1 6 Using Units and Solving Problems A

1. 6 Using Units and Solving Problems A conversion factor is a fraction in which the same quantity is expressed one way in the numerator and another way in the denominator. For example, 1 in = 2. 54 cm, may be written: 1 in 2. 54 cm or 2. 54 cm 1 in

Dimensional Analysis – Tracking Units The use of conversion factors in problem solving is called dimensional analysis or the factor-label method. Ø Example: Convert 12. 00 inches to meters. 12. 00 in × = 30. 48 cm Which conversion factor will cancel inches and give us centimeters? 1 in 2. 54 cm or Convert 4. 35 x 10 -4 kiloliters to microliters Text Practice: 1. 50 b d 2. 54 cm 1 in

Worked Example 1. 8 An average adult has 5. 2 L of blood. What is the volume of blood in cubic meters? Strategy 1 L = 1000 cm 3 and 1 cm = 1 x 10 -2 m. When a unit is raised to a power, the corresponding conversion factor must also be raised to that power in order for the units to cancel appropriately.

Worked Example 1. 3 Ice cubes float in a glass of water because solid water is less dense than liquid water. (a) Calculate the density of ice given that, at 0°C, a cube that is 2. 0 cm on each side has a mass of 7. 36 g, and (b) determine the volume occupied by 23 g of ice at 0°C. Text practice: 1. 24 1. 28 1. 68

Chemistry: Atoms First Second Edition Julia Burdge & Jason Overby Chapter 2 Atoms and the Periodic Table M. Stacey Thomson Pasco-Hernando State College Copyright (c) The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

2. 1 Atoms First An atom contains specific particles. The arrangement of subatomic particles determine the properties of atoms, which in turn determine the properties of all matter. An atom must contain at least 1 proton. The elements are defined by how many protons they have. Examples: gold, oxygen, helium We are going to discuss how just a few of the experiments scientists used to elucidate how atoms are composed.

2. 2 Subatomic Particles and Atomic Structure In the late 1800’s, many scientists were doing research involving radiation, the emission and transmission of energy in the form of waves. They commonly used a cathode ray tube, which consists of two metal plates sealed inside a glass tube from which most of the air has been evacuated.

Subatomic Particles and Atomic Structure When metal plates are connected to a high-voltage source, the negatively charged plate, or cathode, emits an invisible ray. The cathode ray is drawn to the anode where it passes through a small hole. Although invisible, the path is revealed when the ray strikes a phosphor-coated surface producing a bright light. • http: //highered. mcgrawhill. com/sites/0073511161/student_view 0/chapter 2/animations. html# • https: //phet. colorado. edu/en/simulation/balloons

Subatomic Particles and Atomic Structure This prompted him to propose the rays were actually a stream of negatively charged particles. These negatively charged particles are called electrons. By varying the electric field and measuring the degree of deflection of cathode rays, Thomson determined the charge-tomass ratio of electrons to be 1. 76× 108 C/g. (C is coulomb, the derived SI unit of electric charge. )

Subatomic Particles and Atomic Structure Wilhelm Rontgen (1845 -1923) discovered X-rays. They were not deflected by magnetic or electric fields, so they could not consist of charged particles.

Subatomic Particles and Atomic Structure Antoine Becquerel (1852 -1908) discovered radioactivity, the spontaneous emission of radiation. Radioactive substances, such as uranium, produce three common types of radiation. Alpha (α) rays consist of positively charged particles, called α particles. Beta (β) rays, or β particles, are electrons so they are deflected away from the negatively charged plate. Gamma (γ) rays, like X-rays, have no charge and are unaffected by external electric or magnetic fields.

Subatomic Particles and Atomic Structure • Ernest Rutherford used α particles to prove the structure of atoms. • The majority of particles penetrated the gold foil undeflected. • Sometimes, α particles were deflected at a large angle. • Sometimes, α particles bounced back in the direction from which they had come. • https: //phet. colorado. edu/en/simulation/rutherfordscattering • Activity: Propose rational for WHY gold was used and WHY alpha particles were used in this experiment and

Subatomic Particles and Atomic Structure Rutherford proposed a new model for the atom: Positive charge is concentrated in the nucleus. The nucleus accounts for most of an atom’s mass and is an extremely dense central core within the atom. Ø A typical atomic radius is about 100 pm Ø A typical nucleus has a radius of about 5× 10– 3 pm Ø 1 pm = 1× 10– 12 m

Subatomic Particles and Atomic Structure Protons are positively charged particles found in the nucleus. Neutrons are electronically neutral particles found in the nucleus. Neutrons are slightly larger than protons. Text Practice: 2. 8

Study Guide for sections 1. 6, 2. 1 -2. 2 DAY 3, Terms to know: Sections 1. 6, 2. 1 -2. 2 conversion factor, dimensional analysis or factor label, atom, element, radiation, cathode ray tube, cathode, anode, electron, alpha rays, beta rays, gamma rays, x-rays, protons, neutrons DAY 3, Specific outcomes and skills that may be tested on exam 1: Sections 1. 6, 2. 1 -2. 2 • Depending on given data, be able to calculate density or use density to calculate mass or volume • Be able to use dimensional analysis (factor label method) to do unit conversions using any of the units discussed or any relationships given in the problem • Be able to describe what a cathode ray tube is and how that gives information about atomic structure • Be able to describe how measurements of alpha, beta, and gamma rays gave information about atomic structure • Be able to describe how the Rutherford gold experiment gave information about atomic structure

Extra Practice Problems for sections 1. 6, 2. 1 -2. 2 Complete these problems outside of class until you are confident you have learned the SKILLS in this section outlined on the study guide and we will review some of them next class period. 1. 23 1. 27 1. 51 1. 55 1. 59 1. 61 1. 63 1. 65 1. 77 1. 85 1. 95 2. 9

Prep for day 4 Must Watch videos: http: //www. youtube. com/watch? v=m 15 DWkk. Ge_0 (Tyler De. Witt: mass number vs. atomic mass ) https: //www. youtube. com/watch? v=Ebo. We. Wmh 5 Pg (Tyler De. Witt: isotopes) https: //www. youtube. com/watch? v=Gqt. UWy. DR 1 fg (watch first 4: 46 minutes, crash course chemistry: forms of energy) Other helpful videos: https: //www. youtube. com/watch? v=j 3 Fhs. Lb. CJts&list=PLq. OZ 6 FD_RQ 7 k 3 kp 5 B 4 j. Qb. IA 99 gh 73 RFsh (UC-Irvine) https: //www. youtube. com/watch? v=nj. Gz 69 B_p. Ug (Bozeman: atomic structure and history) http: //ocw. mit. edu/courses/chemistry/5 -111 -principles-of-chemical-science-fall-2008/video-lectures/ (MIT lecture 3) Read sections 2. 3 -2. 6, 3. 1