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Explore the journey of atomic structure studies from Democritus to modern theories like Dalton's and Rutherford's models, including key experiments and discoveries. Learn about subatomic particles, isotopes, and the electron cloud model. Unravel the mysteries of protons, neutrons, and electrons and how they form the structure of matter we see today.
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4.1 Studying Atoms Democritus (460-371 B.C.) Democritus believed matter consisted of small, indivisible particles (called atoms) Believed… solid atoms – rough and prickly liquid atoms – round and smooth
4.1 Studying Atoms Aristotle (384-322 B.C.) Aristotle believed matter consisted of four elements Believed that there is no limit to how many times matter can be divided
4.1 Studying Atoms John Dalton (1766-1844) Found that the ratio of Magnesium to Oxygen in the above reaction is always 2:1.
4.1 Studying Atoms Dalton’s Atomic Theory • All elements composed of atoms 2. Atoms of same element have same mass Wooden spheres used by Dalton to model atoms 3. Compounds contain atoms of more than one element 4. In a compound, atoms of different elements combine in the same way
4.1 Studying Atoms Dalton’s Model of the Atom solid sphere
4.1 Studying Atoms J J Thomson (1856-1940) Used a cathode ray tube to study the atom
4.1 Studying Atoms Cathode ray tube
4.1 Studying Atoms Cathode ray tube
4.1 Studying Atoms • beam deflected towards positive charge, away from negative charge • (negatively charge) • beam turns a small paddle wheel • (has mass)
4.1 Studying Atoms most air removed The beam has mass. Where did it come from??? The matter making up this beam must come from the matter making up the metal plates, but its mass was 1/2000th the mass of the lightest known atom (Hydrogen) The atoms making the plates must be made of smaller, negatively charged particles!!!!!!
4.1 Studying Atoms There must be positive charge in the atom also!! But, an atom is neutral. How can it contain negative particles??
4.1 Studying Atoms J J Thomson’s Model of the Atom Dalton model plum pudding model
4.1 Studying Atoms Ernest Rutherford (1871–1937) Discovered that Uranium emits alpha particles
4.1 Studying Atoms Rutherford Gold Foil Experiment
4.1 Studying Atoms Predicted alpha particles would pass right by the atoms in thin, gold foil Wanted to know what happens to alpha particles when they pass through a sheet of gold foil?
4.1 Studying Atoms Rutherford Gold Foil Experiment
4.1 Studying Atoms Many particles were deflected, some more than 90 degrees “It was almost as incredible as if you fired a 15-inch artillery shell at a piece of tissue paper and it came back and hit you”
4.1 Studying Atoms Rutherford’s Model of the Atom Dalton model plum pudding model planetary model
4.1 Studying Atoms The volume of the atom is a trillion times the volume of its nucleus Houston Astrodome nucleus – dense, positively charged mass located in the center of the atom.
4.2 The Structure of the Atom Particle Type Location Charge Symbol Rutherford saw evidence for the existence of two subatomic particles, and predicted the existence of a third. proton nucleus +1 p+ electron outside the nucleus -1 e- neutron nucleus 0 n Protons and neutrons have the same mass, but electrons are much less massive
4.2 The Structure of the Atom 1 H atomic number – equals the number of protons Hydrogen 1.0079 atomic mass With the discovery of subatomic particles, scientists were able to describe the difference between types of atoms Atoms of different elements have different numbers of protons also equals the number of electrons
4.2 The Structure of the Atom number of neutrons number of neutrons = mass number – atomic number mass number – the sum of the protons and neutrons in an atom quite often, the atomic mass rounded to a whole number is equal to the mass number
4.2 The Structure of the Atom How many protons does Oxygen have? How many electrons does Oxygen have?
4.2 The Structure of the Atom What is the atomic number of oxygen? What is the mass number of oxygen?
4.2 The Structure of the Atom 8 O Oxygen mass number 15.999 isotopes – atoms of the same element that have different numbers of neutrons There are three isotopes of oxygen: oxygen-16 oxygen-17 oxygen-18 How many neutrons in oxygen-17?
4.2 The Structure of the Atom 17 Cl How many protons, electrons, and neutrons are there in an atom of chlorine-37? Chlorine 35.453
4.2 The Structure of the Atom How many protons, electrons, and neutrons are there in an atom of carbon-12? 6 C How many protons, electrons, and neutrons are there in an atom of carbon-14? Carbon 12.011
4.3 Modern Atomic Theory What can happen when an atom absorbs energy? - an increase in kinetic energy or a phase change energy may be absorbed by an atom, then emitted as light
4.3 Modern Atomic Theory Niels Bohr (1885-1962) agreed with Rutherford’s model but added something to it energy levels – the possible energies that electrons in an atom can have
4.3 Modern Atomic Theory when it loses the energy it emits it as light when an atom gains energy an electron may move to a higher energy level no two elements have the same set of energy levels, so the emit different colors of light
4.3 Modern Atomic Theory Electron Cloud Model electron cloud model – model of the most likely locations for electrons in an atom (deals with probability)
4.3 Modern Atomic Theory Electron Cloud Model of a Hydrogen Atom
4.3 Modern Atomic Theory orbital – region of space where an electron is likely to be found
4.3 Modern Atomic Theory electron cloud – a good approximation of how electrons behave in their orbitals
4.3 Modern Atomic Theory atoms emit light when their electrons return to ground state electron configuration – arrangement of electrons in the orbital of an atom ground state – electrons are all in their lowest possible energy levels (most stable) excited state – one or more electrons are in a higher energy level than usual (least stable)
Chapter 4 Vocabulary isotopes proton nucleus mass number electron configuration energy levels atomic number neutron orbital electron cloud electron ground state excited state
Chapter 4 Vocabulary isotopes proton nucleus mass number energy levels atomic number neutron orbital electron cloud electron ground state excited state
Chapter 4 Vocabulary isotopes proton mass number energy levels atomic number neutron orbital electron cloud electron ground state excited state
Chapter 4 Vocabulary isotopes proton mass number energy levels atomic number orbital electron cloud electron ground state excited state
Chapter 4 Vocabulary isotopes proton mass number energy levels atomic number electron cloud electron ground state excited state
Chapter 4 Vocabulary isotopes proton mass number energy levels atomic number electron cloud electron ground state
Chapter 4 Vocabulary isotopes proton mass number energy levels electron cloud electron ground state
Chapter 4 Vocabulary proton mass number energy levels electron cloud electron ground state
Chapter 4 Vocabulary proton mass number electron cloud electron ground state
Chapter 4 Vocabulary proton electron cloud electron ground state
Chapter 4 Vocabulary proton electron ground state
