Transcript atoms.
Chapter 4 Atoms 4.1 The Development of the Atomic Theory Atoms are everywhere! • Aluminum containers are lightweight because of the properties of the Al atoms that make them up. • Nanotechnology (making products that are atom-size) is being used to make microsubmarines which will eventually be able to travel in our bodies to detect health problems. U decide…Fact or Fiction • An atom cannot be broken down into smaller parts. • An atom has the same charges throughout. • Atoms are made up of several different particles. Democritus • Beginning of “The Atomic Theory” (~2000 years ago) • Believed all matter consisted of extremely small particles that could not be divided. Called these particles atoms. • Problem no evidence / data to support his theory Dalton Dalton’s Atomic Theory • Like Democritus, proposed atoms could not be divided. • All atoms of a particular element are exactly alike, and atoms of different elements join to form compounds. • Substances join together in consistent ways (Law of Definite Proportions). – Based his theory on experimental evidence. • Example: 100 g of Mg combines with 65.8 g of O. 10 g of Mg combines with 6.58 g of O. Theories can change… • Dalton made some significant contributions to the Atomic Theory, BUT the theory did change over time as more experiments were done and additional data collected. Thomson’s Model Thomson’s Model • First to suggest that atoms were not indivisible. – Based on an electricity experiment with a cathode ray tube. • Particles in the beam must be negative b/c they were attracted to the positive plate. • In a nutshell, Thomson discovered ELECTRONS! Thomson’s Plum Pudding Model • Said that negative charges (electrons) are evenly scattered throughout atoms. • To bring this into 2009, call it the blueberry muffin model or the chocolate chip ice cream model. Rutherford’s Atomic Theory • Worked with a student to find out what happens to positively charged alpha particles when they pass through a thin sheet of gold foil. • He believed the particles would travel straight from their source to the screen that lit up when struck. What actually happened. The Results of Rutherford’s Experiment • The results of Rutherford’s experiment did not match with his predictions. – More particles were deflected than he expected. Some of the particles even acted as if they struck an object and bounced straight back. • SO, Rutherford concluded that the positive charge of an atom is NOT evenly spread throughout. The positive charge is concentrated in a small, central area he called the nucleus. More about Rutherford… • So, in essence, Rutherford discovered PROTONS and the nucleus! • He also proposed that electrons orbited the nucleus of an atom like planets orbit the sun. – Today we know that the nucleus not only contains protons, but also neutrons (which have no charge). FUN FACT • IF AN ATOM was the same size as the Cleveland Browns football stadium, its nucleus would be the size of a marble. – Most of an atom’s volume is the space around the nucleus, not the nucleus itself. Review Questions • 1. Democritus coined what word for a tiny piece of matter that cannot be divided? • Answer – Atom • 2. If 2 g of element X combine with 4 g of element Y to form compound XY, how many grams of element Y would combine with 12 grams of X to form the same compound? • Answer – 24 grams Review Questions • 3. In Rutherford’s experiment, what caused some of the alpha particles to bounce straight back from the gold foil? • -Answer – The positively charged nucleus