chemistry

• Chemical reactions involve the breaking and forming of chemical bonds.
• Dalton's Atomic Theory:

  • Atoms are indivisible in a chemical process
  • All atoms present at the beginning are present at the end
  • Atoms are not created or destroyed, just rearranged
  • Atoms of one element cannot change into atoms of another element
  • Cannot turn Lead into Gold by a chemical reaction
• J.J. Thomson's Cathode Ray Experiment:

  • Cathode rays are streams of negatively charged particles known as electrons
  • All atoms can emit these electrons
  • Proposed that an atom is composed of a uniform, positively charged sphere with electrons embedded like raisins in a pudding or seeds in a watermelon
• Robert Millikan's Oil-Drop Experiment:

  • Determined the mass of an electron to be 9.10938 x 10^-28 g
  • Found the charge of an electron to be -1.602 x 10^-19 C
• Ernest Rutherford's Gold Foil Experiment:

  • Discovered the nucleus of the atom
  • Concluded that the positive charge in atoms is concentrated in the nucleus
  • Postulated that the size of the atom is due to a large empty space around the nucleus
• Rutherford's Nuclear Model of the Atom:

  • Discovered protons (positively charged particles inside the nucleus)
  • James Chadwick discovered neutrons (neutral particles inside the nucleus)
  • Electrons are attracted to protons in the nucleus by the electrostatic force
  • Electrons orbit around the nucleus occupying a large volume of space determining the size of the atom
• Bohr Model:

  • Niels Bohr observed specific colors of light emitted by atoms
  • Proposed that electrons in an atom exist in specific energy levels
  • Electrons can move between energy levels, absorbing and emitting specific amounts of energy corresponding to different colors
• Quantum Model of an Atom:

  • Electrons can only be found in certain energy levels according to Bohr
  • Heisenberg's Uncertainty Principle states the impossibility of knowing both the exact momentum and location of an electron simultaneously
  • Electrons can behave as both waves and particles
  • Schrodinger's Wave Mechanics resulted in a probability equation for atomic orbitals
• Atomic Structure:

  • Atomic Number (Z) is the number of protons in an atom
  • Mass Number (A) is the sum of protons and neutrons in the nucleus
  • Symbol of an atom includes atomic number and mass number
  • Isotopes are atoms of the same element with different numbers of neutrons
• Isotones:

  • Atoms of different elements with the same number of neutrons but different atomic and mass numbers
• Isotones:

  • Atoms of different elements that have the same number of neutrons, but differ in atomic and mass numbers
  • Examples:
  • 14 28 Si
  • 16 30 S
  • 23 11 Na
  • 24 12 Mg
• Isobars:

  • Atoms of different elements that have the same mass numbers
  • Examples:
  • 14 30 Si
  • 16 30 S
  • 40 18 Ar
  • 40 30 Ca
• Atomic Mass or Atomic Weight:

  • The weighted average of the masses of the isotopes of an element and their natural abundance
  • Isotope masses and abundances are obtained experimentally and used to calculate atomic mass, which is portrayed on the periodic table
• The Periodic Table:

  • Dmitri Mendeleev arranged the periodic table in order of increasing atomic weight
  • Elements were added to the right until an element with similar properties to hydrogen is found, forming a new horizontal row or period
  • Elements in vertical columns have similar properties and are called a 'family' or 'group'
• Features of the Periodic Table:

  • Group numbering systems: IUPAC (1-18) or old systems (1A-8A, 1B-8B, IA-VIIIA, IB-VIIIB)
  • Shows element symbol, atomic number, and atomic mass
  • Other properties are optional and given in a key/legend
• Classes of Elements:

  Metals:

  • Majority of elements
  • Shiny, solids at room temp (except mercury), malleable, ductile, conductors of electricity
  • Tend to lose electrons, form alloys like Brass and pewter
• Nonmetals:

  • Lie on the right side of the table (except hydrogen)
  • Do not conduct electricity (except graphite)
  • Gases at room temp (except bromine), tend to accept electrons
• Metalloids or Semimetals:

  • Have properties of both metals and nonmetals
  • Some are shiny and do not conduct electricity
  • Example elements: Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te)
• Other Groupings:

  • Group A: Main-Group Elements
  • Alkali metals, alkaline earth metals, boron group, carbon group, nitrogen group, oxygen group, halogens, noble gases
  • Group B: Transition Metals
  • Lanthanide Series (La to Lu), Actinide Series (Ac to Lr)
• Properties of Certain Groups:

  • Alkali Metals: most reactive, found in compounds in nature
  • Halogens: most reactive nonmetals, exist as diatomic molecules
  • Noble Gases: stable atoms, rarely combine with other elements
• Quantum Numbers:

  • How electrons are arranged in an atom
  • Principal Energy Level (n): shells numbered 1, 2, 3... from inside out, number of electrons in a shell = 2n^2
  • Azimuthal Quantum Number (l): determines subshell label and orbital shape, values from 0 to (n-1)
  • Magnetic Quantum Number (ml): determines number of orbitals within a subshell, values range from -l to +l
  • Electron Spin Quantum Number (ms): each orbital can hold two electrons with opposite spins
• Exercise 3 - 2:

  • Values of quantum numbers (n, l, ml) and maximum number of electrons for each orbital/subshell:
  • 6d: n=6, l=2, ml=-2, -1, 0, 1, 2, electrons=10
  • 4f: n=4, l=3, ml=-3, -2, -1, 0, 1, 2, 3, electrons=14
  • 2s: n=2, l=0, ml=0, electrons=2
  • 5p: n=5, l=1, ml=-1, 0, 1, electrons=6
• Matter is the physical material of the universe; it has mass and occupies space
• A property is any characteristic that allows us to recognize a particular type of matter and distinguish it from others
• All matter is comprised of various combinations of limited elements
• Each element is composed of a unique kind of atom, the building blocks of matter
• Properties of matter relate to the kinds of atoms the matter contains (composition) and the arrangements of these atoms (structure)
• Matter is made up of atoms of the same or different elements combined in different ways to give different properties
• Dalton’s Atomic Theory:

  • Each element is composed of extremely small particles called atoms
  • All atoms of a given element are identical, but different from atoms of other elements
  • Atoms of one element cannot be changed into atoms of a different element by chemical reactions
  • Compounds are formed when atoms of more than one element combine, with a fixed relative number and kind of atoms
• Classifying Matter:

  • Pure Substances: matter with a fixed composition
  • Elements
  • Compounds
  • Mixtures: matter with variable composition
  • Homogenous mixtures: uniform mixtures with indistinguishable components
  • Heterogeneous mixtures: components can be distinguished since the appearance is not uniform throughout
• Substances:

  Elements:

  • Simplest type of matter with unique physical and chemical properties
  • Consists of only one kind of atom and cannot be broken down into a simpler type of matter
  • Most elements exist as populations of atoms in nature

  Compounds:

  • Consists of two or more different elements bonded chemically in a fixed mass ratio
  • Have different properties than the elements they are made up of
  • Can be broken down via chemical reaction
• Molecule:

  • A unit of matter made up of two or more atoms joined in a specific shape or arrangement
  • Elements can exist as groups of individual atoms, molecules, or crystalline structures
  • Compounds can exist as molecules or lattice structures
• Mixtures:

  • Consist of two or more substances physically mixed in any ratio
  • Retain the properties of the component substances
  • Can be separated into their components by physical changes
• Properties of Gases:

  • Gases flow freely, have low densities, are compressible, and form homogenous mixtures in any proportion
  • Volumes of gases are not fixed and are affected by temperature and pressure
  • At higher pressures, gas particles are closer together, decreasing volume
  • At higher temperatures, gas particles move faster, expanding the container and increasing volume
• Properties of Matter:

  • Characteristics of the substance under observation
  • Physical or Chemical properties
  • Intensive or Extensive properties
  • Physical properties can be observed without changing the identity and composition of the substance
  • Chemical properties describe how a substance may change or react with other matter
  • Intensive properties do not depend on the amount of sample being examined
  • Extensive properties depend on the amount of sample or relate to the amount of substance present
• Changes in Matter:

  • Physical change: changes a substance's physical appearance but not its composition
  • Chemical change or reaction: transforms a substance into a chemically different substance
• Energy:

  • Defined as the capacity to do work or transfer heat
  • Work is energy transferred when a force causes displacement
  • Heat is energy used to increase the temperature of an object
  • Energy can exist in different forms and be transformed from one form to another
• Kinetic Energy:

  • Energy of motion
  • Heavier objects possess greater kinetic energy than lighter objects moving at the same speed
  • Kinetic energy of atoms and molecules observed in their state or changes of state
• Potential Energy:

  • Stored energy from attractions and repulsions an object experiences in relation to other objects
  • Electrostatic potential energy arises from interactions between charged particles
  • Coulomb's Law: F = 𝑞1��1/𝑑2
• Units of Energy:

  • One calorie is the energy needed to raise the temperature of one gram of water by 1°C
  • kcal = energy needed to raise the temperature of 1000g of water by 1°C
  • joule
  • In nutrition, calories are capitalized: 1 Cal = 1 kcal