Chapter 10 Electrons in Atoms

1. Chapter 10 Electrons in Atoms Part 1 Waves and Energy

2. Waves and Energy • Describe an atom… • List the three main subatomic particles • Identify the relative electrical charges for each particle. • Describe the nucleus of an atom. • Does your model explain how chemical reactions occur?

3. Waves and Energy • Who started this atom stuff? • What did Dalton contribute? • All elements are composed of tiny indivisible particles called atoms. • Atoms of the same element are identical. The atoms of any one element are different from those of any other element. • Atoms of different elements can mix in whole number ratios to form compounds. • Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element do not change into atoms of another element.

4. Waves and Energy • J.J. Thompson • Provided evidence for the existence of electrons. • What was his model? • Ernest Rutherford • Provided evidence for the existence of a nucleus. • Niels Bohr • Has the electrons in orbits around the nucleus. BUT…Why don’t the electrons crash into the nucleus? • A piece of the nuclear pie is missing….

5. Waves and Energy • Properties of Waves • Frequency is the number of waves that pass a given point in given amount of time. The symbol is v. • Wavelength is the distance from one point on a wave to the similar point on the next wave. The symbol is λ. • Amplitude is the distance from the rest position to the top of a crest or bottom of a trough.

6. Waves and Energy • Ever notice a boat experiencing the passing of waves. Note that the boat rises and falls as the waves pass. The waves do not carry the water rather, they transmit the energy through the water. • The amount of energy the waves transmits is determined by the frequency and amplitude of the waves. • So…. Waves transmit energy.

7. Waves and Energy • Light waves have v and λ. • White light is referred to as the visible spectrum. Remember ROY G BIV?

8. Waves and Energy • Light waves transmit energy. The amount of energy that is transmitted depends upon the frequency. • Enter Max Planck • He suggested that the color of the • light was related to the energy of • the atoms and the energy values • were in whole numbers.

9. Waves and Energy • Enter Albert Einstein. • He worked exclusively with light and proposed that light was emitted in packets and the packets were proportional to the frequency of the light. Thus we have the photon. • E = h v Energy in joules is directly proportional to the frequency v and h is Planck’s constant(6.6262 x 10-34 j/s) • Therefore, each frequency of light has its own specific energy per photon without exception. This allows us to say that light is quantized.

10. Waves and Energy • Quantized light and stand waves. • file://localhost/Physics in Action/ Standing Waves on a Rope Video | MindBites • Wavelengths will change only by factors of one half! • The wave is said to be quantized. What does this mean? • Also, frequency and wavelength are inversely related.

11. Waves and Energy • The electromagnetic spectrum.

12. Waves and Energy • The mathematical relationship for all electromagnetic waves is c = v x λ with c = 3.0 x 10 8 m/s • Reveiw page 336 #’s 1, 3, 5, 7, 8

13. The Hydrogen Atom • The relationship between waves and atom can be demonstrated when an atom can be made to give off waves of different frequencies. • When atoms of an element are electrified, they will give off a bright-line spectrum. These are like fingerprints. Every element and even compounds have unique bls. Let’s see.

14. The Hydrogen Atom • In 1885, Johann Balmer discovered a mathematical progression in the sequence of lines. • E = constant(1/22 – 1/n2) n is an integer with a value greater than 2. This is all for now. • In 1913, Niels Bohr concluded that energy was being added to hydrogen gas in the form of electricity and leaving in the form of light. This light is in specific frequencies(quantized.) He went on to suggest that the atoms of hydrogen are also quantized.

15. The Hydrogen Atom • Something like this is happening. As the atoms absorb specific amounts of energy they become excited and jump to a higher energy level. This is not natural so they fall back and must release the energy absorbed and do so in the form of light. • An analogy from your book about a cat and steps. • Here are the rules. The cat must move up or down by whole steps. No halfsees! Each step requires the same amount of energy. • The result. Hydrogen atoms have specific energy levels.

16. The Hydrogen Atom • http://science.sbcc.edu/physics/solar/sciencesegment/bohratom.swf • The energy required to remove a mole of electrons from a mole of gaseous atoms is called the ionization energy. • For hydrogen is is 1312 kJ. This value is greater than any of the energy needed to “step up” and supports the idea of “steps.”

17. The Modern Model of the Hydrogen Atom • A flaw. All of this works for hydrogen, not any other elements, so…… • A new theory of the atom needed to consider: • The bright line spectra for atoms with many electrons • Fit in to the periodicity of the periodic table. • Don’t throw out all of Bohr’s work. • Enter Schrodinger. He developed equations to describe the energy of electrons. He applied the idea of particle waves to electrons in atoms. Now we have quantum mechanics!!

18. The Modern Model of the Hydrogen Atom • Waves of the electromagnetic spectrum are made up of particles, transfer energy and are quantized. • However, there is no evidence that electrons orbit the nucleus on definite path so Bohr’s idea was trashed. • Using mathematics of quantum mechanics you can predict the probability of finding an electron in a region around the nucleus. This region is called an orbital.

19. The Modern Model of the Hydrogen Atom • Let’s look at a hydrogen atom at ground state.

20. The Modern Model of the Hydrogen Atom • Remember the cat and steps? Our new model still has steps (orbitals) but the steps have steps!! • It goes like this: • 1s where 1 is the step and s is the orbital (this is where Stephen “is confused.” • Each step tells you the • number of orbitals. Step 2 • has 2 orbitals. s and p. • Step 3 has three orbitals: • s, p, d

21. The Modern Model of the Hydrogen Atom • Step 4 has 4 orbitals: s p d f that’s it. • Except each orbital has a corresponding number of orientations. • There is only one s shaped orbital. • There are three p shaped orbitals. • There are five d shaped orbitals. • There are seven f shaped orbitals. • 1.3.5.7

22. The Modern Model of the Hydrogen Atom

23. The Modern Model of the Hydrogen Atom

24. The Modern Model of the Hydrogen Atom

25. The Modern Model of the Hydrogen Atom

26. The Modern Model of the Hydrogen Atom • The quantum of it all. • Quantum number one or n is called the principal quantum number and represents the step or size of the orbital. 1, 2, 3, 4… • Quantum number two is l and designates the shape of the orbital. s, p, d, f • Quantum number three is m and describes the orientation of the s,p,d,f’s • Quantum number four is the spin and is coming soon.

27. Electron Configurations • Now you will learn how to assign an atom’s electrons on the appropriate step and corresponding orbital. • The order of filling goes like this • 1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p. • Here are the rules: • You must start with the lowest energy level(step) n • Only two electrons can fill an orbital. l • You must put one electron in 3p then go back and add the second.

28. Electron Configurations

29. Electron Configurations • Practice Problems # 18,19 page 352 • Construct the electron configuration for 11Na • 1s2, 2s2, 2p6, 3s1 • 38 Sr 1s2,2s2,2p6,3s2,3p6,4s2,3d10,4p6,5s2 but • 1s2,2s2,2p6,3s2,3p6,3d10,4s2,4p6,5s2 • Try these: 20, 21 one of them, 22, 23