Presentation on theme: "Chapter 2: The Atom Atom: The smallest unit of an element that retains the chemical properties of the element."— Presentation transcript:
1 Chapter 2: The AtomAtom: The smallest unit of an element that retains the chemical properties of the element
2 2.2 Matter and Structure Atoms consist of three primary particles. Electrons, Protons & NeutronsNucleus - small, dense, positively charged region in the center of the atom. Contains:protons - positively charged particles, with mass of 1 amu.neutrons - uncharged particles, with mass of 1 amu.2.2 Matter and Structure8
3 Surrounding the nucleus is a diffuse region of negative charge populated by: electrons - negatively charged particles, very little mass2.2 Matter and StructureTable 2.1 Selected Properties of the Subatomic ParticlesName Charge Mass(amu) Mass (grams)Electrons (e) x x 10-28Protons (p) X 10-24Neutrons (n) x 10-24
4 MassNumberCharge of particle92.2 Matter and StructureSymbol ofthe atomAtomic Numberatomic number (Z) - the number of protons in the atommass number (A) - sum of the number of protons and neutrons
5 Calculate the Composition of an Atom Calculate the number of protons, neutrons and electrons in each of the following:2.2 Matter and Structure
6 Isotopes - atoms of the same element having different masses contain same number of protonscontain different numbers of neutronsIsotopes of Hydrogen102.2 Matter and StructureHydrogen(Hydrogen - 1)Deuterium(Hydrogen - 2)Tritium(Hydrogen - 3)
7 Isotopes of the same element have identical chemical properties Some isotopes are radioactiveFind chlorine on the periodic table.What is the atomic number?17What is the mass given?35.45This is not the mass number of an isotope.2.2 Matter and Structure
8 2.2 Matter and Structure What is this number? It is called the atomic mass - the weighed average of the masses of the isotopes that make up chlorine.Chlorine consists of chlorine-35 and chlorine-37 in a 3:1 ratio.The weighed average is an average corrected by the relative amounts of each isotope present in nature.2.2 Matter and Structure
9 2.2 Matter and Structure Ions are Charged Atoms Ions - electrically charged particles that result from a gain or loss of one or more electrons by the parent atom.Cation - positively chargedresult from the loss of electrons23Na 23Na+ + 1e-Anion - negatively chargedresults from the gain of electrons19F + 1 e- 19F-2.2 Matter and Structure10
10 Subatomic particles in ions How many protons neutrons and electrons are in the following ion?2.2 Matter and Structure
11 Development of the Atomic Theory 11Dalton’s Atomic Theory - the first experimentally based theory of atomic structure of the atom.John Daltonearly 1800’sMuch of Dalton’s Theory is still regarded as correct today. See starred items.
12 Postulates of Dalton’s Atomic Theory 1. All matter consists of tiny particles called atoms.*2. An atom cannot be created, divided, destroyed, or converted to any other type of atom.3. Atoms of a particular element have identical properties.2.3 Atomic Theory
13 4. Atoms of different elements have different properties.* 5. Atoms of different elements combine in simple whole-number ratios to produce compounds (stable aggregates of atoms.)*6. Chemical change involves joining, separating, or rearranging atoms.** These postulates are still regarded as true.2.3 Atomic Theory
14 2.3 Atomic Theory Subatomic Particles: Electrons, Protons and Neutrons Electrons were the first subatomic particles to be discovered using the cathode ray tube.2.3 Atomic TheoryIndicated that the particles were negatively charged.
15 2.3 Atomic Theory Protons were the next particle to be discovered Protons have the same size charge but opposite in sign.Proton is1837 times as heavy as electron.NeutronsPostulated to exist in 1920’s but not demonstrated to exist until 1932Almost the same mass as the proton.2.3 Atomic Theory
16 2.3 Atomic Theory The Nucleus 12 The initial ideas of the atom did not have a “nucleus.”“Plum Pudding Model”Earnest Rutherford’s “Gold Foil Experiment” lead to the understanding of the nucleus.2.3 Atomic Theory
17 2.3 Atomic Theory“It was almost as incredible as if you fired a 15-inch shell at a piece of tissue and it came back and hit you.”-Earnest Rutherford.
18 2.3 Atomic Theory Light and Atomic Structure 13 Spectroscopy - absorption or emission of light by atoms (energy changes)Used to understand the electronic structure.To understand the electronic structure, we must first understand light (or electromagnetic radiation.)travels in waves from a sourcespeed of 3.0 x 108 m/s2.3 Atomic Theory
19 Electromagnetic Spectrum high energyshort wavelengthlow energylong wavelength
20 The Bohr Atom 14 Initial understanding of the atom by Niels Bohr Electrons exist in fixed energy levels surrounding the nucleus.Quantization of energyPromotion of electron occurs as it absorbs energyExcited StateEnergy is released as the electron travels back to lower levels.Relaxation
21 Orbit - what Bohr called the fixed energy levels. Ground state - the lowest possible energy state.
22 The orbits are also identified using letters as “quantum numbers” When the electron relaxes (c) the energy released is observed as a single wavelength of light.