UNIT 1 – MATTER AND QUALITATIVE ANALYSIS

UNIT 1 – MATTER AND QUALITATIVE ANALYSIS The Electromagnetic Spectrum, Bohr’s Model, Chemical Bonding

OBJECTIVES

The electromagnetic spectrum • Electromagnetic Energy: light energy that travels in the form of waves • Frequency: the number of cycles per second • Wavelength: he distance between successive crests or troughs in a wave • Nanometer: 10-9 m; unit nm

WAVES

LIGHT AND THE ELECTROMAGNETIC SPECTRUM • There are many different kinds of light: X-rays, ultraviolet, infrared, microwaves are all examples of light • Visible spectrum: the region of the electromagnetic spectrum tat the human eye can see • 400 to 700 nm • A rainbow contains all the colours of visible and near visible light • Continuous Spectrum: an uninterrupted pattern of colours that is observed when a narrow beam of white light passes through a prism

PRISM

VISIBLE SPECTRUM

LINE SPECTRUM • Different types of matter emit different wavelengths of light: • Neon gas emits red light • Sodium ions emit yellow light • Hydrogen gas emits blue/violet light • Each element has a different ‘line spectrum’ • Discontinuous spectrum of light that is produced when light the light from the gas is passed through a type of prism called a spectroscope • You see coloured lines rather than a rainbow

Continuous vs. Line

DIFFERENT ELEMENT, DIFFERENT LINE SPECTRUM: THE ELEMENT ‘FINGERPRINT’

QUESTIONS • Describe the difference between radio waves and X-rays using the concepts of wavelength, frequency, and energy • What range of wavelengths of electromagnetic radiation can the human eye detect • White light is composed of many different colours of light. Explain. • Distinguish between a continuous spectrum and a line spectrum

The bohr-model of the hydrogen atom • Negatively charged particles orbiting positive nucleus according to Rutherford… what is the problem with that? • (+) and (–) attract… atom should collapse on itself • Also, laws of moving charges means that orbiting electrons should emit energy and eventually run out.... • SPIRAL DEATH!!! (whomp whomp… that’s a problem) • MATTER IS VERY STABLE

HYDROGEN GAS LINE SPECTRUM

Nielsbohr • To the rescue!!! • Looking at the discrete line spectrum of hydrogen… observed discrete lines, inferred fixed energy levels of electrons • Inferred electrons are restricted to quantized energy levels • Quantized: possessing specific values or amounts (a quantity) • That is, electron’s can only have specific energy and orbit around the nucleus in orbitals at specific distances, the further away the greater the energy

Explanation • Electrons occupy specific energy states (orbitals) • Can only transfer levels by absorbing the EXACT amount of energy needed between them, to go up OR to give off (emit) the energy difference between lower energy levels.. • Hence, discrete energy levels • In doing so, it either absorbs or emits a particular amount of light…

each atom has slightly different allowable energy differences and different numbers of electrons that can do the transitions, therefore different spectrums for each • Ground state: level the electron wants to be at • Excited state: level with added energy

Each energy level can only have a certain number of electrons in it • 1st = 2 • 2nd = 8 • 3rd = 8

example • Draw the Bohr diagrams for: • Neon • Helium • Carbon • Calcium • Oxygen

THE NUMBER OF ELECTRONS IN THE VALENCE (OUTER) ORBITAL (SHELL) CORRESPONDS TO THE COLUMN (GROUP) THE ELEMENT IS N ON THE PERIODIC TABLE • Ex: Oxygen (Group 6) has 6 electrons in its valence shell; Sodium (group 1) has 1

Homework questions • State the reasons why Rutherford’s model of the atom failed to describe the observed behaviour of matter • Describe Bohr’s model of the atom. How is it similar and how is it different to Rutherford’s Model of the Atom? • What role did Spectroscopy play in helping Bohr come up with his model? • Why do electrons emit light energy when they drop from a higher to lower energy level? • What does it mean by “energy levels are quantized? • Drawing Bohr diagrams

FLAME TESTS https://www.youtube.com/watch?v=d8hpUtRnsYc

Four types of qualitative analysis • Thermal Emission Spectroscopy (TES): substances are identified based on amount of heat they emit • Line spectroscope: substances are identified based on their line spectra • Flame tests: substances are identified based on the colours they emit when placed in a flame • Carbonation: the presence of metals is identified based on the emission of carbon dioxide when reacted with a metal

Lewis symbols • The inner electrons are really just place holders; outer electrons determine reactivity • Chemists shorten Bohr Diagrams to Lewis Structures • Example: Draw the Lewis Structure For • Ca H • N Ne • Li Cl

Polyatomic ions • Ion that is composed of two or more atoms (all of them end in –ate, you will be given a list of these on a test) • Examples: • Sulfate SO42- • Bromate BrO3- • Chlorate ClO3- • Nitrate NO3- • Phosphate PO43-

Forming ionic compounds • Occur when metal and non-metal react with each other • Ionic crystals: solid that consist of a large number of cations and anions arranged in repeating 3D patterns • Ex: Show the formation of Sodium Chloride; Calcium Oxide

Naming ionic compounds • USE IUPAC (International Union of Pure and Applied Chemistry) • METAL + NON-METAL (IDE) • Example: • CaO • NaCl • Al2O3

Writing formulas • Use the criss-cross method • Example: • Sodium Oxide • Rubidium Fluoride • Strontium Nitride

practice • Worksheets!!

UNIT 1 – MATTER AND QUALITATIVE ANALYSIS