The Structure of the Atom Chapter 5 Chemistry 1

Ch5 asgns. From book 5.1&2: 163/28,29,30, : 164/55,56,58,59,61,62 Quiz and Test #1 after 5.1,.2, : 163/42-48,50,51,69-75 Worksheets will also be assigned. Test #2 after 5.3 is covered. 2

It started a long time ago… Today 460 – 370 BC Democritus Beginning of Atomism You cannot divide something in half forever. The smallest piece of matter is called an atom. 3

Today 1808 Democritus Atomism 460 – 370 BC Dalton’s Postulates 4. Compounds are made from combining atoms in simple whole number ratios. 1. All elements are made of tiny indivisible particles called atoms. 2. All atoms of the same element are the same, but different from atoms of every other element. 3. Chemical reactions rearrange atoms but do not create, destroy, or convert atoms from one element to another. Over 2,000 years later John Dalton comes up with the first “modern” atomic theory. 4

Another kind of light? Today Democritus Atomism 460 – 370 BC Dalton “Modern” atomic theory William Crookes invents a tube in which virtually all the gas has been removed. Under high voltage, a ray was emitted from the cathode end of the tube. 5

It started a long time ago… Today Democritus Atomism 460 – 370 BC Dalton “Modern” atomic theory Crookes Cathode rays Cathode rays must be negative. J.J. Thomson discovers the electron 6

Today Democritus Atomism 460 – 370 BC Dalton “Modern” atomic theory Crookes Cathode rays Thomson Discovery of the electron Ernest Rutherford discovers the nucleus It started a long time ago… 7

The size of the atom comes mostly from the space occupied by the electrons The mass of the atom comes mostly from the nucleus Size and mass 8

electrons protons neutrons What happens when you change the number of protons? 9

You obtain a different element! 6 protons in carbon 7 protons in nitrogen 8 protons in oxygen The number of protons is also called the atomic number for that element. 10

electrons protons neutrons What happens when you change the number of electrons? You get an ion – a charged particle. 11

A neutral sodium atom A positive sodium ion Na Na 1+ The protons and electrons cancel each other out One proton is not neutralized by an electron, making this a +1 charged atom One electron short Balanced charges 11 protons 12

A negative oxygen ion O -2 Two electrons are not neutralized by protons, making this a –2 charged atom Two extra electrons 8 protons 13

The electron cloud Except for mass, virtually every property of atoms is determined by electrons, including size and chemical bonding Electrons are very light and fast. They are not organized along orbits around the nucleus. 14

electrons protons neutrons What happens when you change the number of neutrons? 15

Atomic number Neutrons act as “glue.” They hold protons together in the nucleus. 16

mass number: total number of protons and neutrons in a nucleus. Mass number = 6 p + 6 n = C “carbon-12” 17

Mass number Name Carbon-12Carbon-13Carbon-14 # protons # neutrons isotopes: atoms or elements that have the same number of protons in the nucleus but different number of neutrons 18

Number of neutrons for each of 100 lithium atoms randomly sampled from nature It’s an AVERAGE mass! 19

Isotope periodic table (first 4 rows) 20

The periodic table Li + Na + K+K+ Elements in the same column have similar chemical properties. They tend to donate 1 electron. 21

The periodic table F–F– Cl – Br – Elements in the same column have similar chemical properties. They tend to accept 1 electron. 22

23 Assignment: 5.1&2: 163/28,29,30,33-36 and handout(s)

Elements in the same column have similar chemical properties. Electrons are responsible for these chemical properties. Quantum theory explains how the universe behaves on a very small scale. Niels Bohr 24

A wave “particle” We intuitively think of light as a wave and an electron as a particle

A wave “particle” But light waves come in bundles of light (photons) and an electron behaves as a wave

frequency: the rate at which an oscillation repeats; one hertz (Hz) is a frequency of one oscillation per second. wavelength: the distance (separation) between any two successive peaks (or valleys) of a wave.

The higher the frequency, the higher the energy

Electrons Light On the scale of atoms Planck’s constant (h) is used to calculate the energy and wavelength of electrons and photons 4.136x10 -3 eV or or 4.136x10 -3 eV

30 = h = √ 2mE = 6.626x Js √2(9.109x kg)(6.636x J = x m

Light travels as bundles called photons 1 electron volt (eV) = x 10 –19 J. A very small unit of energy Energy of a photon

Wavelength and frequency are related 1 Hertz, Hz = 1 cycle = 1 = s -1 sec sec

33 What is the frequency of a yellow light with wavelength 580 nm? 1 nm = m c = f  --> f = c f = 3 x 10 8 m 580 x ms f = 5.2 x Hz

The wavelength of red laser light is 652 nm. What is its frequency, ? How much energy, E, does a photon of this light have in electron volts? Asked: Frequency and energy Given: Relationships: Solve: Answer: Since 1 Hz = 1/s, the frequency is 4.6 x Hz and the energy is 1.9 eV. 1 nm = m

Wave addition The sum of two waves can give a “bigger” wave.

The sum of two waves can be zero! Wave addition

Imagine a wave (wave 1) inside a box… Wave 1 bounces off the wall and creates wave 2. Could the waves cancel out each other? Wave 1 Wave 2 Wave that “survives” Wave addition

Perfect “fit” Poor “fit”

Allowed Not allowed The wavelength of the electron must be a “multiple” of the “size” of the atom.

Only certain wavelengths are allowed… … and wavelength is related to energy.

The Bohr model Only certain energy levels are allowed Energy is quantized!

Different quantum states can have the same wavelength The Bohr model

orbital: group of quantum states that have similar spatial shapes, labeled s, p, d, and f. 43

Today Democritus Atomism 460 – 370 BC Dalton “Modern” atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Wolfgang Pauli Quantum rule on electron structure Pauli exclusion principle: two electrons in the same atom may never be in the same quantum state. A look at history 44

Quantum states can have the same energy level 45

One electron per quantum state Fill lower- energy levels first Lithium’s 3 rd electron has to go into the 2 nd energy level 46

Electrons settle into the lowest unfilled quantum states 47

1 st row Full energy level 48

2 nd row 49

Orbitals s Principle quantum number 1 Energy levelsQuantum states 50

Orbitals s s p Principle quantum number 1212 Energy levelsQuantum states 51

Orbitals s s s p p Principle quantum number Energy levelsQuantum states 52

Orbitals s s s s p p p d Principle quantum number Energy levelsQuantum states 53

Orbitals s s s s s p p p p d d Principle quantum number

Orbitals s s s s s s p p p p p d d d Principle quantum number

Orbital s Principle quantum number 1 Energy levels Quantum states 56

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Note how the 3p orbital gets filled before 3d 58

Write the electron configuration for silicon. 14 protons There is a net charge of zero, so silicon has 14 electrons. The chart shows that 12 electrons fill up to 3s 2. The remaining 2 electrons go to a 3p orbital. The electron configuration for silicon is: 1s22s22p63s23p2.1s22s22p63s23p2. 59

Electron Arrangement Another link for review S/28Elec-config.pdf 60 Assignment: 5.4: 164/55,56,58,59,61,62 And handout(s)

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CHAPTER 5 The Structure of the Atom 5.4 Light and Spectroscopy

Light is a form of electromagnetic energy that comes from electrons in atoms The human eye can only detect a certain range of that energy: the visible spectrum.

White light from a lamp or the sun is not truly white! Analyzing starlight with a prism (one of the first spectrometers)

Visible light is only a small range in the electromagnetic spectrum

We are surrounded by electromagnetic energy

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prism electron all possible energy levels Light from an incandescent light bulb:

prism electron fixed energy levels Light from pure hydrogen:

Hydrogen atoms can only absorb and emit light of very specific energies.

Remember: only some energy levels are allowed. Why does the atom absorb only specific (discrete) energies? Matter and light

Energy levels Photon (energy) Energy levels Energy of the photon matches a gap between levels Energy (light) is absorbed. Energy of the photon does not match a gap between levels Energy (light) passes through the atom. Matter and light

Energy levels Photon (energy) Energy of the photon matches a gap between levels Energy (light) is absorbed. another photon is emitted specific color (wavelength) Matter and light

Each type of atom has a different electron structure. Each element has unique energy levels like a fingerprint.

Spectrum cards How to read the spectrum cards

Combinations of elements contain spectral lines from both. Spectrum cards

Photon emitted Photon absorbed Energy levels Photon (energy) Energy of the photon matches a gap between levels Reemission of light has two steps:

Visible light is only a small range of the electromagnetic spectrum.

Each type of atom has a different electron structure. Each element has unique energy levels like a fingerprint.

80 Assignment: 5.3: 163/42-48,50,51,71-75 and handout(s)

Quantum Numbers Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals. This is also known as probable location of electrons about the nucleus of an atom. 81

Principal Quantum Number, n Indicates the main energy level occupied by an electron (n=1,2,3,…7) 82

Angular momentum quantum number has 4 basic shapes The values and shapes are l = 0s shape l = 1p l = 2d l = 3f 83

Angular Momentum Quantum Number, l s shape sparknotes.com 84

p shape 85

d shaped orbitals Courtesy of bluelight.ru 86

f orbitals f orbitals are very complex and you will not be responsible for drawing them. The site below has more informtion. AOs/ao4.html 87

Spin quantum number, s, has only two possible values Has only two possible values: +1/2, -1/2. See table 2 on page 110 to get a better idea of the number of orbitals and electrons per energy level. 88

Electron Configurations I.Rules Governing Electron Configurations II.Orbital Notation III.Electron-Configuration Nottion 89

Rules Governing Electron Configurations I.Aufbrau Principle – an electron occupies the lowest-energy orbital that can receive it. Source: This is really a thought process in which we think about building up an atom from the one that preceeds it in atomic number, by adding a proton and neutrons to the nucleus and one electron to the appropriate atomic orbital. 90

II. Pauli Exclusion Principle – no two electrons in the same atom can have the same set of four quantum numbers. Rules Governing Electron Configurations, cont. The box at left shows the different spin states of two electrons in the same orbital. This drawing is the electron configuration of a helium atom’s 1 s orbital. 91

Rules Governing Electron Configurations, cont. III.Hund’s Rule – orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin state. en.citizendium.org 92

Source: chem.wisc.edu Periodic Table: Orbitals 93

Orbital Notation Source: naturalphilosophers.org Pair of electrons in an orbital Unpaired electron Orbital name What element is this showing? Fluorine 94

Sample problems Write the electron configuration notation for Silicon and Scandium (use the Aufbrau diagram) Si has 14 electrons 2 in 1s 2 in 2s 6 in 2p 2 in 3s 2 in 3p written as: 1s 2 2s 2 2p 6 3s 2 3p 2 95

Scandium Electron Configuration Notation Sc has 21 electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 96

Scandium Notations Electron Configuration Notation 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 Orbital Notation __ __ __ __ __ __ __ __ __ __ __ __ __ __ _ 1s 2s 2p 3s 3p 4s 3d 97

Notations,cont. Noble gas notation – back up to the last noble gas prior to the element and add orbitals: [Ar]4s 2 3d 1 Dot notation - shows only the outer shell electrons for an element’s atom (maximum number of e’s in an outer shell is 8) for Sc: 4s 2 for F: 2s 2 2p 5 for Ne: 2s 2 2p Sc : : F : : Ne :... Other info: atoms are more stable when they have a half- filled or completely filled outer shell 98