Chapter 2 Atoms and Elements 2.4 The Atom
Atoms Dalton s Atomic Theory Are tiny particles of matter. Of an element are similar and different from other elements. Of two or more different elements combine to form compounds. Are rearranged to form new combinations in a chemical reaction.
Subatomic Particles Atoms contains subatomic particles. Protons have a positive (+) charge. Electrons have a negative (-) charge. Like charges repel and unlike charges attract. Neutrons are neutral. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
Rutherford s Gold-Foil Experiment
Structure of the Atom An atom consists Of a nucleus that contains protons and neutrons. Of electrons in a large, empty space around the nucleus.
Atomic Mass Scale On the atomic mass scale for subatomic particles 1 atomic mass unit (amu) is defined as 1/12 of the mass of the carbon-12 atom. A proton has a mass of about 1 (1.007) amu. A neutron has a mass of about 1 (1.008) amu. An electron has a very small mass, 0.000549 amu.
TABLE 2.6 Particles in the Atom
Learning Check Identify each statement as describing a 1) proton 2) neutron 3) electron A. Found outside the nucleus. B. Has a positive charge. C. Is neutral. D. Found in the nucleus.
Atomic Number The atomic number Is specific for each element. Is the same for all atoms of an element. Is equal to the number of protons in an atom. Appears above the symbol of an element. Atomic Number Symbol 11 Na
Atomic Number and Protons Examples of atomic number and number of protons: Hydrogen has atomic number 1, every H atom has one proton. Carbon has atomic number 6, every C atom has six protons. Copper has atomic number 29, every Cu atom has 29 protons. Gold has atomic number 79, every Au atom has 79 protons.
Learning Check State the number of protons in each. A. A nitrogen atom 1) 5 protons 2) 7 protons 3) 14 protons B. A sulfur atom 1) 32 protons 2) 16 protons 3) 6 protons C. A barium atom 1) 137 protons 2) 81 protons 3) 56 protons
Number of Electrons in An Atom An atom Of an element is electrically neutral; the net charge of an atom is zero. Has an equal number of protons and electrons. number of protons = number of electrons Of aluminum has 13 protons and 13 electrons. The net charge is zero. 13 protons (13+) + 13 electrons (13 -) = 0
Mass Number The mass number Represents the number of particles in the nucleus. Is equal to the TABLE 2.7 Number of protons + Number of neutrons
Atomic Models
Learning Check An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 30 2) 35 3) 65 B. How many neutrons are in the zinc atom? 1) 30 2) 35 3) 65 C. What is the mass number of a zinc atom that has 37 neutrons? 1) 37 2) 65 3) 67
Learning Check An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is 1) 14 2) 16 3) 34 C. The element is 1) Si 2) Ca 3) Se
Isotopes Isotopes Are atoms of the same element that have different mass numbers. Have the same number of protons, but different numbers of neutrons.
Nuclear Symbols For an atom, the nuclear symbol gives the number of Protons (p + ) Neutrons (n) Electrons (e - ) 16 31 65 O P Zn 8 15 30 8 p + 15 p + 30 p + 8 n 16 n 35 n 8 e - 15 e - 30 e -
Learning Check Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of the following. 12 C 13 C 14 C 6 6 6 protons neutrons electrons
Learning Check Write the nuclear symbols for atoms with the following subatomic particles: A. 8 p +, 8n, 8e - B. 17p +, 20n, 17e - C. 47p +, 60 n, 47 e -
Solution A. 8p +, 8n, 8e - 8 16 O B. 17p +, 20 n, 17e - 37 Cl 17 C. 47p +, 60n, 47e - 107 Ag 47
Learning Check 1. Which of the following pairs are isotopes of the same element? 2. In which of the following pairs do both atoms have 8 neutrons? A. 15 X 15 X 8 7 C. 15 X 16 X 7 8 B. 12 X 14 X 6 6
Solution B. 12 X 14 X 6 6 Both nuclear symbols represent isotopes of carbon with six protons each, but one has 6 neutrons and the other has 8. C. 15 X 16 X 7 8 An atom of nitrogen (7) and an atom of oxygen (8) each have 8 neutrons.
Isotopes of Magnesium In naturally occurring magnesium, there are three Isotopes isotopes. of Mg Atomic Mass 23.99 24.98 25.98 % abundance 78.70 10.13 11.17 24 Mg 25 Mg 26 Mg 12 12 12
Isotopes of Sulfur A sample of naturally occurring sulfur contains several isotopes with the following abundances Isotope % abundance 32 S 95.02 33 S 0.75 34 S 4.21 36 S 0.02 32 S, 33 S, 34 S, 36 S 16 16 16 16
Atomic Mass The atomic mass of an element Is listed below the symbol of each element on the periodic table. Na 22.99 Gives the mass of an average atom of each element compared to 12 C. Is not the same as the mass number.
Some Elements and Their Atomic Mass Most elements have two or more isotopes that contribute to the atomic mass of that element. TABLE 2.9 32.07 amu
Atomic Mass for Cl The atomic mass of chlorine is Based on all naturally occurring Cl isotopes. Not a whole number. The weighted average of 35 Cl and 37 Cl.
Learning Check Using the periodic table, give the atomic mass of each element: A. calcium B. aluminum C. lead D. barium E. iron
Solution Using the periodic table, give the atomic mass of each element: A. calcium 40.08 amu B. aluminum 26.98 amu C. lead 207.2 amu D. barium 137.3 amu E. iron 55.85 amu
Chapter 2 Atoms and Elements 2.7 Electron Energy Levels Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
Electromagnetic Radiation Electromagnetic radiation Is energy that travels as waves through space. Is described in terms of wavelength and frequency. Moves at the speed of light in a vacuum. speed of light = 3.0 x 10 8 m/s
Electromagnetic Spectrum The electromagnetic spectrum Arranges forms of energy from lower to higher. Arranges energy from longer to shorter wavelengths. Shows visible light with wavelengths from 700-400 nm.
Electron Energy Levels Electrons are arranged in specific energy levels that Are labeled n = 1, n = 2, n = 3, and so on. Increase in energy as n increases. Have the electrons with the lowest energy in the first energy level (n=1)closest to the nucleus. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
Energy Level Changes An electron absorbs energy to jump to a higher energy level. When an electron falls to a lower energy level, energy is emitted. In the visible range, the emitted energy appears as a color. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
Energy Emitted
Learning Check In each of the following energy level changes, indicate if energy is 1) absorbed 2) emitted 3) not changed A. An electron moves from the first energy level (n =1 ) to the third energy level (n = 3). B. An electron falls from the third energy level to the second energy level. C. An electron moves within the third energy level.
Solution A. An electron in an atom moves from the first energy level (n =1 ) to the third energy level (n = 3). 1) absorbed B. An electron falls from the third energy level to the second energy level. 2) emitted C. An electron moves within the third energy level. 3) not changed
Energy Diagram for Sublevels