U1: Atomic Structure and Electron Configuration

Molar Mass

Avogadro’s number: 6.02 * 1023, which indicates the particles in a mole of any substance.

Molar Mass: used to refer to the mass of all the molecules in any substance in moles.

Mole: a unit that which measures quantity; 1 mole is equivalent to 6.02 * 1023

Percent Composition: Percent by mass of each element in the compound

● 1 mole of any element = 6.02 * 1023 atoms

● 1 mole = element’s average atomic mass in grams from the periodic table

○ Ex. I mol of potassium = 6.02 * 1023 atoms or 39.1 grams K

● 1 mole of any molecular compound = 6.02 * 1023 moles

● 1 mole of any ionic compound = 6.02 * 1023 (formula units)

○ GFM: Gram formula mass; the mass of one ionic compound

○ Ex. 1 mol of NaCl = 58.5 grams NaCl

● 1 mole of any gas = 22.4 Liter

When masses of atoms, molecules and formula units are measured in grams they are termed as:

● GAM: Gram Atomic Mass

○ Ex. 1 mol of Carbon = 12.01 grams

● GMM: Gram Molecular Mass

○ Ex. 1 mol of H2O = (1.01 * 2) + (16.00) = 18 grams

● GFM: Gram Formula Mass

○ Ex. 1 mol of NaCl = 58.5 grams of NaCl

Formulas and Calculations

Molar Mass = mass (in grams) / moles

● Ex. Calculating the molar mass of a substance if 0.235 moles of the substance has a mass of 45.67 grams.

● Molar Mass = 45.67 grams / 0.235 moles = 194 g/mol

Percent Composition

● Mass percent = total molar mass of an element / molar mass of the whole compound * 100%

● Ex. What is the percent composition by mass of Hydrogen in H2O

○ Molar mass of H2 = (1.01 * 2) = 2.02 grams

○ Molar mass of H2O = (1.01 * 2) + (16.00) = 18.02 grams

○ 2.02/18.02 * 100% = 11.2 % percent composition of H2

Atomic Structure and Electron Configuration

Atomic Number: The number of protons in an atom. The periodic table is arranged by increasing atomic number.

Atomic Mass: The mass of a single atom of an element expressed in atomic mass units (amu).

Electron: Negatively charged particle that is outside the nucleus of a model.

Ion: Atom that has a positive or negative charge, due to an imbalance in the number of protons and electrons

Isotope: An element whose atoms have different numbers of neutrons, but keep the same number of protons.

Neutron: A subatomic particle that has no charge and is in the nucleus.

Nucleus: The positively charged dense center of the atom

Proton: a subatomic particle that has a positive charge and is in the nucleus

Wavelength: Distance between corresponding points of two consecutive waves

Evolution of Atomic Theory

John Dalton (1808)

● Said that elements are made of atoms, and compounds are formed by combining elements in fixed ratios

J.J. Thompson (1898)

● Realized that the beam produced was negative while working with Cathode Rays

● He was able to measure the charge:mass ratio but not individual quantities

● Made the plum pudding model which shows that negatively charged electrons are stuck on a positive cloud

Robert Millikan (1909)

● “Oil Drop Experiment” : He injected drops of charged drops of oil into an electric field and further explained J.J. Thompson’s answers

● Determined the electron’s charge to be 1.6 x 10-19 C.

Ernest Rutherford (1911)

● “Gold Foil Experiment” : He fired a beam of alpha particles at gold foil

○ He expected the alpha particles all to go through and most of them did but a few bounced back

○ He concluded from the experiment that a small, dense, positive nucleus is in the center of the atom and the electrons must move around it at a large radius

Max Planck

● Said that light could only be emitted in certain energies, which was introduced as quantized energy

● Delta E = nhv or E = hv

○ E = energy of photon ( light wave )

○ V = frequency (hz)

○ H = planck’s constant: 6.626 * 10-34 J/Hz

○ n = a whole number

Albert Einstein (1905)

● Said that energy and mass (matter) are interchangeable; they are different forms of the same thing

● Theory of relativity: E = mc2

○ E= Energy

○ M = mass

○ C = speed of light

Louis de Broglie (1923)

● He stated that particles behave like waves

● Lambda = h/mv

○ Lambda = wavelength

○ H = planck’s constant in J/Hz

○ M = mass of the particle

○ V = velocity

Neils Bohr (1913)

● Said that the emission spectrum of hydrogen made only a few bright lines, not a full spectrum.

● He stated based on his observations that electrons jumping around energy levels create those lines.

● Electrons move around the nucleus in a certain circular orbit

○ Energy available to the electron: E = - (2.178 * 10-18J) (z2/n2)

■ Z = atomic number

■ N = energy level (orbit radius #)

■ Negative sign = the lower the n (the closer to the nucleus) the more negative E is

● Disadvantage: Bohr’s model doesn’t work for atoms other than hydrogen and electrons don’t actually move in an circular orbit

Isotopes

● Atoms of the same element with different mass numbers (due to different number of neutrons)

Formation of ions

● When an atom gains or loses electrons, an ion is formed.

● Electron is gained = negative ion

● Electron is lost = positive ion

Wavelength

Frequency = # of waves that pass a certain amount of time

Amplitude = maximum amount of displacement of a particle on the medium from its rest position

Speed of light = C = 3.0 * 108 m/sec

Wavelength denoted by lambda

● Longest wavelength = long wave radio = least energy (red)

● Shortest wavelength = Gamma rays = most energy (violet)

Important relationships

● The longer the wavelength, the lower the frequency (inverse relation)

● The higher the frequency, the higher the energy (direct relation)

● The higher the wavelength, the lower the energy (inverse relation)

● The Electromagnetic Spectrum showcases the different ranges of electromagnetic radiation.

Electron Configuration/Orbitals