Atomic Structure
Put the discoveries in order, with the earliest at the top and the latest at the bottom.
1. Matter is made of atoms. 2. Atoms contain electrons. 3. Atoms are mostly empty space. 4. Atoms have a nucleus with electrons outside it. 5. Light is made of packets. 6. Electrons are in a cloud.
Who was John Dalton?
A British school teacher who invented the atomic theory
Dmitri Mendeleev
A Russian chemist who developed a periodic table of the elements.
Molecule
A covalently bonded group of atoms.
Battery
A group of electrochemical cells that are arranged in a series and continuously convert chemical energy into electrical energy.
Bohr Model
A model of the atom proposed by Bohr in early 1900s. Negatively charged electrons were thought to move in orbits around the nucleus, equally spaced apart from each other and the nucleus.
Electron
A negatively charged subatomic particle located outside the nucleus of an atom.
Photon
A packet of light energy, technically called a quantum of electromagnetic radiation.
Photoelectric Effect
A phenomenon in which electrons are ejected from the surface of a metal when light shines on the metal. This experiment showed that light can remove electrons from atoms. Emission or ejection of electrons from the surface of a metal when a light of certain frequency falls on the surface of the metal. Electrons emitted in this effect can be called photoelectrons. The light which falls on the surface of the metal must be of sufficiently high frequency called as threshold frequency. Thus light knocks off the electrons and thus the flow of electrons will result in the production of electricity.
Proton
A positively charged subatomic particle located in the nucleus.
Chemical Reaction
A process in which substances are converted into new ones with different properties.
Charge
A property of matter that causes it to experience electrical forces.
Cathode Ray
A stream of electrons emitted by the cathode in a vacuum tube. A cathode ray is produced by attaching a battery to a container of atoms in the gas phase. Thomson's experiment showed that a cathode ray would bend when placed between electrically charged plates. The two plates had opposite charges: One plate was negatively charged, and the other was positively charged. The cathode ray bent toward the positive plate
Quantum Mechanics
A theory that explains the behavior of matter and energy on the atomic scale.
Chemical Symbol
An abbreviation for the name of a chemical element; it consists of a single capital letter or a capital letter followed by a small letter.
Isotope
An atom of an element having a specific number of neutrons in the nucleus.
Plum-Pudding Model
An atomic model proposed by Thomson in the late 1800s but not held as true today. Negatively charged electrons were thought to be scattered in a positively charged substance (like raisins scattered in pudding).
Neutron
An uncharged subatomic particle in the nucleus.
Thomson's experiment showed that ______________ the contained ____________ particles called electrons, disproving part of ___________ model.
Atom, Smaller, Dalton's
What did J.J. Thompson's experiment show about atoms?
Atoms contained negatively charged particles (Electrons) He also made a prediction about what atoms looked like. His idea was that an atom was a ball of positive charge, with little negative charges (electrons) scattered around inside. He called his idea the plum-pudding model because the model itself resembled a British pudding dessert filled with raisins. The pudding was the atom, and the raisins were the electrons. Scientists later discovered that the plum-pudding model was inaccurate.
Dalton's idea that __________________ rearrange during chemical reactions is considered _______________ today.
Atoms, True
Robert Millikan
Discovered an electron's charge An American experimental physicist, known for measuring the charge on the electron and for his work on the photoelectric effect.
In the photoelectric effect, what happens when light hits the metal?
Electrons are knocked off atoms, causing electricity to flow.
Albert Einstein (1879-1955)
Explained the photoelectric effect A German-born scientist who moved to the United States after Adolf Hitler came to power. He was best known for his theory of relativity. For a long time, no one could explain why the energy of the light is what determines the photoelectric effect — not the amount of the light. Finally, Albert Einstein published a paper that explained the effect. He would eventually win the Nobel Prize for this discovery. Einstein explained that light came in set amounts of energy. A packet of energy is called a photon. If just one photon has enough energy, it can remove an electron from an atom. Different colors of light have different amounts of energy. This idea was a revolutionary one that led to an entire century of discoveries and was the basis of a scientific field called quantum mechanics. Scientists use quantum mechanics to explain the properties of electrons and light at an atomic level.
Milikan's Oil-Drop Experiment
First, Millikan attached a battery to two metal plates. Millikan found that he could make charged oil droplets float between these two plates. He had to adjust the voltage very carefully so that the electrical forces balanced out the weight of the oil. He did this experiment many times using many different sizes of oil droplets. He carefully measured the amount of voltage needed to hold up each drop. Millikan was attempting to measure the charge of an electron. He used the voltage needed to float the drops to calculate the mass and charge of each drop.
How did Ernest Rutherford contribute to the atomic theory?
He showed that most of an atom's mass is located in the nucleus
Dalton's Ideas
Ideas Still Considered Correct Today: - All matter is made of atoms - Chemical compounds are formed by a combination of two or more different kinds of atoms - A chemical reaction is a rearrangement of atoms Ideas Considered False Today: - Atoms are small and cannot be destroying or divided - All atoms of the same element have identical mass and other properties
How is the Bohr atomic model different from the plum-pudding model?
In Bohr's model, the atom's mass is found at its center instead of distributed throughout.
The Bohr model of the atom had a ______________________ made of and __________________ neutrons, with ___________________ circling outside.
Nucleus, Protons, Electrons
What was Thomson's model of the atom called?
Plum pudding model
Niels Bohr (1885-1962)
Presented an atom models with specific electron orbits A Danish physicist who contributed to understanding atomic structure and quantum mechanics. Scientists were aware that the mass of an atom was located mostly at its center. But a better model than the plum-pudding model was needed. In 1913, a physicist named Niels Bohr introduced his own model, which was called the Bohr model. In it, atoms were made of proton, neutron, and electron particles. Protons are positively charged particles. Neutrons are neutral particles, or particles with no charge. In Bohr's model, the protons and neutrons sat together in the middle of an atom, forming the nucleus. The electrons were on the outside, orbiting the nucleus like planets around the sun. However, just like J. J. Thomson's plum-pudding model, Bohr's atomic model was inaccurate.
John Dalton
Presented the first atomic model British schoolteacher, chemist, and physicist in the early 1800s. He made important advancements in a variety of scientific topics, including a study of color blindness. But Dalton is best remembered for being one of the first people to publish theories about the atom.
The idea that light can act as packets led to what new field of science?
Quantum mechanics
The most recent atomic model is based on _____________ mechanics and states that ______________ are in a cloud outside the _________________.
Quantum, Electrons, Nucleus
Who performed the oil drop experiment?
Robert Millikan
Ernest Rutherford (1871-1937)
Showed that an atom contained a nucleus A British physicist who discovered the atomic nucleus. In 1910, he performed an experiment with gold foil and tiny particles called alpha particles. This experiment changed the atomic model forever. While most particles went straight through the foil, some bounced back at a sharp angle.
J.J. Thomson
Showed that atoms contained electrons. A British physicist credited for the discovery of the electron and of isotopes. In 1897, he performed an experiment that involved cathode rays tubes (sealed air-free glass tubes that contain a wire and are full of gas) He produced a cathode ray by attaching a battery to an air-free tube filled with atoms in the gas phase. He then added some metal plates that had a charge on them, which means the plates produced a force that acted on electrically charged particles. Next, Thompson hooked up electrically charged metal plates to the tube, placing magnetic field coils of both sides. This caused the the beam to bend.
What did Rutherford observe that surprised him?
Some of the alpha particles shot at the gold foil bounced backwards.
Electron Cloud
The area around the nucleus where electrons are most likely to be located.
Nucleus
The center of mass and the positive charge of an atom.
How did Thomson's experiment change Dalton's atomic model?
The discovery of electrons
What does Rutherford's experiment tell us about atoms?
The fact that the alpha particles passed through meant that most of the atoms were made up of empty space. Most of the mass of an atom occupies only a small part of the space within an atom. From this experiment, the atom's nucleus was discovered. The nucleus of an atom takes up only a small amount of space but is the place where most of an atom's mass is contained.
Voltage
The force that causes electrical current to flow.
Gas Phase
The physical state in which a substance has no fixed shape or volume.
