The Physical Setting Chemistry Day 1 slides 3-11 Day 2 slides 12-26

I. Atomic Concepts

The modern model of the atom has evolved over a long period of time through the work of many scientists. Democritus – matter is made up of particles called atoms Dalton – atoms of the same element are alike – solid indivisible spheres J Deutsch 2003

Thomson – discovers electrons – plum pudding model J Deutsch 2003

Bohr – electrons orbit the nucleus Rutherford – gold foil experiment – discovers heavy, + charge nucleus – mostly empty space Bohr – electrons orbit the nucleus J Deutsch 2003

Regents Question: 08/02 #1 Subatomic particles can usually pass undeflected through an atom because the volume of an atom is composed of (1) an uncharged nucleus (2) largely empty space (3) neutrons (4) protons þ J Deutsch 2003

Regents Question: 01/03 #62-64 One model of the atom states that atoms are tiny particles composed of a uniform mixture of positive and negative charges. Scientists conducted an experiment where alpha particles were aimed at a thin layer of gold atoms. Most of the alpha particles passed directly through the gold atoms. A few alpha particles were deflected from their straight-line paths. An illustration of the experiment is shown below. J Deutsch 2003

Regents Question cont’d Most of the alpha particles passed directly through the gold atoms undisturbed. What does this evidence suggest about the structure of the gold atoms? A few of the alpha particles were deflected. What does this evidence suggest about the structure of the gold atoms? How should the original model be revised based on the results of this experiment? Most of the atom is empty space. There is central + charge. The nucleus is +. The atom is not a uniform mixture of + and - charge. Positive charge is located in a heavy central mass. J Deutsch 2003

Regents Question: 06/03 #67 John Dalton was an English scientist who proposed that atoms were hard, indivisible spheres. In the modern model, the atom has a different internal structure. Identify one experiment that led scientists to develop the modern model of the atom. Rutherford’s gold foil experiment J Deutsch 2003

Regents Question cont’d John Dalton was an English scientist who proposed that atoms were hard, indivisible spheres. In the modern model, the atom has a different internal structure. Describe this experiment. State one conclusion about the internal structure of the atom, based on this experiment. Rutherford’s shot alpha particles a piece of gold foil. Most of the alpha particles went through, some were deflected and some were reflected. J Deutsch 2003 Most of the atom is empty space.

An orbital is the area of highest probability of finding an electron. In the wave-mechanical model (electron cloud model), the electrons are in orbitals, which are defined as the regions of the most probable electron location (ground state). An orbital is the area of highest probability of finding an electron. J Deutsch 2003

Regents Question: 06/03 # 5 The region that is the most probable location of an electron in an atom is (1) the nucleus (2) an orbital (3) the excited state (4) an ion þ J Deutsch 2003

Regents Question: 06/02 #2 The modern model of the atom shows that electrons are orbiting the nucleus in fixed paths found in regions called orbitals combined with neutrons in the nucleus located in a solid sphere covering the nucleus þ J Deutsch 2003

Subatomic Particles: Mass Charge Part of the atom Symbol Mass charge Proton 1 amu +1 Neutron 1amu Electron o -1 Mass Charge J Deutsch 2003

J Deutsch 2003

Each atom has a nucleus, with an overall positive charge, surrounded by one or more negatively charged electrons. J Deutsch 2003

Atomic Mass-number of nucleons (protons + neutrons) Atomic number # of protons in the nucleus. # neutrons = mass # - atomic # J Deutsch 2003

# of protons = # of electrons Protons and electrons have equal but opposite charges. The number of protons equals the number of electrons in an atom. The atomic number for an element cannot change but its mass number can. # of protons = # of electrons Therefore, atoms are electrically neutral. J Deutsch 2003

Regents Question: 01/03 #1 þ Which statement best describes electrons? They are positive subatomic particles and are found in the nucleus. They are positive subatomic particles and are found surrounding the nucleus. They are negative subatomic particles and are found in the nucleus. They are negative subatomic particles and are found surrounding the nucleus. þ J Deutsch 2003

Regents Question: 08/02 #4 What is the total number of protons in the nucleus of an atom of potassium-42? (1) 15 (2) 19 (3) 39 (4) 42 The mass number (42) is not necessary to find the number of protons. þ J Deutsch 2003

Regents Question: 06/03 #36 þ The nucleus of an atom of K-42 contains (1) 19 protons and 23 neutrons (2) 19 protons and 42 neutrons (3) 20 protons and 19 neutrons (4) 23 protons and 19 neutrons þ J Deutsch 2003

Regents Question: 06/03 #1 The atomic number of an atom is always equal to the number of its (1) protons, only (2) neutrons, only (3) protons plus neutrons (4) protons plus electrons þ J Deutsch 2003

Regents Question: 06/02 #33 The number of neutrons in the nucleus of an atom can be determined by Adding the atomic number to the mass number Subtracting the atomic number from the mass number Adding the mass number to the atomic mass Subtracting the mass number from the atomic number þ J Deutsch 2003

Regents Question: 06/03 #2 þ Which subatomic particle has no charge? (1) alpha particle (2) beta particle (3) Neutron (4) electron þ J Deutsch 2003

Subatomic particles contained in the nucleus include protons and neutrons. Particles in the nucleus (protons and neutrons) are called nucleons The mass of the atoms is concentrated in the nucleus Electrons are not found in the nucleus, they are in orbitals around the nucleus. The net charge of the nucleus is positive (+) J Deutsch 2003

Regents Question: 06/02 #58-60 In the modern model of the atom, each atom is composed of three major subatomic (or fundamental) particles. Name the subatomic particles contained in the nucleus of the atom. State the charge associated with each type of subatomic particle contained in the nucleus of the atom. What is the net charge of the nucleus? Proton and neutron Proton is positive and the neutron is neutral Positive J Deutsch 2003

The ground state for Na is 2-8-1 valence electrons: The outermost electrons in an atom Importance: the number of valence electrons affects the chemical properties of an element. The ground state for Na is 2-8-1 The valence shell is the third shell. The valence shell contains 1 electron. J Deutsch 2003

If an atom gains or loses electrons it is called an ion. When atoms gain electrons they become negative ions. Flourine gains one electron it becomes F-1

When atoms lose electrons they become positive ions Calcium loses 2 electrons it becomes Ca+2 ion Gaining electrons is negative Losing electrons is positive GEN LEP J Deutsch 2003

Regents Question: 08/02 #2 What is the total number of electrons in the valence shell of an atom of aluminum in the ground state? 8 2 3 (4) 10 þ J Deutsch 2003

Regents Question: 06/03 #51-52 Base your answers to the next two questions on the electron configuration table shown below. What is the total number of valence electrons in an atom of electron configuration X? Which electron configuration represents the excited state of a calcium atom? Element Electron Configuration X 2 –8 –8 –2 Y 2 –8 –7 –3 Z 2 –8 –8 2 2-8-7-3 J Deutsch 2003

Each electron in an atom has its own distinct amount of energy Each electron in an atom has its own distinct amount of energy. Electrons in their lowest energy state are in the ground state. Ground State electron configurations are found on the periodic table. The ground state for Na is 2-8-1 J Deutsch 2003

Regents Question: 06/02 #1 What is the electron configuration of a sulfur atom in the ground state? 2-4 2-6 2-8-4 2-8-6 þ Look at the Periodic Table of the Elements If you do not know the symbol for sulfur, check Table S J Deutsch 2003

Electron Configuration The electron configuration for the ground state of an atom is given on the Periodic Table of the Elements. Electron Configuration J Deutsch 2003

Possible excited states for Na are: When an electron in an atom gains a specific amount of energy, the electron is at a higher energy state (excited state). Possible excited states for Na are: 2-7-2 1-8-2 J Deutsch 2003

When an electron returns from a higher energy state to a lower energy state, a specific amount of energy is emitted. This emitted energy can be used to identify an element. Emission Spectrum J Deutsch 2003

Which element are part of the mixture? J Deutsch 2003

The maximum number of electrons in a principal energy level (shell) is 2n2. Energy level (n) Maximum number of electrons (2n2) 1 2 8 3 18 4 32 J Deutsch 2003

Regents Question: 06/02 #31 In which shell are the valence electrons of the elements in Period 2 found? 1 2 3 4 þ J Deutsch 2003

Regents Question: 06/03 # 3 When the electrons of an excited atom return to a lower energy state, the energy emitted can result in the production of alpha particles (2) Isotopes (3) protons (4) spectra þ J Deutsch 2003

Regents Question: 01/03 # 2 During a flame test, ions of a specific metal are heated in the flam of a gas burner. A characteristic color of light was emitted by these ions in the flame when the electrons Gain energy as they return to lower energy levels Gain energy as they move to higher energy levels Emit energy as they return to lower energy levels Emit energy as they move to higher energy levels þ J Deutsch 2003

Lewis dot Vs. Bohr Diagram Lewis Dot diagrams only show the valence electrons Bohr Diagrams show protons, neutrons and all shells of electrons J Deutsch 2003

Dots represent valence electrons Dots represent valence electrons. Everything else (inner shell electrons and nucleus) is called the Kernel and is represented by the symbol. Phosphorous has 5 valence electrons so we draw 5 dots around the symbol for phosphorous. J Deutsch 2003

It does not matter which side you start from. The correct order to fill in the dots is to make a pair from the first 2 electrons then we fill in one on each side before we pair up. 1 2 Ne 5 3 8 6 4 7 It does not matter which side you start from. J Deutsch 2003

The correct order to fill in the dots is to make a pair from the first 2 electrons then we fill in one on each side before we pair up. 5 8 Ne 1 7 4 2 6 3 This will let you know how many electron pairs and how many unpaired electrons are in the atom’s valence shell J Deutsch 2003

Draw the Lewis Dot Structures of the first 18 elements. J Deutsch 2003

Atoms of an element that contain the same number of protons but a different number of neutrons are called isotopes of that element. Isotopes of Hydrogen 1H – protium 1 proton 0 neutron 2H – deuterium 1 proton 1 neutron 3H – tritium 1 proton 2 neutrons J Deutsch 2003

The number of protons in an atom (atomic number) identifies the element. 6C The sum of the protons and neutrons in an atom (mass number) identifies an isotope.Common notations that represent isotopes include: 14C, carbon-14, C-14. Atomic number is written on the bottom left. Mass number is written on the upper left. J Deutsch 2003

Here are three isotopes of an element: 612C 613C 614C The element is: The number 6 refers to the The numbers 12, 13, and 14 refer to the How many protons and neutrons are in the first isotope? How many protons and neutrons are in the second isotope? How many protons and neutrons are in the third isotope?   J Deutsch 2003

Regents Question: 01/03 #9 An atom of carbon-12 and an atom of carbon-14 differ in Atomic number Atomic mass Nuclear charge Number of electrons þ Carbon-12 and carbon-14 are isotopes. J Deutsch 2003

Regents Question: 06/02 #4 þ All the isotopes of a given atom have the same mass number and same atomic number the same mass number but different atomic numbers different mass numbers but the same atomic number different mass numbers and different atomic number þ J Deutsch 2003

Regents Question: 06/02 #9 Atoms of the same element that have different numbers of neutrons are classified as Charged atoms Charged nuclei Isomers Isotopes þ J Deutsch 2003

Electron Configuration tells us how many electrons in each principal energy level (shell). Atomic Number = 7 Mass Number = 14 7 protons 7 neutrons 7 electrons Electron configuration: 2-5 J Deutsch 2003

The average atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes. Isotope Mass Abundance Calculation 12C 12 98.89% 12 x .9889 = 11.87 13C 13 1.108% 13 x 0.01108 = 0.1440 Atomic Mass (weighted average) 12.01 amu J Deutsch 2003

Regents Question: 06/03 # 4 The atomic mass of an element is calculated using the (1) atomic number and the ratios of its naturally occurring isotopes (2) atomic number and the half-lives of each of its isotopes (3) masses and the ratios of its naturally occurring isotopes (4) masses and the half-lives of each of its isotopes þ J Deutsch 2003

Regents Question: 01/03 #36 Hydrogen has three isotopes with mass numbers of 1, 2, and 3 and has an average atomic mass of 1.00794 amu. This information indicates that Equal number of each isotope are present More isotopes have an atomic mass of 2 or 3 than 1 More isotopes have an atomic mass of 1 rather than 2 of 3 Isotopes have only an atomic mass of 1 þ J Deutsch 2003

Regents Question: 01/03 #9 An atom of carbon-12 and an atom of carbon-14 differ in Atomic number Atomic mass Nuclear charge Number of electrons þ J Deutsch 2003

Regents Question: 06/02 #4 þ All the isotopes of a given atom have the same mass number and same atomic number the same mass number but different atomic numbers different mass numbers but the same atomic number different mass numbers and different atomic number þ J Deutsch 2003

Regents Question: 06/02 #9 Atoms of the same element that have different numbers of neutrons are classified as Charged atoms Charged nuclei Isomers Isotopes þ J Deutsch 2003

Regents Question: 01/03 #36 Hydrogen has three isotopes with mass numbers of 1, 2, and 3 and has an average atomic mass of 1.00794 amu. This information indicates that Equal number of each isotope are present More isotopes have an atomic mass of 2 or 3 than 1 More isotopes have an atomic mass of 1 rather than 2 of 3 Isotopes have only an atomic mass of 1 þ J Deutsch 2003

Regents Question: 01/03 #3 In which list are the elements arranged in order of increasing atomic mass? Cl, K, Ar Fe, Co, Ni Te, I Xe Ne, F, Na þ Look for the masses on the periodic table of the elements. J Deutsch 2003