Chapter 4 – Atomic Structure

Believed… solid atoms – rough and prickly 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

Aristotle believed matter consisted of four elements 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.

Dalton’s Atomic Theory 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

Dalton’s Model of the Atom 4.1 Studying Atoms Dalton’s Model of the Atom solid sphere

Used a cathode ray tube to study the atom 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

beam deflected towards positive charge, away from negative charge 4.1 Studying Atoms beam deflected towards positive charge, away from negative charge (negatively charge) beam turns a small paddle wheel (has mass)

The beam has mass. Where did it come from??? 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!!!!!!

How can it contain negative particles?? 4.1 Studying Atoms But, an atom is neutral. How can it contain negative particles?? There must be positive charge in the atom also!!

J J Thomson’s Model of the Atom 4.1 Studying Atoms J J Thomson’s Model of the Atom Dalton model plum pudding model

4.1 Studying Atoms

Discovered that Uranium emits alpha particles 4.1 Studying Atoms Ernest Rutherford (1871–1937) Discovered that Uranium emits alpha particles

Rutherford Gold Foil Experiment 4.1 Studying Atoms Rutherford Gold Foil Experiment

4.1 Studying Atoms Wanted to know what happens to alpha particles when they pass through a sheet of gold foil? Predicted alpha particles would pass right by the atoms in thin, gold foil

Rutherford Gold Foil Experiment 4.1 Studying Atoms Rutherford Gold Foil Experiment

Many particles were deflected, some more than 90 degrees 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”

Rutherford’s Model of the Atom 4.1 Studying Atoms Rutherford’s Model of the Atom Dalton model plum pudding model planetary model

The volume of the atom is a trillion times the volume of its nucleus 4.1 Studying Atoms nucleus – dense, positively charged mass located in the center of the atom. Houston Astrodome The volume of the atom is a trillion times the volume of its nucleus

4.2 The Structure of the Atom Rutherford saw evidence for the existence of two subatomic particles, and predicted the existence of a third. Particle Type Location Charge Symbol proton nucleus +1 p+ electron outside the nucleus -1 e- neutron nucleus n Protons and neutrons have the same mass, but electrons are much less massive

4.2 The Structure of the Atom

4.2 The Structure of the Atom 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 H Hydrogen 1 1.0079 atomic number – equals the number of protons also equals the number of electrons atomic mass

mass number – the sum of the protons and neutrons in an atom 4.2 The Structure of the Atom mass number – the sum of the protons and neutrons in an atom number of neutrons number of neutrons = mass number – atomic number 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 isotopes – atoms of the same element that have different numbers of neutrons O Oxygen 8 15.999 There are three isotopes of oxygen: oxygen-16 mass number 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

What can happen when an atom absorbs energy? 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

agreed with Rutherford’s model but added something to it 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

when it loses the energy it emits it as light 4.3 Modern Atomic Theory when an atom gains energy an electron may move to a higher energy level when it loses the energy it emits it as light 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)

Electron Cloud Model of a Hydrogen Atom 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 orbital – region of space where an electron is likely to be found

Energy Level, Orbitals, and Electrons 4.3 Modern Atomic Theory electron cloud – a good approximation of how electrons behave in their orbitals Energy Level, Orbitals, and Electrons Energy Level Number of Orbitals Maximum # of Electrons 1 2 4 8 3 9 18 16 32

atoms emit light when their electrons return to ground state 4.3 Modern Atomic Theory 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) atoms emit light when their electrons return to ground state

electron configuration energy levels Chapter 4 Vocabulary isotopes proton nucleus mass number electron configuration energy levels atomic number neutron orbital electron cloud electron ground state excited state

isotopes proton nucleus mass number energy levels atomic number Chapter 4 Vocabulary isotopes proton nucleus mass number energy levels atomic number neutron orbital electron cloud electron ground state excited state

isotopes proton mass number energy levels atomic number neutron Chapter 4 Vocabulary isotopes proton mass number energy levels atomic number neutron orbital electron cloud electron ground state excited state

isotopes proton mass number energy levels atomic number orbital Chapter 4 Vocabulary isotopes proton mass number energy levels atomic number orbital electron cloud electron ground state excited state

isotopes proton mass number energy levels atomic number electron cloud Chapter 4 Vocabulary isotopes proton mass number energy levels atomic number electron cloud electron ground state excited state

isotopes proton mass number energy levels atomic number electron cloud Chapter 4 Vocabulary isotopes proton mass number energy levels atomic number electron cloud electron ground state

isotopes proton mass number energy levels electron cloud electron Chapter 4 Vocabulary isotopes proton mass number energy levels electron cloud electron ground state

proton mass number energy levels electron cloud electron ground state Chapter 4 Vocabulary proton mass number energy levels electron cloud electron ground state

proton mass number 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

Chapter 4 Vocabulary proton electron

Chapter 4 Vocabulary proton

Chapter 4 Vocabulary