Noble-ity Page 175

Entry Task What 3 particles make up an atom? Protons, neutrons, electrons What particles are in the nucleus? Protons & neutrons What is the charge on a proton? positive What is the charge on an electron? negative What is the charge on a neutron? Neutral (no charge) An element is determined by the number of what? protons What happens in an ionic bond? One atom transfers electrons to another atom What happens in a covalent bond? Atoms share electrons equally What happens in a polar covalent bond? Atoms share electrons unequally What do you get when you change the number of electrons on an atom? An ion

Entry Task Which scientist discovered the electron? Thomson Which scientist proposed a model of an atom that contained a nucleus? Rutherford Which scientist proposed the “plum pudding” model of an atom? Thomson Most of the volume of an atom is made up of what? Empty space Most of the mass of an atom is located where? nucleus When looking at white light through a spectroscope (clear lightbulb, sunlight), what did the spectrum look like? A rainbow The electrons in the outermost energy shell of an atom are called? Valence electrons You cut a piece of gold in half repeatedly until you end up with the smallest piece that can still be considered gold. What do you have? An atom What determines bond type? Difference in electronegativities What is the energy required to take an electron from an atom? Ionization energy

Noble-ity Start a new thread/topic Learning Target: What do spectral lines tell me about the structure of an atom? Update TOC

Noble-ity Read Intro p. 175-176 Read Process & Procedure Intro p. 176

Noble-ity P&P#1 Draw the Hydrogen Line Spectrum in your notebook. Label: longest wavelength, shortest wavelength, highest energy, lowest energy Shortest wavelength Highest energy Longest wavelength Lowest energy

Noble-ity P&P#2 2a: How do you know that the Rutherford model of atom structure did not explain line spectra? The Rutherford model of the atom just showed that electrons were outside of the nucleus, but did not specify that they had to be in specific locations around the nucleus.

Noble-ity P&P#2 2b: How do you know that each line is associated with a different amount of energy? Each line has a different color. Color depends on wavelength, and color is a form of light. Light is a form of energy. Therefore, each color corresponds to a different amount of energy.

Noble-ity P&P#2 2c: What makes you think rapidly moving electrons, not rapidly moving protons, are responsible for spectral lines? Protons are about 1800 times heavier than electrons. If light emissions requires a particle to move rapidly between energy states, it would seem more likely that electrons, which are much lighter, would be better able to move quickly.

Noble-ity P&P#2 2d: How were differences in the amount of dark space between lines of color important? Different sized dark spaces separate lines of different color. The different colors are associated with different amounts of energy. The difference in size of dard spaces results from electrons moving between energy levels separated by different amounts of energy.

Noble-ity P&P#4 Read and take notes on Niels Bohr p. 177-178

Niels Bohr Bohr was a Danish physicist Worked with Rutherford to improve the model of the atom Wanted to explain what was wrong with Rutherford’s model

Niels Bohr Most scientists believe that electrons could orbit anywhere around the nucleus. Bohr believed that electrons could only move in specific orbits. How did he prove it?

Niels Bohr He used spectral line data from Hydrogen to prove his point. Spectral lines are unique for each element. The lines only appear at specific wavelengths.

Niels Bohr Bohr predicted that electrons can only absorb a specific amount of energy. He called this a quantum of energy. A quantum of energy is the specific amount of energy needed for an electron to move to a higher energy shell.

Niels Bohr When the electron returns to the lower energy level, the quantum of energy is released as a photon of light  a spectral line seen through a spectroscope Each spectral line corresponds to a quantum of energy.

Niels Bohr When the electron returns to the lower energy level, the quantum of energy is released as a photon of light  a spectral line seen through a spectroscope Each spectral line corresponds to a quantum of energy.

Niels Bohr The reason every element has a different line spectrum is because each element has a different number and arrangement of electrons that can absorb and release different quanta of energy. Each element has a different number of protons attracting the electrons, which means that the energy levels are located at different distances from the nucleus.

Niels Bohr Bohr proposed that electrons only travel is specific paths – called orbits. An electron has a specific amount of energy to keep it in its orbit. It is not losing or gaining energy as long as it stays in its orbit.

Niels Bohr To move to a higher orbit, an electron must absorb an exact quantum of energy. When it jumps back to its lower energy level, it releases an exact quantum of energy (photon of light) Bohr’s model and calculations worked really well for Hydrogen, but were not as accurate for bigger elements.

P&P #6a Sr2+ground state + energy  Sr2+excited state Sr2+excited state  Sr2+ground state + photon Which expression represents an electron of a strontium ion absorbing energy? The first equation because it shows the electron absorbing energy and moving to a higher energy level (excited state)

P&P #6b Sr2+ground state + energy  Sr2+excited state Sr2+excited state  Sr2+ground state + photon Which expression represents an electron of a strontium ion emitting energy? The second one because the energy is being emitted in a photon of light.

P&P #6c Sr2+ground state + energy  Sr2+excited state Sr2+excited state  Sr2+ground state + photon What particle transports energy away from the excited state of a strontium ion when it falls to the ground state? A photon carries the energy. The photon is associated with a unique color of light.

P&P #6d Based on flame tests, what is a reasonable hypothesis about the color of an emitted photon from strontium? Red, since the flame test showed a red color.

P&P #6d Sr2+ground state + energy  Sr2+excited state Sr2+excited state  Sr2+ground state + photon Did the heat of the flame ionize the strontium ion? It was already ionized as a result of dissolving in water. The electrons are moving back and forth between energy levels, they are not being removed from the nucleus (ionized)