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CP Sci 9- 1st Sem.

Gen Chem - 1st Sem.

Matter and Atoms


    1.    Identify the characteristics of matter.

    2.    Compare the particles that make up atoms of elements.

    3.    Describe three types of chemical bonds.


Matter can be described as anything having mass and volume.  Matter can be better defined, though, by separating it into its simplest parts.  Since the atom is the basic unit of matter, we will start there.  A group of similar atoms is called an element.  Here are some elemental facts.
bulletAn element cannot be separated into simpler substances by physical or chemical means.
bulletThere are slightly more than 100 known elements. (listed on the periodic table)
bulletThe periodic table organizes elements by their properties.
bulletCan be represented by a one or two letter abbreviation. (C,H,O,N,P,Na,Cl,Al,Ca)

Atoms are the smallest particle of an element retaining all of its properties.  Though, invisible to the eye and microscope (limited images are possible with the tunneling microscope), you could theorize that an atom of gold would have the same luster and texture (look and feel) as a solid gold bar.  The belief in atoms as the basic building block of matter dates back o the Greek philosophers (450 BC) when Democritus first proposed the existence of atomos (small particles of matter).  Unfortunately Democritus' views were not accepted until the early 1700s.
bullet1803 - Dalton - Atomic Theory of Matter
bullet    Elements are composed of atoms
bullet    Atoms in an element are identical but different from other elements
bullet    Atoms cannot be destroyed or created by physical or chemical reactions
bullet    A give compound always has the same ratios and kinds of atoms


Atoms are made of even smaller subatomic particles called protons, neutrons, and electrons.  

(web.buddyproject.org/web017/ web017/images/atom.JPG)
bulletprotons - have a positive charge, found in the nucleus and have an atomic weight of one
bulletThe number of protons determines the positive charge of the atom
bulletThe number of protons determines the atoms identity
bulletelectrons - have a negative charge, move in the space around the nucleus, the number is equal to protons in a neutral atom and they have no appreciable mass
bulletneutrons - have no net charge, found in the nucleus, and have an atomic weight of one
bulletIn neutral atoms the # of protons = # of electrons


Combinations of elements can form compounds.  Its important to know that compounds are pure substances.  (A compound of H2O contains nothing but H2O.)  Here are some facts regarding compounds.

bulletCompounds form during chemical reactions. (2H2 + O2 = 2H2O)
bulletContains 2 or more elements in definite proportions
bulletCompounds can be separated into their elements by chemical means. (2H2O =  2H2 + O2)
bulletThe symbols used to describe compounds describe the exact amount of atoms on the compound. (C6H12O6)
bulletCannot be separated by physical means.


Atomic Numbers:

    The atomic numbers indicated on the periodic table indicate the number of protons in the nucleus.

(sciencemadesimple.com/ img_static/atom.gif)

bulletThe electrons and neutrons of an atom can change but it cannot change the amount of protons and still be of the same element


Whenever an atom gains or looses electrons it becomes an ion.  You can find the net charge of the atom by subtracting the number of electrons from the atomic number.

bulletIf the result is positive (atomic # > electrons) - cation - overall positive charge
bullet    example: Ca    20(p) - 18(e) = 2+    or    Ca2+
bulletIf the result is negative (atomic # < electrons) - anion - overall negative charge
bullet    example: O     8(p) - 10(e) = 2-        or    O2-


Most elements in the first two rows of the periodic table have at least two known isotopes.  Isotopes have the same number of protons and electrons but differ in the number of neutrons.  (mass - protons = neutrons)

    Example:    hydrogen-1            hydrogen-2            hydrogen-3

(www.cat.cc.md.us/~cminnier/ hisotop.gif)

bulletIsotopes are named after their masses (neutrons + protons) eg: C-12 & C-14


Electron Configurations:

The distribution of electrons in the different electron orbitals is called the electron configuration.  The distribution within the energy levels (n) and suborbitals follows the following principles.

1)    Electrons always fill the available suborbitals based on the suborbital's energy levels (s,p,d,f).
bulletWhen electrons fill only the lowest energy orbitals available, the atom is in its ground state. (Atoms are normally found in this state)

 Combining of atoms or elements depends upon the electrons e- in the outer most valence shell or energy level where the e-  found.

The first shell, innermost level can hold up to 2 electrons.


The second can hold up to 8 electrons.


The third can hold up to 8 electrons.

When the outermost energy level (shell) is holding the maximum number of electrons the atom is stable or unreactive . It does not combine with other atoms. It does not form chemical bonds, or compounds.  


Octet Rule - To be stable an atom will gain, lose, or share electrons to complete the outer most energy level (electron shell).


Ionic bonds & Compounds:

Ionic bonds are formed from the transfer of electrons from one atom to another.  The Ionic bond that forms is the result of the attraction of oppositely charged ions (atoms).  The attraction acts much like the opposite poles of a magnet.  Here are some simple rules for ion formation and naming.
bulletIonic compounds consist of entirely ionic bonds (oppositely charged ions)
bulletThe ionic compound is electronically neutral (positive charges = negative charges)
bulletIons and ionic compounds are frequently more stable than their parent atoms
bulletionic compounds are made from a metal and a nonmetal



Though we have learned about the forming of bonds through the transfer of electrons, the majority of compounds that we come in contact with in our daily lives are formed in a completely different manner.  The difference is that these atoms are covalently bonded. 

A covalent bond is one where the electrons are shared.  A group of covalently bonded atoms is called a molecule.  These molecular substances include DNA, sugar and carbon dioxide.  The molecules can contain as few as 2 atoms and as many as a million.  Rules for covalent bonds:

bulletelectrons are shared in covalent molecules
bulletcovalently bonded molecules follow the octet rule (some exceptions - BF3)
bulletcovalent molecules can form single, double, or triple bonds
bulletcovalent bonds can be rearranged to form different molecules (glucose, fructose, & maltose)


Last modified: September 05, 2004