Presentation on theme: "WARM-UP Studying atoms is difficult because they are too small to see or directly observe even with the best scientific tools. Write a similar example."— Presentation transcript:
1 WARM-UPStudying atoms is difficult because they are too small to see or directly observe even with the best scientific tools. Write a similar example of something that can not be studied directly.
2 Chapter 4: Atomic Structure Atom- The basic building block of matterLearning Targets-I can describe the structure of atoms.I can describe how structure of an atom affects it’s properties.I can create a timeline that shows the developments that lead to the current model of the atom.
4 Ancient Greek Models of atoms BC Democratis- all matter consisted of extremely small particles that could not be divided he called them atoms from the Greek word Atomos which means “uncut” or “indivisiable” BC Aristotle- no limit to the number of times that matter could be divided Accepted until the 1800s
5 The existence of atoms wasn’t scientifically proven until the early 1800s. John Dalton, , English chemist and teacherStudied the behavior of gases in airConcluded that gas contains individual particlesNo matter how large or small the sample the ratio of the elements in compounds is always the same
6 Dalton’s atomic theory All elements are composed of atomsAll atoms of the same element have the same mass and atoms of different elements have different massesCompounds contain atoms of more than one elementIn a particular compound, atoms of different elements always combine in the same way
7 Daltons atomic model Tiny solid spheres with different masses Dalton’s theory explained data from many experiments and thus became widely accepted
8 Although atoms are incredibly small they can now be observed with a scanning tunneling microscope
9 Charged materialsSome materials when rubbed gain the ability to attract or repel other materialsGain either a positive or negative chargeObject with like charges repel or push apart, objects with opposite charges attract or pull togetherCharged particles can flow creating an electric current
10 Thomson’s model of an atom J.J. Thomson, an English physicistWires connect the metal disks at opposite ends of a empty glass tube, one disk becomes negatively charged and one becomes positively chargedA glowing beam appears in the space between the platesThe beam is repelled by a negatively charged metal disk or attracted by a positively charged plates brought near it
11 Thomson’s modelThomson hypothesized the ray was a stream of negatively charged particles contained inside atoms, now called electrons, which are part of all atoms and carry a charge of -1. No matter what metal he used he got the same particles The mass was always 2000 times smaller than the mass of hydrogen atoms (a proton)
12 Thomson’s modelFirst evidence that atoms are made of even smaller particlesAtom is neutral- negative charges scattered throughout an atom filled with a positively charged mass of matter
13 Ernest Rutherford’s Gold Foil Experiment Atom was believed to have its positive charge spread throughout.Rutherford shot alpha particles (large 2 + atoms) at a very thin sheet of gold foil.If the current model of the atom was correct the alpha particles should pass though gold the mass and charge being too small to deflect the alpha particles.
14 Rutherford’s atomic theory Most alpha particles actually passed straight through a small fraction bounced off the gold foil at large anglesAtoms are mostly empty spacePositive charge is concentrated in the nucleus, not evenly distributed, which contains the protons and neutrons and has a positive chargePositive charge varies among elementsEach nucleus must contain at least one proton, each proton is assigned a charge of +1
15 Rutherford’s atomic model All of an atoms positive charge is concentrated in the dense nucleus Electrons are outside the nucleus
16 James chadwick1932 James Chadwick, English physicist did experiments that proved the neutrons existed Concluded that they were neutral because they were not effected by a charged particle Neutrons are contained in the nucleus and have a mass equal to that of a protonCompare the mass, location and charge of protons, neutrons, and electrons.
17 Rutherford's atomic model couldn’t explain chemical properties of elements required knowledge of electron behaviorNiels Bohr ( )Focused on ElectronsAgreed with Rutherford that the nucleus of and atom was surrounded by a large volume of space
18 Electrons are only found in specific circular paths- orbits around the nucleus Each electron orbit has a fixed energy or energy levelAn electron cannot exist between energy levelsThe energy level closest to the nucleus is the lowestAn electron in an atom can move from one energy level to the next when it gains or loses energyEnergy lost can be in the form of lightThe Bohr Model
19 The Quantum Mechanical Model Rutherford-Bohr described the path of an electron as a large object would behave which was inconsistent with theoretical calculations and experimental resultsElectrons move in a much less predictable way then planets in a solar system.Erwin SchrodingerDevised and solved a mathematical equation describing the behavior of the electron in hydrogen atom
20 Quantum Mechanical (Electron Cloud) Model Electron Cloud- visual model of the most likely locations for electrons in an atomBased on the probability of finding an electron with in a certain volume of space surrounding the nucleus is described as a fuzzy cloud where the electron is 90% of the timeMore dense- probability highLess dense- probability low
21 Atomic orbitalsThe electron cloud represents all the orbitals in an atomAn orbital is a region of space around the nucleus where an electron is likely to be foundEach orbital can hold 2 electronsThe lowest energy level has one orbital, the second has four, the third 9 and the fourth 16Electron configuration- the arrangement of electrons in the orbitals of an atomThe most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies this is called the ground state
22 Distinguishing Among Atoms How are atoms of Hydrogen different than atoms of oxygen? Element of different atoms are contain different numbers of protons
23 Atomic Number- the number of protons in the nucleus of an atom of a given element Identifies an ElementAtoms are electrically neutral so the number of electrons are also equal to the atomic number
24 Au Elements can be represented in the following shorthand notation: Mass Number- the number of protons and neutrons in the nucleusExample- carbon has 6 protons and 6 neutrons so the mass number is 12Most the mass of an atom is concentrated in the nucleusThe number of neutrons in an atom is the difference between the mass number and the atomic number.# neutrons = mass # - atomic #symbolMass #Au19779Atomic #Or Gold-197
25 Isotopes- atoms that have the same number of protons but a different number of neutrons Different mass numbersChemically alike- same protons and electrons which are responsible for chemical behavior
26 Atomic MassThe mass of atoms are givin in comparison to carbon-12An atomic mass unit (amu) = 1/12 the mass of a carbon-12 atomCarbon 12 amuFlourine- actual mass x 10 –23 g, atomic mass amu1 proton or neutron- 1 amuAtomic mass- weighted average mass and relative abundance of isotopes as they occur in natureExample- Hydrogen –1, 99 %,Hydrogen- 2, 1% heaverHydrogen- 3Atomic mass