Unit 2 Study Guide

Matter & Its Properties

• Matter is anything that takes up space. Not matter: energy

  • Mass is how much matter is in an object

  • Volume is how much space the object takes up

• Four phases of matter: plasma, solid, liquid, gas

• Solid:

  • Compressibility: Low

  • Structure: Atoms very tight together

  • Shape: Can stand by itself

  • Volume: Low

  • Density: High

• Liquid:

  • Compressibility: Medium

  • Structure: Atoms together, but can flow past each other

  • Shape: Takes the shape of its container

  • Volume: Medium

  • Density: Medium

• Gas:

  • Compressibility: High

  • Structure: Atoms not at all together, bounce all over the place

  • Shape: Doesn’t have one- all over the place

  • Volume: Indefinite

  • Density: Very low

    • Solid to Gas: Sublimation

    • Solid to Liquid: Melting

    • Liquid to Solid: Freezing

    • Liquid to Gas: Evaporation

    • Gas to Liquid: Condensation

    • Gas to Solid: Deposition

• Atoms are the smallest unit of matter that still retains its elemental properties. Molecules are one or more atoms bonded together. Compounds are two or more elements bonded together, and elements are only composed of one element.

  • Physical Properties: can be observed/measured without changing identity of substance

    • ex: mass, melting point, color, state of matter

    • States of matter are physical properties too!

  • Chemical Properties: can only be observed/measured by changing the identity of the substances

    • ex: flammability, reacts with acid, reacts with oxygen

    • All chemical properties relate to a substance’s reactivity!

  • Four common indicators of Chemical Change:

    • Color change

    • Gas released

    • Change in energy

    • Precipitate forms

• Mixture: contains a combination of substances that are not chemically bonded together. Components can be separated physically.

  • Homogeneous Mixture: all components of the mixture are spread evenly throughout; same consistency throughout (ex: lemonade).

  • Heterogeneous Mixture: components NOT evenly distributed; uneven consistency throughout (ex: candy salad- I didn’t get a peach ring 😢)

• Pure substance: contains only one element or only one compound. All components of the substance are exactly the same.

Atomic Theory & History of the Atom

• John Dalton- Father of the Atomic Theory

  • Experimented with oxygen + nitric oxide over water. First to use empirical evidence to support particulate theory of matter.

  • Dalton’s Atomic Theory:

    • All matter made up of atoms

    • Atoms of the same element have the same size, mass, etc.; atoms of different elements differ in size, mass, etc. (Partially incorrect)

    • Atoms cannot be subdivided, created, or destroyed (Partially incorrect)

    • Atoms of different elements combine in simple, whole number ratios to form chemical compounds (Partially incorrect)

    • In chemical reactions, atoms are combined, separated, or rearranged

• JJ Thomson- Discovered the electron

  • Did the cathode ray tube experiment

  • Developed the Plum Pudding Model:

    • atoms are not uniform/indivisible- they are a uniform, positively charged mass (pudding) with negatively charged particles/electrons (plums) that have extremely small mass in comparison.

    • Electrically neutral overall

• Ernest Rutherford- Discovered the nucleus

  • Did the Gold foil experiment with alpha particles:

    • few particles unexpectedly bounced back

    • proves that the mass of the gold foil concentrated in a very small volume compared to the larger volume of the whole object

• Niels Bohr- Created the Bohr Atomic Model with electron orbits

  • described electrons as existing in discrete energy levels/orbits like ladder rungs

  • electrons can only exist in one energy level or another- no in-betweens

  • energy levels farther away = more energetic electrons

• Modern Atomic Theory-

  • electrons do not move in set orbits- electrons move randomly

  • electrons with more energy tend to be found farther from the nucleus

  • one can only calculate the probability of where one might find an electron, but never the exact placement of an electron

Structure of the Atom-

• Basic structure of atom:

  • Nucleus- where protons and neutrons reside

  • Electron cloud- where electrons are most likely to be found

• Protons are positive with a mass of 1 and a size of 0.8 fm

• Neutrons are neutral with a mass of 1 and a size of 0.8 fm

• Electrons are negative with a mass of almost 0 and a size of 0.07 fm

• Atomic number: the number of protons in an element- found above the atomic symbol on the periodic table

• Atomic mass: the total number of protons and neutrons, can be found underneath the atomic symbol on the periodic table

  • Average atomic mass: the average weight of all the different isotopes of a particular element

  • Relative atomic mass: average atomic mass when compared to the mass of the Carbon 12 atom

  • Calculate average atomic mass: ((mass of isotope 1)(%abundance of isotope)+(mass of isotope 2)(%abundance of isotope)…)/100

The Electromagnetic Spectrum and the Nature of Light

• The electromagnetic spectrum from lowest energy to highest energy: radio, microwave, infrared, visible, ultraviolet, x-ray, gamma

• Energy and frequency are directly proportional

• Frequency and wavelength are inversely proportional

• Energy and wavelength are also inversely proportional

• Electromagnetic radiation: a form of energy that exhibits wave-like behavior as it travels

• Photon- a particle of Electromagnetic Radiation

• Quantum- a discrete amount of energy

• Dual-wave particle nature of light: Electromagnetic radiation has properties of both waves and particles

• Bohr’s atomic model & line emission spectrum of hydrogen:

  • When electrons get excited, they will temporarily jump up to a higher energy level, then immediately move back, releasing a photon as energy as it moves back to its previous energy level

  • Bohr explained the line spectrum of the hydrogen atom by assuming that atoms moved in circular orbits and that only orbits with certain radii were allowed

Quantum Model of the Atom

• The Heisenberg Uncertainty Principle says that is it impossible to know both the position and the velocity of an electron

• Erwin Schrodinger’s wave functions describe the probability of finding an electron in a given place.

• The most current model of the atom is called the quantum model of the atom.

  • Atoms exist in orbitals- regions of space in the electron cloud where an electron is most likely to be found (~90%)

  • Inputting data into Schrodinger’s wave equations can tell us which orbital an electron will be found in

  • An electron cloud is ordered into energy levels, subshells, and orbitals

    • each energy level is divided into subshells

      • each subshell is divided into a certain number of orbitals

        • each orbital contains a maximum of 2 electrons

    • s subshells contain only one orbital (s for single) = 2 electrons

    • p subshells contain three orbitals (p for three peas in a pod) = 6 electrons

    • d subshells contain five orbitals = 10 electrons (d for dix electrons)

    • f subshells contain seven orbitals = 14 electrons (f for fourteen electrons)

  • Each energy level holds only a certain number of subshells

    • Level 1 = s = 2 electrons

    • Level 2 = s + p = 8 electrons

    • Level 3 = s + p + d = 18 electrons

    • Level 4 = s + p + d + f = 32 electrons

Electron Configuration

• Aufbau Principle - electrons will always occupy the lowest energy orbital available

• Hund’s Rule - orbitals of equal energy are each occupied by a single electron before any orbital is occupied by a second electron

• Pauli Exclusion Principle - a maximum of two electrons will occupy a single orbital, each with an opposite spin

• Electron configuration - a list of all the electrons in an atom that states the energy level and subshell of each