Chemistry

• ATOMIC MODELS

  1. Billiard Ball Model (John Dalton) - the atom is hard and indestructible
  2. Plum Pudding Model (JJ Thompson) - electrons are embedded in a positively-charged sphere
  3. Nuclear Model (Ernest Rutherford) - the mass and all the positive charge of an atom is concentrated in the nucleus
  4. Planetary Model (Niels Bohr) - electrons travel around the nucleus in a circular orbit; their energy is proportional to their distance from the nucleus
  5. Quantum Model (several scientists) - the electron is a wave found in orbitals
• atomic number (Z)

  number of protons in the nucleus; also equal to the number of electrons, if the atom is neutral
• mass number (A)


  protons + neutrons
• THE ATOMIC THEORY

  • all matter are made up of atoms
  • all atoms of an element have identical chemical and physical properties
  • atoms of different elements have different sets of chemical and physical properties
• alkali metals


  highly reactive metals; have one excess electron which they tend to lose, thus they usually have a charge of +1; usually form compounds with halogens; e.g. Na
• halogens


  highly reactive non-metals; lack one electron on their outer shell which they try to acquire from other atoms, thus they usually have a charge of -1; usually forms compounds with alkali metals; e.g. Cl
• noble gases


  or inert gases; unreactive, very stable elements owing to their full outer shell of eight electrons; e.g. Ne
• metalloids


  have both metallic and non-metallic properties; e.g. B
• non-metals


  elements to the right of the metalloids; e.g. Cl
• metals


  all elements to the left of the metalloids (except H); e.g. Na
• isotopes

  atoms of the same element that differ in the number of neutrons
• THE NUCLEI OF THE 3 ISOTOPES OF HYDROGEN

  1. Protium - 0 neutron, 1 proton
  2. Deuterium - 1 neutron, 1 proton
  3. Tritium - 2 neutrons, 1 proton
• Octet Rule


  states that elements gain or lose electrons so that they will have the same number as the nearest noble gas
• ion - charged atom

  • anion - negatively-charged; gain in electrons; electrons > protons
  • cation - positively-charged; loss of electrons; electrons < protons
• ionization energy - energy required to remove an electron from an atom
• electron affinity - energy released when an electron is added to an atom
• electronegativity - ability to attract electrons; e.g. Cl has high electronegativity since it lacks one electron in its outermost shell thus it attracts an electron to make it more stable; it usually has a -1 charge (Cl-); increases as atomic size decreases
• atomic size/radius - one-half the distance between the two nuclei in two adjacent metal atoms or in a diatomic molecule
• valence electrons - the number of "excess" electrons of an atom; e.g. Na has one valence electron, having one "excess" electron
• Aufbau Principle - every element has the same electronic configuration as the element before it in the periodic table, plus one extra
• Hund's Rule - electrons tend to stay unpaired in orbitals with equal energies; e.g. in the preceding example for Si, there is an electron in each py and px (instead of both electrons being in px and none in py) since these two orbitals have the same energy level
• TYPES OF SOLUTIONS

  • unsaturated - can still dissolve more solute
  • saturated - already contains the maximum amount of solute
  • supersaturated - used pressure or heat to dissolve more than the usual amount of solute
• chemical change - formation of new substance
• SIGNS OF CHEMICAL CHANGE

  • color, odor, taste change
  • gas production/burning
  • decomposition
• MEASURING VOLUMES

  • regular solids - measure the dimensions (e.g. sides, radius) then compute using formula
  • irregular solids - water displacement (volume is equal to the rise in water level)
  • liquids - use a graduated cylinder
  • gases - no definite volume (compressible), pressure is usually measured instead
• GAS LAWS

  • Boyle's Law; p1V1 = p2V2
  • Charles' Law; V1/T1 = V2/T2
  • Gay-Lussac's Law; p1/T1 = p2/T2
  • Combined Gas Law
  • Avogadro's Law; V1/n1 = V2/n2
  • Ideal Gas Law ; pV = nRT
  • Dalton's Law of Partial Pressures; Pa = xaPt
• KINETIC MOLECULAR THEORY OF GASES

  • particles in a gas are infinitely small
  • particles in a gas are in constant random motion
  • gases do not experience intermolecular forces
  • gas molecules undergo perfectly elastic collisions (they bounce perfectly off one another)
  • the kinetic energies of gas molecules are directly proportional to their temperatures (the hotter, the faster the molecules move)
• Law of Conservation of Mass


  in any chemical reaction, the total mass of the reactants is equal to the mass of the products
• Law of Definite Proportion/Composition


  the ratio of the elements in a compound is always the same; e.g. water is always composed of two H atoms for every one O atom
• Law of Multiple Proportions


  $mA1/mA2 =$$ratio of small whole numbers$
• empirical formula - chemical formula in lowest terms

  molecular formula -actual chemical formula
• Avogadro's Number; 1 mole = 6.02 x 10^23

  • number of particles; these particles are molecules if the substance is a compound, or atoms if the substance is an element
• LAWS OF THERMODYNAMICS

  1. First Law (Law of Conservation of Energy) - energy can neither be created nor destroyed. It can only change forms.
  2. Second Law - entropy, or S, is the degree of disorder
  3. Third Law - Entropy at -273.15 K is zero
• HESS' LAW

  • Enthalpy, or $ΔH$, is the heat transferred between system and surroundings at constant pressure
  • For a reaction with two or more steps, the enthalpy is the sum of the enthalpies of the steps
• Specific Heat - amount of energy needed to raise the temperature of a substance by one degree; in J/kg-C; decreases as mass and temperature to be attained increases

  $q=$$mcΔT$
• temperature - hotness or coldness

  heat - total kinetic energy of molecules

  sensible heat - heat lost or gained during a change in temperature

  latent heat - heat lost or gained during a phase change
• redox - reduction-oxidation; change in oxidation number of elements in the reaction due to transfer of electrons
• FACTORS THAT INCREASE RATES OF REACTIONS

  • higher temperatures
  • higher concentration of reactants
  • large surface area of reactants
  • addition of catalyst (substance that increases the rate of reaction without itself being consumed)
• Ionic Compound - or salt, formed by a cation and an anion wherein there is a transfer of electrons so that each atom has the same number of electrons as the nearest noble gas
• Covalent Compound - the compound formed by atoms that share electrons so that each has the same number of electrons as the nearest noble gas