Isotopes & Ions

4.7; 4.10

Subatomic Particles

Remember Dalton? Remember Dalton’s atomic theory?

“All atoms of a given element are identical”.

WRONG! All atoms of the same element contain the same number of protons and electrons, but atoms of a given element may have different numbers of neutrons.

Isotopes All atoms of an element have the same number of protons

The number of protons in an atom of a given element is the same as the atomic number found on the Periodic Table

Atoms of an element with different numbers of neutrons are called isotopes

All isotopes of an element are chemically identical undergo the exact same chemical reactions

Isotopes of an element have different masses Isotopes are identified by their mass numbers

mass number = protons + neutrons

Isotope Notation

Examples1. Determine the number of each

of the three types of subatomic particles for each of the following:1. 60

20Co2. 37

17Cl3. 238

92U2. Write the symbol for each of

the following atoms1. A cesium atom with 77 neutrons2. An iron atom with a mass number

of 56

Average Atomic Mass Carbon has a mass listed of 12.011 a.m.u., but no isotope of carbon has a mass of 12.011.

How is this the mass reported for carbon?

Atomic masses are the weighted average of the masses of the isotopes.

Sample Problem Carbon has 13 naturally occurring isotopes, however, only two isotopes are stable, carbon-12 and carbon-13. 98.93% of all carbon is carbon-12 while 1.03% is carbon-13. All other isotopes are insignificant in abundance. What is the average atomic mass of carbon?

Try another one

1.Element Xa (imaginary) occurs in three forms, Xa-82 (82.0 amu), Xa-83 (83.0 amu), and Xa-85 (85.0 amu). The relative abundances of the atomic masses are 0.35%, 3.65%, and 96.0% respectively. Calculate the average atomic mass of the imaginary element, Xa.

IONS A charged entity is called an ion.

IMPORTANT: PROTONS STAY IN THE NUCLEUS; IONS ARE FORMED THROUGH THE GAIN OR LOSS OF ELECTRONS!!!

A positive ion is called a cation formed when an atom loses electrons

A negatively charged ion is called an anion formed when an atom gains electrons

Cations vs Anions