Chapter 4 Section 4. There are about 118 known types of atoms. Each element has it’s own type of atom. All atoms of an element have to have one.

Chapter 4Section 4

There are about 118 known types of atoms. Each element has it’s own type of atom. All atoms of an element have to have one

common factor, just like all cells of a particular person will have the same DNA.

The identifying factor of an atom is the ATOMIC NUMBER.

The atomic number is the number of p+ in the atom.

contains protons and neutrons The number of protons in all atoms of the

same element will be the same is positively charged Contains all of the mass of the atom Each proton and each neutron will add

1amu to the mass of the atom The atomic number (found on the

periodic table) is the number of protons

The atomic mass of an atom is equal to the number of protons + the number of neutrons

Atomic mass = p+ + n To find the number of neutrons, subtract the

atomic number from the atomic mass Ex: Phosphorus

atomic number = 15mass # = 31number of neutron = 31-15

16 neutrons

Phosphorus15 p+16n

Atoms that have the same number of p+ but different numbers of n

Neon-20 Neon-21 Neon-22

# p+

#n

Mass #

# e-

When an element name or symbol appears as name-x, the x stands for the mass number of that isotope.

The number appearing on the periodic table is actually an average atomic mass

This number is the weighted average of the masses of the isotopes of an element

This number accounts for the relative abundance of different isotopes of the element

1. Multiply the mass of each isotope by its natural abundance, expressed as a decimal.

2. Add the products.

Example: Element X has two natural isotopes. The isotope with a mass of 10.012amu has a relative abundance of 19.91%. The isotope with a mass of 11.009amu has a relative abundance of 80.09%. Calculate the atomic mass of this element.

Isotope Mass x Abundance as a Decimal =

Product

X-10 10.012 .1991 1.993amu

X-11 11.009 .8009 8.817amu

Add the Products 10.810

Multiply your percentage per category by the weight of each category expressed as a decimal.

Add your answers.Homework 10% 60%Lab 25% 75%Quiz 25% 86%Tests 40% 50%

Your average is NOT 67.75%

Category Weight of Category as a Decimal

Grade in Category

Product

HW .10 60 6

Lab .25 75 18.75

Quiz .25 86 21.5

Test .40 50 20

Add the products! 66.25%

Multiply the mass of the isotope by the percent abundance (expressed as a decimal)

Repeat the first step for each isotope Add the products of the answers from your

first two steps.

Isotope Mass of the Isotope

% abundance (as a decimal)

Product

Boron - 10 10.013 .199

Boron - 11 11.009 .801

Average Atomic Mass