Chemistry is based on qualitative observations and

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: eriments a source of fascination, e challenge. Chemistry is based on qualitative observations and quantitative measurements. Law of conservation of mass: In a chemical reaction, the total mass of the reactants must be equal to the total mass of the products. Similarly; Law of conservation of energy: During any process, energy is neither created not destroyed. We need a common language and a common set of units. (SI) •  meter •  kg •  K •  s •  mol Compound units; e.g. density “Answers” must have the appropriate units. “Dimensional analysis” Intensive properties: Independent of amount. e.g. density Extensive properties: Dependent of amount. e.g. mass Does not really apply at the nanoscale. ! CdSe nanocrystals In describing measurements, we need to be cognizant of and sensitive to the “accuracy” of a measurement or result; i.e. how close are we to the “actual” value. We often use “percentage error”. We must also know what the precision of a result is; i.e. reproducibility. (±?) The precision is indicated by the number of significant figures. By 2050 world energy needs will double! Oil will be mostly depleted in next 50 to 60 years. How much is a Quad? Need new energy sources and more efficient energy conversion & storage. 1,000,000,000,000,000 MThus, 100 Quadsnow! ust start to plan is: (Actually, we are already late.) 100,000,000,000,000,000!!! 7! Courtesy: H. Kung @ DOE Atoms & Molecules " All substances are either atoms or molecules (group of atoms joined or “bonded” together). " Any substance that cannot be broken down into simpler substances is called an element. " A substance that can be broken down is a compound. Definition: " An element is a substance that consists only of atoms with the same nuclear charge. " Although ca. 120 elements; only 40 (or so) “really count”. States of Matter Solid! Liquid! Gas! A solid has a fixed volume and a fixed shape. A liquid has a definite volume but no specific shape. (Takes the shape of the container.) A gas fills the entire volume of its container and thus has no definite shape. Liquid Crystals (4th state of matter)...
View Full Document

This document was uploaded on 11/06/2013.

Ask a homework question - tutors are online