IonsAn atom that carries an electrical charge is called an ionIf the atom loses electrons, the atom becomes positively charged (because the number of positively charged protons will be more the number of electrons) If the atom gains electrons, the atom becomes negatively charged (because there are more negative charges than positive)

Ions

The number of protons does not change in an ion.

The number of neutrons does not change in an ion.

So, both the atomic number and the atomic mass remain the same.

IonsThis atom has lost an electron. Now it has one more proton than electron.

One more proton means one more positive charge.

This makes the total charge of the atom POSITIVE.

This atom has gained an electron. Now it has one less proton than electron.

One less proton means one less positive charge.

This makes the total charge of the atom NEGATIVE.

IsotopesThe number of protons for a given atom never changes.

The number of neutrons can change. 

Two atoms with different numbers of neutrons are called isotopes

Isotopes have the same atomic #

Isotopes have different atomic Mass #’s

Isotopes

Isotope Notation

Isotope Notation uses a symbol to convey information about an

isotope of a particular element.

23

Na 11

Isotope Notation

Is the # of protons (p+) in the atomAND

23

Na 11 Atomic Number

The # of electrons (e-) IF the atom is electrically neutral ( i.e., not an ion). This number is on the periodic table.

Mass Number

Is the number of protons plus the number of neutrons. This number tells us the kind of isotope. This number is NOT on the periodic table.

For this isotope

11 p+

+ 11e-

0 net charge

Isotope Notation

23

Na 11

23

Na+

11

For this isotope

11 p+

+ 10e-

1+ net charge

Isotope Notation

23

Na 11 Atomic Number

The # of protons + the # of neutrons

Calculate the number of neutrons for this isotope.

23 (neutrons + protons) - 11 protons = 12 neutrons

Mass Number

Atomic MassIs the weighted average mass of all the isotopes

of one element in atomic mass units (amu).In other words, it is the mass of one average atom*.Two measurements are needed in order to calculate this average.

1.The percent abundance (% abundance,) also known as how often the isotope occurs in nature.2.The mass of one atom of one isotope. Atomic mass is also known as

Weighted Average Atomic MassAverage Atomic Mass

Atomic Mass

Here is the formula you need to know in order to calculate the average atomic mass.

Average Atomic Mass = [(Mass of Isotope 1) x (% abundance of Isotope 1)]+ [(Mass of Isotope 2) x (% abundance of Isotope 2)]+ and so on for the 3rd and remaining isotopes.

The average atomic mass is written on the periodic table

Mass Number vs. Atomic Mass

Mass number = # protons + # neutrons(This number is specific for one isotope.)

Atomic mass = weighted average mass of all the isotopes of one element in atomic mass units (amu).

(The atomic mass is on the periodic table.)