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The Atom Chapter 2
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Dalton’s Atomic Theory (1803)
Do you know which of these statements are still valid? Elements are made up of atoms that are indivisible and indestructible. All atoms of an element have the same mass. No two different elements have the same mass. Compounds consist of small whole number ratios of elements. Elements are not changed during chemical reaction. False! False! True! True!
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Models of the Atom
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1903 Thomson – The plum pudding model
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Rutherford’s Alpha Scattering Experiment
Movie Movie
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The Results! Most of the positive alpha rays passed right through the Au as if there was nothing there. A few came really close to something very positive because they were deflected off at an angle. Fewer still collided with something very small and very dense because they bounced back towards the alpha ray source.
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Rutherford model Nucleus is dense and positive
Most of the mass of the atom is in the nucleus Electrons are outside the nucleus Most of the volume of an atom is empty space
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Subatomic Particles Particle symbol location charge mass
Electron e- orbital /1836 Proton p+ nucleus +1 1 Neutron n nucleus 0 1 The relative mass of the electrons is a good indication of why most of the atom is empty space. The electrons occupy most of the volume of an atom, and their mass is negligible. The positive charge of the dense nucleus comes from the charge of the protons.
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Describing Individual Atoms
Example:
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Lets see if you have it! Fill in the blanks:
Symbol neutrons protons electrons 60Co 81Br 27 33 27 - 35 46 36 65Cu2+
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Isotopes Stable? Isotopes are atoms with the same number of protons but different numbers of neutrons. Same element, different mass. Some isotopes are stable, others are not. The masses on the periodic table are weighted averages. Isotopes of hydrogen and carbon.
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Chlorine Chlorine is 75% chlorine-35 and 25% chlorine-37. What is the average mass?
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Which wave has the higher frequency?
Wave Nature of Light Wavelength – the distance light travels to complete one cycle. Frequency – the number of wave cycles in one second. Red light Which wave has the higher frequency? UV
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Radiant Energy Spectrum
High energy, short waves Low energy, long waves The radiant energy spectrum is continuous. Notice that harmful waves, like gamma rays and x-rays have very short wavelengths and very high energies.
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Bohr Model of Atom (Year: 1913)
nucleus Energy Levels Electrons are organized into discrete energy levels.
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Discontinuous line spectra of atoms!
What was the evidence? link Electrons release energy when they go from the excited state to the ground state. This energy is seen as lines in the spectra of atoms. Discontinuous line spectra of atoms!
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Final Statements on the Bohr model
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The electron as a wave Einstein, “Light, a wave, can have particle like properties” De Brolie, “particles, like electrons, can have wave-like properties” Scrödinger, “Came up with an equation that describes an electron” The Players
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The outcome n, principle quantum number. Correlates with shell of Bohr model l, subshell. Correlates with type of orbital, s p d or f. ml, orientation. px, py or pz. s, spin. or
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Energy Levels and Subshells
Each energy level is divided into sublevels, often called subshells. Types of subshells: s, p, d, f Number of subshells in an energy level depends on the energy level. E. Level Subshell s s,p s,p,d s,p,d,f
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Subshells and Orbitals
Electrons exist in orbitals. Most probable location for finding an electron. The number of orbitals depends on the subshell 2 electrons per orbital s orbitals come in groups of 1 p orbitals come in groups of 3 d orbitals come in groups of 5
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How does a 1s orbital differ from a 3s orbital?
S orbitals S orbitals are spherical Each successive s orbital is larger than the one that came before. They overlap each other surrounding the nucleus. 1s 3s 2s How does a 1s orbital differ from a 3s orbital?
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How many electrons fit in a 2 p orbital?
p Orbitals How many electrons fit in a 2 p orbital? 2 electrons in any type of orbital The three orbitals are only different by their orientation in space. pz py px
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The first shell only has an s orbital
The second shell has s& p orbitals The third shell has s, p d orbitals
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Orbitals in the third shell
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Electron Configurations
(Shell-subshell notation) 4d3 Energy level Subshell Number of electrons Lets investigate Electron Housing!
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Electron Configuration - N
5p 5s 4p 3d EPOT 4s 3p 3s 1s2 means 2 electrons in the 1s subshell. Note that the electrons have opposite spin since they are in the same orbital. 2s2 means 2 electrons in the 2s subshell. 2p3 means 3 electrons in the 2p subshell. Note Hund’s rule in filling in the 2p subshell: no orbital in a subshell has 2 electrons until every orbital in the subshell has one electron. 2p 2s Each arrow represents an electron 1s2 2s2 2p3 1s
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Electron Configuration - Na
5p 5s 4p 3d EPOT 4s 3p 3s Click the screen to get the electron configuration. 2p 2s Each arrow represents an electron 1s2 2s2 2p6 3s1 1s
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Electron Configuration - V
3d EPOT 4s 3p 3s V has 23 electrons. Note that the 4s fills before the 3d subshell because it is slightly lower in energy. Click the screen to get the electron configuration. 2p 2s Each arrow represents an electron 1s2 2s2 2p6 3s2 3p6 4s2 3d3 1s
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n = energy level = period number
An Easier Way n = energy level = period number ns subshell (n-1)d subshell np subshell H He 1 2 3 4 5 6 You can use the periodic table to do this, if you will learn what is being filled in each section. Each block represents the addition of one more electron.
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Electron Configuration – Al
1s2 2s2 2p6 3s2 3p1 ns subshell (n-1)d subshell np subshell 1 2 3 4 5 6 Click the screen to get the electron configuration.
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Electron Configuration - Co
1s2 2s2 2p6 3s2 3p6 4s2 3d7 ns subshell (n-1)d subshell np subshell 1 2 3 4 5 6 First imagine filling in the electrons in the boxes. Keep adding electrons until you get to the element’s position on the table. Then write your electron configuration. Click the screen to get the electron configuration.
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Electron Configuration - Sr
1s2 2s2 2p6 3s2 3p6 4s2 3d104p65s2 ns subshell (n-1)d subshell np subshell 1 2 3 4 5 6 Click the screen to get the electron configuration.
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