Transcript atom
Chapter 4 Atomic Structure Section 4-1 Objectives • Describe ancient Greek models of matter • List the main points of Dalton’s atomic theory and describe his evidence for the existence of atoms • Explain how Thomson and Rutherford used data from experiments to produce their atomic models derivation of the word “atom” ? • “a” – not • “tomos” - cutting • Matter can only be subdivided as small as an elemental particle: THE ATOM Democritus • About 400 BC • World is made of 2 things – 1) empty space – 2) tiny particles called “atoms” Aristotle • Matter is continuous and NOT MADE OF ATOMS • few believers in atoms for nearly 2,000 yrs • WHY????????????????? Dalton’s Theory • Dalton produced the theory that all matter is made up of individual particles called atoms, which cannot be divided. Main Points to Dalton’s Theory • All elements are composed of atoms • All atoms of the same element have the same mass, and atoms of different elements have different masses • Compounds contain atoms of more than one element • In a particular compound, atoms of different elements always combine in the same way. Early Research on Atomic Particles • Eventually exceptions were discovered to Dalton’s Atomic Theory…….. J.J Thompson • Created Cathode Ray Tube Experiment Cathode Ray Studies of the mid 1800’s What did these observations mean? • Glowing ray in cathode tube was made of particles • Particles that composed cathode rays are negatively charged called electrons • Thomson’s experiments provided the first evidence that atoms are made of even smaller particles Thomson’s Model • • • • Called “Plum Pudding” Looks like chocolate chip ice cream Chocolate is negative particles Vanilla ice cream is positively charged matter Rutherford’s Atomic Theory • The gold foil experiment Teacher Demo Investigating Charged Objects • Pg 102 Observations • Most positive particles passed through the gold foil • About 1 in 8,000 particles bounced almost straight back Discovery of the Nucleus • Rutherford’s experiment discovered the nucleus • Nucleus is a dense, positively charged mass located in the center of the atom. • According to Rutherford’s model, all of an atom’s positive charge is concentrated in its nucleus. Beaker Breaker 1. The gold foil experiment was done by _________ 2. The cathode ray tube experiment was done by ___________ 3. Who discovered the nucleus?____________ Section 4-2 The structure of an Atom Objectives • Identify three subatomic particles and compare their properties • Distinguish the atomic number of an element from the mass number of an isotope, and use these numbers to describe the structure of atoms Definitions • Use your book to define the following 2. Electron- 3. Neutron- 4. Atomic number- 5. Mass Number- 6. Isotopes- 1. Proton – Properties of Subatomic Particles • Protons, electrons, and neutrons are subatomic particles Protons • A proton is a positively charged subatomic particle that is found in the nucleus of an atom • Each proton is assigned a 1+ charge • Some nuclei contain more than 100 protons Electrons • An electron is a negatively charged subatomic particle that is found in the space outside the nucleus. • Each electron has a charge of 1 -. Neutrons • A neutron is a neutral subatomic particle that is found in the nucleus of an atom. • It has a mass almost exactly equal to that of a proton • James Chadwick designed an experiment to show that neutrons exist. Comparing Subatomic Particles • Protons, electrons, and neutrons can be distinguished by mass, charge and location in an atom. • Protons and neutrons have almost the same mass • Electrons have a charge that is opposite of the charge of a proton • Protons and neutrons are found in the nucleus, but electrons are found in the space outside the nucleus. Atomic Number • The atomic number of an element equals the number of protons in an atom of that element • Atoms of different elements have different numbers of protons. • Atomic number also tells you the number of electrons • Ex: Sulfur atomic number = 16 • Ex : Carbon (C ) atomic number = 6 Mass Number • The mass number of an atom is the sum of the protons and neutrons in the nucleus of that atom • Ex: Aluminum has 13 protons and 14 neutrons has a mass number of 27 • If you know the atomic number and the mass number of an atom, you can find the number of neutrons by subtracting. • Mass number – Atomic number = Number of neutrons Isotopes • Isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons. • Ex Oxygen -16 ( 8 protons and 8 neutrons) Oxygen – 17 ( 8 protons and 9 neutrons) Oxygen -18 ( 8 protons and 10 neutrons) Beaker Breaker • A __________is a neutral subatomic particle that is found in the nucleus • An electron has a _________charge • ______and ________are located in the nucleus, while_______are located outside the nucleus Section 4-3 Modern Atomic Theory Objectives • Describe Bohr’s model of the atom and the evidence for energy levels • Explain how the electron cloud model represents the behavior and locations of electron in atoms • Distinguish the ground state from excited states of an atom based on electron configurations Bohr’s Model • Model of atom looks like a solar system with planets revolving around a sun • Model focused on electrons Bohr’s Model and energy levels • The possible energies that electrons in an atom can have are called energy levels. • Energy levels are like steps on a staircase, an electron cannot exist between energy levels • An electron in an atom can move from one energy level to another when the atom gains or loses energy Evidence for Energy Levels • Scientist can measure the energy gained when electrons absorb energy and move to a higher energy level. • They can measure the energy released when the electron returns to a lower energy level Beaker Breaker 1. An___________ cloud is a visual model of the most likely locations for electrons in an atom. 2. Which scientist is the responsible for the discovery of neutrons? 3. When electrons move to a higher energy level do they absorb or release energy? Flame Test Lab • Read page 116 “evidence for energy levels” in the book Question : How do these substances produces light of different colors? Electron Cloud Model • An electron cloud is a visual model of the most likely locations for electrons in an atom. • Scientists use the electron cloud model to describe the possible locations of electrons around the nucleus • Ex: blades on a propeller of an airplane Modern Atom 1. Louis de Broglie – proposes that moving particles like electrons have some properties of waves. 2. Erwin Schrodinger develops mathematical equations to describe the motion of electrons in atoms (electron cloud). 3. James Chadwick- confirms the existence of neutrons in the nucleus, which have no charge Drawings of Atoms Atomic Orbitals • An orbital is a region of space around the nucleus where an electron is likely to be found • An electron cloud is a good approximation of how electrons behave in their orbitals. • Higher energy levels have more than one orbital Electron Configurations • An electron configuration is the arrangement of electrons in the orbitals of an atom • The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies • When all the electrons in an atom have the lowest possible energies, the atom is said to be in its ground state.