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Atoms CHAPTER 3 Section 1: Inside the Atom Compare & contrast protons, neutrons, & electrons Describe the forces that hold the particles of atoms together Define atomic number & mass number Describe ions & isotopes Inside the Atom Atomic mass unit (amu) atomic number Electron isotope Mass number neutron Proton quark ion nucleus Inside the Atom Atoms are the smallest particles of an element that still have that element’s properties Building blocks of matter Extremely Even small small particles make up atoms Inside the Atom Nucleus=center of an atom (plural is nuclei) Most of the atom’s mass is here, but not its diameter If an atom was the size of a football stadium, the nucleus would be a pea Inside the Atom Protons= positive electric charge in the nucleus The number of protons in an atom determine its properties Neutrons=particle with no charge in the nucleus Atoms of an element can have the same number of protons & neutrons Inside the Atom Electrons= negative electric charged particle outside the nucleus Opposite Atoms but equal charge of a proton have the same number of electrons & protons (makes the atom electrically neutral) Inside the Atom Opposites attract Negative Why is attracted to positive doesn’t the nucleus fall apart? Strong force Inside the Atom Electrons are soooooooooooooooooooooooooooooooooo ooooooooooooooooooooooooooooooooooo small, they have almost no mass and we can ignore it. The mass of an atom is in the nucleus, measured in atomic mass unit (amu) Inside the Atom 1 amu= 1 proton 1 amu=1 neutron The sum of the number of protons and neutrons is equal to the total mass of the atom Atomic #=number of protons (unique for each element Mass #=number of protons plus neutrons Inside the Atom Inside the Atom Ion=atom They that has lost or gained electrons have a positive or negative charge They don’t have the same # of protons and neutrons Atoms that lost electrons become positive cations Atoms that gained electrons become negative anions Inside the Atom Isotopes= atoms of the same element but with different number of neutrons Many occur naturally, the most common gives us the average atomic mass Inside the Atom Inside the Atom Isotopes are named for the mass number Carbon with 7 neutrons and 6 protons would be called carbon-13 Carbon with 8 neutrons and 6 protons would be called carbon-14 Inside the Atom Quarks= tinier particles that make up protons and neutrons 3 for protons and 3 for neutrons Their charges give protons & neutrons their respective charges Held together by gluons Section 2: History of the Atom State Democritus’s ideas about the atom Outline Dalton’s atomic theory Explain how Thomson discovered electrons Describe nucleus how Rutherford found the History of the Atom We could not see atoms before 1981 Scanning The tunneling microscopes idea of an atom was from ancient Greece & Democritus History of the Atom Democritus wanted to know what would happen if you cut something into smaller, and smaller, and smaller pieces He thought eventually you couldn’t cut any more He called “uncuttable” pieces atomos History of the Atom Aristotle was more famous & influential than Democritus He thought atoms were stupid and rejected the idea It was more than 2000 years later before we knew Democritus was smarter than Aristotle History of the Atom John Dalton, around 1800, brought Democritus’s ideas back Dalton studied pressure of gases, and concluded that gases are made of tiny particles in constant motion He also found that compounds are always made of the same elements in the same ratios Water is always H2O, never H3O or HO2 History of the Atom Dalton also found that different compounds were made of different elements or ratios Water is made of different things than sugar From this Dalton reasoned this happens because elements are made of tiny particles that can combine in many different ways ATOMS History of the Atom Dalton’s Atomic Theory All substances are made of atoms. Atoms are the smallest particles of matter & cannot be divided All atoms of the same element are alike, atoms of different elements are different Atoms join together to form compounds & compounds always has the same kinds & ratio of atoms History of the Atom Dalton’s Theory is widely accepted, except the part about atoms being the smallest particles. Electrons, protons, neutrons, quarks History of the Atom Thomson used a vacuum tube and an electric current The flow of electricity bent towards a positive plate, showing that electrons are negatively charged. History of the Atom History of the Atom Thomson developed the Plum Pudding Model He thought that since electrons are negative, the rest of the atom must be positive to cancel it out Atoms & electrons are like plum pudding, plums scattered through it History of the Atom History of the Atom Rutherford discovered the nucleus with gold foil & a beam of alpha particles (positive charge) He shot alpha particles at gold foil and thought they would go straight through He found that most particles went straight through, but some came straight back & some went off in weird angles History of the Atom Rutherford concluded that Thomson was wrong with his model. There is only a small center of the atom that is positive, the rest is empty space He came up with the planetary model, where electrons orbit the nucleus Section 3: Modern Atomic Theory Define energy levels Describe the electron cloud and orbitals Electron Cloud Energy Level Orbital Modern Atomic Theory Rutherford had the best model of the atom so far, but Niels Bohr created a better and more useful model Bohr’s Model of the Atom Modern Atomic Theory Bohr research electrons in the early 1900s. He discovered electrons stay in orbits @ fixed distances from the nucleus Rutherford thought they orbit randomly Modern Atomic Theory Bohr’s model uses the idea of energy levels Energy levels are locations @ fixed distances from the nucleus and are the only place electrons are found Electrons between can be on one energy level, but not in Modern Atomic Theory The energy level with the least energy is closest to the nucleus, and as you move further away energy increases Electrons can jump from one level to another If atoms absorb energy, electrons can jump up If atom emit energy, the electrons jump down Modern Atomic Theory Fireworks are an example of electrons jumping up and moving back down to their energy level When an atom absorbs energy, electrons jump up in energy level When the electrons go back to their original level they emit energy in the form of light Different arrangements of electrons give different colors of light Modern Atomic Theory Modern Atomic Theory We cannot know where electrons are at a given point of time They move too fast and don’t travel in a fixed path Electrons travel like a wave Modern Atomic Theory Today we have the electron cloud model The model shows a general area where electrons are likely to be Modern Atomic Theory Some regions of the cloud are denser than other The denser regions are where electrons are most likely to be Each orbital can only have 2 electrons each Different energy levels have different numbers of orbital Modern Atomic Theory Different energy levels have different max numbers of electrons First Four Energy Levels and Their Orbitals Energy Level Number of Orbitals Max. No. of Electrons (@ 2 per orbital) 1 1 2 2 4 8 3 9 18 4 16 32
