STAAR Chemistry Review Topic: Atomic Structure TEKS 6 – The student knows and understands the historical development of atomic theory. 6A - E

Student Expectation (SE) 6A – understand the experimental design and conclusions used in the development of modern atomic theory, including Dalton's Postulates, Thomson's discovery of electron properties, Rutherford's nuclear atom, and Bohr's nuclear atom;

INDEX CARD TIME! TITLE: Dalton’s Four Postulates About The Atom FRONT: Describe each of the four postulates Dalton proposed about the atom BACK: Which of these are considered incorrect today?

Mini Review: Dalton’s Atom John Dalton’s Postulates about the atom include: 1.Elements are made of small, indivisible particles called atoms 2.All atoms of a given element are identical 3.Atoms of a given element are different from those of any other element and have different atomic masses.

Mini Review: Dalton’s Atom 4. In a chemical reaction, atoms of one element combine in whole number ratios with atoms of different elements. Chemical reactions rearrange atoms but do not change atoms to new elements. Today we know that atoms of the same element are not necessarily identical because they can contain different numbers of neutrons (isotopes)!

INDEX CARD TIME! TITLE: JJ Thomson and The Electron FRONT: Which experiment lead to the discovery of the electron? Explain how the experimental evidence demonstrated the existence of the electron. BACK: Draw a sketch of what Thompson thought the atom looked like.

Mini-Review - Electrons JJ Thomson’ s cathode ray experiment lead to the discovery of the electron. This experiment involved glass tubes containing gas at low pressure with electrodes at each end. When the electrodes were connected to an electric current a cathode ray was produced.

Mini-Review - Electrons The cathode rays were attracted to positively charged metal plates, and repelled by negatively charged plates, so Thomson hypothesized these “rays” were beams of negatively charged, particles, the electron!

Mini-Review - Electrons Tompson’s model of the atom was that the atom was like a blueberry muffin - the batter is the positively charged region of the atom, with negative blueberries scattered throughout. Tompson called it the plum-pudding model, after a gross British dessert with plums randomly scattered in a cake. Blueberry muffins are easier to remember, since you’ve seen one before!

INDEX CARD TIME! TITLE: Rutherford and the Nucleus FRONT: Which experiment lead to the discovery of the nucleus? Explain how the experimental evidence demonstrated the existence of the nucleus. BACK: Draw a sketch of what Rutherford thought the atom looked like.

Mini-Review - Rutherford Rutherford conducted the gold foil experiment to test Thomson’s model of the atom. Rutherford shot a beam of positively-charged, high energy alpha particles through a piece of gold foil (like aluminum foil, but made of gold). Rutherford thought that if the positive charge was distributed evenly throughout the atom, most of the alpha particles would pass straight through without deflection.

However, a small portion of the atoms were actually deflected back toward the source of the alpha particles, and did not pass through the foil. Rutherford hypothesized that the alpha particles struck a small, dense region of positive charge at the center of the atom called the nucleus. Student pictures should incorporate a nucleus of positive charge in the center of the atom. Neutrons hadn’t been discovered yet!

Student Expectation (SE) 6B – understand the electromagnetic spectrum and the mathematical relationships between energy, frequency, and wavelength of light;

INDEX CARD TIME! TITLE: The Electromagnetic Spectrum FRONT: What is it? What is the highest energy item on the right of spectrum, and the lowest energy item on the left? BACK: Which color of light is the Highest energy? The lowest?

Electromagnetic Spectrum The electromagnetic spectrum is a visual representation of all the wavelengths and frequencies of electromagnetic radiation. Notice that the visible spectrum of light makes up only a small portion of the entire electromagnetic spectrum. (See diagram next slide). From low to high energy/frequency the electromagnetic spectrum contains radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays

Mini-Review Low energy High energy

Student Expectation (SE) 6C – calculate the wavelength, frequency, and energy of light using Planck's constant and the speed of light;

INDEX CARD TIME! TITLE: Calculating energy, frequency, and wavelength FRONT: What are the two equations needed to calculate the energy, frequency, or wavelength of light ? BACK: What are the given constant Values for the two equations?

Mini-Review: Light Calculations Equation: c = f x ʎ Where c = speed of light, f = frequency, ʎ = wavelength Units for frequency are hertz (Hz) Units for wavelength are nanometers (nm) for light, but can be a metric value of meters for other forms of electromagnetic radiation. Constant: c = 3.00 x 10 8 m/s

Mini-Review: Light Calculations E = h x f Where E=energy, h= Planck’s constant, f = frequency Units for frequency are hertz (Hz) Units for energy are Constants: h = x J/s

Student Expectation (SE) 6D – use isotopic composition to calculate average atomic mass of an element;

INDEX CARD TIME! TITLE: Isotopes and Average Atomic Mass FRONT: How do you calculate average atomic mass? Back: What does average atomic mass represent?

Average Atomic Mass Average atomic mass of an element is The average mass that is weighted based on the abundance of each of the atom’s isotopes. To calculate any average atomic mass you need to know each isotope of the element, it’s percent abundance, and the mass of each isotope.

Calculating Average Atomic Mass 1.Convert all percent abundance values into decimal form (divide by 100). 2.Multiply the atomic mass by the decimal percent abundance for each isotope. 3.Add the multiplied mass times abundance values for each isotope value together. 4.The unit for atomic mass is amu!

Calculating Average Atomic Mass IsotopeAtomic Mass (amu) Relative Abundance % Decimal Relative Abundance Carbon % Carbon % Carbon amu x = amu Carbon x = amu Average Atomic Mass = = amu

Student Expectation (SE) 6E – express the arrangement of electrons in atoms through electron configurations and Lewis valence electron dot structures.

INDEX CARD TIME! FIRST: Describe to your table partner how to do both regular and noble gas electron configurations. TITLE: Electron configuration FRONT: Write down the directions you just discussed for both types of electron configuration. BACK: Describe where the S, P, D, and F blocks are on the periodic table

Electron Configuration An electron configuration describes which atomic orbitals hold the atom’s electrons. Electrons occupy the atomic orbitals with the lowest energies first. The easiest way to write an electron configuration is using the periodic table. You need to look at the period and blocks of the periodic table to fill in full electron configurations. See the diagram on the next page.

Electron Configuration The electron configuration for hydrogen is 1s 1 The first number one indicates the principal energy level, the letter s indicates the sublevel and type of atomic orbital, and the superscript (exponent) 1 indicates the number of electrons in the s orbital.

INDEX CARD TIME! TITLE: Lewis Dot Structures FRONT: How do you know how many dots to draw on a Lewis Dot Structure? BACK: Draw a Lewis Dot Structure for 8 elements (A Lewis Dot Structure for an element with 1, 2, 3, 4, 5, 6, 7, and 8 v.e.’s)

Mini-Review You draw a dot for each valence electron an element has for a Lewis Dot Structure. See next slide for element examples…

Mini-Review

* Review slide information directly from Texas STAAR Review and Practice by Pearson