The Structure of the Atom

Transcription

1 The Structure of the Atom 1

2 The Atom as Matter Dalton s atomic theory had problems It considered atoms to be hard, indivisible particles Did not explain why atoms reacted Also did not explain why atoms had varying abilities to combine with each other 2

3 Need for a New Theory Continued research on the nature of the atom after 1885 led to more understanding of the atomic structure Scientist of importance included Becquerel Thomson Rutherford Chadwick 3

4 Parts of the Atom Three fundamental particles Protons Neutrons Electrons The number and arrangement of these three particles determines the nature and properties of the different kinds of atoms. 4

5 Electron Discovered by J.J. Thomson in 1897 Represented with a negative sign, or e, e- Has the mass of only 1/1837th that of the hydrogen atom Name is derived from Greek elektron - means amber- rub a piece of amber with fur or wool, it will attract light objects Cause of attraction is an electrical charge 5

6 Protons Discovered by Ernest Rutherford in 1919 Represented with a + sign, the letter p, or p+ Charge is equal and opposite of an electron Mass is 1836/1837 that of an Hydrogen atom 6

7 Gold Foil Experiment 7

8 Neutrons Discovered by James Chadwick in 1932 Represented with the letter n, 0, n 0 They have no charge, thus they are neutral has about the same mass as that of a proton 8

9 Summation of the Parts Particle Symbol Charge Mass in amu Location in Atom Electron e, -, e- Negative, Surrounding the nucleus Proton p, +, p+ Positive, Inside the Nucleus Neutron n, 0, n 0 Neutral, Inside the Nucleus 9

10 The Electron Theory of Atomic Structure Understand that the knowledge and understanding of the structure of the atom is not by direct observation but rather how the energy is absorbed or given off by large number of atoms 10

11 Terminology Atoms are described by scientist in terms of particles and energy due to this phenomenon We will discuss this idea in more detail later Called Quantum Mechanics 11

12 Model One of the first major developments in this model is derived from Niels Bohr came up with the idea of a nucleus and shells of electrons Postulated that a strong electrical force kept the tiny universe intact 12

13 The Atom Nucleus= where protons and neutrons are found at Positive charge most massive area Then a Cloud of electrons orbiting outside of the nucleus negative charge areas where electrons are relatively found at are called shells or energy levels Electrons spin on their axis 13

14 Shells, Orbitals and Erwin Muller 14

15 The Idea The idea was that there was a shell general region of electron movement around the nucleus Electrons generally stay in the region unless they are excited Each shell or region is a specific distance Orbitals are the paths that the electron goes within a shell Erwin Muller helped in this by photographing the location of atoms in metal crystals 15

16 Electrons Electrons also spin while they revolve This spinning creates a magnetic field Electrons that spin opposite of one another are attracted to each other (Just like magnets) Pauli exclusion principle (1925)- no more than 2 e- can occupy the same orbital (Due to Spin) 16

17 Orderly Arrangement of Electrons Each atom has one or more shells depending upon the number of protons and electrons Since orbitals are limiting, then there are only a certain number of electrons that can fit in one orbital 17

18 Think Think about the periodic table and all that you have learned before What is the maximum capacity of this orbital? Based on Pauli Exclusion Principle, what is true about the spins? 18

19 Think Activity Let s see if we can figure out some patterns. 19

20 Energy Sublevels or Subshells Quantum Mechanics aka Quantum Theory Niels Bohr developed the theory that electrons revolve at definite energy levels, and this is the basis of Quantum Theory In order for an electron to move it must gain or lose energy The amount of energy an electron must give off or take on is the difference between its original energy level and the one below it or above it 20

21 How to See it We can see this change by using a spectroscope we see the light being emitted as the electron changes its orbital This is the foundations of quantum theory 21

22 Transformation Overall this change of energy is a change from electrical energy or heat into light the color (energy) of the light depends upon the change or changes in energy levels made by the electrons The jumps from outer to inner energy levels are revealed by the characteristic lines observed for different elements in the spectroscope 22

23 Element Spectroscopy 23

24 The s, p, d, f In orbitals you have subshells (energy sublevels) We designate these levels with letters like s,p,d,f Get out your Periodic Tables All electrons within a specific energy sublevel have the same amount of energy 24

25 s- Orbitals Smallest amount of energy the other orbitals will have increasing energies these levels have definite amounts or packets of energy also called quantum 25

26 p, d, and f Let s take a look at the periodic table and lets see how this all fits Remember how I taught you to fold the periodic table- now we use it again 26

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28 Atomic Structure The number of electrons in any atom equals the number of protons Atomic Number this determines the element!!!! Great way to classify elements into an orderly arrangement called the periodic table ground state is always neutral (protons equal electrons) 28

29 Chemical Activity Atoms with a full octet or filled outer shells do not combine with other atoms they are inert Noble gases Incomplete filled shells tend to combine with other kinds of atoms whose shells are also not filled do this by sharing, gaining, or losing electrons Chemical activity is determined by outermost electrons also called valence electrons 29

30 Practice Shells Let s draw some atoms based on old ideas 30

31 Three Rules of Filling Electrons always occupy orbitals of the lowest energy available There can be a maximum of only two electrons in any given orbital. (spins will be opposite- Pauli s Exclusion principle) Electrons are added successively filling subshells with electrons in a specific order based on increasing energies of the subshells. 31

32 New Eyes Filling orbitals and how to write electron configuration Let s Practice 32

33 Last Items What are Isotopes. We have been looking at the periodic table and the Atomic Mass Unit is not an even number. Why Those numbers are based on the abundancy of the isotopes. 33

34 Isotopes Isotopes- an element that varies due to number of neutrons Remember that the element is determined by the number of protons. Isotopes have different weights and this difference can cause some elements to have different radioactivity note that the chemical properties remain virtually the same 34

35 Calculations of Neutrons Take the difference between Atomic Mass and Atomic Number in order to determine the number of neutrons AN Isotope would be like C 12 and C 14 C 14 is the isotope because C 12 is the norm 35

36 Antimatter 1929 Dirac made a prediction that there must exist extraordinary electrons or particles that have the same mass but are opposite in charge. 3 years later Anderson proved that there were positrons These particles make up antimatter and may be controlled by antigravity More can be found at Antimatter:Mirror of the Universe 36