Unit 2 test: Structures and Properties of Matter

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44 Terms

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Atomic Theories

Democritus hypothesized that atoms are matter that can’t be cut anymore

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John Dalton

  • billiard ball model

  • element consist of atoms

  • atoms cannot be created, destroyed, or divided

  • atoms of same element have identical size, mass, and properties

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J.J Thomson

  • Plum puddling model

  • discovered the electron

  • used a high-voltage, evacuated glass tube to discover that cathode rays were streams of negatively charged particles, which he called electrons

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Robert Millikan

  • found the mass of the electron

  • used charged oil droplets to determine the charge on the electron

  • he adjusted the voltage across 2 charged plates so he could halt the fall of the oil drops

  • then he calculated the charge on the oil drop therefore he calculated the mass of an electron

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Henri Becquerel

  • demonstrated that uranium atoms are capable of spontaneously emitting energy, particles, or waves that travel through space

  • this is called radioactivity

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3 types of radioactive emissions

  • Alpha particles (He2+)

  • Beta particle (e-)

  • Gamma ray

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Ernest Rutherford

  • the nucleus

  • using gold foil experiment

  • he concluded the atom had a nucleus (a dense, possibly charged center made of protons)

  • electrons orbited the nucleus

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Chadwick

  • the neutron

  • calculated the mass of a nuclei but the calculations didn’t match the associated charge. He concluded that missing mass is neutrons

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Classical Theories of Light

  • it was believed that light existed as a steam of particles

  • Huygens proposed that light is a wave (refraction, reflection, and diffraction support the wave theory of light)

  • Maxwell proposed that light existed as an electromagnetic wave (known as the electromagnetic spectrum)

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Hertz

  • the photoelectric effect - electrons are emitted by matter that absorbs energy from shortwave electromagnetic radiation

  • it was believed that the intensity of light shining in metal determines kinetic energy of the electrons emitted

  • hertz said it’s the colour of light

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Planck

  • Quantum

  • when a solid black object is heated it glows red, white then blue

  • Planck noticed it reached a peak then decreased

  • this signified that energy can be gained or lost in whole number multiples

  • light was emitted in bursts not a stream

  • light behaves as a particle

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Einstein

  • photons - EM radiation is a stream of particles called photons (units of light energy)

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Problems with Bohr’s planetary model

  • if electrons were accelerating, photons of electromagnetic radiation should be emitted

  • this would result in the electron being attracted towards the nucleus and collapsing into it

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Spectroscopy

  • study of light

  • By looking at the patterns of light absorbed or emitted, scientists can identify what a substance is made of and learn about its structure.

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Dark line spectrum

  • happens when white light passes through a cooler gas.

  • analyze what’s left

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The Bohr atomic model

  • Electrons orbit the nucleus in fixed paths (like planets around the sun).

  • Each orbit has a specific energy level.

  • Electrons can jump to higher or lower orbits by absorbing or releasing energy (as light).

  • The light released makes up an element’s spectrum.

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Successes of bohrs model

  • his model gives a reasonable explanation for mendeleev’s periodic law: periods result from the filling of electron energy levels

  • max electrons in each energy level correspond to number of elements in each period

  • explained the line spectrum of hydrogen

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Failures of Bohrs model

  • could not predict the spectra of ions of more than one electron

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Louis de broglie

de Brogloe

  • if light can behave like a particle, then any particle should also be able to act like a wave

  • therefore, electrons have wave properties

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Erwin Schrodinger

  • used math and statistics

  • He proposed the quantum mechanical model of the atom.

  • Instead of electrons moving in fixed orbits (like Bohr said), Schrödinger showed that electrons exist in regions called orbitals—areas where they’re most likely to be found.

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Heisenberg Uncertainly Principle

  • you can’t know both the exact position and speed of a particle at the same time.

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Orbitals vs Orbits

Orbitals

  • 2 electrons

  • 3D

  • Distance from the nucleus varies

  • No set path

Orbits

  • 2n² electrons

  • 2D

  • Distance from the nucleus is fixed

  • Path is elliptical or circular

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Pauli Exclusion Principle

no two electrons have the same four quantum numbers

quantum

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Aufbau Principle

an energy level must be filled before moving on to the next higher energy level

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Hund’s rule

each orbital at the same energy level must have one electron in it before any orbital can contain two electrons

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Exceptions in electron configurations

Chromium, Silver and copper

Cu: [Ar] 4s^1 3d^10

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Ionic compounds

  • electrons are transferred to elements w higher electronegativity

  • ionic bond is between oppositely charged ions

  • isoelectric - having the same number of electrons

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Molecular compounds

  • form because of attractions of electrons from one atom to the nucleus of the other

  • atoms share electrons

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non-polar molecules

  • only has non-polar bonds (no dipole)

  • when the sum of the individual bond dipoles is zero (they cancel each other out)

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dipole- dipole

  • attract each other by lining up so their opposite ends are together

  • in a liquid, dipoles attract and repel each other, so an equilibrium has to be reached

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Hydrogen Bonding

  • strong dipole-dipole force

  • Hydrogen is covalently bonded to a highly electronegative atom (N,O, F) no Cl

  • hydrogen is attracted to the partically negative charge on a neighbouring molecule

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how does hydrogen bonding affect a substance’s physical properties

a substance

  • they increase boiling points

  • important in bio and organic molecules

  • no hydrogen bonds = no life

  • proteins and DNA would not exist as they rely on hydro bonds for structure

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London Dispersion

  • between non-polar molecules

  • an increase as molecular mass increases (increases boiling points)

  • explains why noble gases can freeze to form solids

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intermolecular forces + physical properties

strengths on bonds:

Ionic>Hydrogen bonds>dipole-dipole>london dispersion

  • stronger the bond, the higher the boiling point, melting point, surface tension, and viscosity

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4 types of solids

  • Ionic solids

  • Metallic solids

  • Molecular solids

  • Network solids

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Ionic Solids

  • Form between the interaction of a metal with a non-metal ion

  • strong ionic bond holds them together

  • properties: Hard, brittle, dissolves in water, high melting point, good conductor of electricity when dissolved

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Metallic Crystals

  • closely packed metal atoms held together by electrostatic interactions and free-moving electrons

  • common properties: shiny, good conductor of thermal energy and electricity

  • don’t have similar properties as each other (electron sea theory)

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electron Sea theory

  • metals are composed of closely packed atoms whose valence electrons are free to move

  • positively charged nuclei are fixed while the electrons are mobile

  • as electrons move from one positive nucleus to another, they hold the positively charged nuclei together

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molecular crystals

  • similar to ionic crystal lattice but more complex

  • ex: ice can form many different crystals (snowflakes)

  • intermolecular forces will determine its structure and properties

  • intermolecular force is london-dispersion, resulting in lower melting points, less hard, doesn’t conduct electricity well

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Covalent network crystals

  • ex: diamonds

  • strong intermolecular forces are working

  • electrons don’t move freely

  • properties: very high melting point, extremely hard, not good conductor on electricity

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Carbon

  • carbon atoms can form different structures

  • this causes structures that are formed from carbon to have different properties

c

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Diamonds

  • carbon forms a tetrahedral structure

  • very hard, not good conductors of electricity

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Graphite

  • has a trigonal planar arrangement also forms hexagonal sheet between layers - contains strong covalent bonds in the plane and weaker london-dispersion between the graphite sheet layers)

  • bc of arrangement, electrons can break loose

  • slippery, black, good electrical conductor

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Quartz

  • Made of silicone and oxygen (SiO2)

  • when silica is heated and cooled it forms quartz glass, a more disorganized structure