2Bell RingerThe ancient Greek philosopher Democritus coined what word for a tiny piece of matter that cannot be divided?ElementElectronAtomMoleculeDalton’s theory (~1800; based on behavior of gasses) included all but one of the following points. Which is not from Dalton?All elements are composed of atoms.Most of an atom’s mass is in its nucleus.Compounds contain atoms of more than one element.In a specific compound, atoms of different elements always combine in the same way.J. J. Thomson’s gas tube electrical experiments (~1897) provided first evidence of:AtomsNucleusSubatomic particlesElementsRutherford’s gold foil experiment (~1914) provided evidence for one of these:Negative and positive charges are spread evenly throughout an atom.Alpha particles have a positive charge.Gold is not as dense as previously thought.There is a dense, positively charged mass in the center of an atom.
3Properties of Subatomic Particles J.J. Thomson was the first to detect subatomic particles (later named electrons)Electron:Negatively charged subatomic particle.Found in the space outside the nucleus.Very light mass (~1/2000 of Hydrogen atom)Charge of 1-.
4Thomson’s Model of the Atom Thomson’s ExperimentsIn his experiments, J. J. Thomson used a sealed tube containing a very small amount of gas.Sealed tube filled with gas at low pressureGlowing beamPositive plateMetal diskNegative plateMetal diskMetal diskSource of electric currentSource of electric current4
5Properties of Subatomic Particles Rutherford found positive charge varies among the elements.Based on experiments with gold and other elements.Proton:Positively charged subatomic particleFound in the nucleus of an atom.Charge of 1+.Each nucleus contains at least one proton.
6Rutherford’s Atomic Theory The Gold Foil ExperimentAlpha particlesUndeflected particleDeflected particleGold atomsSlitBeam of alpha particlesAlpha particlesScreenSource of alpha particlesNucleus6
7Properties of Subatomic Particles James Chadwick the English physicist carried out an experiment to show that neutrons exist.Radioactive decay produced particles about the mass of a proton but without any charge.Proved the particles produced were neutral because a charged object did not deflect their paths.Neutron:Neutral (no charge) subatomic particleFound in the nucleus of an atom.Mass ~ equal to that of a proton.
8Comparing Subatomic Particles Everything we know about subatomic particles is based on how the particles behave in experiments.Scientists still do not have an instrument that can show the inside of an atom.
9Comparing Subatomic Particles MassProtons and neutrons have almost the same mass.Mass of ~2000 electrons = the mass of one proton.ChargeAn electron charge (-1) is equal in size but the opposite sign of a proton charge (+1).Neutrons have no charge.Location in the atomNucleus - Protons and neutronsOutside the nucleus - electrons
10Subatomic Particles - Protons Atoms of different elements have different numbers of protons.Atomic Number = Number of protons in an atom of that element.For any given element:All atoms have same atomic number.Hydrogen has 1 proton; atomic number = 1.Helium has 2 two protons; atomic number = 2Etc.Each element has a unique atomic number.
11Atomic Number and Mass Number Each element has a different atomic number.A The atomic number of sulfur (S) is 16.B The atomic number of iron (Fe) is 26.C The atomic number of silver (Ag) is 47.
12Atomic Number and Mass Number Atoms are neutral when:Each positive charge in an atom is balanced by a negative charge.i.e. # of protons = # of electronsEach proton has an electron to offset its chargeExamples:Hydrogen atomic number = 1Each neutral hydrogen atom has 1 proton & 1 electron.Sulfur atomic number = 16Each neutral sulfur atom has 16 protons & 16 electrons.
13Atomic Number and Mass Number Mass Number = Sum of protons + neutrons.To find # of neutrons (when mass # & atomic # are known):# of neutrons = mass # - atomic #Example: Aluminum with mass # = 27Mass # = 27Atomic # = 13.protons = 14 neutrons
15Charged AtomsAn atom becomes charged when it looses or gains an electron (e-).Positive Charge = loss of e-’sH becomes H+1Negative Charge = gaining of e-’sH becomes H-1Electrons are the only subatomic particle that can be gained or lost.
16Isotopes Isotopes = same element; different # neutrons Isotopes of an element:Same # of protonsi.e. same atomic numberDifferent # of neutronsDifferent atomic mass because of the neutrons
17Isotopes Isotopes are referred to by mass number For example, oxygen has 3 isotopes:“oxygen 16”, “oxygen 17”, and “oxygen 18”All three oxygen isotopes have same reactionsExamples:All combine with hydrogen to form waterAll combine with iron to form rust.
18IsotopesMost elements: Physical and chemical properties of all isotopes are very similar.Hydrogen is an exception.Hydrogen-1 no neutrons (most H is hydrogen-1)Hydrogen-2 has one neutronHydrogen-3 has two neutrons.Because a hydrogen-1 atom has only one proton, adding a neutron doubles its mass.
19Isotopes Heavy Water - hydrogen-2 atoms & oxygen-16 Hydrogen-2 atoms twice the mass of Hydrogen-1Properties of heavy water are different from the properties of ordinary water.
20Assessment QuestionsOf the subatomic particles that form the atom, the one with the smallest mass is:Neutron.ElectronProtonNucleus20
21Assessment QuestionsOf the subatomic particles that form the atom, the one with the positive charge is:Neutron.ElectronProtonNucleus
22Assessment QuestionsOf the subatomic particles that form the atom, the one with the neutral charge is:Neutron.ElectronProtonNucleus22
23Assessment QuestionsOf the subatomic particles that form the atom, which ones are found in the nucleus?Neutron.ElectronProtonNone23
24Assessment Questions In which way do isotopes of an element differ? number of electrons in the atomnumber of protons in the atomnumber of neutrons in the atomnet charge of the atom