Download Chemistry Notes - Mater Academy Lakes High School

Unit 3. The Chemistry of Life
Topic 1. Basic Chemistry
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Composition of Matter
Matter - Everything in universe is composed of matter
o Matter is anything that occupies space or has mass
 Mass – quantity of matter an object has
 Weight – pull of gravity on an object
Elements
o Pure substances that cannot be broken down chemically into simpler kinds of matter
o More than 100 elements (92 naturally occurring)
o 90% of the mass of an organism is composed of 4 elements (oxygen, carbon, hydrogen and nitrogen)
o Each element unique chemical symbol
 Consists of 1-2 letters
 First letter is always capitalized
Atoms
o The simplest particle of an element that retains all the properties of that element
o Properties of atoms determine the structure and properties of the matter they compose
o Our understanding of the structure of atoms based on scientific models, not observation
o The Nucleus
 Central core
 Consists of positive charged protons and neutral neutrons
 Positively charged
 Contains most of the mass of the atom
 The Protons
 All atoms of a given element have the same number of protons
 Number of protons called the atomic number
 Number of protons balanced by an equal number of negatively charged electrons
 The Neutrons
 The number varies slightly among atoms of the same element
 Different number of neutrons produces isotopes of the same element
 Atomic Mass
 Protons & neutrons are found in the nucleus of an atom
 Protons and neutrons each have a mass of 1 amu (atomic mass unit)
 The atomic mass of an atom is found by adding the number of protons & neutrons in an atom
o The Electrons
 Negatively charged high energy particles with little or no mass
 Travel at very high speeds at various distances (energy levels) from the nucleus
 Electrons in the same energy level are approximately the same distance from the nucleus
 Outer energy levels have more energy than inner levels
 Each level holds only a certain number of electrons
 Electrons in the same energy level are approximately the same distance from the nucleus
 Outer energy levels have more energy than inner levels
 Each level holds only a certain number of electrons
o Energy Levels
 Atoms have 7 energy levels
 The levels are K (closest to the nucleus), L, M, N, O, P, Q (furthest from the nucleus)
 The K level can only hold 2 electrons
 Levels L – Q can hold 8 electrons (octet rule)
Periodic Table
o Elements are arranged by their atomic number on the Periodic Table
o The horizontal rows are called Periods & tell the number of energy levels
o Vertical groups are called Families & tell the outermost number of electrons
Elements and Isotopes
o A chemical element is a pure substance that consists entirely of one type of atom.
o The number of protons in an atom of an element is the element's atomic number.
o Atoms of the same element that differ in the number of neutrons they contain are known as isotopes.
o Because they have the same number of electrons, all isotopes of an element have the same chemical properties.
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o Radioactive Isotopes
 Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate
over time
 Radioactive isotopes can be used
 to determine the ages of rocks and fossils
 to treat cancer.
 to kill bacteria that cause food to spoil
 as labels or “tracers” to follow the movement of substances within an organism
Compounds
o Most elements do not exist by themselves
o Readily combine with other elements in a predictable fashion
o A compound is a pure substance made up of atoms of two or more elements
o The proportion of atoms are always fixed
o Chemical formula shows the kind and proportion of atoms of each element that occurs in a particular compound
o The physical and chemical properties of a compound differ from the physical and chemical properties of the
individual elements that compose it
Molecules
o Molecules are the simplest part of a substance that retains all of the properties of the substance and exists in a free
state
o Some molecules are large and complex
Chemical Formulas
o Subscript after a symbol tell the number of atoms of each element
o H20 has 2 atoms of hydrogen & 1 atom of oxygen
o Coefficients before a formula tell the number of molecules
o 3O2 represents 3 molecules of oxygen or (3x2) or 6 atoms of oxygen
Chemical Bonds
o The tendency of elements to combine and form compounds depends on the number and arrangement of electrons in
their outermost energy level
o Atoms are most stable when their outer most energy level is filled
o Most atoms are not stable in their natural state
o Tend to react (combine) with other atoms in order to become more stable (undergo chemical reactions)
o In chemical reactions bonds are broken; atoms rearranged and new chemical bonds are formed that store energy
Chemical Bonds Types
o Ionic bonds
 Some atoms become stable by losing or gaining electrons
 Atoms that gain electrons are called negative ions (Anions)
 Atoms that loose electrons are called positive ions (Cations)
 Because positive and negative electrical charges attract each other ionic bonds form
o Covalent bonds
 Sometimes electrons are shared by atoms instead of being transferred.
 Formed when two atoms share one or more pairs of electrons
 The structure that results when atoms are joined together by covalent bonds is called a molecule
Polar bonds
o Ionic bonds are polar (one side has more electrons than the other)
o Covalent bonds between elements with different number of protons in their nucleus can be polar if the molecular
structure is not perfectly symmetric.
 For example: In water, oxygen has a higher number of protons and pulls electrons more than hydrogen can.
The result is a polar bond where electrons are shared unequally between oxygen and hydrogen.
Wall der Waals Forces
o Polar molecules have one side more negative than the other.
o The negative side attracts the positive side of another molecule
o When molecules are close together, a slight attraction can develop between the oppositely charged regions of
nearby molecules.
o Unlike chemical bonds, atoms are not joined together by the sharing of electrons.
o This is a physical connection based on magnetism/electricity and attraction between different charges
o This connections is what holds molecules together to form a substance