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The Structure of the Atom

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Presentation on theme: "The Structure of the Atom"— Presentation transcript:

1 The Structure of the Atom
Chapter 4 The Structure of the Atom

2 Are they all the same size?
How big is an atom? Are they all the same size? What do they look like? How dense are they? How much do they weigh?

3 Are they all the same size?
How big is an atom? Are they all the same size? What do they look like? How dense are they? How much do they weigh?

4 How big is an atom? 1 Atom (see it?)

5 How Big Is An Atom? If an apple was the size of the Earth, each atom in the apple would be about the size of…an apple! …and that atom’s nucleus would be about the size of an apple compared to the Earth. There are about 6,000,000,000,000,000,000,000 atoms in a drop of water.

6 So How big are they??? Reallllllllllllllllllllllllllllllllllllllllllllllllllllyyyyyyyy small! In the year 2000, it was estimated that 6 billion people lived on Earth! The number of copper atoms in ONE solid copper penny is 5 billion times bigger!

7 World Population 7 300 000 000 Atoms in a penny 29 000 000 000 000 000 000 000

8 Are they all the same size?
How big is an atom? Are they all the same size? What do they look like? How dense are they? How much do they weigh?

9 Are They All The Same Size?
The “biggest” atom (Cesium) is about 10 times larger than the smallest atom (Hydrogen)

10 Are they all the same size?
How big is an atom? Are they all the same size? What do they look like? How dense are they? How much do they weigh?

11 While we can’t see them, we can sense them!
Can We See Atoms? NO! While we can’t see them, we can sense them!

12 Scanning Tunneling Electron Microscope (STM)

13 How an STM works The STM consists of the following:
A very small, sharp tip that conducts electricity (probe) A rapid piezoelectric scanning device to which the tip is mounted Electronic components to supply current to the tip, control the scanner and accept the signals from the motion sensor Computer to control the system and do data analysis (data collection, processing, display) The STM works like this: A current is supplied to the tip (probe) while the scanner rapidly moves the tip across the surface of a conducting sample. When the tip encounters an atom, the flow of electrons between the atom and the tip changes. The computer registers the change in current with the x,y-position of the atom. The scanner continues to position the tip over each x,y-point on the sample surface, registering a current for each point. The computer collects the data and plots a map of current over the surface that corresponds to a map of the atomic positions.

14 Scanning Tunneling Electron Microscope (STM)
Gold atoms Silicon atoms

15 Not only can the probe sense the atoms electron cloud, it was discovered that it can also manipulate the atoms!

16 Scanning Tunneling Electron Microscope (STM) “Corrals”
“Round” Iron atoms on copper “Stadium” Iron atoms on copper

17 Scanning Tunneling Electron Microscope (STM) “IBM Scientists Playing”
“Atom” in Japanese Iron atoms on copper “carbon monoxide man” Carbon monoxide on platinum “IBM” Xenon on nickel

18 Are they all the same size?
How big is an atom? Are they all the same size? What do they look like? How dense are they? How much do they weigh?

19 An atom: Virtually zero
Density Water: 1.0 g/cm3 Aluminum: 2.7 g/cm3 Gold: 19.3 g/cm3 Iron: 7.8 g/cm3 Air: g/cm3 Core of the Sun: 150 g/cm3 An atom: Virtually zero Atomic Nucleus: 400,000,000,000,000 g/cm3 Q: If an atom’s nucleus is 2.7 trillion times more dense than the core of the sun, but a whole atom is less dense than air, what can you deduce about the make-up of an atom?

20 Are they all the same size?
How big is an atom? Are they all the same size? What do they look like? How dense are they? How much do they weigh?

21 It takes 6.02x1023 atoms of Carbon to make 12 grams*
Atomic Mass A hydrogen atom, the lightest atom, has a mass of about grams. The heaviest atom so far discovered has a mass about 283 times as much as hydrogen. It takes 6.02x1023 atoms of Carbon to make 12 grams* The mass is so small, we give it its own unit to make the numbers easier to work with. An atomic mass unit is 1/12th the mass of 1 Carbon atom (about the mass of a hydrogen atom). *That 6.02x1023 number is called Avogadro’s Number. But it’s nickname is the “mole”…

22 Most Chemistry is Invisible
Chemistry is about understanding how individual atoms interact with each other. But we can’t see that… So we look at massive quantities of atoms (moles) to determine properties and observe reactions, and infer what’s happening at the atomic level. So most chemistry is conducted in the imagination! Interesting Note: If biological science worked this way, you’d have to have so many kittens to see their properties and interactions, that they’d take up as much space as…the Earth.

23 The Atom and Periodic Table in 400B.C. – Democritis
First proposed the idea that matter might be made up of particles too small to see.

24 The Atom and Periodic Table in 1808 – John Dalton
Early concepts of the Periodic Table and varying masses of elements.

25 The Atom and Periodic Table in 1808 – John Dalton
Dalton’s Atomic Theory Elements are made up of submicroscopic indivisible particles called atoms Atoms of a given element are identical in size and properties Atoms of different elements can physically mix together or can chemically combine with one another in simple whole number ratios to form compounds. Chemical reactions work by combining and rearranging atoms. Which of Dalton’s theories still stand?

26 4.2 Subatomic Particles and the nuclear atom
Thomson (1897) – Cathode-Ray Experiments: discovered the electron . Established the charge to mass ratio for these particles

27 Cathode Ray Tube

28 The Atom and Periodic Table in 1900 – J. J. Thompson
Discovering the Electron The Atomic Cookie (aka Plum Pudding) model This atom stuff is making me hungry!

29 4.2 Subatomic Particles and the nuclear atom
Millikan (1909) – Oil-Drop Experiment: determined the mass of the electron.

30 4.2 Subatomic Particles and the nuclear atom
Combined with the charge/mass ratio from Thomson, he was able to accurately calculate the mass of a single electron to be 1/1840 the mass of a hydrogen nucleus (proton)! Even with his primitive equipment, his value was within 1% of the accepted value that we use today!

31 4.3 Subatomic Particles and the nuclear atom
Rutherford (1911) – Gold Foil Experiment: discovered the nucleus and basic structure of the atom. Electrons are outside the positively charged nucleus. Most of the atom is empty space.

32 Gold Foil Experiment

33

34 4.3 Subatomic Particles and the nuclear atom
Rutherford (1920) – Concluded there must be a particle in the nucleus carrying a charge equal but opposite of the electron and he called it a proton. James Chadwick (1932) - discovered the existence of a neutrally charged particle in the nucleus called the neutron.

35 4.4 Subatomic Particles and the nuclear atom
Symbol Location Relative Electrical Charge Relative Mass Actual Mass (g) Electron e- Outside Nucleus 1- 1/1840 9.11×10-28 Proton p+ Nucleus 1+ 1 1.673×10-24 Neutron n0 Nucleus 1 1.673×10-24

36 How many protons does chlorine have?
4.4 Atomic Number How do atoms of one element differ from those of another element? Each element has a different number of protons. Atomic number - # protons in the nucleus of an atom Identifies the element Ex: What makes an atom a hydrogen atom is that it has 1 proton in its nucleus. How many protons does chlorine have? 17 17 How many electrons? 17

37 4.6 Isotopes Thomson (1910) – It’s discovered that neon consists of atoms with 2 different masses. WHY? Isotope – atoms with the same number of protons, but different numbers of neutrons. Neon-22 p+ = n0 = Neon-20 p+ = n0 = 10 10 12 10

38 4.5 Mass Number If not all atoms of an element are identical, how can we tell them apart? Mass number – the total number of particles in the nucleus Mass number = # protons + # neutrons MASS NUMBER IS NOT ON THE PERIODIC TABLE!!! Mass number 6 Mass number 7

39 Element name – mass number
Hyphen Notation Symbol Notation Element name – mass number Mass # symbol Atomic # Potassium-41 p+ = e- = n0 = 19 19 p+ = e- = n0 = 19 22 19 22

40 Different Isotopes can have different chemical properties…

41 Computing the “normal” number of Neutrons in an atom:
Try this one… What’s its atomic number? ____________ What’s its atomic weight? ____________ What’s its atomic weight, rounded to the nearest whole number? ______________ How many neutrons will it normally have? ___________ C Carbon

42 Computing the “normal” number of Neutrons in an atom:
Try this one… What’s its atomic number? ____________ What’s its atomic weight? ____________ What’s its atomic weight, rounded to the nearest whole number? ______________ How many neutrons will it normally have? ___________ Au Gold

43 4.7 Atomic Mass Atomic mass – because the mass of atoms is so small (proton = 1.67×10-24g) we simplify atomic masses by measuring them in atomic mass units. Atomic mass unit (amu) – 1/12 the mass of carbon-12.

44 4.7 Atomic Mass If elements have isotopes with different atomic masses, what is the atomic mass on the periodic table? Atomic Mass – weighted average mass of the isotopes of an element. This is found by summing the mass contribution of each isotope of the element.

45 There are 2 naturally occurring isotopes of copper – copper-63 and copper-65. If copper-63 has a mass of amu and 69.17% abundance and copper-65 has a mass of amu and 30.83% abundance, what is the average atomic mass of copper? 1. First, calculate the mass contribution of each isotope to the average atomic mass, being sure to convert each percent to a fractional abundance.

46 For copper-63: Mass contribution = ( amu)(.6917) = 43.53 amu For copper-65: Mass contribution = ( amu)(.3083) = 20.02 amu 2. Finally, the average atomic mass of the element is the sum of the mass contributions of each isotope. 63.55 amu

47 To try on your own.. Element X has two natural isotopes. The isotope with a mass of amu has a relative abundance of 19.91%. The isotope with a mass of amu has a relative abundance of 80.09%. Calculate the atomic mass of this element and name it.

48 p. 105 #61 Lithium has two naturally occurring isotopes. Lithium-6 has an atomic mass of 6.015amu and lithium-7 has an atomic mass of 7.016amu. The atomic mass of lithium is amu. What is the percentage of lithium-7 in nature?

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