Preparation for
General
Chemistry
Prof. Darrin M. York•
Compare and contrast the common states of matter: solid, liquid, and gas.•
Describe the classifications of matter: pure substances (elements and compounds), and mixtures (heterogeneous and homogeneous).•
Describe what constitutes the chemical identity of a pure substance.•
State the law of conservation of mass.•
Distinguish whether a process corresponds to a chemical or physical change.•
Characterize properties as being either chemical or physical in nature, and extensive or intensive.Chemistry
is the study of matter, the changes that
matter undergoes and the energy associated with these
changes.
Atoms are the fundamental building blocks of matter.
The word “atom” derives from the Greek word “atomos” which means “indivisible.
Matter is composed of atoms that may be connected to one another by chemical bonds. There are different types of chemical bonds, and different ways that chemical bonds give rise to various types of compounds.
Chemical bonds are a form of attraction between atoms that connect
them to one another and allow formation of chemical substances
There are different types of chemical bonds•
Covalent – involve shared electrons and are directional•
Ionic – involve electrostatic force between oppositely charged ionscaffeine, C8H10N4O2 table salt, NaCl sodium,Na Covalent Bond Ionic Bond Metallic Bond
Chemical identity of matter is determined by the atoms from which it is composed, together with the chemical bonds that tie them together, and in some cases geometrical structure.
trans-dichloroethylene Tb = 60.2 °C cis-dichloroethylene Tb = 48.5 °C diamond C graphite C H Cl H Cl fulminate cyanate H Cl Cl H O C N C N O
•
The
law of conservation of mass
states that mass is neither created nor
destroyed in any chemical or physical process.
•
Although matter may be converted from one form into another, the
total amount of mass remains constant.
We can classify matter based on:
•
physical state (solid, liquid or gas)•
composition (pure substance or mixture)Liquid
State
Solid Gas Mixture
Composition
PureSubstance
Homogeneous Heterogeneous Element Compound
•
Solid: particles are packed close to each other in fixed locations. Solids retain their shape (do not flow), and are fairly incompressible.•
Liquid: particles are packed close to each other but are not in fixed locations. Liquids also are fairly incompressible, but can flow and take the shape of a container (but do not necessarily fill it).•
Gas: particles are generally far away from each other and free to move relative to one another. Gases are easily compressed and fill the volume of their containers.•
A pure substance (or simply a “substance”) is a form of matter that has
definite (constant) composition and distinct properties.
•
A mixture is a physical combination of two or more substances.
Mixture
Composition
Pure Substance Homogeneous Heterogeneous Element CompoundAn
element
consists of only one type
of atom, whereas a
compound
consists of more than one type of
atom.
Pure Substance
Element Compound
Elements can be either:
•
atomic (made of individual atoms), e.g. the noble gases•
molecular (made of molecules)e.g. O2, O3, Br2, or P4 (white phosphorus)
•
covalent or metallic crystal network e.g., diamond (solid C), Ag metal•
Different chemical forms of the same element are called allotropes.silver,Ag
model of atomic element
phosphorus, P4
Compounds are made up of more than one type of atom.
They can be composed of either molecules (C2H5OH), ions (NaCl), or network solids (SiO2).
Isomers are compounds with the same chemical formula, but with different chemical structure. Quartz, SiO2 Ethanol, C2H5OH Sodium Chloride, NaCl
A
homogeneous
mixture
has components that are
uniform throughout.
They are also called
solutions
.
A
heterogeneous
mixture is
not uniform throughout, as
the components are
discernible by the naked eye.
Examples: Sand, granite, smogIn
physical changes
the
chemical identity of the
substance does not change,
only the physical state.
Examples: melting, freezing, evaporation, condensation, sublimation, deposition.
In
chemical changes
the chemical identity of one
or more substances changes; e.g., one substance is
converted into another.
•
Examples: oxidation of metals (e.g., rusting or iron, corrosion of copper, tarnishing of silver), combustion, electrolysis of water, neutralization of an acid by a base.CH4 + 2O2 → CO2 + 2H2O
Physical properties
can be observed and measured without
changing the identity of the substance (i.e., without undergoing a
chemical change).
Chemical properties
can not be observed without converting
the substance into another substance (i.e., without undergoing a
chemical change).
Extensive properties
Intensive properties
Depend on the amount of matter.
Example: mass, volume, number
of particles, energy.
Do not depend on the amount of
matter.
Examples: temperature, density,
boiling point, hardness, color,
concentration.
•
The three common states of matter are solids, liquids and gases, and each has a set of distinct physical properties that allow them to be distinguished.•
Matter can be classified by physical state, or by composition as pure substances or mixtures.•
Chemical identity is determined by the atoms contained in a substance,together with their chemical bonding and geometrical arrangement.
