WEEK TWO -- CHAPTER 4: Atoms, Molecules and Ions

 

Now it is time to get the heart of the matter--or more specifically, how atoms form molecules and produce matter. We will begin by discussing the theory of the atom, what particles make up the atom and differences between different atoms. Remember, atoms are elements, they are simply the smallest particle of an element that can be identified as that element.

 

ATOMS--Dalton's Atomic Theory

 

ATOMIC PARTICLES:

Atoms consist of three subatomic particles:

 

 

Particle

Mass (kg)

Mass (amu)#

Charge*

Electron

9.10939 x 10 -31

0.00055

- 1

Proton

1.67262 x 10 -27

1.00728

+1

Neutron

1.67493 x 10 -27

1.00866

0

    # 1 amu (atomic mass unit) = 1.66054 x 10 -27 kg       * unit charge = 1.602 x 10 -19 C (coulomb)

 

ELECTRONS:

 

 

PROTONS:

NEUTRONS:

ATOMIC NUMBER:

MASS NUMBER:

ELEMENTAL SYMBOLS:

                      AXZ

Elemental symbols are typically written as above where X is the element symbol with the mass number as a superscript and the atomic number as a subscript.

 

ISOTOPES:


        # p          6                         6                           6

        # e          6                         6                            6

        # n          6                         7                            8

 

mass C = (0.989)(12.0000) + (0.011)(13.0000) = 12.011 amu

 

ATOMIC MASSES:

Because atoms are too small to weigh individually, we have had to develop a relative mass scale for elements on the periodic table:

PERIODIC TABLE:

MOLECULES AND IONS:

Compounds and elements are pure substances which are the basic building blocks of all matter The following chart should clarify the relationship between pure substances, elements, compounds, atoms and molecules :

 

Notice that both elements and compounds are pure substances. Atoms are the smallest particles that can be identified as a particular element, and molecules are the smallest particles that can be identified as a particular compound. Elements can also occur in a molecular form in which the same type of elements (atoms) are chemically combined, such as two oxygen atoms, O, which form molecular oxygen, O2, when chemically combined. There are some elements, which you should know, that only occur naturally (under normal conditions) in their molecular forms. They are called diatomic molecules or, sometimes, molecular elements and they are: hydrogen, H2; nitrogen, N2; oxygen, O2; fluorine, F2; chlorine, Cl2; bromine, Br2; iodine, I2.   Compounds are chemical combinations of elements (atoms) of different types, such as water, H2O or carbon dioxide, CO2. Let us look further at the formation of compounds, both molecular compounds and ionic compounds.

MOLECULES:

It would be wise, at this point, to obtain a model set of your own. The ability to actually build a 3-dimensional model will enable you to "see" the spatial nature of the compounds that we talk about.

IONS:

 

IONS IN THE BODY

K+ and Mg2+ are predominantly inside the cell and are important for nerve impulse transmission.

Na+ and Ca2+ and found outside the cell and are important in the formation of bones, teeth, clotting, regulation of heart rhythm and Na+ is important in nerve sensitivity and muscle control. 

All 1st row transition metals except Ti are biologically active.

High Zn ion intake induces Cu ion deficiency and Cu and Fe ion deficiencies can disrupt sleep as they are integral in the biological production of neurotransmitters which affect brain activity.

 

 

Formulas and Relative Masses:

Ca cation and O anion are chemically combined in a 1:1 ratio

mass Ca combined                           8.02 g
mass CaO after combination        11.22 g
mass O combined                            3.20 g
therefore the relative mass of Ca : O is 8.02 /3.20 = 2.51 so Ca is 2.51 times heavier than O

Electrical Properties of Solutions:

When substances dissolve in water, the basic particles from which they are made (molecules in molecular substances and ions in ionic substances) are separated by the water molecules. We will discuss this in much more detail in Chapter 13--Solutions

Sample Problems:

 

SYMBOL

 

CHARGE

 

# of Protons

 

# of Neutrons

# of Electrons

          31P15

0

15

16

15

         79Br35

0

35

44

35

         55Mn25

+2

25

30

23

Notice that the charges of the ions are never written in the formula and the formula always describes a neutral substance

isotopes always have the same number of protons (which mean they are defined as the same element) hence, have the same symbol & atomic number but have different numbers of neutrons, hence different mass numbers

Below are listed some of the more common monotomic and polyatomic ions.   Know the ion names, symbols and charges--you will need this information in the next chapter.

Remember, each ion (whether monotomic or polyatomic) is considered an individual unit and remains so during chemical reactions (at least at this point on your path toward chemical knowledge!)

COMMON IONS

Positive

Negative

Hydrogen

H+

Hydroxide

OH-

Sodium

Na+

Fluoride

F-

Potassium

K+

Chloride

Cl-

Ammonium

NH4+

Bromide

Br-

Silver

Ag+

Iodide

I-

Copper(I)

Cu+

Nitrate

NO3-

Copper(II)

Cu+2

Nitrite

NO2-

Barium

Ba+2

Perchlorate

ClO4-

Calcium

Ca+2

Chlorate

ClO3-

Zinc

Zn+2

Chlorite

ClO2-

Nickel

Ni+2

Hypochlorite

ClO-

Magnesium

Mg+2

Acetate

C2H3O2-

Cobalt(II)

Co+2

Sulfide

S-2

Iron(II)

Fe+2

Sulfate

SO4-2

Manganese(II)

Mn+2

Sulfite

SO3-2

Mercury(II)

Hg+2

Oxide

O-2

Aluminum

Al+3

Carbonate

CO3-2

Iron(III)

Fe+3

Phosphate

PO4-3

Chromium(III)

Cr+3

Bisulfate

HSO4-

Cobalt(III)

Co+3

Bicarbonate

HCO3-

    Cyanide

CN-

    Chromate

CrO4-2

    Dichromate

Cr2O7-2

 

 

 

 

Click here to go to Chapter 5 Chemical Formulas and Names