Chemistry

Chemical substances and processes are essential for our existence, providing sustenance, keeping us clean and healthy, fabricating electronic devices, enabling transportation, and much more

 

  • Chemistry is the study of the composition, properties, and interactions of matter

  • Attempts to understand the behavior of matter extend back more then 2500 years

    • Greeks: Matter consists of four elements: Earth, Fire, Air, and Water

    • Alchemist attempted to transform "base metals" into noble metal"

 

Knowledge of Chemistry is central to understanding a wide range of scientific disciplines. This diagram shows just some of the interrelationships between Chemistry and other fields

 

The Scientific Method

  • Chemistry is a science based on observation and experimentation

  • Chemists often formulate a hypothesis: a tentative explanation of observations

  • The laws of science summarize a vast number of experimental observations, and describe or predict some facet of the natural world

  • Theory: A well-substantiated, comprehensive, testable explanation of a particular aspect of nature

 

  • Mass is a measure of the amount of matter in an object

  • Weight refers to the force that gravity exerts on an object

  • An object's mass is the same on the earth and the moon but its weight is different

  • The Law of conservation of matter states that there is no detectable change in the total quantity of matter present when the matter converts from one type to another

  • This is true for both chemical and physical changes

  • An element is a type of pure substances that cannot be broken down into simpler substances by chemical changes; the basic building block in chemistry

  • The known elements are displayed in the periodic table

    • There are more than 100 known elements

    • Ninety of these occur naturally

    • Two dozen or so have been created in laboratories

  •  Pure substances have constant composition

    • Elements: Pure substance that cannot be broken down into simpler substances by chemical changes

      • Consist of one type of element

      • Examples: Gold (Au), Phosphorus (P), Oxygen (O)

    • Compounds: Pure substance that can be broken down into simpler substances by chemical changes

      • Consist of two or more types of elements chemically bonded

      • The properties of compounds are different from the uncombined elements making up the compound

  • A mixture is composed of two or more types of matter that can be present in varying amounts and can be separated by physical changes

  • Evaporation is an example of physical change

  • There are two types of mixtures: homogenous mixtures and heterogeneous mixtures

  • A homogenous mixture exhibits a uniform composition an appears visually the same throughout

    • Another name for a homogenous mixture is a solution

    • Homogenous mixtures is the same; from top to bottom it is uniform throughout and when everything mixes with each other

  • A heterogenous mixture has a composition that varies from point to point

    • Heterogeneous mixtures is mixed up; it is not uniform throughout the sample

  • An Atom is the smallest particle of an element that has the properties of that element and can enter into a chemical combination

    • Idea first proposed by Greek philosophers, Leucippus and Democritus, in the 5th century BCE

    • The 19th century, John Dalton of England supported this hypothesis with quantitative measurements

  • A molecule consists of two of more atoms connected by strong forces known as chemical bonds

  • Properties: the characteristics that enables us to distinguish one substance from another

  • Physical Property: a characteristic of matter that is not associated with a change in its chemical composition (density, color)

  • Physical Change: a change in the state or properties of matter without any accompanying change in its chemical composition

  • Chemical Property: the change of one type of matter into another type of matter (flammability, toxicity, acidity, reactivity)

  • Extensive Property: depends on the amount of matter present (mass, volume)

  • Intensive Property : does not depend on the amount of matter present (density, temperature)

  • Chemistry: the study of matter

  • Matter: something with mass and volume

  • Measurements: provide the information that is the basis of most hypotheses, theories, and laws

    • Measurements need to include number and units

  • Temperatures

  • Volume: the amount of space occupied by an object

    • Must be cubed and often used as ML or L

  • Density: the ration of mass to volume

    • Mass per unit volume