EXCITED STATES SPECTRA Used to identify types of elements 19

20 EXAMPLE OF REGENTS QUESTION REVIEW The atomic number of a certain element is 11, and its atomic mass number is 23. How many protons and neutrons does this atom have, and what is its chemical symbol? Sodium 11 protons; 12 neutrons Na each principal energy level, n, has n sublevels. This means the first has one sublevel, the second has two, the third has three, etc. The sublevels are named s, p, d, and f. 20

21 At each additional sublevel, the number of available orbitals is increased by two: s = 1, p = 3, d = 5, f = 7 each orbital can hold only two electrons, which must be of opposite spin So s holds 2, p holds 6 (2 electrons times the number of orbitals, which for the p sublevel is equal to 3), d holds 10, and f holds 14. ORBITAL NOTATION Orbital notation is basically just another way of expressing the electron configuration of an atom. It is very useful in determining quantum numbers as well as electron pairing. The orbital notation for sulfur would be represented as follows: 21