Internal Structure of an Atom, Ions and Isotopes

Transcription

1 Internal Structure of an Atom, Ions and Isotopes Electrons, Protons, Neutrons, Ions, Isotopes, Metals & Non-metals, Ions, Periodic Table, Thompson s Experiment, Rutherford s Experiment, Chadwick s Experiment, Atomic Number, Atomic Mass, Mass Number

2 The Beginnings of Atomic Theory Who came up with the first theory of atoms? In the fourth century BCE, the Greek philosopher Democritus suggested that the universe was made of indivisible units called atoms. Democritus did not have evidence for his atomic theory. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

3 ..\..\..\..\Videos\John Dalton's Atomic Theory.mp4 Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

4 Dalton agreed with Democritus: Elements are made up of atoms. Atoms cannot be divided, created, or destroyed. What did Dalton add to the atomic theory? According to Dalton, 1. All atoms of a given element were exactly alike, 2. Atoms of different elements could join to form compounds. (This joining is called a chemical reaction.) 3. The elements join in definite proportions or ratios Example Water is always 2 parts hydrogen and 1 part oxygen, H 2 O Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

5 Thomson s Model of the Atom How did Thomson discover the electron? Thomson s cathode-ray tube experiment suggested that cathode rays were made of negatively charged particles that came from inside atoms.

6 Thomson s Model of the Atom, continued Thomson developed the plum-pudding model. In his cathode-ray tube experiment, Thomson had discovered electrons. electron: a subatomic particle that has a negative charge Thomson s plum-pudding model: electrons are spread throughout the atom, like blueberries in a muffin

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8 The Experiment and data A paddle wheel placed in the path of the cathode ray moves away from the negatively charged cathode and toward the positively charged anode

9 Data/ Results The green ray bent away from a negative charge and a negative magnetic field and towards positive fields. No matter what gas was used the ray spun the paddle wheel and bent away from negative towards positive. Furthermore, experimental evidence showed atoms to be electrically neutral (they would not be deflected by negative or positive charges)

10 Cathode Ray The cathode ray is attracted to a positive electrical charge and repelled by a positive electrical charge. Thus the ray must be negative. When cathode rays hit a paddle wheel, the wheel spins and moves. Thus the ray is made out of particles. All elements produce cathode rays in a cathode ray tube Thus all matter contains the negatively charged particles that make up a cathode ray. Matter is made up of atoms thus the cathode ray particles are a component of an atom called electrons A cathode ray is a stream of electrons.

11 Chapter 1 Section 3 Elements Types of Elements Gold, copper, and aluminum are metals

12 Chapter 1 Section 3 Elements Types of Elements Metals A metal is an element that is a good electrical conductor of electrical charge and a good heat conductor. most are solids at room temperature malleable - they can be hammered or rolled into thin sheets ductile - they can be drawn into a fine wire

13 Chapter 1 Section 3 Elements Types of Elements Nonmetals A nonmetal is an element that is a poor conductor of electrical charge and a poor conductor of heat. Properties of nonmetals many are gases solids are brittle

14 Chapter 1 Section 3 Elements Types of Elements Various nonmetal elements (a) carbon, (b) sulfur, (c) phosphorus, and (d) iodine

15 Atomic number Symbol Molar mass & atomic mass Periodic Table Rows are called periods. There are 7 periods on the periodic table. Columns are called groups. There are 18 groups on the periodic table. Read the table like a book, from left to right. Metals lose electrons become cations (+) Non-metals gain electrons become anions (-) Metals to the left of the stairs, non-metals to the right.

16 Metals are to the left of the stairs (exception hydrogen which is a gas. Non-metals are to the right of the stairs. Non-metals gain electrons and become negative. Metals lose electrons and become positive ions.

17 Metals (except H, which is is a non-metal) Metalloids Non-metals (includes the Nobel Gasses) Noble Gases Metals to the left of the stairs, non-metals to the right.

18 Ions An ion is an atom or group atoms that has a positive or negative charge. A positive ion is known as a cation. A cation has more positive charge than negitive charge Thus it has a positive charge. A negative ion is known as an anion. An anion has more negative charge than positive charge Thus it has a negative charge. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

19 Ions An ion is an atom or group atoms that has a positive or negative charge. A positive ion is known as a cation. If an atom loses an electron it has more protons than electrons. Thus it has a positive charge A negative ion is known as an anion. If an atom gains an electron it has more electrons than protons. Thus it has a negative charge. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

20 1+, 2+ Ion charges Metals (+) Noble Gases; No ions 3+, 4-,3-,2-,1- Transition metals Metalloids Metals (H is a non-metal but it Usually forms positive(1+) ion Non-metals (excluding the Noble Gases) gain e-, become ions (anions)

21 1+ 2+ Ion Charges Metals lose electrons to become positive ions (cations) Non-metals (excluding the Noble Gases) gain electrons to become negative ions (anions) Metals (H is a non-metal) Non-metals (includes the Noble Gases)

22 Ions An ion is an atom or group atoms that has a positive or negative charge. A positive ion is known as a cation. A cation has more positive charge than negitive charge Thus it has a positive charge. A negative ion is known as an anion. An anion has more negative charge than positive charge Thus it has a negative charge. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

23 Hydrogen is a non-metal Elements from opposite ends of the table usually form ionic compounds. Metal ion + non-metal ion = ionic compounds Positive & negative ions attract & form ionic compounds. Ionic compounds do not conduct electricity in the solid state; but do conduct in the liquid state or when dissolved. Ionic compounds have very high melting & boiling points and are very hard.

24 Molecular compounds are made from non-metals and do not involve ions. The compound form by sharing electrons. These compounds are poor conductors of heat and electricity. The have lower melting points and boiling points than ionic compounds. Some examples include H 2 O, CO 2, NH 3 (ammonia). an ionic bond.

25 Ernest Rutherford

26 In 1911 Ernest Rutherford decided to test Thompson s theory that states the atom is net neutral at any given point He did this by shooting positively charged particles, called alpha particles, at atoms.

27 Thomson Model of the Atom Thompson theory states the atom is net neutral at any given point.

28 Rutherford s 1st hypothesis: the positively charged alpha particles will scatter per the figure because the Thompson theory states the atom is net neutral at any given point The figure shows how the alpha particle scattering would look like if the Thompson theory was correct.

29 Rutherford s 1st hypothesis: the positively charged alpha particles will scatter per figure 8-13 because the Thompson theory states the atom is net neutral at any given point. Rutherford s experiment gave a result that hypothesis could not explain.

30 Figure 8-13 show how the alpha particle scattering would look like if the Thompson theory was correct. Figure 8-14 show the actual results of the alpha particle scattering experiment. Rutherford s 2nd hypothesis: An atom has a very small positively charged nucleus which is surrounded by electrons.

31 Rutherford s Model of the Atom, continued Rutherford conducted the gold-foil experiment. Rutherford discovered the nucleus. nucleus: an atom s central region, which is made up of protons and neutrons

32 Rutherford s Conclusions All of an atom s positive charge is concentrated in a very small core at the atom s center, which Rutherford called the nucleus. Almost all the mass of the atom is in the nucleus. The negatively charged electrons move around the nucleus.

33 Rutherford s Conclusions Also noted that if the entire atom is the size of a football stadium, the nucleus would be about the size of a marble sitting on the 50-yd line with almost all the mass in the nucleus. Hundred times smaller than shown

34 The Discovery of the Neutron Discovered in 1932 by James Chadwick (England ) Chadwick bombarded alpha particles(helium nuclei) at Beryllium. Neutrons were emitted and in turn hit paraffin and ejected protons from the paraffin..

35 Discovery of the Neutron Chadwick bombarded alpha particles(helium nuclei) at Beryllium. Neutrons were emitted and in turn hit paraffin and ejected protons from the paraffin.

36 Discovery of the Neutron James Chadwick discovered a neutron Is a Unique Particle, (not an electron or a proton ) Is essentially the same mass as an Proton Has no Charge With the Proton, Makes up the Nucleus

37 Chapter 3 Section 2 The Structure of the Atom Properties of Subatomic Particles Charge -1.6 x Clb amu kg 9.0 x x Clb 0 coulombs (Clb) 1.70 x x 10-27

38 Chapter 4 Section 2 The Structure of the Atom Properties of Subatomic Particles Charge of a proton = +1.6 x Coulombs Charge of an electron = -1.6 x Coulombs Relative Mass or Location Outside the nucleus p Inside the nucleus Inside the nucleus Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

39 Ions An ion is an atom or group atoms that has a positive or negative charge. A positive ion is known as a cation. If an atom loses an electron it has more protons than electrons. Thus it has a positive charge A negative ion is known as an anion. If an atom gains an electron it has more electrons than protons. Thus it has a negative charge. Charge = (p + ) + (-e - ) p+ = number of protons as a positive number Chapter menu Resources -e - = number of electrons as a negative number Copyright by Holt, Rinehart and Winston. All rights reserved.

40 Metals lose electrons and become positive ions. 11 electrons 10 electrons

41 11 e - 10 e - Loss of e - = positive ion Charge = (p + ) (e - ) (+11) + (-10) = +1

42 9 e - 10 e - Gain of e - = negitive ion Charge = (p + ) (e - ) Charge = (+9) - (10) = -1

43 Non metals gain electrons become negative ions 8 electrons 10 electrons Gaining 2 e - = negative ion that is 2 negative + 2 e -

44 8 electrons Non metals gain electrons become negative ions 10 electrons + 2 e - Charge = (p + ) (e - ) Charge = (+8) (10) = -2

45 Atoms Section 2 What Is in an Atom? Each element has a unique number of protons. Atoms have no overall charge. Because there is an equal number of protons and electrons, the charges cancel out. The electric force holds the atom together. Positive protons are attracted to negative electrons by the electric force.

46 The atomic number is the number of protons. Chapter 3 The atomic number is the smaller whole number. The atomic number can be written on the top or the bottom of the square. Atomic number (Z) = 8 Z is the symbol for atomic number Neutrons 8 Note that atoms have equal numbers of protons and electrons. Atoms are electrically neutral. Thus, the atomic number is also the number of the atom s

47 Atomic Number What do atoms of an element have in common with other atoms of the same element? The number of protons determines each element s identity. atomic number: the number of protons in the nucleus of an atom Atoms of each element have the same number of protons, but they can have different numbers of neutrons.

48 Chapter 4 Section 3 Counting Atoms Atomic Number Atoms of different elements have different numbers of protons. Atoms of the same element all have the same number of protons. The atomic number of an element is the number of protons in the nucleus of that element. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

49 Atoms Section 2 Mass Number atomic number (z): the number of protons in the nucleus of an atom The mass number equals the total number of subatomic particles in the nucleus. mass number (m): the sum of the numbers of protons and neutrons in the nucleus of an atom m = nº + p + Note: mass number is not found on the Periodic Table

50 Atoms Section 2 Mass Number is the number of protons plus the number of neutrons m n º = 5 nº + p+ = m = 10 m = 10 = p + = 5

51 Chapter 3 Section 3 Counting Atoms Isotopes Isotopes are atoms of the same element that have different masses. The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons. Most of the elements consist of mixtures of isotopes. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

52 Isotopes of Hydrogen: You are breathing in all of these isotopes with every breath you take because hydrogen is in the air and elements exist as mixtures of their isotopes.

53 Chapter 4 Section 3 Counting Atoms Isotopes Isotopes are atoms of the same element that have different masses. The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons. Most of the elements consist of mixtures of isotopes. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

54 Atoms Section 2 Isotopes Why do isotopes of the same element (which have the same number of protons) have different atomic masses? Isotopes of an element vary in mass because their numbers of neutrons differ. Elements always naturally exist as a mixture of their isotopes.

55 Designating Isotopes Hyphen notation: The mass number is written with a hyphen after the name of the element. uranium-238 Nuclear symbol: The superscript indicates the mass number (m) and the subscript indicates the atomic number (z) = the number of protons (p) U The general formula for a nuclear symbol is m z X or m p X Where X represents the element s symbol.

56 Chapter 4 Section 3 Counting Atoms Designating Isotopes Hyphen notation: The mass number is written with a hyphen after the name of the element. uranium-238 Nuclear symbol: The superscript indicates the mass number (m) and the subscript indicates the atomic number (z) = the number of protons U Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

57 Atoms Section 2 Isotopes Some isotopes are more common than others. radioisotopes: unstable isotopes that emit radiation and decay into other isotopes The number of neutrons can be calculated. number of neutrons = mass number atomic number

58 Atoms Section 2 Atomic Masses Average atomic mass is a weighted average. Isotope abundance determines the average atomic mass. Example: Chlorine-35 is more abundant than chlorine-37, so chlorine s average atomic mass ( u) is closer to 35 than to 37.

59 Mass Spectrometer Determining the relative mass and the relative abundance of isotopes. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

60 Chapter 4 Section 3 Counting Atoms Isotopes Isotopes are atoms of the same element that have different masses. The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons. Most of the elements consist of mixtures of isotopes. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.