Chemistry

• Changes in matter essential to daily life include digesting and assimilating food, synthesizing polymers for clothing, containers, cookware, credit cards, and refining crude oil into gasoline and other products
• Chemistry is based on observation and experimentation, involving answering questions and explaining observations using the laws and theories of chemistry
• The scientific method in chemistry involves observation, experimentation, hypothesis testing, and theory development based on reproducible experiments
• Scientific theories are comprehensive, testable explanations of particular aspects of nature, accepted because they provide satisfactory explanations and can be modified with new data
• Chemists study matter and energy in three domains: macroscopic (large, visible), microscopic (small, often imagined), and symbolic (representations like chemical symbols, formulas, equations)
• The macroscopic domain includes everyday and laboratory chemistry, where physical and chemical properties are observed and measured
• The microscopic domain includes atoms, molecules, ions, electrons, protons, neutrons, and chemical bonds, often too small to be seen even with standard microscopes
• The symbolic domain contains specialized language like chemical symbols, formulas, equations, graphs, and drawings, helping interpret behavior of the macroscopic domain in terms of the microscopic domain
• Matter is defined as anything that occupies space and has mass, existing in three states: solid (rigid, definite shape), liquid (flows, takes shape of container), and gas (takes shape and volume of its container)
• The three most common states or phases of matter are solid, liquid, and gas
• A fourth state of matter, plasma, occurs naturally in the interiors of stars
• Plasma is a gaseous state of matter that contains appreciable numbers of electrically charged particles
• Plasmas are found in high-temperature environments like lightning strikes, certain television screens, and specialized analytical instruments
• Plasma torches can be used to cut metal
• In a plasma television, plasma emits ultraviolet light to display specific colors
• Some samples of matter exhibit properties of solids, liquids, and/or gases simultaneously, especially when composed of many small pieces
• Matter can have properties of more than one state when it is a mixture, like clouds being a mixture of air and tiny particles of water
• The mass of an object is a measure of the amount of matter in it
• Weight refers to the force that gravity exerts on an object, directly proportional to the object's mass
• An astronaut's mass does not change when going to the moon, but her weight on the moon is one-sixth of her earth-bound weight
• The law of conservation of matter states that there is no detectable change in the total quantity of matter present during conversions or changes among states of matter
• An atom is the smallest particle of an element that has the properties of that element and can enter into a chemical combination
• Atoms and molecules are the building blocks of matter
• Atoms are so small that their size is difficult to imagine, and they are the basis of all matter
• Molecules consist of two or more atoms joined by strong forces called chemical bonds
• Molecules may consist of two or more identical atoms or two or more different atoms
• Water molecules contain two hydrogen atoms and one oxygen atom
• Glucose molecules contain 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms
• Molecules are incredibly small and light
• If an ordinary glass of water were enlarged to the size of the earth, the water molecules inside it would be about the size of golf balls
• Pure substances have a constant composition and all specimens of a pure substance have exactly the same makeup and properties
• Pure substances can be classified into elements and compounds
• Elements are pure substances that cannot be broken down into simpler substances by chemical changes
• Compounds are pure substances that can be broken down by chemical changes
• Mercury(II) oxide can be broken down by heat into the elements mercury and oxygen
• The compound sucrose can be broken down into the element carbon and the compound water
• Silver(I) chloride can be broken down into its elements, silver and chlorine, by absorption of light
• Mixtures can be classified into heterogeneous mixtures and homogeneous mixtures
• Heterogeneous mixtures have a composition that varies from point to point
• Homogeneous mixtures, also called solutions, exhibit a uniform composition and appear visually the same throughout