2 Atoms Matter is made of atoms Atoms are the basic building block of matter
3 History of the Atom 400 BC Democritus THE ATOM IS AN INDIVISIBLE PARTICLEthe atom is the smallest particle of matter1808 DaltonTHE SOLID SPHERE MODELatoms are solid , indestructible spheres (like billiard balls)1897 J.J. ThompsonTHE RAISIN BUN MODELatoms are solid spheres made up of solid positive mass with tiny negative particles embedded in the positive
4 History of the Atom 1911 Rutherford THE PLANETARY MODEL the atom is composed of a positive nucleus and negative electrons which surround the nucleusatom is mostly empty spaceGold foil experiment
5 The Gold Foil Experiment by Rutherford PredictionIn accordance to the J.J. Thomson model of an atom, the alpha particles should have passed directly through the gold foil for all instances.Observationmost of the alpha particles passed straight through the foil, a small percentage of them were deflected at an angles and some were even backscattered.Conclusiontwo conclusions: one, an atom is mostly empty space and scattered electrons and two, an atom must have a positively charged centre that contains most of its mass
6 History of the Atom 1913 Niels Bohr electrons orbit the nucleus in different energy levelselectrons can move from one level to another by gaining or losing packets of energyelectrons are more stable when they are closer to the nucleus1932 Sir James Chadwickthe nucleus contains particles called neutrons and positively charge protons
8 Structure of the Atom Consists of sub-atomic particles. protons neutronselectronsProtons and neutrons are located in the nucleusElectrons orbit the nucleus
9 Determining the number of subatomic particles Each element has an atomic number and a mass numberAtomic number = no. of protons= no. of electronsMass number = no. of protons + no. of neutronsTherefore, no. of neutrons = mass number – atomic number
10 Example: How many protons, neutrons and electrons does carbon have? Atomic number = 6Mass number = 12Number of protons: 6Number of neutrons: 12-6 = 6Number of electrons: 6
11 Atomic SymbolAn international recognized system that allows anyone to commuicate information about the atommass numberAEchemical symbolZatomic number
12 Isotopes and ionsIsotope is an atom of an element with a different number of neutrons and hence a different mass number.An Ion is an atom that has lost or gained electron/s.
13 The Bohr ModelElectrons move around the nucleus in fixed energy levels called shells.Shells close to the nucleus are lower in energy while shells farther away are high in energy.Shells are number outwards from the nucleus (1,2,3..) and are also lettered (K,L,M,N...)
14 Number of electrons in shells Different shells hold different numbers of electrons. The maximum number of electrons that can fit into a shell is 2n2 (n = shell number)Shell number (n) Representative letter Maximum number of electronsin this shell (2n2)1 K X = 22 L X = 83 M X = 184 N X = 32
15 Drawing Atoms Bohr diagram number of protons and neutrons written in the centerelectrons drawn in circular orbits around the nucleus10 P10 N
16 Example: Chlorine Atomic number is 17. Mass number is 35. 17 protons and electrons17 P18 NMass number is 35.= 18 neutrons
17 Subshells Subshells are energy levels found within shells. There are four different types of subshellsNamed- s, p, d, f .Subshell energy: s<p<d<fsubshellNumber of electronss2p6d10f14
25 ShellSubshell Orbital Orbital is the 3 dimensional space around a nucleus in which electrons are most likely to be foundEach orbital can hold up to 2 electrons.Timberlake LecturePLUS 2000
26 Orbitals s subshell: spherical 1 orbital-2 electrons zp subshell: pair of lobes3 orbital- 6electronsxyShape represents electron density (not a path the electron follows)
27 d subshell: double dumpbells 5 orbital-10 electrons xyxyyzxzz2x2-y2
28 Ground state and excited state At ground state the electron is at its lowest possible energy level (electrons are as close to the nucleus as possible).Example: Sodium (Z=11)Ground state electron configuration: 2, 8, 1
29 Evidence for the Bohr Model If atoms are given large amounts of energy (heat, light or electricity), the electrons can jump to an orbit further away from the nucleus. The atom is then in an excited state.FluorineGround stateF: 1s2 2s2 2p5Exited stateF*: 1s2 2s1 2p5 3s1
30 Evidence for the Bohr Model When the electrons return to the ground state, they release this energy in the form of light. The light released has a specific wavelength corresponding to the difference between the energy levels.
31 Frequency An = 3Frequency Bn = 2Frequency Cn = 1
33 Evidence for the Bohr Model Emission Spectra are emissions of light from atoms that have been heated or provided with energy.
34 Evidence for the Bohr Model Emission Spectra are different for each material.FeThey can be used to determine the identity of an unknown sample of an element.
35 HydrogenHeliumPractise1) Draw 2 Bohr-Rutherford diagrams for lithium; one in the ground state and one in the excited state. Make sure to include the energy put into the system, and energy released.2) Explain why different elements have different emission line spectrums.
36 PractiseIdentify each of the unknown gases based on the emission line spectrums provided. The 4 possibilities are oxygen, hydrogen, helium and neon.ABCD