Chapter 4 Table of Contents Section 1 Development of the Atomic Theory

Chapter 4 Table of Contents Section 1 Development of the Atomic Theory
Atoms Table of Contents Section 1 Development of the Atomic Theory Section 2 The Atom

Section 1 Development of the Atomic Theory
Chapter 4 Objectives Describe some of the experiments that led to the current atomic theory. Compare the different models of the atom. Explain how the atomic theory has changed as scientists have discovered new information about the atom.

The Beginning of the Atomic Theory
Section 1 Development of the Atomic Theory Chapter 4 The Beginning of the Atomic Theory Early Greeks proposed matter comprised of: Fire, earth, water, air Democritus, a Greek philosopher Around 440 BCE thought that you could have a particle that could not be cut. Called it an atomos. Aristotle, another Greek philosopher, disagreed Basis: What holds the atoms together? Democritus couldn’t answer the question

The Beginning of the Atomic Theory, continued
Section 1 Development of the Atomic Theory Chapter 4 The Beginning of the Atomic Theory, continued Democritus was right: Matter is made of particles, called atoms. atom is the smallest particle into which an element can be divided and still be the same substance.

2000 Years of Psuedochemistry
Alchemy Most alchemists were mystics or fakes Obsessed with turning cheap lead into expensive gold But: Discovered many elements Learned how to prepare mineral acids

First True Chemist Robert Boyle (1627-1691)
The Skeptical Chemist (1661) First quantitative experiments Defined an element if it could not be broken down into a simpler substance Based on experience in metallurgy Boyle still thought you could turn one metal into another

The Problem with Combustion
17th & 18th Centuries dealt with issues of ‘combustion’ Georg Stall, Germany, Suggested “phlogiston” flowed out of burning material Burning in a closed container stopped because the jar became saturated with ‘phlogiston’. Joseph Priestly, English, Discovered oxygen Proposed that oxygen was ‘dephlogisticated air’

Combustion & Fundamental Laws
By late 18th century, combustion had been studied. Carbon dioxide, nitrogen, oxygen had been discovered. Many other element discovered. Antoine Lavoisier, French ( ) Based on experiments postulated “Mass is neither created or destroyed” Law of Conservation of Mass Proved combustion involved oxygen, not ‘phlogiston’

What is Proust’s Law? Law of Definite Proportion
A given compound always contains exactly the same proportion of elements by mass.

What is the Law of Multiple Proportions?
When 2 elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers

Example: Nitrogen and Oxygen. What is the ratio of masses of Nitrogen that combines with oxygen: Compound A: 1.750g Compound B: g Compound C: g

Example Answers: Ratios of Element 2: A/B = 1.750/0.875 = 2/1
B/C = 0.875/ = 2/1 A/C = 1.750/ = 4/1

Dalton’s Atomic Theory Based on Experiments
Section 1 Development of the Atomic Theory Chapter 4 Dalton’s Atomic Theory Based on Experiments John Dalton published his atomic theory in 1803. His theory stated all substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed. Atoms of the same element are exactly alike, and atoms of different elements are different. Atoms join with other atoms to make new substances. Not Quite Correct Prepared first table of atomic masses

Keys to Atomic Formulas
Actually published by: Joseph Gay-Lussac, French, Measured volumes of gasses that reacted together Amadeo Avogadro, Italian, Interpreted Gay-Lussac results by proposing that at the same temperature and pressure, equal volumes of different gasses contain the same number of particles Not accepted for 50 years.

Definition of an Atom The smallest particle of an element that retains the properties of the element How small? World population in 2000 was about 6 billion One penny contains 5 billion times more atoms

Only with ‘scanning tunneling microscopes
Can we See Atoms Only with ‘scanning tunneling microscopes Nanotechnolgy manipulates individual atoms to make very small devices Next generation of computers will have wires one or two atoms wide (smaller, less power, less heat)

Pictures

Sub-Atomic Particles and Nuclear Atoms
Chapter 4, Section 2 Sub-Atomic Particles and Nuclear Atoms

Accidental Discoveries?
Does anything get discovered by accident? Yes Vulcanized rubber Aspartame (Nutrasweet) Electrons

Self Taught Class Who it is? When? What did He do?
How was it important to understanding the Atom?

Discovering the Electron
Sir William Crookes, early 1800’s What is the relationship between electricity and matter? Static from combs Static from carpets Recent inventions: Vacuum pump Cathode Ray Tube (CRT) Cathode (+) at one end of vacuum tube Anode (-) at other end

Crookes was in a darkened room. Noticed flashes of light within his tube (coated inside with light producing chemicals) Further work: “rays” going from cathode end to anode end (hence cathode ray tube) Cathode Ray Tube is basis for TV and computer monitors

Crookes CRT

Thompson’s Discovery of Electrons
Section 1 Development of the Atomic Theory Chapter 4 Thompson’s Discovery of Electrons Thompson experimented with a cathode-ray tube. He discovered negatively charged particles known as electrons.

Chapter 4 Thompson’s Cathode-Ray Tube Experiment
Section 1 Development of the Atomic Theory Chapter 4 Thompson’s Cathode-Ray Tube Experiment

Thompson’s Model Thompson proposed a new model of the atom.
electrons are mixed throughout an atom, like plums in a pudding (or raisins in raisin bread). Called Plum Pudding model

By late 1800’s Further work led to conclusion that: Cathode Rays were actually stream of charged particles Particles carried a negative charge These particles were found in all matter Particles were called ‘electrons’ CRISIS: Dalton was wrong, Atoms did have smaller particles

1909 – Robert Millikin (US) Determined charge of an electron Determined mass of an electron 9.11 X 10-28g = 1/1840 mass of a hydrogen atom

Rutherford’s Atomic “Shooting Gallery”
Section 1 Development of the Atomic Theory Chapter 4 Rutherford’s Atomic “Shooting Gallery” In 1909, Ernest Rutherford aimed a beam of small, positively charged particles at a thin sheet of gold foil. The next slide shows his experiment. Surprising Results Rutherford expected the particles to pass right through the gold in a straight line. To Rutherford’s great surprise, some of the particles were deflected.

Chapter 4 Rutherford’s Gold-Foil Experiment
Section 1 Development of the Atomic Theory Chapter 4 Rutherford’s Gold-Foil Experiment

The Nuclear Atom Rutherford concluded Thompson was wrong:
There must be a tiny, very dense region of the atom, called the ‘nucleus’ Must be very dense (like all the mass of an atom) Must have a positive charge to keep the electrons attracted Between atoms and nucleus must be a lot of empty space How Much? Nucleus the size of a quarter has electrons over 1 mile away

The Nuclear Atom Rutherford Model Explains:
Why alpha particles (electrons) bend on their way through nucleus Why some alpha particles are deflected at very sharp angles Did not explain all of the Atom’s Mass

Where Are the Electrons?
Section 1 Development of the Atomic Theory Chapter 4 Where Are the Electrons? Far from the Nucleus Rutherford proposed that in the center of the atom is a tiny, positively charged part called the nucleus.

Discovering Protons and Neutrons
1919 Rutherford Later Experiments Concluded nucleus must contain positive particles called ‘protons’ With co-worker James Chadwick showed nucleus also contained a neutral particle called ‘neutron’ Mass of neutron almost same as proton No electrical charge

Summary to Date Atoms are composed of:
Protons (+ charge, 1 mass unit) Neutrons (no charge, 1 mass unit) Electrons (- charge, very little mass) Most of an atom’s size is electrons moving through empty space Electrons are held to nucleus by +/- electrical attraction

Summary of Models

Section 3 How Atoms Differ

Chapter 4 Objectives Describe the size of an atom.
Section 3 The Atom Objectives Describe the size of an atom. Name the parts of an atom. State how atoms of different elements differ. State how isotopes differ. Calculate atomic masses. Describe the role of electrons in an atom.

Chapter 4 How Small Is an Atom?
Section 3 The Atom How Small Is an Atom? Scientists know that aluminum is made of average-sized atoms. An aluminum atom has a diameter of about cm.

Chapter 4 What Is an Atom Made Of? The Nucleus
Section 3 The Atom What Is an Atom Made Of? The Nucleus Protons are positively charged particles Neutrons have no electrical charge. Outside the Nucleus Electrons are the negatively charged particles in electron clouds.

Chapter 4 Section 3 The Atom Parts of an Atom

Chapter 4 What Is an Atom Made Of? The Nucleus
Section 3 The Atom What Is an Atom Made Of? The Nucleus positively charged particles called protons. Each proton has a mass of about 1 amu. The SI unit used to express the masses of particles in atoms is the atomic mass unit (amu). Neutrons In nucleus that have no electrical charge. Neutrons have a mass of about 1 amu

What Is an Atom Made Of?, continued
Chapter 4 Section 3 The Atom What Is an Atom Made Of?, continued Outside the Nucleus Electrons are negatively charged particles in atoms. Electrons are found around the nucleus within electron clouds. The charges of protons and electrons are opposite but equal, so their charges cancel out. Because an atom has no overall charge, it is neutral.

How Do Atoms of Different Elements Differ?
Chapter 4 Section 2 The Atom How Do Atoms of Different Elements Differ? Starting Simply The hydrogen atom has one proton and one electron. The helium atom has two protons, two neutrons, and two electrons.

How Do Atoms of Different Elements Differ?, continued
Chapter 4 Section 2 The Atom How Do Atoms of Different Elements Differ?, continued Building Bigger Atoms For bigger atoms, simply add protons, neutrons, and electrons. Protons and Atomic Number atomic number = number of protons Atomic mass = number of protons + number of neutrons

Atoms Atoms are electrically neutral, so:
Protons = Electrons = Atomic Number Neutrons does not have a specific relationship to protons Atomic Mass = Protons + Neutrons Electrons have almost no mass

Reading the Periodic Table
Name Atomic Number Symbol Avg. Atomic Mass

Periodic Table

Reading the Periodic Table - Quiz
How Many Protons are in Boron (B) Platinum (Pt) How many electrons are in: Radium (Ra) Magnesium (Mg) An element contains 66 electrons. What is it? An element contains 14 protons. What is it? 5 78 88 12 Dysprosium Silicon

Calculating Protons & Neutrons
Element Atomic Mass Atomic Number Protons Neutrons Electrons B 24.305 8 19 11 5 5 6 5 Mg 12 12 12 12 16 8 8 8 O K 39 19 20 19

Why are Atomic Masses not Even Numbers?
What is the atomic mass of Carbon (C)? 12.011 What is the atomic mass of Chlorine (Cl)? 35.453 If Protons = 1 and Neutrons = 1, where does the .453 come from?

Why not whole Numbers? Mass of both Neutron and Proton is 1.67x10-24
Small units/hard to work with Scientists set standard based on Carbon 12 1 atomic mass unit = 1/12 of carbon atom So Silicon is instead of 30 This is only part of the reason…

Chapter 4 Section 2 The Atom Isotopes have the same number of protons but different numbers of neutrons.

Isotopes Another thing Dalton got wrong
Isotopes occur as a mixture in nature Example Potassium: 93.25% have 20 neutrons 6.7302% have 22 neutrons 0.117% have 21 neutrons ALL have 19 Protons and 19 Electrons Isotopes have the Same Atomic Number but a Different Atomic Mass

Chapter 4 Isotopes, continued Telling Isotopes Apart
Section 2 The Atom Isotopes, continued Telling Isotopes Apart by its mass number. How Many Neutrons? Calculate Neutrons = Atomic Mass – Atomic number Properties of Isotopes An unstable atom has a nucleus that will change over time. This type is radioactive.

Chapter 4 Section 2 The Atom Isotopes, continued

Chapter 4 Isotopes, continued Naming Isotopes
Section 2 The Atom Isotopes, continued Naming Isotopes Write the name of the element followed by a hyphen and the mass number. Example: C-14 is Carbon 14 (8 neutrons) instead of 6 (C-12 is normal) Calculating the Mass of an Element The atomic mass of an element is the weighted average of the masses of the isotopes of that element.

Chapter 4 Section 3 The Atom Math Focus

Unstable Nuclei and Radioactive Decay
Section 4.4

Radioactivity Some substances spontaneously emit radiation – radioactivity The rays and particles emitted are called “radiation”. Radioactive elements change their identity – they can change into another element They do this because the nuclei are unstable Changes to atom’s nucleus is called a nuclear reaction Something else Dalton got wrong.

Radioactive Decay Radioactive elements emit energy as radiation
This is called ‘radioactive decay’ Unstable atoms undergo radioactive decay until they form stable atoms

Types of Radiation Alpha Radiation – emitting a positively charged particle - α Beta Radiation – emitting a negatively charged particle - β Gamma Radiation – High energy radiation with no mass - γ

α Alpha Radiation Alpha radiation Made up of Alpha particles
Alpha particles have 2 protons, 2 neutrons Alpha particles have a 2+ charge α

+ Nuclear Equations Nuclear Equations
transmutation - an element is transformed into a new element. This can occur by natural or artificial means. loss of an a particle radium is emitting an a particle +

Beta Radiation Beta Radiation is fast moving electrons
Attracted to positive charged items Charge is 1-

Gamma Radiation High Energy radiation with no mass No charge
Usually accompany alpha and beta radiation Account for most of the energy lost during radioactive decay

The Important Role of Electrons
Chapter 4 Section 2 The Atom The Important Role of Electrons The electrons at the outer layer of the atom are important to the atom’s interactions with its environment. Energy Levels Each electron cloud exists at a certain energy level.

The Important Role of Electrons, continued
Chapter 4 Section 2 The Atom The Important Role of Electrons, continued Valence Electrons Outer layer (or cloud or energy level) of the atom are Valence Electrons Most likely to be lost if the atom loses electrons. The outermost energy level is also where the atom is most likely to gain electrons. Valence Electrons Are The BONDING Agents Gaining/losing/sharing electrons results in chemical bonds

Ions: Electron-Proton Imbalance
Chemical Bonds Chemical bonds are made by gaining, losing, or sharing electrons to fill up the outer electron shells Ions: Electron-Proton Imbalance Ions are formed when an atom loses or gains electrons, leaving an unequal number of protons and electrons.

What Makes Nuclear Stability?
Biggest factor is neutron to proton ratio Will be discussed in Chapter 25 Atoms with either too many or too few neutrons will be radioactive

Review Explain how unstable atoms gain stability? Atoms gain stability by losing energy as emitted radiation. Complete the following table: Particle Symbol Mass (amu) Charge α β γ 4 2 He +2 4 -1 β 1/1840 -1 γ

He β γ Review α β γ Particle Symbol Mass (amu) Charge 4 +2 1/1840 -1 4
4 2 He -1 β γ

Review Classify each as a chemical reaction, nuclear reaction, or neither Thorium emits a beta particle: Nuclear Two atoms share electrons to form a bond: Chemical A sample of pure sulfur emits heat as it slowly cools: Neither A piece of iron rusts: chemical

Chapter 4 Concept Mapping
Atoms Concept Mapping Use the terms below to complete the concept map on the next slide. nucleus mass number isotopes protons atoms electrons atomic number neutrons

Chapter 4 Atoms

End of Chapter 4 Show

Chapter 4 Standardized Test Preparation FCAT For the following questions, write your answers on a separate sheet of paper.

Chapter 4 Standardized Test Preparation 1. British chemist and schoolteacher John Dalton published a theory that defined atoms in Included in his theory was the idea that atoms are small particles which cannot be divided. One of the first major challenges to this theory came nearly 100 years later. Another British scientist, J.J. Thomson, created an experiment using a cathode-ray tube and discovered the existence of negatively charged subatomic particles. What was the effect of this new information? Continued on next slide

Chapter 4 Question 1, continued
Standardized Test Preparation Question 1, continued A. Dalton’s theory was not changed and is still believed to be true. B. Dalton’s theory had to be modified in response to the new information. C. Two different theories of atoms were developed and used by different scientists. D. Thomson’s experiment was changed so that its results matched Dalton’s theory.

Chapter 4 Standardized Test Preparation 2. The illustration below shows a model of an isotope of boron. What is the mass of the isotope shown? F. 5 G. 10 H. 11 I. 16

Chapter 4 3. What is the difference between an isotope and an ion?
Standardized Test Preparation 3. What is the difference between an isotope and an ion? A. An isotope is an atom that has a different number of electrons than other atoms of the same element have. An ion is a particle that has an equal number of protons and neutrons. B. An isotope is an atom that has a different number of protons than other atoms of the same element have. An ion is a particle that has an equal number of protons and electrons. C. An isotope is an atom that has a different number of neutrons than other atoms of the same element have. An ion is a particle that has an unequal number of protons and electrons. D. An isotope is an atom that has a different number of protons than other atoms of the same element have. An ion is a particle that has an unequal number of protons and electrons.

Chapter 4 Standardized Test Preparation 4. British scientist Ernest Rutherford proposed a new model of the atom in The diagram below shows his model of the atom. Continued on next slide

Standardized Test Preparation Question 4, continued 4. What did this model add to atomic theory? F. the idea that an atom has a dense, negatively charged nucleus with electrons surrounding the nucleus at a distance G. the idea that an atom has a dense, positively charged nucleus with electrons surrounding the nucleus at a distance H. the idea that an atom has a dense, neutrally charged nucleus with electrons surrounding the nucleus in an electron cloud I. the idea that an atom has a dense, positively charged nucleus with electrons surrounding the nucleus in an electron cloud

Chapter 4 5. Which one of the following is true of a neutron?
Standardized Test Preparation 5. Which one of the following is true of a neutron? A. A neutron has half the mass of a proton. B. A neutron has the same mass as an electron. C. A neutron is a little more massive than a proton. D. A neutron is a little more massive than an electron.

Chapter 4 Standardized Test Preparation 6. Austrian physicist Erwin Schrödinger and German physicist Werner Heisenberg expanded atomic theory in the 20th century. They accepted some of the work of earlier scientists, but they added to atomic theory with new ideas about electrons. They did not agree with Neils Bohr’s model that had electrons moving in definite paths around the nucleus of an atom. Schrödinger and Heisenberg concluded that one cannot know exactly where electrons are in an atom. One can only predict where electrons are likely to be found. Continued on next slide

Standardized Test Preparation Question 6, continued 6. What was one of the main contributions of Schrödinger and Heisenberg to atomic theory? Current theory identifies regions where electrons are likely to be found. What are these regions called?

Standardized Test Preparation Question 6, continued 6. What was one of the main contributions of Schrödinger and Heisenberg to atomic theory? Current theory identifies regions where electrons are likely to be found. What are these regions called? Full credit answers should include the following points: One of the main contributions of Schrödinger and Heisenberg was the idea that electrons do not travel in definite paths around the nucleus. Electron clouds are the regions where electrons are likely to be found, according to current atomic theory.

Chapter 4 Thompson’s Cathode-Ray Tube Experiment
Section 1 Development of the Atomic Theory Chapter 4 Thompson’s Cathode-Ray Tube Experiment

Chapter 4 Rutherford’s Gold-Foil Experiment
Section 1 Development of the Atomic Theory Chapter 4 Rutherford’s Gold-Foil Experiment

Section 1 Development of the Atomic Theory
Chapter 4

Chapter 4 Section 2 The Atom Parts of an Atom

Chapter 4 Section 2 The Atom

Chapter 4 Standardized Test Preparation

Chapter 4 Section 2 The Atom Math Focus

Comparing Models of the Atom
Section 1 Development of the Atomic Theory Chapter 4 Comparing Models of the Atom

Where Are the Electrons?, continued
Section 1 Development of the Atomic Theory Chapter 4 Where Are the Electrons?, continued The Modern Atomic Theory According to the current theory, there are regions inside the atom where electrons are likely to found. These regions are called electron clouds.

Review Atoms are made of protons, neutrons, and electrons
Protons: Mass = 1 amu, charge = +1 Location: nucleus Neutrons: Mass = 1 amu, charge = 0 Electrons: Mass = almost 0, charge = -1 Location: Outside nucleus, far away

Review

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Chapter 4 Table of Contents Section 1 Development of the Atomic Theory

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