Physical Science: Concepts in Action
4.1: Studying Atoms
4.2: The Structure of an Atom
4.3: Modern Atomic Theory
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| 978196113 | Why have scientists developed atomic models? | Atoms are too small to be seen. | |
| 978196114 | What do you know about the GREEK Model of the atom? | --They thought it was INDIVISIBLE (so they thought atoms could NOT be broken down) --Only atoms of earth, air, water, and fire existed (Aristotle). | |
| 978196115 | What was Dalton's atomic theory? | Dalton proposed the theory that all matter is made up of individual particles called atoms, which cannot be divided. Main points: • All elements are made up of atoms • All atoms of the same element have the same mass, and atoms of different elements have different masses. (all oxygen atoms have the same mass; and the mass of oxygen is always different from every other element's mass) • Compounds contain atoms of more than one element. (ex: NaCl) • In a particular compound, atoms of different elements always combine in the same way. | |
| 978196116 | IMPORTANT: not all of Dalton's ideas were right. Which one wasn't? | Dalton was incorrect in stating that atoms cannot be divided. Atoms CAN be divided. | |
| 978196117 | What did Dalton's model look like? | Tiny, solid sphere | |
| 978196118 | DESCRIBE Thomson's experiments. What did he do, and what did he observe when he did this? | 1. Used a sealed tube of gas (so most of the air is gone). 2. Metal disk at each end of the tube. 3. Wires connect metal disks to electricity source. 4. When current is on, one disk is negatively charged; the other is positively charged. 5. A glowing beam then appears in the space between the disks. | |
| 978196119 | Thomson's hypothesis, based on his experiments: | HYPOTHESIS: the beam was a stream of charged particles that Interacted with the air in the tube and caused the air to glow. | |
| 978196120 | How did Thomson test his hypothesis that the beam was a stream of charged particles that interacted with the air in the tube and caused the air to glow? | To test his hypothesis, Thomson placed a pair of charged metal plates on either side of the glass tube. (There were still metal disks on the ends. He added plates to the sides). The plates caused the beam to deflect (bend) from its straight path. Thomson observed that the beam was repelled by the negatively charged plate and attracted by the positively charged plate. | |
| 978196121 | THOMSON'S hypothesis: the beam was a stream of charged particles that interacted with the air in the tube and caused the air to glow. What was his conclusion, then, when his new experiment caused the beam to bend? | Thomson concluded that the particles in the beam had a negative charge because they were attracted to the positive plate. | |
| 978196122 | Thomson had to determine where the particles in the beam came from. Where did he hypothesize they came from? | He hypothesized they came from inside atoms. SO, if they came from inside atoms, then atoms MUST BE DIVISIBLE. Two pieces of evidence supported his belief that these particles came from inside atoms: 1. No matter what metal he used for the disk, the particles produced were identical. 2. The particles each had about 1/2000 the mass of a hydrogen atom, the lightest atom. (so if it's smaller than the smallest atom, it must be subatomic, or smaller than the atom) | |
| 978196123 | WHOSE EXPERIMENTS provided the first evidence that atoms are made of even smaller particles? | J.J. Thomson: Tube/beam experiment. | |
| 978196124 | DESCRIBE THOMSON'S MODEL (what does it look like? What other name is given to it? Why is it made this way?) | Thomson's model is the "plum pudding" model, after a traditional English dessert. You might want to think of it as the "chocolate chip ice cream" model. Atoms are neutral (no positive or negative charge) Positive and negative charges must be equal in an atom for it to be neutral For Thomson's model: negatively charged particles are the chocolate chips. Those chocolate chips should be spread evenly throughout the positively-charged matter, the ice cream. KEY: Thomson's model has the negative charges spread evenly throughout positively-charged matter. | |
| 978196125 | RUTHERFORD'S MODEL | According to Rutherford's model, all of an atom's positive charge is concentrated in its nucleus (instead of the positive matter making up most of the atom with those negatively-charged chocolate chips or plums spread evenly throughout). | |
| 978196126 | Rutherford discovered that uranium emits fast-moving particles that have a positive charge. He called these fast-moving particles ________________________. | ALPHA PARTICLES | |
| 978196127 | Rutherford based his hypothesis off of the _____________________ model. | THOMSON | |
| 978196128 | RUTHERFORD'S HYPOTHESIS | Rutherford hypothesized that the mass and charge at any location in the gold would be too small to change the path of an alpha particle (remember, he's thinking that he's shooting small particles through this model that has only a few "chips" or "plums" scattered throughout the atom that would stand in his way). He predicted that most particles he shoots toward the gold foil would travel in a __________________ path from their source to a screen that lit up when struck. Those few that did not pass straight through would be deflected only slightly. (straight) | |
| 978196129 | WHAT ACTUALLY HAPPENED IN RUTHERFORD'S EXPERIMENT? | 1. Aimed the narrow beam of alpha particles at the gold foil. a. Screen around the gold made of a material that produced a flash of light when struck by a fast-moving alpha particle. By observing the flash, he could figure out the path of an alpha particle after it passed through the gold. b. Locations of the flashes on the screen did not support Rutherford's prediction that they would go straight through. More particles were deflected than he expected. One of every 20,000 was deflected by more than 90 degrees. Some particles even bounced straight back (as if they'd run into a wall). | |
| 978196130 | WHAT DID RUTHERFORD CONCLUDE BASED ON HIS EXPERIMENT? | The deflected particles most have come close to another charged object, and the closer they came to the charged object, the more they were deflected. Other particles passed through the gold without being deflected, though. Rutherford concluded that the positive charge of an atom is NOT evenly spread throughout the atom. (Therefore: disagreed with Thomson's chocolate chip/plum pudding model) INSTEAD, it is concentrated in a very small, central area that Rutherford called the NUCLEUS. The alpha particles whose paths were deflected by more than 90 degrees came very close to a nucleus. The alpha particles whose paths were not bent moved through the space surrounding the nuclei without coming close to it at all. | |
| 978196131 | What is the nucleus, and who discovered it? | The nucleus is a dense, positively charged mass located in the center of the atom. According to Rutherford's model, all of an atom's positive charge is concentrated in its nucleus. | |
| 978196132 | HOW BIG IS THE NUCLEUS OF AN ATOM? | VERY SMALL. The total volume of an atom is about a trillion times the volume of its nucleus. | |
| 978196133 | NAME and DESCRIBE the three subatomic particles. | PROTONS: a positively charged subatomic particle that is found in the nucleus of an atom. Each proton is assigned a charge of 1+. Some nuclei contain more than 100 protons. Rutherford concluded: different elements have different numbers of protons. STILL: they all have a 1+ charge. ELECTRONS: a negatively charged subatomic particle that is found in the space outside the nucleus. SMALL. (1/1836 the mass of a proton) The charge of an electron is opposite (but equal in size of charge) that of a proton. NEUTRONS: a neutral subatomic particle that is found in the nucleus of an atom. It has a mass almost exactly equal to that of a proton. | |
| 978196134 | The discovery of _______________ __________________ allowed scientists to describe the differences between atoms of different elements. | SUBATOMIC PARTICLES | |
| 978196135 | What determines an element's atomic number? | Short answer: the number of protons that are in each atom of the element. The atoms of any given element always have the same number of protons. REMEMBER: the number of protons NEVER changes. Hydrogen always has 1. Oxygen always has 8. Atoms of different elements have different number of protons. Each positive charge in an atom is balanced by a negative charge because atoms are neutral. SO: the number of electrons and the number of protons are equal in a neutral atom. | |
| 978196136 | MASS NUMBER: | The sum of the protons and neutrons in the nucleus of an atom. MASS# = # protons(atomic number) + #neutrons #NEUTRONS = Mass # - #Protons(atomic number) #Protons = Mass # - #Neutrons | |
| 978196137 | ISOTOPES: | Are atoms of the same element that have different numbers of neutrons and different mass numbers. Isotopes of an element have the SAME ATOMIC NUMBER but DIFFERENT MASS NUMBERS because they have different numbers of neutrons. Hard to notice any difference in the physical or chemical properties of their isotopes. Hydrogen is an exception. | |
| 978196138 | ISOTOPE OR ATOM?? | Remember: look at the Periodic Table for mass. If the mass differs from what is on that chart, you probably have an ISOTOPE and not an atom. Example: Oxygen Atomic Number: 8 Meaning: EVERY atom of oxygen has 8 protons. Mass Number: Number of Protons + Number of neutrons | |
| 978196139 | ISOTOPE OR ATOM?? | If this particular Oxygen as a mass of 16, we know for SURE the atom has 8 protons. We know that mass = protons + neutrons, so we know 16 = 8 + (#neutrons) Algebraically, we determine: 16 - 8 = #neutrons. SO, 8 = #neutrons. We look at the table: to be an "atom" and not an "isotope," the mass is supposed to be 16. SO: Oxygen with a mass of 16 has 8 protons, 8 neutrons, and is an atom, NOT an isotope. If the Oxygen had a mass of 17, we would still know the atom has 8 protons (remember, NUMBER OF PROTONS NEVER CHANGES) We know that mass = protons + neutrons, so we know 17 = 8 + (#neutrons) Algebraically, we determine 17 - 8 = #neutrons. SO, 9 = #neutrons. | |
| 978196140 | BOHR'S MODEL | -Agreed with Rutherford's model of a nucleus surrounded by a large volume of space -However, unlike Rutherford's, Bohr's model focused on ELECTRONS. -A description of the arrangement of electrons in an atom is the centerpiece of the modern atomic model. | |
| 978196141 | BOHR'S MODEL AND ENERGY LEVELS How are electrons positioned, how do they move, and what are energy levels? | Electrons move with constant speed in fixed orbits around the nucleus (like planets around a sun) Each electron in an atom has a specific amount of energy. If the atom gains or loses energy, the energy of electrons can change. ENERGY LEVELS: the possible energies that electrons in an atom can have. | |
| 978196142 | ENERGY LEVELS: | Must move through the energy levels in whole steps. They cannot exist BETWEEN levels. Each step away from the nucleus is a higher energy level. IMPORTANT: no two elements have the same set of energy levels. An electron in an atom can move from one energy level to another when the atom gains or loses energy. An electron may move up/go down two energy levels if it gains/loses the right amount of energy. The size of the jump between energy levels determines the amount of energy gained or lost. | |
| 978196143 | What evidence is there that electrons can move from one energy level to another? | Scientists can measure the energy gained when electrons absorb energy and move to a higher energy level. They can measure the energy released when the electron returns to a lower energy level. Think: fireworks: electrons move between energy levels. Heat produced by the explosion causes some electrons to move to higher energy levels. When those electrons move back to lower energy levels, they rlelease energy (some of which is visible light). Because no two elements have the same set of energy levels, different elements give off different colors of light. | |
| 978196144 | What was Bohr correct about? What was he wrong about? | CORRECT: assigning energy levels to electrons INCORRECT: assuming that electrons moved like planets in a solar system | |
| 978196145 | What must scientists deal with when trying to predict the locations and motions of electrons in atoms? What visual model tells them the most likely locations of electrons in an atom? | PROBABILITY. ELECTRON CLOUD. Additional: The cloud is denser at those locations where the probability of finding an electron. Scientists use the electron cloud model to describe the possible locations of electrons around the nucleus. (Propeller of an airplane example) | |
| 978196146 | ORBITAL | An orbital is a region of space around the nucleus where an electron is likely to be found. (p. 117 has a good example of this: if we mapped everywhere you'd been every 10 minutes over the course of a week by marking the spots you were in with a dot, we would have a model of your orbital. Wouldn't catch every location you ever visit, but it would be a good representation of where you were likely to be. The dots on your map are a good representation of how you behave in your orbital). An electron cloud is a good approximation of how electrons behave in their orbitals. | |
| 978196147 | How many orbitals are in the 1, 2, 3, 4th Energy levels? What is the maximum number of electrons in each? | 1: 1 orbital, 2 electrons 2: 4 orbitals, 8 electrons 3: 9 orbitals, 18 electrons 4: 16 orbitals, 32 electrons | |
| 978196148 | ELECTRON CONFIGURATION | An electron configuration is the arrangement of electrons in the orbitals of an atom. | |
| 978196149 | What is the most stable electron configuration? | The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies | |
| 978196150 | GROUND STATE | When all the electrons in an atom have the lowest possible energies. (p. 118 example of lithium) |
