Chapter 4 Atomic Structure The Periodic Table Section

Chapter 4 “Atomic Structure & The Periodic Table ”

Section 4. 1 Defining the Atom l OBJECTIVES: Explain how the current atomic theory was developed and changed l Describe the modern atomic model of the atom l l Key terms: l atom, electron, nucleus, proton, neutron, energy level, atomic number, atomic mass, isotope

Section 4. 1 Defining the Atom l The Greek philosopher Democritus (460 B. C. – 370 B. C. ) was among the first to suggest the existence of atoms (from the Greek word “atomos”) l He believed that atoms were indivisible and indestructible l His ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method – but just philosophy

John Dalton’s Atom l l During the 19 th century simple laws of chemical reactivity had been observed In 1803 John Dalton proposed the idea of the atom to help explain these observations

John Dalton’s Model l Dalton's theory can be summarized as follows: l l Matter is composed of small particles called atoms. All atoms of an element are identical, but are different from those of any other element. During chemical reactions, atoms are neither created nor destroyed, but are simply rearranged. Atoms always combine in whole number multiples of each other. For example, 1: 1, 1: 2, 2: 3 or 1: 3. Beryllium + Oxygen 1: 1 Hydrogen + Oxygen 2: 1

J. J. Thomson (in 1897) J. J. Thomson discovered that “cathode rays” are… …deflected by electric and magnetic fields electric field lines “cathode rays” Crooke’s tube … (–) particles J. J. Thomson ++++++ – – – electrons phosphorescent screen

Thomson’s Atomic Model J. J. Thomson believed that the electrons were like plums embedded in a positively charged “pudding, ” thus it was called the “plum pudding” model.

Ernest Rutherford’s Gold Foil Experiment - 1911 §Alpha particles were fired at a thin sheet of gold foil § Particles that hit on the detecting screen (film) are recorded

Rutherford’s Findings Most of the particles passed right through § A few particles were deflected § VERY FEW were greatly deflected § Conclusions: a) The nucleus is small b) The nucleus is dense c) The nucleus is positively charged

DISCOVERY OF THE NUCLEUS Rutherford had discovered the atomic nucleus. His proposed model of the atom: - The positive electric charge of an atom is in the nucleus - Most of the mass of the atom is in the nucleus - The nucleus is very small (like a point) - Negative electrons move around the nucleus like planets around the Sun - The negative charges are attracted to the positive nucleus “like gravity” attracts planets - He called this the: "atomic planetary model".

Thomson’s Dalton’s Rutherford’s (also Plum the. Pudding Greek) Model – + + – – + + N + – – – – + +– + 1. Elements are – made –Isof oto pe s! atoms. indivisible particles called not e 2. Atoms of the same element are exactly r a s m Ato e. l b i s i iv alike; in particular, indthey have the same mass.

Recent Atomic Models Max Planck (1900): Proposed that amounts of energy are quantized only certain values are allowed Niels Bohr (1913): e– can possess only certain amounts of energy, and can therefore be only certain distances from nucleus. planetary (Bohr) model e– found here N e– never found here

quantum mechanical model electron cloud model charge cloud model Schroedinger, Pauli, Heisenberg, Dirac (up to 1940): According to the QMM, we never know for certain where the e– are in an atom, but the equations of the QMM tell us the probability that we will find an electron at a certain distance from the nucleus.

History of the Atom Review fire earth air 1. water 2. 3. 4. 5. 6. Democritus (460 B. C. ) The smallest things are atoms, (Aristotle there are only 4 elements) Dalton’s “Billiard ball” model (1803) Atoms are round balls that join in precise ratios (H 2 O not H 3 O Thompson “Plum pudding” model (1897) Negative electrons in a positive “pudding”. Rutherford model (around 1912) Atoms are mostly empty space with a nucleus that has almost 100% of the atom’s mass. Bohr Model (1913): Electrons occur only in certain orbits (in layers like an onion) Quantum Cloud Model: Electrons occur only in certain cloud regions (Erwin Schrödinger and Werner Heisenburg )

l Read Pages 102 – 108 and complete the Introduction to Atoms Review handout. (Due Weds 11/5) l When done start on the Atomic Model Poster Project……….

The Evolution of Atomic Models Project l l l You will work on your own for this project You draw all five models of the atom as it evolved from Democritus to the Quantum Cloud Model The poster must show the following: l l l The historical person who thought of each model (Drawing, name, dates, interesting facts) A accurate picture/drawing of the model The key points/ideas and facts about the model You can use your Physical Science text (chp. 4, pg 102 -106) and/or internet research to help provide historical and scientific facts and detail for your poster On the back of the poster your must draw an accurate Bohr Diagram of Carbon-12

Today’s lesson…… What’s inside an atom?

The Atom l Today we know that there is something more fundamental than earth, water, air, and fire. . . By convention there is color, By convention sweetness, By convention bitterness, But in reality there atoms and space. -Democritus (di MAHK ruh tuhs) ~ 440 B. C. l Around 1900, people thought of atoms as round spheres with bits of electric charge bouncing around inside (remember Thompson & Rutherford? ) l But is the atom really fundamental? Are there basic building blocks that make up an atom?

Today you are going to read and fill in an idea tree using the reading handout on atomic structure

The atom is made up of three fundamental particles The Electron Has a negative charge Mass is almost zero Found in clouds outside the nucleus The Proton Has a positive charge Is in the nucleus Has ~1800 X more mass than an electron The Neutron Has no charge Is in the nucleus Has about the same mass as a proton

The Building Blocks of Atoms: What is inside an atom?

The Building Blocks of Atoms: What is inside an atom?

Details about atom particles

But are electrons, protons and neutrons really fundamental particles? What do you think? http: //education. jlab. org/atomtour/listofparticles. html

Bohr Atom Review (Before Bohr Lights Lab) When an electron temporarily occupies an energy state greater than its ground or normal state, it is in an excited state. An electron can become excited if it is given extra energy, such as if it absorbs a photon, or packet of light, or collides with a nearby atom or particle (heat energy) Electrons do not stay in excited states for very long - they soon return to their ground states, emitting a photon with the same energy as the one that was absorbed. http: //www. visionlearning. com/library/flash_viewer. php? oid=134 7&mid=51

When Heated, Every Element Produces Unique Colors of Light l l l If energy is added to an atom the electrons “jump” to a higher energy level. When they fall back down they give off light the color of which depends upon how far they jumped (it explained the lines in a spectroscope) This can be used to identify elements like a fingerprint. e-

Bohr Lights Lab Bohr Models: Electron Layers make colors Purpose: l When energy is added to an atom, it’s electrons jump to higher layers. Eventually the electrons cool and fall back down. As they do the energy that made them jump is released as a certain color of light. Every element has a different arrangement of electrons, so they all jump and fall in unique ways. Therefore every element produces different colors of light when it is heated. This was the major proof that Neils Bohr had that his model of the atom was on the right track. Procedure: The wavelengths of the waves of visible light are measured in angstroms (1Å = one hundred millionth of a centimeter). The color of various wavelengths of visible light are as follows: Red 6300 to 7000 green 4900 to 5300 Orange 5800 to 6300 blue 4300 to 4900 Yellow 5300 to 5800 violet 4000 to 4300 1. Label the grid below, starting with 4000 Å on the left and going up to 7000Å on the right. Then use color pencils to shade in the appropriate colors. l

Bohr Lights Lab (continued) Procedure: 2. Next you will use the spectroscope to look at some lights. Each bulb contains a different element. Every element gives off different lines of color when heated because they all have different numbers of electrons that are jumping to higher layers. Allowing spectroscopes to identify exactly what any thing is of made of:

Tomorrow’s Lesson l What l makes a element? http: //ippex. pppl. gov/interactive/matter/ele ments. html