Vocabulary: Objectives: Read Chapter 17; pages:

Transcription

1 Read Chapter 17; pages: Objectives: - Identify the name and symbols of common elements; Identify quarks as subatomic particles of matter; Describe the electron cloud model of the atom; Explain how electrons are arranged in an atom; Compute the atomic mass and mass number of an atom; Identify the components of isotopes; Interpret the average atomic mass of an element; Explain the composition of the periodic table; Use the periodic table to obtain information; Explain what the terms metal, nonmetal, and metalloid mean; Vocabulary: Atom Nucleus Proton Neutron Electron Quark Electron Cloud Period Atomic Number Mass Number Isotope Average Atomic Mass Periodic Table Group Electron dot diagram

2 Properties of Atoms and the Periodic Table PSc.2.1 Understand types, properties, and structure of matter. PSc Classify matter as: homogeneous or heterogeneous; pure substance or mixture; element or compound; metals, nonmetals, or metalloids; solution, colloid, or suspension. PSc Explain the phases of matter and the physical changes that matter undergo. PSc Compare physical and chemical properties of various types of matter. PSc Interpret data presented in Bohr model diagrams and dot diagrams for atom and ions of elements 1 through 18. PSc.2.2 Understand chemical bonding and chemical interactions. PSc Infer valence electrons, oxidation number, and reactivity of an element based on its location in the Periodic Table. PSc Infer the type of chemical bond that occurs, whether covalent, ionic, or metallic, in a given substance. PSc Predict chemical formulas and names for simple compounds based on knowledge of bond formation and naming conventions. PSc Exemplify the laws of conservation of mass by balancing chemical equations. PSc Classify types of reactions such as synthesis, decomposition, single replacement or double replacement. PSc Summarize the characteristics and interactions of acids and bases. PSc.2.3 Understand the role of the nucleus in radiation and radioactivity. PSc Compare nuclear reactions including alpha decay, beta decay, and gamma decay: nuclear fusion and nuclear fission PSc2.3.2 Exemplify the radioactive decay of unstable nuclei using the concept of half-life.

3 CHAPTER 17 Properties of Atoms and the Periodic Table November 2016

4 Structure of the Atom Chemical symbols consist of one capital letter or a capital letter plus one or two smaller letters. Each letter or pair of letters is a chemical symbol, which is a short or abbreviated way to write the name of an element.

5 Some elements are derived from Latin, named in honor of: scientists, places, or for their properties. Other elements are named by following international committee rules. For some elements, the symbol is the first letter of the element s name. Because scientists worldwide use this system, everyone understands what the symbols mean.

6 Atomic Components An element is matter that s composed of one type of atom, which is the smallest piece of matter that still retains the property of the element. Atoms are composed of particles called protons, neutrons, and electrons.

7 Protons and neutrons are found in a small positively charged center of the atom called the nucleus that is surrounded by a cloud containing electrons. Protons are particles with an electrical charge of 1+. Neutrons are neutral particles, that do not have an electrical charge. Electrons are particles with an electrical charge of 1.

8 Quarks Subatomic Particles Scientists confirmed the existence of six uniquely different quarks: Up, Down, Charm, Strange, Bottom and the last discovered is known as a Top quark. Protons and neutrons are made up of these quarks. Scientists theorize that an arrangement of three quarks held together with the strong nuclear force produces a proton. Another arrangement of three quarks produces a neutron.

9 Quarks (Flavors) and Leptons Protons are made up of two UP quarks (2/3 + 2/3 = +4/3) and one Down quark (-1/3), netting a positive one charge; Neutrons are composed of two DOWN Quarks [(-1/3) + (-1/3) = -2/3] and One UP Quark (+2/3), netting a net zero charge. Electrons have a negative charge, equal to and opposite to a proton, and are made from subatomic particles called Leptons.

10 Models Tools for Scientists To study the atom, scientists have developed scaled-up models that they can use to visualize how the atom is constructed. For the model to be useful, it must support all of the information that is known about matter and the behavior of atoms. As more information about the atom is collected, scientists change their models to include the new information.

11 Around 400 B.C. Democritus proposed that elements consisted of tiny, solid particles that count not be subdivided. He called these particles atomos, meaning uncuttable or unbreakable. However, Aristotle, the Greek philosopher, disputed Democritus s theory and proposed that matter was composed of four things: Earth, Air, Water, and Fire. Aristotle s incorrect theory was accepted for about 2,000 years.

12 In the 1800s, John Dalton, an English scientist, was able to offer proof that atoms exist. His model of the atom, was a solid sphere, much like a billiard ball. Yet, his modernization of the atom provided a physical explanation for chemical reactions. English physicist, Joseph John Thomson (1904) inferred from his cathode-ray tube experiment that atoms contained small negatively charged particles. He thought these electrons were evenly embedded throughout a positively charged sphere, much like currants in plum pudding or maybe like chocolate chips in cookie dough.

13 In 1911, British physicist, Ernest Rutherford, proposed that almost all the mass of an atom and all its positive charges were concentrated in a central atomic nucleus surrounded by electrons, traveling in an area which was believed to be empty space. In 1913, Danish physicist Niels Bohr hypothesized that electrons traveled in fixed orbits around the atom s nucleus. James Chadwick, a student of Rutherford, concluded that the nucleus contained positive protons and natural neutrons.

14 The Electron Cloud Model By 1926, scientists had developed the electron cloud model of the atom that is in use today. An electron cloud is the area around the nucleus of an atom where its electrons are most likely found. The electron cloud is 100,000 times larger than the diameter of the nucleus, yet the electron is about 1,836 times smaller than the proton. Because an electron's mass is small and moving so quickly around the nucleus, it is impossible to describe its exact location in an atom.

15 Electron Cloud Structure In a neutral atom, the number of electrons is equal to the number of protons. Therefore, a carbon atom, with an atomic number of six, has six protons and six electrons. The electrons are located in the electron cloud surrounding the nucleus. Scientists have found that electrons within the electron cloud have different amounts of energy. Electrons fill energy levels from the inner levels (closer to the nucleus) to the outer levels (farther from the nucleus). Energy levels nearer the nucleus have lower energy than those levels that are farther away.

16 Electron cloud energy levels are named using numbers one to seven and letters K through Q. The maximum number of electrons in the first four energy levels are shown below: Levels 2 and above, are considered full if they have 8 electrons in their outer most energy level.

17 Masses of Atoms FYI: The name Helium comes from Helios, meaning Sun. Helium was first found in the Sun. Scientists found this element by means of line spectrum.

18 Atomic Mass The nucleus contains most of the mass of the atom because protons and neutrons are far more massive than electrons. Per the table, the mass of a proton is about the same as that of a neutron. If the mass of a nucleus was a textbook, then the mass of an electron would be a paperclip.

19 The Atomic Mass Unit (amu) is the unit of measurement used for atomic particles. The mass of a proton and or neutron is almost equal to one amu and defined as one-twelfth the mass of a carbon atom containing six protons and six neutrons.

20 Protons Identify the Element The number of protons tells you what type of atom you have and vice versa. For example, every nitrogen atom has seven protons; and all atoms with seven protons are nitrogen atoms. The number of protons in an atom is equal to a number called the Atomic Number.

21 If you know the mass number and the atomic number of an atom, you can calculate the number of neutrons. Remember, the mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus of an atom. Ex: Boron atom atomic mass (11) minus atomic number (5) equals six neutrons; Ex: Carbon atom atomic mass (12) minus atomic number (6) equals six neutrons;

22 Isotopes Not all atoms of an element have the same number of neutrons. Atoms of the same element, having different numbers of neutrons, are called isotopes. For example isotopes of boron can have five neutrons or six neutrons. Boron-10 has five protons and five neutrons, whereas, Boron-11 has five protons and six neutrons.

23 The average atomic mass of an element is the weighted-average mass of the mixture of its isotopes. For example, four out of five atoms of boron, are boron-11, and one out of five is boron-10. Find the weighted-average or the average atomic mass of boron, use the following: 0.80(11) (10) = 10.8 amu The avg. atomic mass of the element boron is 10.8 amu; note the avg. atomic mass of boron (see periodic table) is ; very, very, close.

24 The Periodic Table

25 Organizing the Elements Periodic means "repeated in a pattern." In the late 1800s, Dmitri Mendeleev (men dee leave), a Russian chemist, inventor organized the known elements of the time in order of increasing atomic masses. Mendeleev left blank spaces for elements not yet discovered in his periodic table to keep the elements properly lined up according to their chemical properties. From this information, he was able to predict the properties and the mass numbers of new elements that had not yet been discovered.

26 Although Mendeleev s arrangement of elements was successful, several elements, such as nickel and cobalt were misaligned by atomic mass, and as a result, did not match the physical and chemical properties of their groups they were placed in. In 1913, the work of Henry G.J. Moseley, a young English scientist, led to the arrangement of elements based on their increasing atomic numbers, based upon number of protons, from left to right, instead of an arrangement based on atomic masses. This arrangement corrected all of the misalignments, including Cobalt and Nickel. The IUPAC, International Union of Pure and Applied Chemistry, finalized the latest Periodic Table of Elements in 2016.

27 The Atom and the Periodic Table The vertical columns in the periodic table are called Groups or families, and are numbered 1 through 18 and sometimes numbered 1A 8A. Elements in each group have similar chemical and physical properties For example: In Group 11, copper, silver and gold all have similar properties: Each of those metals are shiny metal and are good conductors of electricity and heat.

28 It is important to understand the link between the location on the periodic table, chemical properties, and the structure of the atom. Elements that are in the same group have the same number of electrons in their outer energy level. And it is the number of electrons in the outer energy level that determines the chemical properties of the element.

29 Periods (horizontal rows) The first period has both hydrogen and helium; the atomic number for hydrogen is ONE and has only ONE electron; the atomic number for helium is two, and has two electrons in energy level one; b/c energy level one and only have two electrons, it is complete or full.

30 The second period begins with lithium, which has three electrons two in energy level one and one in energy level two. Neon is the last element in the second period, its atomic number is 10, as a result, there are two electrons in its first energy level, and eight electrons in its the second energy level, which is now full.

31 The third period begins with sodium, which has 11 electrons two in energy level one, 8 in energy level two, and one electron in the third energy level; Argon is the last element in the third period, its atomic number is 18; as a result, there are 2 electrons in its first energy level, 8 electrons in its second energy level, and 8 electrons in the third energy level, which is now full;

32 Elements that are in the same group have the same number of electrons in their outer energy level, which are called valence electrons. These outer electrons are so important in determining the chemical properties of an element that a special way to represent them has been developed. The Lewis Dot Diagram, displays the electrons in the outer energy level and uses the symbol of the element and dots to represent the electrons in the outer energy level.

33 Electron Dot Diagrams Electron dot diagrams are used also to show how the electrons in the outer energy level, or valence electrons are bonded when elements combine to form compounds. Gilbert Newton Lewis ( ) American chemist was instrumental in developing a bonding theory based on the number of electrons in the outermost valence shell of the atom, shown as an electron dot diagram.

34 Same Group Similar Properties The elements in Group 17, are known as the halogens, and have the following electron dot diagram similar to chlorine. All halogens, have seven electrons in their outer most energy levels. Since all the members of a group on the periodic table have the same number of electrons in their outer energy level, group members will undergo chemical reactions in similar ways.

35 Group 17, are halogens, and share a common property to form compounds readily with elements in Group 1. Group 1 elements, like sodium, reacts easily with the element chlorine, which is in Group 17. The result is the compound sodium chloride, or NaCl known as ordinary table salt and or halite.

36 Not all elements will combine readily with other elements. Elements in Group 18 have complete outer energy levels. This special configuration makes Group 18 elements relatively unreactive He Ne Ar Kr

37 Regions on the Periodic Table The periodic table has several regions with specific names. The horizontal rows of elements on the periodic table are called periods. The elements increase by one proton and one electron as you go from left to right in a period, meaning their atomic number increases (L-2-R).

38 Metal Region on the Periodic Table All of the elements in the blue squares are METALS. Most metals exist as solids at room temperature, are shiny, and can be drawn into wires or pounded into sheets, and are good conductors of heat and electricity. Examples of some metals are iron, zinc, and copper.

39 Nonmetal Region on the Periodic Table Those elements on the right side of the periodic table, in yellow, are classified as NONMETALS. Most nonmetals at room temperature are gases and brittle, and poor conductors of both heat and electricity. Some nonmetal examples are oxygen, bromine, and carbon.

40 Metalloid Region on the Periodic Table The elements in Green are METALLOIDS or semiconductors. They have some properties of both metals and nonmetals. Some examples are: boron and silicon.

41 A Growing Family In 1994, scientists at the Heavy-Ion Research Laboratory in Darmstadt, Germany, discovered element 111; its One-isotope, was discovered in 1998, and had a lifespan of sec. In 1996, element 112 was discovered in a laboratory. As of 1998, only one isotope of the element 112 had been found. The life span of this isotope was seconds Both of these elements are produced in the lab by joining smaller atoms into a single atom.

42 A Growing Family cont. On 28 November 2016, the International Union of Pure and Applied Chemistry (IUPAC) approved the name and symbols for the four final elements: Nihonium (Nh), Moscovium (Mc), Tennessine (Ts), and Oganesson (Og), respectively for elements 113, 115, 117, and

43 Elements in the Universe Using the technology that is available today, scientists are finding the same elements throughout the universe. Many scientists believe that hydrogen and helium are the building blocks for other elements; and when stars go supernova a mixture of elements, including the heavy elements such as iron, are flung into the galaxy. Some of these elements are found only in trace amounts in Earth s crust, and others have been found only in stars.

44 Let s Review

45 Answer : A Which is the smallest piece of matter that still retains the property of the element? a. Atom b. quark c. neutron d. proton

46 Answer : B What particles are found in the nucleus of an atom? A. protons and electrons B. protons and neutrons C. neutrons and electrons D. quarks and electrons

47 Answer : C Which of the following methods would be most useful for describing atoms? A) visualizing with a microscope B) observing in a test tube C) constructing a model D) touching with bare hands

48 Answer : D An atom containing six positive charges and six negative charges has charge. A) a positive B) a negative C) a strong negative D) no net

49 Answer : D Atoms consist of a positively charged center called a(n). A) proton B) neutron C) electron D) nucleus

50 Answer : A Which of the following atomic particles is electrically neutral? A) neutron B) proton C) electron D) positron

51 Answer : C What nineteenth-century English scientist offered proof that atoms existed? A) Aristotle B) Democritus C) John Dalton D) Isaac Newton

52 Answer : B Aristotle believed that matter was and not composed of smaller particles. A) composed of atoms B) uniform throughout C) composed of molecules D) capable of being broken down into smaller parts

53 Answer: B The atomic mass of an element is of that element. A) the average mass of an atom B) the number of protons plus the number of neutrons of an atom C) the number of protons in each atom D) the number of electrons in each atom

54 Answer: D The of an element is the number of of an atom of that element. A) atomic mass, electrons in the nucleus B) mass number, neutrons in the nucleus C) mass number, protons plus neutrons in the outermost energy level D) atomic number, protons in the nucleus

55 Answer : C The of an atom is the number of neutrons plus protons. A) atomic number B) nucleus number C) mass number D) half-life

56 Answer : B are atoms of the same element that have different numbers of neutrons. A) Compounds B) Isotopes C) proton particles D) quarks

57 Answer : B The atomic number of manganese is 25; its mass number is 55. How many neutrons does an atom of manganese have in its nucleus? A) 25 B) 30 C) 55 D) 80

58 Answer : A The mass of an electron is. A) negligible B) the mass of the neutrons plus the mass of the protons C) equal to the mass of a proton D) equal to the mass of the nucleus

59 If a hydrogen atom has 2 neutrons and 1 proton, what is the atomic mass? Atomic Mass = 3 If potassium-40 has 19 protons, what is the atomic number and how many neutrons does it have? Atomic number = 19 neutrons = 21

60 Answer : B The is a chart created by chemists to organize the elements according to repeated changes on properties. A) mass number B) periodic table C) isotope D) metalloid list

61 Answer : D Which of the following best describes the three general groups of elements? A) metals, nonmetals, and noble gases B) metals, metalloids, and synthetics C) solid, liquid, and gas D) metals, metalloids, and nonmetals

62 Answer : A The name of every element can be abbreviated using a. A) chemical symbol B) mass number C) Roman numeral D) Greek letter

63 Answer : D Which of the following is the correct chemical symbol for carbon? A) Ca B) Car C) Crbn D) C

64 Answer : A A(n) is a method of representing atoms and the electrons in their outer energy levels. A) electron dot diagram B) chemical symbol C) chemical formula D) chemical equation

65 The number of which type of particle determines the identity of an element? A) electrons B) neutrons C) protons Answer : C D) photons

66 Answer : D The first proposal that there is a smallest particle beyond which a substance cannot be divided was made by A) Aristotle. B) Mendeleev. C) Thomson. D) Democritus.

67 Answer : B Which of the following is an element that would have similar properties to those of neon? A. Aluminum B. Argon C. Arsenic D. Silver

68 How many outer level electrons do lithium and potassium have? A. 1 Answer : A B. 2 C. 3 D. 4

69 Answer : A How many quarks have been found to exist? A. Six B. Eight C. ten D. twelve

70 How are the elements arranged in the periodic table? Answer The elements are arranged by increasing atomic number and by changes in physical and chemical properties.

71 What do the dots in this electron dot diagram represent? Answer The dots represent the electrons in the outer energy level, called valence electrons.