CHAPTER 4 Elements Compounds, Mixtures Elements, the Simplest Substances An element is a pure substance that cannot be separated into simpler substances by physical or chemical means. Only One Type of Particle A substance in which there is only one type of particle is a pure substance. Elements are made of particles called atoms. Properties of Elements Each element can be identified by its unique set of properties. An element may share a property with another element, but other properties can help you tell the elements apart. Identifying Elements by Their Properties Elements can be identified by using their physical properties and their chemical properties. Classifying Elements by Their Properties Categories of Elements Three major categories are: Metals are shiny, and they conduct heat energy and electric current. Nonmetals conduct heat and electricity poorly. Metalloids have properties of both metals and nonmetals
Classifying Elements by Their Properties, continued Categories Are Similar By knowing the category to which an unfamiliar element belongs, you can predict some of its properties. The next slide show examples and properties of metals, nonmetals, and metalloids. Compounds: Made of Elements A compound is a pure substance composed of two or more elements that are chemically combined. Elements combine by reacting with one another. A particle of a compound is a called a molecule. Molecules of compounds are formed when atoms of two or more elements join together. Compounds: Made of Elements The Ratio of Elements in a Compound Elements join in a specific ratio according to their masses to form a compound. For example, every sample of water has a 1:8 mass ratio of hydrogen and oxygen. Properties of Compounds Each compound can be identified by its physical and chemical properties. Properties: Compounds Versus Elements A compound has properties that differ from those of the elements that form it. Breaking Down Compounds Compounds can be broken down into their elements or into simpler compounds by chemical changes. Methods of Breaking Down Compounds Sometimes, energy is needed for a chemical change to happen. Two ways to add energy are to apply heat and to apply an electric current Compounds in Your World Compounds in Nature Some compounds found in nature are proteins, carbon dioxide, and carbohydrates. Compounds in Industry Some compounds must be broken down for use in industry. Other compounds, are made in industry for use as medicines, food preservatives, and synthetic fabrics.
Mixtures A mixture is two or more substances that s mixed together but can be separated out. Properties of Mixtures Mixtures can be separated by using physical changes Physical changes do not change the identities of the substances. Separation of Mixtures 1. Distillation the separation of a liquid based on the boiling point 2. Using a magnet to separate metals 3. Centrifuge used to separate substances of different densities 4. Evaporation used to separate substances from a liquid.
The components of a mixture do not need to be mixed in a definite ratio. For example, granite is a mixture of three minerals. Different ratios of the minerals give granite different colors, but the mixture is always called granite. Solutions A solution is a mixture that appears to be a single substance. The process in which particles of substances separate and spread evenly throughout a mixture is known asdissolving_. In a solution, The solute dissolves. The solvent does the dissolving. Examples of Solutions Liquid solutions include soft drinks, Gasoline, tap water. Solutions may also be gases, such as air Solutions may also be a solid, such as steel. Alloys are solid solutions of metals or nonmetals dissolved in metals. The particles in solutions are so small that they never settle out. they cannot be removed by filtering. They do not scatter light Concentration of a Solution A measure of the amount of solute dissolved in a solvent is concentration.
Concentrated or Dilute? Solutions can be described as being concentrated or diluted But these two terms do not tell you the amount of solute that is dissolved. Solubility is the ability of a solute to dissolve in a solvent at a certain temperature. The solubility of most solids in water increases with temperature What is the concentration of a solution that has 35g of salt dissolved in 175ml of water? Step 1: The equation for finding concentration is: Concentration = Step 2 : Replace grams of solute and the milliliters of solvent Concentration = =