Introduction to Chemistry

Chapter 2 Properties of Matter In this chapter: Introduction to matter through a discussion of properties that you can observe. How matter is classified Properties used to described materials

Section 2.2 Classifying Matter Classifying Items People classify objects for different reasons. Classifying foods into groups, such as grains, vegetables, and fruits helps people plan meals that maintain a healthy diet. Biologists classify organisms into groups that have similar characteristics, which makes the relationships among organisms easier to see. 1. Devise a classification system for the following items: orange, lime, plum, apple, pear, rose, violet, daisy, gold, and silver. 2. Explain what criteria you used to place items into each category of your classification system.

Inquiry Activity p. 37 Read the procedure, work in pairs Purpose: Identify various properties of matter that can be used to describe materials. Discuss materials with partner and record observations. “Think about it” in Journal (Title and date)

Classifying Matter Property (physical or chemical)– an essential or distinctive quality of thing; used to identify: gold – color, texture, streak Properties are based on composition Composition: Pure substances and mixtures

Pure Substances Always has the same fixed, uniform composition (salt-every grain tastes the same) 2 Categories Elements Compounds

Pure Substance - Elements Listed on Periodic Table Cannot be broken down into simpler substances (copper → copper atoms) Are written in symbols

Pure Substance - Compounds Substance made from 2 or more simpler substances and can be broken down into those simpler substances (H20) Properties of compound differ from elements (H & O gases; H2O – liquid) Elements always in a fixed proportion - SiO2

Mixtures Properties can vary because composition is not fixed Tend to retain some properties of individual substances Classifications: -Heterogeneous -Homogeneous

Heterogeneous Mixtures Hetero – “different”; genus – “kind” Parts are noticeably different for each other Sand: color, grain size

Homogeneous Mixtures Substances are so evenly distributed that it is hard to distinguish between them Kool-Aid (after it is stirred) Brass – copper and zinc

Particle Size Based on the size of the largest particle Solution Suspension Colloid

Solution Dissolves to form homogeneous mixture Too small to settle out; do not separate into distinct layers Are not trapped in a filter Can see through them; too small to scatter light Ex: Tap water

Suspension Heterogeneous mixture that separates into layers Larger particles can be filtered Are cloudy; larger particles scatter light

Colloids Particles are intermediate in size between small solution particles and the larger suspension particles Do not separate into layers Cannot be filtered; too small Light is scattered; cloudy but uniform Borderline between hetero- and homogeneous Ex. Fog (low beam lights on car)

Section 2.2

Section 2.3-Chemical Properties A chemical property is any ability to produce a change in the composition of matter. Chemical properties can be observed only when the substances in a sample of matter are changing into different substances. Examples: Flammability Reactivity

Flammability – ability to burn in the presence of oxygen. Reactivity – describes how readily a substance combines chemically with another substance. Oxygen highly reactive Nitrogen not highly reactive

Chemical Change Occurs when a substance reacts and forms one or more new substances. 3 common types of evidences: Change in color-match turns black Production of gas-vinegar+baking soda→CO2 Formation of precipitate – any solid that forms and separates from a liquid

Physical or Chemical Change Physical – composition does not change Sharpened pencil Chemical – composition changes Iron + oxygen → Fe2O3 (rust)