Branches of Chemistry, Matter, Accuracy and Precision

Matter

anything that occupies space

Pure Substance

has a constant composition and properties that are constant throughout the sample

Pure Substance | Element

substance that cannot be broken down into other substances through chemical means

Pure Substances | Compound

substance made up of two or more different elements that are joined together in a fixed ration

Ionic Compound

composed of discrete ions or charged species

• metal reacts with nonmetal

• metal - becomes positive or cation (for losing/donating electron)

• nonmetal - becomes negative or anion (for gaining electron)

Properties of Ionic Compounds

• solid (due to strong forces of attraction)

• high melting points and boiling points

• soluble in water but not in nonpolar liquids

• conduct electricity when melted (they are strong electrolytes; does not conduct in solid but does in molten and aqueous state)

• hard

• very reactive

Covalent Compound

molecule formed by covalent bonds, in which atoms share one or more pairs of valence electrons

Properties of Covalent Molecular Compounds

• high volatility

• weak bonds

• insoluble in water

• low melting point

• form a molecule

• form between two nonmetals

Covalent Network Substances

consists of a network of atoms of the same or different elements connected to each other by covalent bonds

• its networks extend throughout the crystalline structure

• one of the hardest materials on earth

• have high melting points

• poor conductivity

Properties of Covalent Network Substances

• high melting point

• very hard

• nonconducting

• insoluble (in any solvent due to the difficulty of solvating such a very large molecule)

Properties of Matter | Physical Properties

observed or measured without changing the composition of matter

Properties of Matter | Intensive Properties (under physical)

physical property that will be the same regardless of the amount of matter

Properties of Matter | Extensive Properties (under physical)

physical property that will change if the amount of matter changes

Properties of Matter | Chemical Property

characteristic ability of a substance to react to form new substances

• they include its flammability and susceptibility to corrosion

  • reactivity, flammability, toxicity, ability to oxidize, heat of combustion

Changes in Matter | Physical Change

occurs when a substance or object changes its appearance, phase, or is used in a mixture

• does not change the molecular structure of a substance

Types of Physical Change | Sublimation

solid to gas

Types of Physical Change | Melting

solid to liquid

Types of Physical Change | Freezing

liquid to solid

Types of Physical Change | Boiling/Evaporation

liquid to gas

Types of Physical Change | Condensation

gas to liquid

Changes in Matter | Chemical Change

occurs when the substance’s composition is changed

• bonds are broken and new ones are formed

Chemical Change | Combination or Synthesis

two or more reactants unite to form a single product

A + B → AB

Chemical Change | Decomposition

single reactant is decomposed or broken down into two or more products

AB → A + B

Chemical Change | Substitution or Single Replacement

a single free element replaces or is substituted for one of the elements in a compound

• free element = more reactive than the one it replaces

A + BC → B + AC

Zn + 2HCl → H2 + ZnCl2

Chemical Change | Double Displacement Replacement

“exchange of partners” positive combines with negative (first), negative combines with positive (second)

AB + CD → AD + CB

Ba2+Cl- + Na+SO4²- → Ba2+ SO4²- + Na+Cl-

Chemical Change | Combustion

compound containing carbon and hydrogen (sometimes oxygen) combines with oxygen gas to produce CO2 & H2O

• CxHy(O2) +O2 → CO2 + H2O

• will always result to CO2 and H2O regardless of the reactants

Analytical Chemistry

deals with the separation, identification and quantification of chemical substances (analytes) in a given sample

Physical Chemistry

studies the physical properties of chemical compounds using laws and concepts of physics (e.g., motion, energy, force, time thermodynamics, quantum chemistry)

Inorganic Chemistry

studies compounds that are not organic (does no have the C-H bonds)

Organic Chemistry

studies chemical compounds that contain the element C and C-H bonds

Biochemistry

studies the structure, composition, and chemical reactions of chemical components of living systems to understand how and why chemical reactions occur

Accuracy

refers to the closeness of a measured value to a standard or known value

Precision

refers to the closeness of two or more measurements to each other