The Atom: basic unit of all matter

The Atom is composed of many small particles. We are going to concentrate on the THREE MAIN ONES:

•Inside the nucleus there are TWO ……the Proton (has a positive charge) and the

Neutron (neutral)

•Outside of the nucleus, roams the electron (has a negative

charge)

The Nucleus: The central core of the atom.

Provides the mass of the atom.

Has an overall positive charge due to the protons within.

Mass number: the number of protons + the number of neutrons

Atomic number: the number of protons

You should notice that each has its own number of proton(s) and thus, an equivalent number of electrons, since all atoms are neutral until they react with another.

# of # ofprotons = electrons

Determining an Atom’s Mass Number and

Atomic Number by Using the Periodic Table

7

14.00674

N

Atomic Number

Element’s symbol

Relative Atomic Mass

What about that Mass NUMBER???????So, from the periodic table you can determine the number of protons since it is the same as the atomic number. But, how do you determine the number of neutrons? Well, remember the definition of isotopes? Each atom has at least two isotopic forms. So, we have two ways to determine the number of protons for an individual atom. First, from a special symbol, like the C-14 or C-12. The 14 and the 12 are the given mass numbers for that atom. So, given this info, all you have to do is:

Remember the mass number = #p + #n and, so mass number - #p = # neutrons

#14 - 6p = 8 neutrons and #12 - 6p = 6 neutrons

You try some:

Li -7: #p = ____, # e = _____, # n = ____

P- 31: #p = ____, # e = _____, # n = ____

Pb-207: #p = ____, # e = _____, # n = ____

Cl-35: #p = ____, # e = _____, # n = ____

Answers: Li-7 has 3 protons, 3 electrons, 4 neutrons

P-31 has 15 protons, 15 electrons, 16 neutrons

Pb-207 has 82 protons, 82 electrons, 125 neutrons

Cl-35 has 17 protons, 17 electrons, 18 neutrons

If you are not given this symbol with the mass number, you can still determine the mass number for the most abundant isotopic form for that atom. For example, if you look on the periodic table for Carbon, you will see a value underneath its symbol - the RELATIVE ATOMIC MASS of 12.011. This mass is a special average mass for all of the isotopes that exist for that atom. It takes into consideration HOW abundant each isotope is. So, the most abundant isotope has the most influence on this mass! So, if you round this number to the nearest whole number you have the MASS NUMBER FOR THE MOST COMMON ISOTOPE.

A few examples, determine the #p, #e, #n:

53 16 13

I S Al

126.90447 32.066 26.981539

Answers:

Iodine has 53 protons, 53 electrons, 74 neutrons

Sulfur has 16 protons, 16 electrons, 16 neutrons

Aluminum has 13 protons, 13 electrons, 14 neutrons

More on those electrons!!!

Electrons exist outside of the nucleus, are extremely small and so are nearly weightless, and move at the speed of light!!!!!! So, they do not add much to the mass of the atom but they do control the chemical activity of the atom and the SIZE of the atom because of all that motion.

Electron Clouds

Electrons are moving constantly. So, it is impossible to know, at any given moment, their exact position. So, we say that they exist in a region of space known as the electron cloud.

Since electrons are negative they want to get close to the positive nucleus. But, since negative repels negative, electrons have to arrange themselves in special orbits called energy levels. They do this in order to be close to the positive nucleus yet, not repelling each other too much.

Shapes of the Electron Clouds

Energy LevelsThe first energy level can only hold up to TWO electrons to be STABLE. The secondenergy level can hold up to EIGHT electrons.The third can hold up to 18 electrons. This

can be determined by using the following formula: 2(n2) ; where the n = energy level #So, what could the 4th hold?____the 5th?___

Valence electrons – outermost electrons from the nucleus

*Most atoms want to have 8 valence electrons because it is the most stableconfiguratiion!!!! (The Great Eight = an octet)

e- e-

Only the simplest of atoms can be realistically drawn.

Drawing an atom of Fluorine (F-19)

____#protons____# electrons____#neutrons

How many electrons would fluorine like to get, to be stable?__________

e- e- e- e-

e-e-

e- e-

e-

1e 2e 3e 4e 5e 6e 7e 8e

Number of Valence Electrons in a Family

Draw an atom of:

hydrogen(H-1) oxygen (O-16) hydrogen (H-1)

Let’s bond these 2 hydrogen and 1 oxygen together to make

……….

e-e- e- e-

e- e-

e- e-

e-

e-

e-e-

We just created a COVALENT BOND. This is a bond in which two or more atoms SHARE electrons so that they all become more stable.Partial charges should

be drawn on water since it is polar. More on this later!

e- e-

e- e-

e- e-

e-

e-

Ionic Bonding

Some elements do not want to share electrons because their nucleus is so strong it actually takes the electrons from another atom. This strong atom which GAINS electrons (which are negative) becomes a NEGATIVE- charged ION, OR ANION.

Ion: an atom that has lost or gained ELECTRONS!

The weaker atom, which loses an electron or more, becomes a POSITIVE-charged ion, a CATION.

Once these atoms become IONS, they are now attracted to one another and so you have what is called an IONIC BOND.

Diagram of what happens in an Ionic Bond

Draw a sodium (Na) Draw a chlorine (Cl

e-

e- e- e-

e- e-

e- e-

e-

e- e-

e- e- e-

e- e-

e- e-

e-

e-

e-

e-e-

e-

e-

e-e-

e-e-

Once done, charges should be drawn in since you no longer have neutral atoms but IONS!

e-e-

What would be easier (require less energy)?

To give away 1 or 2 electrons or bring in 6 or 7 electrons in order to gain that octet?

Ionic Bonds and Cations

So: Metals are found on the left side of the periodic table. Metals in column 1 have only one valence electron and in column 2 have only 2 valence electrons. These metal families are most likely to give away their electron(s) to become positive cations. In other words, most metals become cations when involved in ionic bonds, especially those in Family 1 and Family 2.

Some Metal Examples

GoldSodium

Mercury

Zinc

Ionic Bonds and Anions

What columns on the periodic table have 5, 6, or 7valence electrons?_________What would be easier (require less energy)? To give away 5, 6 or 7 electrons or bring in 1, 2, or 3 electrons to gain that octet?

So: Nonmetals are found on the upper, right corner of the periodic table. Atoms in these families, such as families 16 and 17, have 6 and 7 electrons, resp. and are most likely going to gain electrons when involved in an ionic bond. In other words, the nonmetals become the anions when involved in an ionic bond.

How do you know what kind of bond will form?

Once you get into chemistry, you will be given some rules used to determine this with care. Since you are in Biology class for now, we are going to use a general-rule-of-thumb.

It is the following:

If the atoms joining, are on the right hand side of the stair step (nonmetals), you can assume the bond(s) will be covalent. If the atoms joining, are from opposite sides of the table (a metal with a nonmetal), you can assume the bond will be ionic.

Examples: NaCl is …..

H2O is …..

CO2 is ….. Your Turn:

CuF is _________

SO3 is _________

NO2 is _________

ionic

covalent

covalent

Venn Diagram:

Identify TWO similarities and TWO differences with IONIC and COVALENT bonds.