4-2 Notes Discovering Parts of the Atom Chapter 4, Lesson 2

So... ... a neutron walks into Starbucks and orders a drink. The barista promptly serves him his drink. "How much will that be?" asks the neutron. "For you?" replies the barista, "no charge!" (get it?)

Thomson - Electrons In 1897, English scientist J.J. Thomson discovered electrons while doing an experiment to see how electric currents affected cathode rays.

Thomson - Electrons A cathode ray is a stream of particles that can be seen when an electric current passes through a vacuum tube. The ray travels from a negatively charged disk at one end to a positively charged disk at the other end.

Thomson - Electrons Thomson discovered the cathode rays did not travel in a straight line, but bent towards the positively charged plate.

Thomson - Electrons Opposite charges attract, so cathode ray particles must be negative if they are attracted to something positive. He named the particles electrons.

Thomson - Electrons He also said (like Dalton), that an atom was a solid sphere He added that an atom had a positive charge spread evenly throughout, with electrons mixed in to balance the charge.

Rutherford – Nucleus (Protons & Neutrons) (1899) Students of Ernest Rutherford shot alpha particles (protons + neutrons) through gold foil.

Rutherford – Nucleus (Protons & Neutrons) (1899) 2 protons bound to 2 neutrons (a Helium nucleus)

Rutherford – Nucleus (Protons & Neutrons) Rutherford thought the path of the alpha particles would bend only slightly because there was not anything big enough to strongly repel them.

Rutherford – Nucleus (Protons & Neutrons) Most particles did pass straight through. Some particles were strongly bounced to the side. One in about 8000 bounced completely backwards.

Rutherford – Nucleus (Protons & Neutrons) Rutherford believed the alpha particles were hitting something with a positive charge and relatively large mass.

Rutherford – Nucleus (Protons & Neutrons) He revised the atomic model: The atom is mostly empty space with the nucleus in the middle. He discovered the proton, and predicted the existence of the neutron. His model did not accurately explain how electrons are arranged in the atom.

Bohr - Hydrogen Atom (1913) A Danish scientist, Niels Bohr, studied the hydrogen atom and then proposed a new model for the arrangement of electrons in an atom. Bohr studied under both Thomson and Rutherford.

Bohr - Hydrogen Atom Bohr thought electrons traveled in circles with a certain diameter. Bohr studied hydrogen because it has only one electron. When atoms are excited, they absorb and release energy in the form of light.

Bohr - Hydrogen Atom A spectral line is a single wavelength of light that can be seen when the light from an excited element is passed through a prism. When excited, hydrogen and neon give off unique narrow bands of light on the spectrum.

Bohr - Hydrogen Atom An energy level is a region in space corresponding to a certain energy through which an electron moves (similar to a planet’s orbit).

Bohr - Hydrogen Atom He said that electrons move in specific orbits that are a set distance outside the nucleus. Each energy level can hold a certain number of electrons according to these rules: Bohr’s Model

Bohr - Hydrogen Atom The first level holds 2 electrons, the second level holds 8 electrons. 10 Ne Neon 20.18 Neon’s atomic number = 10 It has 10 protons. It has 10 electrons.

Bohr - Hydrogen Atom Ne The lowest level is filled first. 10 Neon 20.18 Ne

Bohr - Hydrogen Atom Ne The lowest level is filled first. 10 Neon 20.18 Ne

Bohr - Hydrogen Atom Ne The lowest level is filled first. 10 Neon 20.18 Ne

Bohr - Hydrogen Atom The second level has no electrons until the first level is full. 10 Ne Neon 20.18 Ne

Bohr - Hydrogen Atom The second level has no electrons until the first level is full. 10 Ne Neon 20.18 Ne

Bohr - Hydrogen Atom The second level has no electrons until the first level is full. 10 Ne Neon 20.18 Ne

Bohr - Hydrogen Atom The second level has no electrons until the first level is full. 10 Ne Neon 20.18 Ne

Bohr - Hydrogen Atom The second level has no electrons until the first level is full. 10 Ne Neon 20.18 Ne

Bohr - Hydrogen Atom The second level has no electrons until the first level is full. 10 Ne Neon 20.18 Ne

Bohr - Hydrogen Atom The second level has no electrons until the first level is full. 10 Ne Neon 20.18 Ne

Bohr - Hydrogen Atom The second level has no electrons until the first level is full. 10 Ne Neon 20.18 Ne

Bohr - Hydrogen Atom The second level has no electrons until the first level is full. 10 Ne Neon 20.18 Ne

Bohr - Hydrogen Atom Ne Li The last energy level may or may not be filled to the max. Ne Li 10 Ne Neon 20.18 3 Li Lithium 6.94

Bohr - Hydrogen Atom An element will react with other elements to try to receive a full outer energy level. (also known as “completing the octet”)

Bohr - Hydrogen Atom This diagram shows how electrons are placed in the elements with atomic numbers 1–10 (according to Bohr’s model)

Bohr - Hydrogen Atom Different numbers of electrons in outer energy level results in different elements. Unreactive elements have a full outer energy level. Elements with incomplete outer energy levels are likely to form compounds.  

Bohr - Hydrogen Atom Atomic Model http://glencoe.mcgraw-hill.com/sites/0078741858/student_view0/brainpop_movies.html# Atomic Model

Modern - Electron Cloud Model Today scientists think of an electron in an atom as being in an electron cloud, which is a region surrounding an atomic nucleus where an electron is most likely to be found. Electron Cloud Model

Modern - Electron Cloud Model Electrons are more likely to be near the nucleus because they are attracted to the positive charge of the protons.

An excited hydrogen atom emits narrow bands of light called ____. 4.2 Discovering Parts of the Atom A B C D An excited hydrogen atom emits narrow bands of light called ____. A energy lines B wave lines C spectral lines D wavelengths

Elements that do not react with other elements must have ____. 4.2 Discovering Parts of the Atom A B C D Elements that do not react with other elements must have ____. A completely filled energy levels B excited electrons C empty energy levels D the same number of protons and neutrons

A because they were repelled by the protons in the foil 4.2 Discovering Parts of the Atom A B C D In the gold foil experiment, why did some particles pass straight through the foil? A because they were repelled by the protons in the foil B because they were attracted by the protons in the foil C because atoms have no effect on charged particles D because atoms are mostly empty spaces

Atoms of the same element always have the same number of ____. A electrons B neutrons C ions D protons

An electron moves into a higher energy level. What must have happened? A The electron released energy. B The electron absorbed energy. C The atom gained a negative charge. D The atom gained a positive charge.

A spectral line is caused by ____. A an excited electron releasing energy and falling to a lower energy level B an excited electron absorbing electricity and jumping to a higher energy level C an atom gaining an ionic charge D an atom losing a proton

4-2 Vocab Text p. 182-194 charge Thomson's Atomic model research Rutherford's Atomic model visible spectral line energy levels Bohr's Atomic model electron cloud electromagnetic spectrum